%%
%% %CopyrightBegin%
%%
%% SPDX-License-Identifier: Apache-2.0
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%% Copyright Ericsson AB 1997-2026. All Rights Reserved.
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%% Licensed under the Apache License, Version 2.0 (the "License");
%% you may not use this file except in compliance with the License.
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%% distributed under the License is distributed on an "AS IS" BASIS,
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-module(disk_log).
-moduledoc """
`disk_log` is a disk-based term logger that enables efficient logging of items
on files.

Three types of logs are supported:

- **halt logs** - Appends items to a single file, which size can be limited by
  the `disk_log` module.

- **wrap logs** - Uses a sequence of wrap log files of limited size. As a wrap
  log file is filled up, further items are logged on to the next file in the
  sequence, starting all over with the first file when the last file is filled
  up.

- **rotate logs** - Uses a sequence of rotate log files of limited size. As a
  log file is filled up, it is rotated and then compressed. There is one active
  log file and upto the configured number of compressed log files. Only
  externally formatted logs are supported. It follows the same naming convention
  as the handler logger_std_h for Logger. For more details about the naming
  convention check the file parameter for `open/1`.

  It follows the same naming convention as that for the compressed files for
  Linux's logrotate and BSD's newsyslog.

For efficiency reasons, items are always written to files as binaries.

Two formats of the log files are supported:

- **internal format** - Supports automatic repair of log files that are not
  properly closed and enables efficient reading of logged items in _chunks_
  using a set of functions defined in this module. This is the only way to read
  internally formatted logs. An item logged to an internally formatted log must
  not occupy more than 4 GB of disk space (the size must fit in 4 bytes).

- **external format** - Leaves it up to the user to read and interpret the
  logged data. The `disk_log` module cannot repair externally formatted logs.

For each open disk log, one process handles requests made to the disk log. This
process is created when `open/1` is called, provided there exists no process
handling the disk log. A process that opens a disk log can be an _owner_ or an
anonymous _user_ of the disk log. Each owner is linked to the disk log process,
and an owner can close the disk log either explicitly (by calling
[`close/1`](`close/1`)) or by terminating.

Owners can subscribe to _notifications_, messages of the form
`{disk_log, Node, Log, Info}`, which are sent from the disk log process when
certain events occur, see the functions and in particular the
[`open/1`](`open/1`) option [`notify`](`m:disk_log#notify`). A log can have many
owners, but a process cannot own a log more than once. However, the same process
can open the log as a user more than once.

For a disk log process to close its file properly and terminate, it must be
closed by its owners and once by some non-owner process for each time the log
was used anonymously. The users are counted and there must not be any users left
when the disk log process terminates.

Items can be logged _synchronously_ by using functions `log/2`, `blog/2`,
`log_terms/2`, and `blog_terms/2`. For each of these functions, the caller is
put on hold until the items are logged (but not necessarily written, use
[`sync/1`](`sync/1`) to ensure that). By adding an `a` to each of the mentioned
function names, we get functions that log items _asynchronously_. Asynchronous
functions do not wait for the disk log process to write the items to the file,
but return the control to the caller more or less immediately.

When using the internal format for logs, use functions `log/2`, `log_terms/2`,
`alog/2`, and `alog_terms/2`. These functions log one or more Erlang terms. By
prefixing each of the functions with a `b` (for "binary"), we get the
corresponding `blog()` functions for the external format. These functions log
one or more chunks of bytes. For example, to log the string `"hello"` in ASCII
format, you can use [`disk_log:blog(Log, "hello")`](`blog/2`), or
[`disk_log:blog(Log, list_to_binary("hello"))`](`blog/2`). The two alternatives
are equally efficient.

The `blog()` functions can also be used for internally formatted logs, but in
this case they must be called with binaries constructed with calls to
[`term_to_binary/1`](`erlang:term_to_binary/1`). There is no check to ensure
this, it is entirely the responsibility of the caller. If these functions are
called with binaries that do not correspond to Erlang terms, the
[`chunk/2,3`](`chunk/3`) and automatic repair functions fail. The corresponding
terms (not the binaries) are returned when [`chunk/2,3`](`chunk/3`) is called.

An open disk log is only accessible from the node where the disk log process
runs. All processes on the node where the disk log process runs can log items or
otherwise change, inspect, or close the log.

Errors are reported differently for asynchronous log attempts and other uses of
the `m:disk_log` module. When used synchronously, this module replies with an
error message, but when called asynchronously, this module does not know where
to send the error message. Instead, owners subscribing to notifications receive
an `error_status` message.

The `m:disk_log` module does not report errors to the `m:error_logger` module. It
is up to the caller to decide whether to employ the error logger. Function
`format_error/1` can be used to produce readable messages from error replies.
However, information events are sent to the error logger in two situations,
namely when a log is repaired, or when a file is missing while reading chunks.

Error message `no_such_log` means that the specified disk log is not open.
Nothing is said about whether the disk log files exist or not.

> #### Note {: .info }
>
> If an attempt to reopen or truncate a log fails (see
> [`reopen/2,3`](`reopen/3`) and [`truncate/1,2`](`truncate/2`)) the disk log
> process terminates immediately. Before the process terminates, links to owners
> and blocking processes (see [`block/1,2`](`block/2`)) are removed. The effect
> is that the links work in one direction only. Any process using a disk log
> must check for error message `no_such_log` if some other process truncates or
> reopens the log simultaneously.

### See Also

`m:file`, `m:wrap_log_reader`
""".

-compile([{nowarn_possibly_unsafe_function, {erlang, binary_to_term, 1}},
          nowarn_deprecated_catch]).

%% Efficient file based log - process part

-export([start/0, istart_link/1, 
	 log/2, log_terms/2, blog/2, blog_terms/2,
	 alog/2, alog_terms/2, balog/2, balog_terms/2,
	 close/1, sync/1, open/1, 
	 truncate/1, truncate/2, btruncate/2,
	 reopen/2, reopen/3, breopen/3, inc_wrap_file/1, change_size/2,
	 change_notify/3, change_header/2, 
	 chunk/2, chunk/3, bchunk/2, bchunk/3, chunk_step/3, chunk_info/1,
	 block/1, block/2, unblock/1, info/1, format_error/1,
	 all/0, next_file/1]).

%% Internal exports
-export([init/2, internal_open/2,
	 system_continue/3, system_terminate/4, system_code_change/4]).

%% To be used by disk_log_h.erl (not (yet) in Erlang/OTP) only.
-export([ll_open/1, ll_close/1, do_log/2, do_sync/1, do_info/2]).

%% To be used by wrap_log_reader only.
-export([ichunk_end/2]).

%% To be used for debugging only:
-export([pid2name/1]).

-export_type([continuation/0]).

-deprecated([{inc_wrap_file, 1, "use disk_log:next_file/1 instead"}]).

-removed([{accessible_logs, 0, "use disk_log:all/0 instead"},
          {lclose, 1, "use disk_log:close/1 instead"},
          {lclose, 2, "use disk_log:close/1 instead"}]).

-type dlog_state_error() :: 'ok' | {'error', term()}.

-record(state, {queue = [],
		messages = [],
		parent,
		server,
		cnt = 0           :: non_neg_integer(),
		args,
		error_status = ok :: dlog_state_error(),
		cache_error = ok     %% cache write error after timeout
	       }).

-include("disk_log.hrl").

-define(failure(Error, Function, Arg), 
	{{failed, Error}, [{?MODULE, Function, Arg}]}).

%%-define(PROFILE(C), C).
-define(PROFILE(C), void).

-compile({inline,[{log_loop,6},{log_end_sync,2},{replies,2},{rflat,1}]}).

%%%----------------------------------------------------------------------
%%% Contract type specifications
%%%----------------------------------------------------------------------

-doc """
Chunk continuation returned by [`chunk/2,3`](`chunk/3`),
[`bchunk/2,3`](`bchunk/3`), or [`chunk_step/3`](`chunk_step/3`).
""".
-opaque continuation() :: #continuation{}.

-type file_error()     :: term().  % XXX: refine
-type invalid_header() :: term().  % XXX: refine

%%%----------------------------------------------------------------------
%%% API
%%%----------------------------------------------------------------------

%%-----------------------------------------------------------------
%% This module implements the API, and the processes for each log.
%% There is one process per log.
%%-----------------------------------------------------------------      

-type open_error_rsn() :: 'no_such_log'
                        | {'badarg', term()}
                        | {'size_mismatch', CurrentSize :: dlog_size(),
                           NewSize :: dlog_size()}
                        | {'arg_mismatch', OptionName :: dlog_optattr(),
                           CurrentValue :: term(), Value :: term()}
                        | {'name_already_open', Log :: log()}
                        | {'open_read_write', Log :: log()}
                        | {'open_read_only', Log :: log()}
                        | {'need_repair', Log :: log()}
                        | {'not_a_log_file', FileName :: file:filename()}
                        | {'invalid_index_file', FileName :: file:filename()}
                        | {'invalid_header', invalid_header()}
                        | {'file_error', file:filename(), file_error()}
                        | {'node_already_open', Log :: log()}.
-type open_ret()       :: {'ok', Log :: log()}
                        | {'repaired', Log :: log(),
                           {'recovered', Rec :: non_neg_integer()},
                           {'badbytes', Bad :: non_neg_integer()}}
                        | {'error', open_error_rsn()}.

-doc """
Open a new disk_log file for reading or writing.

Parameter `ArgL` is a list of the following options:

- **`{name, Log}`** - Specifies the log name. This name must be passed on as a
  parameter in all subsequent logging operations. A name must always be
  supplied.

- **`{file, FileName}`** - Specifies the name of the file to be used for logged
  terms. If this value is omitted and the log name is an atom or a string, the
  filename defaults to `lists:concat([Log, ".LOG"])` for halt logs.

  For wrap logs, this is the base name of the files. Each file in a wrap log is
  called `<FileName>.N`, where `N` is an integer. Each wrap log also has two
  files called `<FileName>.idx` and `<FileName>.siz`.

  For rotate logs, this is the name of the active log file. The compressed files
  are named as `<FileName>.N.gz`, where `N` is an integer and `<FileName>.0.gz`
  is the latest compressed log file. All the compressed files are renamed at
  each rotation so that the latest files have the smallest index. The maximum
  value for N is the value of `MaxNoFiles` minus 1.

- **`{linkto, LinkTo}`[](){: #linkto } **  
   If `LinkTo` is a pid, it becomes an owner of the log. If `LinkTo` is `none`, the
  log records that it is used anonymously by some process by incrementing the `users`
  counter. By default, the process that calls [`open/1`](`open/1`) owns the log.

- **`{repair, Repair}`** - If `Repair` is `true`, the current log file is
  repaired, if needed. As the restoration is initiated, a message is output on
  the error log. If `false` is specified, no automatic repair is attempted.
  Instead, the tuple `{error, {need_repair, Log}}` is returned if an attempt is
  made to open a corrupt log file. If `truncate` is specified, the log file
  becomes truncated, creating an empty log, regardless of previous content.
  Defaults to `true`, which has no effect on logs opened in read-only mode.

- **`{type, Type}`** - The log type. Defaults to `halt`.

- **`{format, Format}`** - Disk log format. Defaults to `internal`.

- **`{size, Size}`** - Log size.

  When a halt log has reached its maximum size, all attempts to log more items
  are rejected. Defaults to `infinity`, which for halt implies that there is no
  maximum size.

  For wrap and rotate logs, parameter `Size` can be a pair
  `{MaxNoBytes, MaxNoFiles}`. For wrap logs it can also be `infinity`. In the
  latter case, if the files of an existing wrap log with the same name can be
  found, the size is read from the existing wrap log, otherwise an error is
  returned.

  Wrap logs write at most `MaxNoBytes` bytes on each file and use `MaxNoFiles`
  files before starting all over with the first wrap log file. Regardless of
  `MaxNoBytes`, at least the header (if there is one) and one item are written
  on each wrap log file before wrapping to the next file.

  The first time an existing wrap log is opened, that is, when the disk log
  process is created, the value of the option `size` is allowed to differ from
  the current log size, and the size of the disk log is changed as per
  `change_size/2`.

  When opening an existing wrap log, it is not necessary to supply a value for
  option `size`, but if the log is already open, that is, the disk log process
  exists, the supplied value must equal the current log size, otherwise the
  tuple `{error, {size_mismatch, CurrentSize, NewSize}}` is returned.

  > #### Note {: .info }
  >
  > Before Erlang/OTP 24.0, the supplied value of option `size` was to be equal
  > to the current log size when opening an existing wrap log for the first
  > time, that is, when creating the disk log process.

  Rotate logs write at most `MaxNoBytes` bytes on the active log file and keep
  the latest `MaxNoFiles` compressed files. Regardless of `MaxNoBytes`, at least
  the header (if there is one) and one item are written on each rotate log file
  before rotation.

  When opening an already open halt log, option `size` is ignored.

- **`{notify, boolean()}`**{: #notify } - If `true`, the log owners are notified
  when certain log events occur. Defaults to `false`. The owners are sent one of the
  following messages when an event occurs:

  - **`{disk_log, Node, Log, {wrap, NoLostItems}}`** - Sent when a wrap log has
    filled up one of its files and a new file is opened. `NoLostItems` is the
    number of previously logged items that were lost when truncating existing
    files.

  - **`{disk_log, Node, Log, {truncated, NoLostItems}}`** - Sent when a log is
    truncated or reopened. For halt logs `NoLostItems` is the number of items
    written on the log since the disk log process was created. For wrap logs
    `NoLostItems` is the number of items on all wrap log files.

  - **`{disk_log, Node, Log, {read_only, Items}}`** - Sent when an asynchronous
    log attempt is made to a log file opened in read-only mode. `Items` is the
    items from the log attempt.

  - **`{disk_log, Node, Log, {blocked_log, Items}}`** - Sent when an
    asynchronous log attempt is made to a blocked log that does not queue log
    attempts. `Items` is the items from the log attempt.

  - **`{disk_log, Node, Log, {format_external, Items}}`** - Sent when function
    [`alog/2`](`alog/2`) or [`alog_terms/2`](`alog_terms/2`) is used for
    internally formatted logs. `Items` is the items from the log attempt.

  - **`{disk_log, Node, Log, full}`** - Sent when an attempt to log items to a
    wrap log would write more bytes than the limit set by option `size`.

  - **`{disk_log, Node, Log, {error_status, Status}}`** - Sent when the error
    status changes. The error status is defined by the outcome of the last
    attempt to log items to the log, or to truncate the log, or the last use of
    function [`sync/1`](`sync/1`), [`inc_wrap_file/1`](`inc_wrap_file/1`), or
    [`change_size/2`](`change_size/2`). `Status` is either `ok` or
    `{error, Error}`, the former is the initial value.

- **`{head, Head}`** - Specifies a header to be written first on the log file.
  If the log is a wrap or rotate log, the item `Head` is written first in each
  new file. `Head` is to be a term if the format is `internal`, otherwise an
  `t:iodata/0`. Defaults to `none`, which means that no header is written first
  on the file.

- **`{head_func, {M,F,A}}`** - Specifies a function to be called each time a new
  log file is opened. The call `M:F(A)` is assumed to return `{ok, Head}`. The
  item `Head` is written first in each file. `Head` is to be a term if the
  format is `internal`, otherwise an `t:iodata/0`.

- **`{mode, Mode}`** - Specifies if the log is to be opened in read-only or
  read-write mode. Defaults to `read_write`.

- **`{quiet, Boolean}`** - Specifies if messages will be sent to `error_logger`
  on recoverable errors with the log files. Defaults to `false`.

[`open/1`](`open/1`) returns `{ok, Log}` if the log file is successfully opened.
If the file is successfully repaired, the tuple
`{repaired, Log, {recovered, Rec}, {badbytes, Bad}}` is returned, where `Rec` is
the number of whole Erlang terms found in the file and `Bad` is the number of
bytes in the file that are non-Erlang terms.

When a disk log is opened in read-write mode, any existing log file is checked
for. If there is none, a new empty log is created, otherwise the existing file
is opened at the position after the last logged item, and the logging of items
starts from there. If the format is `internal` and the existing file is not
recognized as an internally formatted log, a tuple
`{error, {not_a_log_file, FileName}}` is returned.

[`open/1`](`open/1`) cannot be used for changing the values of options of an
open log. When there are prior owners or users of a log, all option values
except `name`, `linkto`, and `notify` are only checked against the values
supplied before as option values to function [`open/1`](`open/1`),
[`change_header/2`](`change_header/2`), [`change_notify/3`](`change_notify/3`),
or [`change_size/2`](`change_size/2`). Thus, none of the options except `name`
is mandatory. If some specified value differs from the current value, a tuple
`{error, {arg_mismatch, OptionName, CurrentValue, Value}}` is returned.

> #### Note {: .info }
>
> If an owner attempts to open a log as owner once again, it is acknowledged
> with the return value `{ok, Log}`, but the state of the disk log is not
> affected.

A log file can be opened more than once by giving different values to option
`name` or by using the same file when opening a log on different nodes. It is up
to the user of module `disk_log` to ensure that not more than one disk log
process has write access to any file, otherwise the file can be corrupted.

If an attempt to open a log file for the first time fails, the disk log process
terminates with the EXIT message `{{failed,Reason},[{disk_log,open,1}]}`. The
function returns `{error, Reason}` for all other errors.
""".
-spec open(ArgL) -> open_ret() when
      ArgL :: dlog_options().
open(A) ->
    disk_log_server:open(check_arg(A, #arg{options = A})).

-type log_error_rsn() :: 'no_such_log' | 'nonode' | {'read_only_mode', log()}
                       | {'format_external', log()} | {'blocked_log', log()}
                       | {'full', log()} | {'invalid_header', invalid_header()}
                       | {'file_error', file:filename(), file_error()}.

-doc """
Synchronously appends a term to a internally formatted disk log. Returns `ok`
or `{error, Reason}` when the term is written to disk.

Terms are written by the ordinary `write()` function of the operating system.
Hence, it is not guaranteed that the term is written to disk, it can linger in
the operating system kernel for a while. To ensure that the item is written to disk,
function `sync/1` must be called.

Owners subscribing to notifications are notified of an error with an
`error_status` message if the error reason tag is `invalid_header` or
`file_error`.
""".
-spec log(Log, Term) -> ok | {error, Reason :: log_error_rsn()} when
      Log :: log(),
      Term :: term().
log(Log, Term) -> 
    req(Log, {log, internal, [term_to_binary(Term)]}).

-doc """
Equivalent to `log/2` except that it is used for externally formatted logs.

`blog/2` can also be used for internally formatted logs
if the binaries are constructed with calls to `term_to_binary/1`.
""".
-spec blog(Log, Bytes) -> ok | {error, Reason :: log_error_rsn()} when
      Log :: log(),
      Bytes :: iodata().
blog(Log, Bytes) ->
    req(Log, {log, external, [ensure_binary(Bytes)]}).

-doc """
Synchronously appends a list of items to an internally formatted log.

It is more efficient to use this functions instead of [`log/2`](`log/2`). The specified
list is split into as large sublists as possible (limited by the size of wrap log files),
and each sublist is logged as one single item, which reduces the overhead.

Owners subscribing to notifications are notified of an error with an
`error_status` message if the error reason tag is `invalid_header` or
`file_error`.
""".
-spec log_terms(Log, TermList) -> ok | {error, Reason :: log_error_rsn()} when
      Log :: log(),
      TermList :: [term()].
log_terms(Log, Terms) ->
    Bs = terms2bins(Terms),
    req(Log, {log, internal, Bs}).

-doc """
Equivalent to `log_terms/2` except that it is used for externally formatted logs.

`blog_terms/2` can also be used for internally formatted logs
if the binaries are constructed with calls to `term_to_binary/1`.
""".
-spec blog_terms(Log, BytesList) ->
                        ok | {error, Reason :: log_error_rsn()} when
      Log :: log(),
      BytesList :: [iodata()].
blog_terms(Log, Bytess) ->
    Bs = ensure_binary_list(Bytess),
    req(Log, {log, external, Bs}).

-type notify_ret() :: 'ok' | {'error', 'no_such_log'}.

-doc """
Asynchronously version of `log/2`.

Owners subscribing to notifications receive message `read_only`, `blocked_log`,
or `format_external` if the item cannot be written on the log, and possibly one
of the messages `wrap`, `full`, or `error_status` if an item is written on the
log. Message `error_status` is sent if something is wrong with the header
function or if a file error occurs.
""".
-spec alog(Log, Term) -> notify_ret() when
      Log :: log(),
      Term :: term().
alog(Log, Term) -> 
    notify(Log, {alog, internal, [term_to_binary(Term)]}).

-doc """
Asynchronously version of `log_terms/2`.

Owners subscribing to notifications receive message `read_only`, `blocked_log`,
or `format_external` if the items cannot be written on the log, and possibly one
or more of the messages `wrap`, `full`, and `error_status` if items are written
on the log. Message `error_status` is sent if something is wrong with the header
function or if a file error occurs.
""".
-spec alog_terms(Log, TermList) -> notify_ret() when
      Log :: log(),
      TermList :: [term()].
alog_terms(Log, Terms) ->
    Bs = terms2bins(Terms),
    notify(Log, {alog, internal, Bs}).

-doc """
Asynchronously version of `blog/2`.

Owners subscribing to notifications receive message `read_only`, `blocked_log`,
or `format_external` if the item cannot be written on the log, and possibly one
of the messages `wrap`, `full`, or `error_status` if an item is written on the
log. Message `error_status` is sent if something is wrong with the header
function or if a file error occurs.
""".
-spec balog(Log, Bytes) -> notify_ret() when
      Log :: log(),
      Bytes :: iodata().
balog(Log, Bytes) ->
    notify(Log, {alog, external, [ensure_binary(Bytes)]}).

-doc """
Asynchronously version of `blog_terms/2`.

Owners subscribing to notifications receive message `read_only`, `blocked_log`,
or `format_external` if the items cannot be written on the log, and possibly one
or more of the messages `wrap`, `full`, and `error_status` if items are written
on the log. Message `error_status` is sent if something is wrong with the header
function or if a file error occurs.
""".
-spec balog_terms(Log, ByteList) -> notify_ret() when
      Log :: log(),
      ByteList :: [iodata()].
balog_terms(Log, Bytess) ->
    Bs = ensure_binary_list(Bytess),
    notify(Log, {alog, external, Bs}).

-type close_error_rsn() ::'no_such_log' | 'nonode'
                         | {'file_error', file:filename(), file_error()}.

-doc """
Closes a disk log properly.

An internally formatted log must be closed before the Erlang system is stopped.
Otherwise, the log is regarded as unclosed and the automatic repair procedure is
activated next time the log is opened.

The disk log process is not terminated as long as there are owners or users of
the log. All owners must close the log, possibly by terminating. Also, any other
process, not only the processes that have opened the log anonymously, can
decrement the `users` counter by closing the log. Attempts to close a log by a
process that is not an owner are ignored if there are no users.

If the log is blocked by the closing process, the log is also unblocked.
""".
-spec close(Log) -> 'ok' | {'error', close_error_rsn()} when
      Log :: log().
close(Log) -> 
    req(Log, close).

-type trunc_error_rsn() :: 'no_such_log' | 'nonode'
                         | {'read_only_mode', log()}
                         | {'blocked_log', log()}
                         | {'invalid_header', invalid_header()}
                         | {'file_error', file:filename(), file_error()}.

-doc """
Equivalent to [`truncate(Log, Head)`](`truncate/2`) where `Head` is
the `Head` specified in `open/1`.

This function can be used for both internally and externally
formatted logs.
""".
-spec truncate(Log) -> 'ok' | {'error', trunc_error_rsn()} when
      Log :: log().
truncate(Log) -> 
    req(Log, {truncate, none, truncate, 1}).

-doc """
Removes all items from an internally formatted disk log. The argument `Head` or
is written first in the newly truncated log.

The header argument is used only once. Next time a wrap/rotate log file is opened,
the header given to [`open/1`](`open/1`) is used.

Owners subscribing to notifications receive a `truncate` message.

If the attempt to truncate the log fails, the disk log process terminates with
the EXIT message `{{failed,Reason},[{disk_log,Fun,Arity}]}`. Other processes
having requests queued receive the message
`{disk_log, Node, {error, disk_log_stopped}}`.
""".
-spec truncate(Log, Head) -> 'ok' | {'error', trunc_error_rsn()} when
      Log :: log(),
      Head :: term().
truncate(Log, Head) ->
    req(Log, {truncate, {ok, term_to_binary(Head)}, truncate, 2}).

-doc "Equivalent to `truncate/2` for externally formatted logs.".
-spec btruncate(Log, BHead) -> 'ok' | {'error', trunc_error_rsn()} when
      Log :: log(),
      BHead :: iodata().
btruncate(Log, Head) ->
    req(Log, {truncate, {ok, ensure_binary(Head)}, btruncate, 2}).

-type reopen_error_rsn() :: no_such_log
                          | nonode
                          | {read_only_mode, log()}
                          | {blocked_log, log()}
                          | {same_file_name, log()} |
                            {invalid_index_file, file:filename()}
                          | {invalid_header, invalid_header()}
                          | {'file_error', file:filename(), file_error()}.

-doc """
Equivalent to [`reopen(Log, File, Head)`](`reopen/3`) where `Head` is
the `Head` specified in `open/1`.
""".
-spec reopen(Log, File) -> 'ok' | {'error', reopen_error_rsn()} when
      Log :: log(),
      File :: file:filename().
reopen(Log, NewFile) ->
    req(Log, {reopen, NewFile, none, reopen, 2}).

-doc """
Renames an internally formatted log file to `File` and then recreates a new log file. If a
wrap/rotate log exists, `File` is used as the base name of the renamed files.

Writes the value of `Head` first in the newly opened log file. The header argument
is used only once. Next time a wrap/rotate log file is opened, the header given to
[`open/1`](`open/1`) is used.

Owners subscribing to notifications receive a `truncate` message.

Upon failure to reopen the log, the disk log process terminates with the EXIT
message `{{failed,Error},[{disk_log,Fun,Arity}]}`. Other processes having
requests queued receive the message
`{disk_log, Node, {error, disk_log_stopped}}`.
""".
-spec reopen(Log, File, Head) -> 'ok' | {'error', reopen_error_rsn()} when
      Log :: log(),
      File :: file:filename(),
      Head :: term().
reopen(Log, NewFile, NewHead) ->
    req(Log, {reopen, NewFile, {ok, term_to_binary(NewHead)}, reopen, 3}).

-doc """
Equivalent to `reopen` except that it is used for externally formatted logs.
""".
-spec breopen(Log, File, BHead) -> 'ok' | {'error', reopen_error_rsn()} when
      Log :: log(),
      File :: file:filename(),
      BHead :: iodata().
breopen(Log, NewFile, NewHead) ->
    req(Log, {reopen, NewFile, {ok, ensure_binary(NewHead)}, breopen, 3}).

-type next_file_error_rsn() :: 'no_such_log' | 'nonode'
                            | {'read_only_mode', log()}
                            | {'blocked_log', log()} | {'halt_log', log()}
                            | {'rotate_log', log()}
                            | {'invalid_header', invalid_header()}
                            | {'file_error', file:filename(), file_error()}.

-doc """
For wrap logs, it forces the disk log to start logging to the next log file. It
can be used, for example, with [`change_size/2`](`change_size/2`) to reduce the
amount of disk space allocated by the disk log.

Owners subscribing to notifications normally receive a `wrap` message, but if an
error occurs with a reason tag of `invalid_header` or `file_error`, an
`error_status` message is sent.

For rotate logs, it forces rotation of the currently active log file, compresses
it and opens a new active file for logging.
""".
-doc(#{since => <<"OTP 26.0">>}).
-spec next_file(Log) -> 'ok' | {'error', next_file_error_rsn()} when
      Log :: log().
next_file(Log) -> 
    req(Log, next_file).

-type inc_wrap_error_rsn() :: next_file_error_rsn().

-doc """
Forces the internally formatted disk log to start logging to the next log file.
It can be used, for example, with [`change_size/2`](`change_size/2`) to reduce
the amount of disk space allocated by the disk log.

Owners subscribing to notifications normally receive a `wrap` message, but if an
error occurs with a reason tag of `invalid_header` or `file_error`, an
`error_status` message is sent.
""".
-spec inc_wrap_file(Log) -> 'ok' | {'error', inc_wrap_error_rsn()} when
      Log :: log().
inc_wrap_file(Log) -> 
    req(Log, inc_wrap_file).

-doc """
Changes the size of an open log. For a halt log, the size can always be
increased, but it cannot be decreased to something less than the current file
size.

For a wrap or rotate log, both the size and the number of files can always be
increased, as long as the number of files does not exceed 65000. For wrap logs,
if the maximum number of files is decreased, the change is not valid until the
current file is full and the log wraps to the next file. The redundant files are
removed the next time the log wraps around, that is, starts to log to file
number 1.

As an example, assume that the old maximum number of files is 10 and that the
new maximum number of files is 6. If the current file number is not greater than
the new maximum number of files, files 7-10 are removed when file 6 is full and
the log starts to write to file number 1 again. Otherwise, the files greater
than the current file are removed when the current file is full (for example, if
the current file is 8, files 9 and 10 are removed). The files between the new
maximum number of files and the current file (that is, files 7 and 8) are
removed the next time file 6 is full.

For rotate logs, if the maximum number of files is decreased, the redundant
files are deleted instantly.

If the size of the files is decreased, the change immediately affects the
current log. It does not change the size of log files already full until the
next time they are used.

If the log size is decreased, for example, to save space, function
`next_file/1`, can be used to force the log to wrap.
""".
-spec change_size(Log, Size) -> 'ok' | {'error', Reason} when
      Log :: log(),
      Size :: dlog_size(),
      Reason :: no_such_log | nonode | {read_only_mode, Log}
              | {blocked_log, Log}
              | {new_size_too_small, Log, CurrentSize :: pos_integer()}
              | {badarg, size}
              | {file_error, file:filename(), file_error()}.
change_size(Log, NewSize) -> 
    req(Log, {change_size, NewSize}).

-doc "Changes the value of option `notify` for an owner of a disk log.".
-spec change_notify(Log, Owner, Notify) -> 'ok' | {'error', Reason} when
      Log :: log(),
      Owner :: pid(),
      Notify :: boolean(),
      Reason :: no_such_log | nonode | {blocked_log, Log}
              | {badarg, notify} | {not_owner, Owner}.
change_notify(Log, Pid, NewNotify) -> 
    req(Log, {change_notify, Pid, NewNotify}).

-doc "Changes the value of option `head` or `head_func` for an owner of a disk log.".
-spec change_header(Log, Header) -> 'ok' | {'error', Reason} when
      Log :: log(),
      Header :: {head, dlog_head_opt()}
              | {head_func, MFA :: {atom(), atom(), list()}},
      Reason :: no_such_log | nonode | {read_only_mode, Log}
              | {blocked_log, Log} | {badarg, head}.
change_header(Log, NewHead) ->
    req(Log, {change_header, NewHead}).

-type sync_error_rsn() :: 'no_such_log' | 'nonode' | {'read_only_mode', log()}
                        | {'blocked_log', log()}
                        | {'file_error', file:filename(), file_error()}.

-doc """
Ensures that the contents of the log are written to the disk. This is usually a
rather expensive operation.
""".
-spec sync(Log) -> 'ok' | {'error', sync_error_rsn()} when
      Log :: log().
sync(Log) -> 
    req(Log, sync).

-type block_error_rsn() :: 'no_such_log' | 'nonode' | {'blocked_log', log()}.

-doc(#{equiv => block(Log, true)}).
-spec block(Log) -> 'ok' | {'error', block_error_rsn()} when
      Log :: log().
block(Log) -> 
    block(Log, true).

-doc """
With a call to `block/2` a process can block a log.

If the blocking process is not an owner of the log, a temporary link is created
between the disk log process and the blocking process. The link ensures that the disk log is
unblocked if the blocking process terminates without first closing or unblocking
the log.

Any process can probe a blocked log with [`info/1`](`info/1`) or close it with
[`close/1`](`close/1`). The blocking process can also use functions [`chunk/2,3`](`chunk/3`),
[`bchunk/2,3`](`chunk/3`), [`chunk_step/3`](`chunk_step/3`), and [`unblock/1`](`unblock/1`)
without being affected by the block. Any other attempt than those mentioned so
far to update or read a blocked log suspends the calling process until the log
is unblocked or returns error message `{blocked_log, Log}`, depending on whether
the value of `QueueLogRecords` is `true` or `false`.
""".
-spec block(Log, QueueLogRecords) -> 'ok' | {'error', block_error_rsn()} when
      Log :: log(),
      QueueLogRecords :: boolean().
block(Log, QueueLogRecords) -> 
    req(Log, {block, QueueLogRecords}).

-type unblock_error_rsn() :: 'no_such_log' | 'nonode'
                           | {'not_blocked', log()}
                           | {'not_blocked_by_pid', log()}.

-doc "Unblocks a log. A log can only be unblocked by the blocking process.".
-spec unblock(Log) -> 'ok' | {'error', unblock_error_rsn()} when
      Log :: log().
unblock(Log) ->
    req(Log, unblock).

-doc """
Given the error returned by any function in this module, this function returns a
descriptive string of the error in English.

For file errors, function [`format_error/1`](`format_error/1`) in module
[`file`](`file:format_error/1`) is called.
""".
-spec format_error(Error) -> io_lib:chars() when
      Error :: term().
format_error(Error) ->
    do_format_error(Error).

-type dlog_info() :: {name, Log :: log()}
                   | {file, File :: file:filename()}
                   | {type, Type :: dlog_type()}
                   | {format, Format :: dlog_format()}
                   | {size, Size :: dlog_size()}
                   | {mode, Mode :: dlog_mode()}
                   | {owners, [{pid(), Notify :: boolean()}]}
                   | {users, Users :: non_neg_integer()}
                   | {status, Status ::
                        ok | {blocked, QueueLogRecords :: boolean()}}
                   | {node, Node :: node()}
                   | {head, Head :: none
                                  | {head, binary()}
                                  | (MFA :: {atom(), atom(), list()})}
                   | {no_written_items, NoWrittenItems ::non_neg_integer()}
                   | {full, Full :: boolean}
                   | {no_current_bytes, non_neg_integer()}
                   | {no_current_items, non_neg_integer()}
                   | {no_items, non_neg_integer()}
                   | {current_file, pos_integer()}
                   | {no_overflows, {SinceLogWasOpened :: non_neg_integer(),
                                     SinceLastInfo :: non_neg_integer()}}.
-doc """
Returns a list of `{Tag, Value}` pairs describing a log running on the node.

The following pairs are returned for all logs:

- **`{name, Log}`** - `Log` is the log name as specified by the
  [`open/1`](`open/1`) option `name`.

- **`{file, File}`** - For halt logs `File` is the filename, and for wrap logs
  `File` is the base name.

- **`{type, Type}`** - `Type` is the log type as specified by the
  [`open/1`](`open/1`) option `type`.

- **`{format, Format}`** - `Format` is the log format as specified by the
  [`open/1`](`open/1`) option `format`.

- **`{size, Size}`** - `Size` is the log size as specified by the
  [`open/1`](`open/1`) option `size`, or the size set by
  [`change_size/2`](`change_size/2`). The value set by
  [`change_size/2`](`change_size/2`) is reflected immediately.

- **`{mode, Mode}`** - `Mode` is the log mode as specified by the
  [`open/1`](`open/1`) option `mode`.

- **`{owners, [{pid(), Notify}]}`** - `Notify` is the value set by the
  [`open/1`](`open/1`) option `notify` or function
  [`change_notify/3`](`change_notify/3`) for the owners of the log.

- **`{users, Users}`** - `Users` is the number of anonymous users of the log,
  see the [`open/1`](`open/1`) option [`linkto`](`m:disk_log#linkto`).

- **`{status, Status}`** - `Status` is `ok` or `{blocked, QueueLogRecords}` as
  set by functions `block/1,2` and [`unblock/1`](`unblock/1`).

- **`{node, Node}`** - The information returned by the current invocation of
  function [`info/1`](`info/1`) is gathered from the disk log process running on
  `Node`.

The following pairs are returned for all logs opened in `read_write` mode:

- **`{head, Head}`** - Depending on the value of the [`open/1`](`open/1`)
  options `head` and `head_func`, or set by function
  [`change_header/2`](`change_header/2`), the value of `Head` is `none`
  (default), `{head, H}` (`head` option), or `{M,F,A}` (`head_func` option).

- **`{no_written_items, NoWrittenItems}`** - `NoWrittenItems` is the number of
  items written to the log since the disk log process was created.

The following pair is returned for halt logs opened in `read_write` mode:

- **`{full, Full}`** - `Full` is `true` or `false` depending on whether the halt
  log is full or not.

The following pairs are returned for wrap logs opened in `read_write` mode:

- **`{no_current_bytes, integer() >= 0}`** - The number of bytes written to the
  current wrap log file.

- **`{no_current_items, integer() >= 0}`** - The number of items written to the
  current wrap log file, header inclusive.

- **`{no_items, integer() >= 0}`** - The total number of items in all wrap log
  files.

- **`{current_file, integer()}`** - The ordinal for the current wrap log file in
  the range `1..MaxNoFiles`, where `MaxNoFiles` is specified by the
  [`open/1`](`open/1`) option `size` or set by
  [`change_size/2`](`change_size/2`).

- **`{no_overflows, {SinceLogWasOpened, SinceLastInfo}}`** - `SinceLogWasOpened`
  (`SinceLastInfo`) is the number of times a wrap log file has been filled up
  and a new one is opened or [`inc_wrap_file/1`](`inc_wrap_file/1`) has been
  called since the disk log was last opened ([`info/1`](`info/1`) was last
  called). The first time `info/2` is called after a log was (re)opened or
  truncated, the two values are equal.

Notice that functions [`chunk/2,3`](`chunk/3`), [`bchunk/2,3`](`bchunk/3`), and
[`chunk_step/3`](`chunk_step/3`) do not affect any value returned by
[`info/1`](`info/1`).
""".
-spec info(Log) -> InfoList | {'error', no_such_log} when
      Log :: log(),
      InfoList :: [dlog_info()].
info(Log) -> 
    req(Log, info).

-doc """
Returns the log name given the pid of a disk log process on the current node, or
`undefined` if the specified pid is not a disk log process.

This function is meant to be used for debugging only.
""".
-spec pid2name(Pid) -> {'ok', Log} | 'undefined' when
      Pid :: pid(),
      Log :: log().
pid2name(Pid) ->
    disk_log_server:start(),
    case ets:lookup(?DISK_LOG_PID_TABLE, Pid) of
        [] -> undefined;
        [{_Pid, Log}] -> {ok, Log}
    end.

%% This function Takes 3 args, a Log, a Continuation and N.
%% It returns a {Cont2, ObjList} | eof | {error, Reason}
%% The initial continuation is the atom 'start'

-type chunk_error_rsn() :: no_such_log
                         | {format_external, log()}
                         | {blocked_log, log()}
                         | {badarg, continuation}
                         | {not_internal_wrap, log()}
                         | {corrupt_log_file, FileName :: file:filename()}
                         | {file_error, file:filename(), file_error()}.

-type chunk_ret() :: {Continuation2 :: continuation(), Terms :: [term()]}
                   | {Continuation2 :: continuation(),
                      Terms :: [term()],
                      Badbytes :: non_neg_integer()}
                   | eof
                   | {error, Reason :: chunk_error_rsn()}.

-doc(#{equiv => chunk(Log, Continuation, infinity)}).
-spec chunk(Log, Continuation) -> chunk_ret() when
      Log :: log(),
      Continuation :: start | continuation().
chunk(Log, Cont) ->
    chunk(Log, Cont, infinity).

-doc """
Efficiently reads the terms that are appended to an internally formatted log.

It minimizes disk I/O by reading 64 kilobyte chunks from the file.

The first time `chunk()` is called, an initial continuation, the
atom `start`, must be provided.

When [`chunk/3`](`chunk/3`) is called, `N` controls the maximum number of terms
that are read from the log in each chunk. `infinity` means
that all the terms contained in the 64 kilobyte chunk are read. If less than `N`
terms are returned, this does not necessarily mean that the end of the file is
reached.

`chunk/3` returns a tuple `{Continuation2, Terms}`, where `Terms` is a list of
terms found in the log. `Continuation2` is yet another continuation, which must
be passed on to any subsequent calls to `chunk()`. With a series of calls to
`chunk()`, all terms from a log can be extracted.

`chunk/3` returns a tuple `{Continuation2, Terms, Badbytes}` if the log is
opened in read-only mode and the read chunk is corrupt. `Badbytes` is the number
of bytes in the file found not to be Erlang terms in the chunk. Notice that the
log is not repaired. When trying to read chunks from a log opened in read-write
mode, tuple `{corrupt_log_file, FileName}` is returned if the read chunk is
corrupt.

`chunk/3` returns `eof` when the end of the log is reached, or `{error, Reason}`
if an error occurs. If a wrap log file is missing, a message is output on the
error log.

When [`chunk/2,3`](`chunk/3`) is used with wrap logs, the returned continuation might not be
valid in the next call to `chunk/3`. This is because the log can wrap and delete
the file into which the continuation points. To prevent this, the log can be
blocked during the search.
""".
-spec chunk(Log, Continuation, N) -> chunk_ret() when
      Log :: log(),
      Continuation :: start | continuation(),
      N :: pos_integer() | infinity.
chunk(Log, Cont, infinity) ->
    %% There cannot be more than ?MAX_CHUNK_SIZE terms in a chunk.
    ichunk(Log, Cont, ?MAX_CHUNK_SIZE);
chunk(Log, Cont, N) when is_integer(N), N > 0 ->
    ichunk(Log, Cont, N).

ichunk(Log, start, N) ->
    R = req(Log, {chunk, 0, [], N}),
    ichunk_end(R, Log);
ichunk(Log, More, N) when is_record(More, continuation) ->
    R = req2(More#continuation.pid, 
	     {chunk, More#continuation.pos, More#continuation.b, N}),
    ichunk_end(R, Log);
ichunk(_Log, _, _) ->
    {error, {badarg, continuation}}.

-doc false.
ichunk_end({C, R}, Log) when is_record(C, continuation) ->
    ichunk_end(R, read_write, Log, C, 0);
ichunk_end({C, R, Bad}, Log) when is_record(C, continuation) ->
    ichunk_end(R, read_only, Log, C, Bad);
ichunk_end(R, _Log) ->
    R.

%% Create the terms on the client's heap, not the server's.
%% The list of binaries is reversed.
ichunk_end(R, Mode, Log, C, Bad) ->
    case catch bins2terms(R, []) of
	{'EXIT', _} ->
	    RR = lists:reverse(R),
	    ichunk_bad_end(RR, Mode, Log, C, Bad, []);
	Ts when Bad > 0 ->
	    {C, Ts, Bad};
	Ts when Bad =:= 0 ->
	    {C, Ts}
    end.

bins2terms([], L) ->
    L;
bins2terms([B | Bs], L) ->
    bins2terms(Bs, [binary_to_term(B) | L]).

ichunk_bad_end([B | Bs], Mode, Log, C, Bad, A) ->
    case catch binary_to_term(B) of
	{'EXIT', _} when read_write =:= Mode ->
	    InfoList = info(Log),
	    {value, {file, FileName}} = lists:keysearch(file, 1, InfoList),
            File = case C#continuation.pos of
		       Pos when is_integer(Pos) -> FileName; % halt log 
		       {FileNo, _} -> add_ext(FileName, FileNo) % wrap log
		   end,
	    {error, {corrupt_log_file, File}};
	{'EXIT', _} when read_only =:= Mode ->
	    Reread = lists:foldl(fun(Bin, Sz) -> 
                                         Sz + byte_size(Bin) + ?HEADERSZ 
                                 end, 0, Bs),
	    NewPos = case C#continuation.pos of
			 Pos when is_integer(Pos) -> Pos-Reread;
			 {FileNo, Pos} -> {FileNo, Pos-Reread}
		     end,
	    NewBad = Bad + byte_size(B),
	    {C#continuation{pos = NewPos, b = []}, lists:reverse(A), NewBad};
	T ->
	    ichunk_bad_end(Bs, Mode, Log, C, Bad, [T | A])
    end.

-type bchunk_ret() :: {Continuation2 :: continuation(),
                       Binaries :: [binary()]}
                    | {Continuation2 :: continuation(),
                       Binaries :: [binary()],
                       Badbytes :: non_neg_integer()}
                    | eof
                    | {error, Reason :: chunk_error_rsn()}.

-doc(#{equiv => bchunk(Log, Cont, infinity)}).
-spec bchunk(Log, Continuation) -> bchunk_ret() when
      Log :: log(),
      Continuation :: start | continuation().
bchunk(Log, Cont) ->
    bchunk(Log, Cont, infinity).

-doc """
Equivalent to [`chunk(Log, Continuation, N)`](`chunk/3`) except that
it returns the binaries read from the file, that is it does not call
`binary_to_term/1`.
""".
-spec bchunk(Log, Continuation, N) -> bchunk_ret() when
      Log :: log(),
      Continuation :: start | continuation(),
      N :: pos_integer() | infinity.
bchunk(Log, Cont, infinity) ->
    %% There cannot be more than ?MAX_CHUNK_SIZE terms in a chunk.
    bichunk(Log, Cont, ?MAX_CHUNK_SIZE);
bchunk(Log, Cont, N) when is_integer(N), N > 0 ->
    bichunk(Log, Cont, N).

bichunk(Log, start, N) ->
    R = req(Log, {chunk, 0, [], N}),
    bichunk_end(R);
bichunk(_Log, #continuation{pid = Pid, pos = Pos, b = B}, N) ->
    R = req2(Pid, {chunk, Pos, B, N}),
    bichunk_end(R);
bichunk(_Log, _, _) ->
    {error, {badarg, continuation}}.

bichunk_end({C = #continuation{}, R}) ->
    {C, lists:reverse(R)};
bichunk_end({C = #continuation{}, R, Bad}) ->
    {C, lists:reverse(R), Bad};
bichunk_end(R) ->
    R.

-doc """
Can be used with [`chunk/2,3`](`chunk/3`) and [`bchunk/2,3`](`chunk/3`) to
search through an internally formatted wrap log.

It takes as argument a continuation as returned by [`chunk/2,3`](`chunk/3`),
[`bchunk/2,3`](`bchunk/3`), or [`chunk_step/3`](`chunk_step/3`), and steps
forward (or backward) `Step` files in the wrap log. The continuation returned,
points to the first log item in the new current file.

If atom `start` is specified as continuation, the first file of the wrap log is
chosen as the new current file.

If the wrap log is not full because all files are not yet used,
`{error, end_of_log}` is returned if trying to step outside the log.
""".
-spec chunk_step(Log, Continuation, Step) ->
                        {'ok', any()} | {'error', Reason} when
      Log :: log(),
      Continuation :: start | continuation(),
      Step :: integer(),
      Reason :: no_such_log | end_of_log | {format_external, Log}
              | {blocked_log, Log}  | {badarg, continuation}
              | {file_error, file:filename(), file_error()}.
chunk_step(Log, Cont, N) when is_integer(N) ->
    ichunk_step(Log, Cont, N).

ichunk_step(Log, start, N) ->
    req(Log, {chunk_step, 0, N});
ichunk_step(_Log, More, N) when is_record(More, continuation) ->
    req2(More#continuation.pid, {chunk_step, More#continuation.pos, N});
ichunk_step(_Log, _, _) ->
    {error, {badarg, continuation}}.

-doc """
Returns the pair `{node, Node}`, describing the chunk continuation returned by
`chunk/2,3`, [`bchunk/2,3`](`bchunk/3`), or [`chunk_step/3`](`chunk_step/3`).

Terms are read from the disk log running on `Node`.
""".
-spec chunk_info(Continuation) -> InfoList | {error, Reason} when
      Continuation :: continuation(),
      InfoList :: [{node, Node :: node()}, ...],
      Reason :: {no_continuation, Continuation}.
chunk_info(More = #continuation{}) ->
   [{node, node(More#continuation.pid)}];
chunk_info(BadCont) ->
   {error, {no_continuation, BadCont}}.

-doc "Returns the names of the disk logs accessible on the current node.".
-doc(#{since => <<"OTP 24.0">>}).
-spec all() -> [Log] when
      Log :: log().
all() ->
    disk_log_server:all().

-doc false.
istart_link(Server) ->  
    {ok, proc_lib:spawn_link(disk_log, init, [self(), Server])}.

%% Only for backwards compatibility, could probably be removed.
-doc false.
-spec start() -> 'ok'.
start() ->
    disk_log_server:start().

-doc false.
internal_open(Pid, A) ->
    req2(Pid, {internal_open, A}).

%%% ll_open() and ll_close() are used by disk_log_h.erl, a module not
%%% (yet) in Erlang/OTP.

%% -spec ll_open(dlog_options()) -> {'ok', Res :: _, #log{}, Cnt :: _} | Error.
-doc false.
ll_open(A) ->
    case check_arg(A, #arg{options = A}) of
	{ok, L} -> do_open(L);
	Error -> Error
    end.

%% -> closed | throw(Error)
-doc false.
ll_close(Log) ->
    close_disk_log2(Log).

check_arg([], Res) ->
    Ret = case Res#arg.head of
	      none ->
		  {ok, Res};
	      _ ->
		  case check_head(Res#arg.head, Res#arg.format) of
		      {ok, Head} ->
			  {ok, Res#arg{head = Head}};
		      Error ->
			  Error
		  end
	  end,

    if  %% check result
	Res#arg.name =:= 0 -> 
	    {error, {badarg, name}};
	Res#arg.file =:= none ->
	    case catch lists:concat([Res#arg.name, ".LOG"]) of
		{'EXIT',_} -> {error, {badarg, file}};
		FName ->  check_arg([], Res#arg{file = FName})
	    end;
	Res#arg.repair =:= truncate, Res#arg.mode =:= read_only ->
	    {error, {badarg, repair_read_only}};
	Res#arg.type =:= halt, is_tuple(Res#arg.size) ->
	    {error, {badarg, size}};
	Res#arg.type =:= wrap ->
	    {OldSize, Version} = 
		disk_log_1:read_size_file_version(Res#arg.file),
	    check_wrap_arg(Ret, OldSize, Version);
        Res#arg.type =:= rotate ->
            case Ret of
                {ok, Patched} ->
                    {ok, Patched#arg{format = external}};
                _ ->
                    Ret
            end;
	true ->
	    Ret
    end;
check_arg([{file, F} | Tail], Res) when is_list(F) ->
    check_arg(Tail, Res#arg{file = F});
check_arg([{file, F} | Tail], Res) when is_atom(F) ->
    check_arg(Tail, Res#arg{file = F});
check_arg([{linkto, Pid} |Tail], Res) when is_pid(Pid) ->
    check_arg(Tail, Res#arg{linkto = Pid});
check_arg([{linkto, none} |Tail], Res) ->
    check_arg(Tail, Res#arg{linkto = none});
check_arg([{name, Name}|Tail], Res) ->
    check_arg(Tail, Res#arg{name = Name});
check_arg([{repair, true}|Tail], Res) ->
    check_arg(Tail, Res#arg{repair = true});
check_arg([{repair, false}|Tail], Res) ->
    check_arg(Tail, Res#arg{repair = false});
check_arg([{repair, truncate}|Tail], Res) ->
    check_arg(Tail, Res#arg{repair = truncate});
check_arg([{size, Int}|Tail], Res) when is_integer(Int), Int > 0 ->
    check_arg(Tail, Res#arg{size = Int});
check_arg([{size, infinity}|Tail], Res) ->
    check_arg(Tail, Res#arg{size = infinity});
check_arg([{size, {MaxB,MaxF}}|Tail], Res) when is_integer(MaxB), 
                                                is_integer(MaxF),
						MaxB > 0, MaxB =< ?MAX_BYTES,
						MaxF > 0, MaxF < ?MAX_FILES ->
    check_arg(Tail, Res#arg{size = {MaxB, MaxF}});
check_arg([{type, rotate}|Tail], Res) ->
    check_arg(Tail, Res#arg{type = rotate});
check_arg([{type, wrap}|Tail], Res) ->
    check_arg(Tail, Res#arg{type = wrap});
check_arg([{type, halt}|Tail], Res) ->
    check_arg(Tail, Res#arg{type = halt});
check_arg([{format, internal}|Tail], Res) ->
    check_arg(Tail, Res#arg{format = internal});
check_arg([{format, external}|Tail], Res) ->
    check_arg(Tail, Res#arg{format = external});
check_arg([{notify, true}|Tail], Res) ->
    check_arg(Tail, Res#arg{notify = true});
check_arg([{notify, false}|Tail], Res) ->
    check_arg(Tail, Res#arg{notify = false});
check_arg([{head_func, HeadFunc}|Tail], Res)  ->
    check_arg(Tail, Res#arg{head = {head_func, HeadFunc}});
check_arg([{head, Term}|Tail], Res) ->
    check_arg(Tail, Res#arg{head = {head, Term}});
check_arg([{mode, read_only}|Tail], Res) ->
    check_arg(Tail, Res#arg{mode = read_only});
check_arg([{mode, read_write}|Tail], Res) ->
    check_arg(Tail, Res#arg{mode = read_write});
check_arg([{quiet, Boolean}|Tail], Res) when is_boolean(Boolean) ->
    check_arg(Tail, Res#arg{quiet = Boolean});
check_arg(Arg, _) ->
    {error, {badarg, Arg}}.

check_wrap_arg({ok, Res}, {0,0}, _Version) when Res#arg.size =:= infinity ->
    {error, {badarg, size}};
check_wrap_arg({ok, Res}, OldSize, Version) when Res#arg.size =:= infinity ->
    {ok,  Res#arg{version = Version, old_size = OldSize, size = OldSize}};
check_wrap_arg({ok, Res}, {0,0}, Version) ->
    {ok, Res#arg{version = Version, old_size = Res#arg.size}};
check_wrap_arg({ok, Res}, OldSize, Version) when OldSize =:= Res#arg.size ->
    {ok, Res#arg{version = Version, old_size = OldSize}};
check_wrap_arg({ok, Res}, OldSize, Version) when Res#arg.repair =:= truncate,
                                                 is_tuple(Res#arg.size) ->
    {ok, Res#arg{version = Version, old_size = OldSize}};
check_wrap_arg({ok, Res}, OldSize, _Version) when Res#arg.size =/= OldSize,
                                                  Res#arg.mode =:= read_only ->
    {error, {size_mismatch, OldSize, Res#arg.size}};
check_wrap_arg({ok, Res}, OldSize, Version) when is_tuple(Res#arg.size) ->
    {ok, Res#arg{version = Version, old_size = OldSize}};
check_wrap_arg({ok, _Res}, _OldSize, _Version) ->
    {error, {badarg, size}};
check_wrap_arg(Ret, _OldSize, _Version) ->
    Ret.

%%%-----------------------------------------------------------------
%%% Server functions
%%%-----------------------------------------------------------------
-doc false.
init(Parent, Server) ->
    ?PROFILE(ep:do()),
    process_flag(trap_exit, true),
    loop(#state{parent = Parent, server = Server}).

loop(#state{messages = []}=State) ->
    receive
	Message ->
	    handle(Message, State)
    end;
loop(#state{messages = [M | Ms]}=State) ->
    handle(M, State#state{messages = Ms}).

handle({From, write_cache}, S) when From =:= self() ->
    case catch do_write_cache(get(log)) of
        ok ->
            loop(S);
        Error ->
	    loop(S#state{cache_error = Error})
    end;
handle({From, {log, Format, B}}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{status = ok, format=external}=L when Format =:= internal ->
	    reply(From, {error, {format_external, L#log.name}}, S);
	#log{status = ok, format=LogFormat} ->
	    log_loop(S, From, [B], [], iolist_size(B), LogFormat);
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({alog, Format, B}=Message, S) ->
    case get(log) of
	#log{mode = read_only} ->
	    notify_owners({read_only,B}),
	    loop(S);
	#log{status = ok, format = external} when Format =:= internal ->
	    notify_owners({format_external, B}),
	    loop(S);
	#log{status = ok, format=LogFormat} ->
	    log_loop(S, [], [B], [], iolist_size(B), LogFormat);
	#log{status = {blocked, false}} ->
	    notify_owners({blocked_log, B}),
	    loop(S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {block, QueueLogRecs}}=Message, S) ->
    case get(log) of
	#log{status = ok}=L ->
	    do_block(From, QueueLogRecs, L),
	    reply(From, ok, S);
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, unblock}, S) ->
    case get(log) of
	#log{status = ok}=L ->
	    reply(From, {error, {not_blocked, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    S2 = do_unblock(L, S),
	    reply(From, ok, S2);
	L ->
	    reply(From, {error, {not_blocked_by_pid, L#log.name}}, S)
    end;
handle({From, sync}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{status = ok, format=LogFormat} ->
            log_loop(S, [], [], [From], 0, LogFormat);
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {truncate, Head, F, A}}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{status = ok} when S#state.cache_error =/= ok ->
	    loop(cache_error(S, [From]));
	#log{status = ok}=L ->
	    H = merge_head(Head, L#log.head),
	    case catch do_trunc(L, H) of
		ok ->
		    erase(is_full),
		    notify_owners({truncated, S#state.cnt}),
		    N = if H =:= none -> 0; true -> 1 end,
		    reply(From, ok, (state_ok(S))#state{cnt = N});
		Error ->
		    do_exit(S, From, Error, ?failure(Error, F, A))
	    end;
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {chunk, Pos, B, N}}=Message,  S) ->
    case get(log) of
	#log{status = ok} when S#state.cache_error =/= ok ->
	    loop(cache_error(S, [From]));
	#log{status = ok}=L ->
	    R = do_chunk(L, Pos, B, N),
	    reply(From, R, S);
	#log{blocked_by = From}=L ->
	    R = do_chunk(L, Pos, B, N),
	    reply(From, R, S);
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_L ->
	    enqueue(Message, S)
    end;
handle({From, {chunk_step, Pos, N}}=Message,  S) ->
    case get(log) of
	#log{status = ok} when S#state.cache_error =/= ok ->
	    loop(cache_error(S, [From]));
	#log{status = ok}=L ->
	    R = do_chunk_step(L, Pos, N),
	    reply(From, R, S);
	#log{blocked_by = From}=L ->
	    R = do_chunk_step(L, Pos, N),
	    reply(From, R, S);
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {change_notify, Pid, NewNotify}}=Message, S) ->
    case get(log) of
	#log{status = ok}=L ->
	    case do_change_notify(L, Pid, NewNotify) of
		{ok, L1} ->
		    put(log, L1),
		    reply(From, ok, S);
		Error ->
		    reply(From, Error, S)
	    end;
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {change_header, NewHead}}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{status = ok, format = Format}=L ->
	    case check_head(NewHead, Format) of
		{ok, Head} ->
		    put(log, L#log{head = mk_head(Head, Format)}),
		    reply(From, ok, S);
		Error ->
		    reply(From, Error, S)
	    end;
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {change_size, NewSize}}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{status = ok}=L ->
	    case check_size(L#log.type, NewSize) of
		ok ->
		    case catch do_change_size(L, NewSize) of % does the put
			ok ->
			    reply(From, ok, S);
			{big, CurSize} ->
			    reply(From, 
				  {error, 
				   {new_size_too_small, L#log.name, CurSize}},
				  S);
			Else ->
			    reply(From, Else, state_err(S, Else))
		    end;
		not_ok ->
		    reply(From, {error, {badarg, size}}, S)
	    end;
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, inc_wrap_file}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{type = halt}=L ->
	    reply(From, {error, {halt_log, L#log.name}}, S);
	#log{type = rotate}=L ->
	    reply(From, {error, {rotate_log, L#log.name}}, S);
	#log{status = ok} when S#state.cache_error =/= ok ->
	    loop(cache_error(S, [From]));
	#log{status = ok}=L ->
	    case catch do_inc_wrap_file(L) of
		{ok, L2, Lost} ->
		    put(log, L2),
		    notify_owners({L#log.type, Lost}),
		    reply(From, ok, S#state{cnt = S#state.cnt-Lost});
		{error, Error, L2} ->
		    put(log, L2),		    
		    reply(From, Error, state_err(S, Error))
	    end;
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, next_file}=Message, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{type = halt}=L ->
	    reply(From, {error, {halt_log, L#log.name}}, S);
	#log{status = ok} when S#state.cache_error =/= ok ->
	    loop(cache_error(S, [From]));
	#log{status = ok, type = wrap}=L ->
	    case catch do_inc_wrap_file(L) of
		{ok, L2, Lost} ->
		    put(log, L2),
		    notify_owners({L#log.type, Lost}),
		    reply(From, ok, S#state{cnt = S#state.cnt-Lost});
		{error, Error, L2} ->
		    put(log, L2),		    
		    reply(From, Error, state_err(S, Error))
	    end;
        #log{status = ok, type = rotate}=L ->
            {ok, L2} = do_inc_rotate_file(L),
	    put(log, L2),
	    reply(From, ok, S);
	#log{status = {blocked, false}}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	#log{blocked_by = From}=L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S);
	_ ->
	    enqueue(Message, S)
    end;
handle({From, {reopen, NewFile, Head, F, A}}, S) ->
    case get(log) of
	#log{mode = read_only}=L ->
	    reply(From, {error, {read_only_mode, L#log.name}}, S);
	#log{status = ok} when S#state.cache_error =/= ok ->
	    loop(cache_error(S, [From]));
	#log{status = ok, filename = NewFile}=L ->
	    reply(From, {error, {same_file_name, L#log.name}}, S);
	#log{status = ok}=L ->
	    case catch close_disk_log2(L) of
		closed ->
		    File = L#log.filename,
		    case catch rename_file(File, NewFile, L) of
			ok ->
			    H = merge_head(Head, L#log.head),
			    case do_open((S#state.args)#arg{name = L#log.name,
							    repair = truncate,
							    head = H,
							    file = File}) of
				{ok, Res, L2, Cnt} ->
				    put(log, L2#log{owners = L#log.owners,
						    head = L#log.head,
						    users = L#log.users}),
				    notify_owners({truncated, S#state.cnt}),
				    erase(is_full),
				    case Res of
					{error, _} ->
					    do_exit(S, From, Res, 
						    ?failure(Res, F, A));
					_ ->
					    reply(From, ok, S#state{cnt = Cnt})
				    end;
				Res ->
				    do_exit(S, From, Res, ?failure(Res, F, A))
			    end;
			Error ->
			    do_exit(S, From, Error, ?failure(Error, reopen, 2))
		    end;
		Error ->
		    do_exit(S, From, Error, ?failure(Error, F, A))
	    end;
	L ->
	    reply(From, {error, {blocked_log, L#log.name}}, S)
    end;
handle({Server, {internal_open, A}}, S) ->
    case get(log) of
	undefined ->
	    case do_open(A) of % does the put
		{ok, Res, L, Cnt} ->
		    put(log, opening_pid(A#arg.linkto, A#arg.notify, L)),
                    #arg{size = Size, old_size = OldSize} = A,
                    S1 = S#state{args=A, cnt=Cnt},
                    case Size =:= OldSize of
                        true ->
                            reply(Server, Res, S1);
                        false ->
                            case catch do_change_size(get(log), Size) of % does the put
                                ok ->
                                    reply(Server, Res, S1);
                                {big, _CurSize} ->
                                    %% Note: halt logs are opened even if the
                                    %% given size is too small.
                                    reply(Server, Res, S1);
                                Else ->
                                    reply(Server, Else, S1)
                            end
                    end;
		Res ->
		    do_fast_exit(S, Server, Res)
	    end;
	L ->
	    TestH = mk_head(A#arg.head, A#arg.format),
	    case compare_arg(A#arg.options, S#state.args, TestH, L#log.head) of
		ok ->
		    case add_pid(A#arg.linkto, A#arg.notify, L) of
			{ok, L1} ->
			    put(log, L1),
			    reply(Server, {ok, L#log.name}, S);
			Error ->
			    reply(Server, Error, S)
		    end;
		Error ->
		    reply(Server, Error, S)
	    end
    end;
handle({From, close}, S) ->
    case do_close(From, S) of
	{stop, S1} ->
	    do_exit(S1, From, ok, normal);
	{continue, S1} ->
	    reply(From, ok, S1)
    end;
handle({From, info}, S) ->
    reply(From, do_info(get(log), S#state.cnt), S);
handle({'EXIT', From, Reason}, #state{parent=From}=S) ->
    %% Parent orders shutdown.
    _ = do_stop(S),
    exit(Reason);
handle({'EXIT', From, Reason}, #state{server=From}=S) ->
    %% The server is gone.
    _ = do_stop(S),
    exit(Reason);
handle({'EXIT', From, _Reason}, S) ->
    L = get(log),
    case is_owner(From, L) of
	{true, _Notify} ->
	    case close_owner(From, L, S) of
		{stop, S1} ->
		    _ = do_stop(S1),
		    exit(normal);
		{continue, S1} ->
		    loop(S1)
	    end;
	false ->
	    %% 'users' is not decremented.
	    S1 = do_unblock(From, get(log), S),
	    loop(S1)
    end;
handle({system, From, Req}, S) ->
    sys:handle_system_msg(Req, From, S#state.parent, ?MODULE, [], S);
handle(_, S) ->
    loop(S).

enqueue(Message, #state{queue = Queue}=S) ->
    loop(S#state{queue = [Message | Queue]}).

%% Collect further log and sync requests already in the mailbox or queued

-define(MAX_LOOK_AHEAD, 64*1024).

%% Inlined.
log_loop(#state{cache_error = CE}=S, Pids, _Bins, _Sync, _Sz, _F) when CE =/= ok ->
    loop(cache_error(S, Pids));
log_loop(#state{}=S, Pids, Bins, Sync, Sz, _F) when Sz > ?MAX_LOOK_AHEAD ->
    loop(log_end(S, Pids, Bins, Sync, Sz));
log_loop(#state{messages = []}=S, Pids, Bins, Sync, Sz, F) ->
    receive
	Message ->
            log_loop(Message, Pids, Bins, Sync, Sz, F, S)
    after 0 ->
	    loop(log_end(S, Pids, Bins, Sync, Sz))
    end;
log_loop(#state{messages = [M | Ms]}=S, Pids, Bins, Sync, Sz, F) ->
    S1 = S#state{messages = Ms},
    log_loop(M, Pids, Bins, Sync, Sz, F, S1).

%% Items logged after the last sync request found are sync:ed as well.
log_loop({alog, internal, B}, Pids, Bins, Sync, Sz, internal=F, S) ->
    %% alog of terms allowed for the internal format only
    log_loop(S, Pids, [B | Bins], Sync, Sz+iolist_size(B), F);
log_loop({alog, binary, B}, Pids, Bins, Sync, Sz, F, S) ->
    log_loop(S, Pids, [B | Bins], Sync, Sz+iolist_size(B), F);
log_loop({From, {log, internal, B}}, Pids, Bins, Sync, Sz, internal=F, S) ->
    %% log of terms allowed for the internal format only
    log_loop(S, [From | Pids], [B | Bins], Sync, Sz+iolist_size(B), F);
log_loop({From, {log, binary, B}}, Pids, Bins, Sync, Sz, F, S) ->
    log_loop(S, [From | Pids], [B | Bins], Sync, Sz+iolist_size(B), F);
log_loop({From, sync}, Pids, Bins, Sync, Sz, F, S) ->
    log_loop(S, Pids, Bins, [From | Sync], Sz, F);
log_loop(Message, Pids, Bins, Sync, Sz, _F, S) ->
    NS = log_end(S, Pids, Bins, Sync, Sz),
    handle(Message, NS).

log_end(S, [], [], Sync, _Sz) ->
    log_end_sync(S, Sync);
log_end(#state{cnt = Cnt}=S, Pids, Bins, Sync, Sz) ->
    case do_log(get(log), rflat(Bins), Sz) of
	N when is_integer(N) ->
	    ok = replies(Pids, ok),
	    S1 = (state_ok(S))#state{cnt = Cnt + N},
	    log_end_sync(S1, Sync);
        {error, {error, {full, _Name}}, N} when Pids =:= [] ->
            log_end_sync(state_ok(S#state{cnt = Cnt + N}), Sync);
	{error, Error, N} ->
	    ok = replies(Pids, Error),
	    state_err(S#state{cnt = Cnt + N}, Error)
    end.

%% Inlined.
log_end_sync(S, []) ->
    S;
log_end_sync(S, Sync) ->
    Res = do_sync(get(log)),
    ok = replies(Sync, Res),
    state_err(S, Res).

%% Inlined.
rflat([B]) -> B;
rflat(B) -> rflat(B, []).

rflat([B | Bs], L) ->
    rflat(Bs, B ++ L);
rflat([], L) -> L.

%% -> {ok, Log} | {error, Error}
do_change_notify(L, Pid, Notify) ->
    case is_owner(Pid, L) of
	{true, Notify} ->
	    {ok, L};
	{true, _OldNotify} when Notify =/= true, Notify =/= false ->
	    {error, {badarg, notify}};
	{true, _OldNotify} ->
	    Owners = lists:keydelete(Pid, 1, L#log.owners),
	    L1 = L#log{owners = [{Pid, Notify} | Owners]},
	    {ok, L1};
	false ->
	    {error, {not_owner, Pid}}
    end.

%% -> {stop, S} | {continue, S}
do_close(Pid, S) ->
    L = get(log),
    case is_owner(Pid, L) of
	{true, _Notify} ->
	    close_owner(Pid, L, S);
	false ->
	    close_user(Pid, L, S)
    end.

%% -> {stop, S} | {continue, S}
close_owner(Pid, L, S) ->
    L1 = L#log{owners = lists:keydelete(Pid, 1, L#log.owners)},
    put(log, L1),
    S2 = do_unblock(Pid, get(log), S),
    unlink(Pid),
    do_close2(L1, S2).

%% -> {stop, S} | {continue, S}
close_user(Pid, #log{users=Users}=L, S) when Users > 0 ->
    L1 = L#log{users = Users - 1},
    put(log, L1),
    S2 = do_unblock(Pid, get(log), S),
    do_close2(L1, S2);
close_user(_Pid, _L, S) ->
    {continue, S}.

do_close2(#log{users = 0, owners = []}, S) ->
    {stop, S};
do_close2(_L, S) ->
    {continue, S}.

%%-----------------------------------------------------------------
%% Callback functions for system messages handling.
%%-----------------------------------------------------------------
-doc false.
system_continue(_Parent, _, State) ->
    loop(State).

-doc false.
-spec system_terminate(_, _, _, #state{}) -> no_return().
system_terminate(Reason, _Parent, _, State) ->
    _ = do_stop(State),
    exit(Reason).

%%-----------------------------------------------------------------
%% Temporary code for upgrade.
%%-----------------------------------------------------------------
-doc false.
system_code_change(State, _Module, _OldVsn, _Extra) ->
    {ok, State}.


%%%----------------------------------------------------------------------
%%% Internal functions
%%%----------------------------------------------------------------------
-spec do_exit(#state{}, pid(), _, _) -> no_return().
do_exit(S, From, Message0, Reason) ->
    R = do_stop(S),
    Message = case S#state.cache_error of
		  Err when Err =/= ok -> Err;
		  _ when R =:= closed -> Message0;
		  _ when Message0 =:= ok -> R;
		  _ -> Message0
	      end,
    _ = disk_log_server:close(self()),
    ok = replies(From, Message),
    ?PROFILE(ep:done()),
    exit(Reason).

-spec do_fast_exit(#state{}, pid(), _) -> no_return().
do_fast_exit(S, Server, Message) ->
    _ = do_stop(S),
    Server ! {disk_log, self(), Message},
    exit(normal).

%% -> closed | Error
do_stop(S) ->
    proc_q(S#state.queue ++ S#state.messages),
    close_disk_log(get(log)).

proc_q([{From, _R}|Tail]) when is_pid(From) ->
    From ! {disk_log, self(), {error, disk_log_stopped}},
    proc_q(Tail);
proc_q([_|T]) -> %% async stuff 
    proc_q(T);
proc_q([]) ->
    ok.

%% -> log()
opening_pid(Pid, Notify, L) ->
    {ok, L1} = add_pid(Pid, Notify, L),
    L1.

%% -> {ok, log()} | Error
add_pid(Pid, Notify, L) when is_pid(Pid) ->
    case is_owner(Pid, L) of
	false ->
            link(Pid),
	    {ok, L#log{owners = [{Pid, Notify} | L#log.owners]}};
	{true, Notify}  ->
%%	    {error, {pid_already_connected, L#log.name}};
	    {ok, L};
	{true, CurNotify} when Notify =/= CurNotify ->
	    {error, {arg_mismatch, notify, CurNotify, Notify}}
    end;
add_pid(_NotAPid, _Notify, L) ->
    {ok, L#log{users = L#log.users + 1}}.

unblock_pid(#log{blocked_by = none}) ->
    ok;
unblock_pid(#log{blocked_by = Pid}=L) ->
    case is_owner(Pid, L) of
	{true, _Notify} ->
	    ok;
	false ->
	    unlink(Pid)
    end.

%% -> true | false
is_owner(Pid, L) ->
    case lists:keysearch(Pid, 1, L#log.owners) of
	{value, {_Pid, Notify}} ->
	    {true, Notify};
	false ->
	    false
    end.

%% ok | throw(Error)
rename_file(File, NewFile, #log{type = halt}) ->
    case file:rename(File, NewFile) of
        ok ->
            ok;
        Else ->
            file_error(NewFile, Else)
    end;
rename_file(File, NewFile, #log{type = wrap}) ->
    rename_file(wrap_file_extensions(File), File, NewFile, ok);
rename_file(File, NewFile, #log{type = rotate, extra = Handle}) ->
    {_MaxB, MaxF} = disk_log_1:get_rotate_size(Handle),
    disk_log_1:rotate_files(Handle#rotate_handle.file, MaxF),
    rename_file(rotate_file_extensions(File, MaxF), File, NewFile, ok).

rename_file([Ext|Exts], File, NewFile0, Res) ->
    NewFile = add_ext(NewFile0, Ext),
    NRes = case file:rename(add_ext(File, Ext), NewFile) of
	       ok ->
		   Res;
	       Else ->
		   file_error(NewFile, Else)
	   end,
    rename_file(Exts, File, NewFile0, NRes);
rename_file([], _File, _NewFiles, Res) -> Res.

file_error(FileName, {error, Error}) ->
    {error, {file_error, FileName, Error}}.

%% "Old" error messages have been kept, arg_mismatch has been added.
%%-spec compare_arg(dlog_options(), #arg{}, 
compare_arg([], _A, none, _OrigHead) ->
    % no header option given
    ok;
compare_arg([], _A, Head, OrigHead) when Head =/= OrigHead ->
    {error, {arg_mismatch, head, OrigHead, Head}};
compare_arg([], _A, _Head, _OrigHead) ->
    ok;
compare_arg([{Attr, Val} | Tail], A, Head, OrigHead) ->
    case compare_arg(Attr, Val, A) of
	{not_ok, OrigVal} -> 
	    {error, {arg_mismatch, Attr, OrigVal, Val}};
	ok -> 
	    compare_arg(Tail, A, Head, OrigHead);
	Error -> 
	    Error
    end.

-spec compare_arg(atom(), _, #arg{}) ->
	     'ok' | {'not_ok', _} | {'error', {atom(), _}}.
compare_arg(file, F, A) when F =/= A#arg.file ->
    {error, {name_already_open, A#arg.name}};
compare_arg(mode, read_only, A) when A#arg.mode =:= read_write ->
    {error, {open_read_write, A#arg.name}};
compare_arg(mode, read_write, A) when A#arg.mode =:= read_only ->
    {error, {open_read_only, A#arg.name}};
compare_arg(type, T, A) when T =/= A#arg.type ->
    {not_ok, A#arg.type};
compare_arg(format, F, A) when F =/= A#arg.format ->
    {not_ok, A#arg.format};
compare_arg(repair, R, A) when R =/= A#arg.repair ->
    %% not used, but check it anyway...
    {not_ok, A#arg.repair};
compare_arg(size, Sz, A) when Sz =/= A#arg.size, A#arg.type =:= wrap ->
    %% Note: if the given size does not match the size of an open
    %% halt log, the given size is ignored.
    {error, {size_mismatch, A#arg.size, Sz}};
compare_arg(_Attr, _Val, _A) -> 
    ok.

%% -> {ok, Res, log(), Cnt} | Error
do_open(#arg{type = rotate} = A) ->
    #arg{name = Name, size = Size, mode = Mode, head = Head0,
         format = Format, type = Type, file = FName} = A,
    Head = mk_head(Head0, Format),
    case disk_log_1:open_rotate_log_file(FName, Size, Head) of
        {ok, RotHandle} ->
            L = #log{name = Name, type = Type, format = Format,
                     filename = FName, size = Size, mode = Mode,
                     extra = RotHandle, format_type = rotate_ext,
                     head = Head},
            {ok, {ok, Name}, L, 0};
        Error ->
            Error
    end;
do_open(A) ->
    #arg{type = Type, format = Format, name = Name, head = Head0,
         file = FName, repair = Repair, size = Size, mode = Mode,
         quiet = Quiet, version = V, old_size = OldSize} = A,
    disk_log_1:set_quiet(Quiet),
    Head = mk_head(Head0, Format),
    case do_open2(Type, Format, Name, FName, Repair, OldSize, Mode, Head, V) of
        {ok, Ret, Extra, FormatType, NoItems} ->
            L = #log{name = Name, type = Type, format = Format,
                     filename = FName, size = Size,
                     format_type = FormatType, head = Head, mode = Mode,
                     version = V, extra = Extra},
            {ok, Ret, L, NoItems};
        Error ->
            Error
    end.

mk_head({head, Term}, internal) -> {ok, term_to_binary(Term)};
mk_head({head, Bytes}, external) -> {ok, ensure_binary(Bytes)};
mk_head(H, _) -> H.

terms2bins([T | Ts]) ->
    [term_to_binary(T) | terms2bins(Ts)];
terms2bins([]) ->
    [].

ensure_binary_list(Bs) ->
    ensure_binary_list(Bs, Bs).

ensure_binary_list([B | Bs], Bs0) when is_binary(B) ->
    ensure_binary_list(Bs, Bs0);
ensure_binary_list([], Bs0) ->
    Bs0;
ensure_binary_list(_, Bs0) ->
    make_binary_list(Bs0).

make_binary_list([B | Bs]) ->
    [ensure_binary(B) | make_binary_list(Bs)];
make_binary_list([]) ->
    [].

ensure_binary(Bytes) ->
    iolist_to_binary(Bytes).

%%-----------------------------------------------------------------
%% Change size of the logs in runtime.
%%-----------------------------------------------------------------
%% -> ok | {big, CurSize} | throw(Error)
do_change_size(#log{type = halt}=L, NewSize) ->
    Halt = L#log.extra,
    CurB = Halt#halt.curB,
    NewLog = L#log{extra = Halt#halt{size = NewSize}},
    if
	NewSize =:= infinity ->
	    erase(is_full),
	    put(log, NewLog),
	    ok;
	CurB =< NewSize ->
	    erase(is_full),
	    put(log, NewLog),
	    ok;
	true ->
	    {big, CurB}
    end;
do_change_size(#log{type = wrap}=L, NewSize) ->
    #log{extra = Extra, version = Version} = L,
    {ok, Handle} = disk_log_1:change_size_wrap(Extra, NewSize, Version),
    erase(is_full),
    put(log, L#log{extra = Handle}),
    ok;
do_change_size(#log{type =rotate, extra = Extra} = L, NewSize) ->
    {ok, Handle} = disk_log_1:change_size_rotate(Extra, NewSize),
    erase(is_full),
    put(log, L#log{extra = Handle}),
    ok.

%% -> {ok, Head} | Error; Head = none | {head, H} | {M,F,A}
check_head({head, none}, _Format) ->
    {ok, none};
check_head({head_func, {M, F, A}}, _Format) when is_atom(M), 
                                                 is_atom(F), 
                                                 is_list(A) ->
    {ok, {M, F, A}};
check_head({head, Head}, external) ->
    case catch ensure_binary(Head) of
	{'EXIT', _} ->
	    {error, {badarg, head}};
	_ ->
	    {ok, {head, Head}}
    end;
check_head({head, Term}, internal) ->
    {ok, {head, Term}};
check_head(_Head, _Format) ->
    {error, {badarg, head}}.

check_size(halt, NewSize) when is_integer(NewSize), NewSize > 0 ->
    ok;
check_size(halt, infinity) ->
    ok;
check_size(Type, {NewMaxB,NewMaxF}) when
    (Type =:= wrap orelse Type =:= rotate) andalso
    is_integer(NewMaxB), is_integer(NewMaxF),
    NewMaxB > 0, NewMaxB =< ?MAX_BYTES, NewMaxF > 0, NewMaxF < ?MAX_FILES ->
    ok;
check_size(_, _) ->
    not_ok.

%%-----------------------------------------------------------------
%% Increment a wrap log.
%%-----------------------------------------------------------------
%% -> {ok, log(), Lost} | {error, Error, log()}
do_inc_wrap_file(L) ->
    #log{format = Format, extra = Handle} = L,
    case Format of
	internal ->
	    case disk_log_1:mf_int_inc(Handle, L#log.head) of
		{ok, Handle2, Lost} ->
		    {ok, L#log{extra = Handle2}, Lost};
		{error, Error, Handle2} ->
		    {error, Error, L#log{extra = Handle2}}
	    end;
	external ->
	    case disk_log_1:mf_ext_inc(Handle, L#log.head) of
		{ok, Handle2, Lost} ->
		    {ok, L#log{extra = Handle2}, Lost};
		{error, Error, Handle2} ->
		    {error, Error, L#log{extra = Handle2}}
	    end
    end.

%%-----------------------------------------------------------------
%% Force log rotation.
%%-----------------------------------------------------------------
%% -> {ok, log()}
do_inc_rotate_file(#log{extra = Handle, head = Head} = L) ->
    Handle2 = disk_log_1:do_rotate(Handle, Head),
    {ok, L#log{extra = Handle2}}.

%%-----------------------------------------------------------------
%% Open a log file.
%%-----------------------------------------------------------------
%% -> {ok, Reply, log(), Cnt} | Error
%% Note: the header is always written, even if the log size is too small.
do_open2(halt, internal, Name, FName, Repair, Size, Mode, Head, _V) ->
    case catch disk_log_1:int_open(FName, Repair, Mode, Head) of
	{ok, {_Alloc, FdC, {NoItems, _NoBytes}, FileSize}} ->
            Halt = #halt{fdc = FdC, curB = FileSize, size = Size},
	    {ok, {ok, Name}, Halt, halt_int, NoItems};
	{repaired, FdC, Rec, Bad, FileSize} ->
            Halt = #halt{fdc = FdC, curB = FileSize, size = Size},
	    {ok, {repaired, Name, {recovered, Rec}, {badbytes, Bad}},
             Halt, halt_int, Rec};
	Error ->
	    Error
    end;
do_open2(wrap, internal, Name, FName, Repair, Size, Mode, Head, V) ->
    {MaxB, MaxF} = Size,
    case catch 
      disk_log_1:mf_int_open(FName, MaxB, MaxF, Repair, Mode, Head, V) of
	{ok, Handle, Cnt} ->
	    {ok, {ok, Name}, Handle, wrap_int, Cnt};
	{repaired, Handle, Rec, Bad, Cnt} ->
	    {ok, {repaired, Name, {recovered, Rec}, {badbytes, Bad}},
	     Handle, wrap_int, Cnt};
	Error ->
	    Error
    end;
do_open2(halt, external, Name, FName, Repair, Size, Mode, Head, _V) ->
    case catch disk_log_1:ext_open(FName, Repair, Mode, Head) of
	{ok, {_Alloc, FdC, {NoItems, _NoBytes}, FileSize}} ->
            Halt = #halt{fdc = FdC, curB = FileSize, size = Size},
	    {ok, {ok, Name}, Halt, halt_ext, NoItems};
	Error ->
	    Error
    end;
do_open2(wrap, external, Name, FName, Repair, Size, Mode, Head, V) ->
    {MaxB, MaxF} = Size,
    case catch 
      disk_log_1:mf_ext_open(FName, MaxB, MaxF, Repair, Mode, Head, V) of
	{ok, Handle, Cnt} ->
	    {ok, {ok, Name}, Handle, wrap_ext, Cnt};
	Error ->
	    Error
    end.

%% -> closed | Error
close_disk_log(undefined) ->
    closed;
close_disk_log(L) ->
    unblock_pid(L),
    F = fun({Pid, _}) -> 
		unlink(Pid) 
	end,
    lists:foreach(F, L#log.owners),
    R = (catch close_disk_log2(L)),
    erase(log),
    R.

-spec close_disk_log2(#log{}) -> 'closed'. % | throw(Error)

close_disk_log2(L) ->
    case L of
	#log{format_type = halt_int, mode = Mode, extra = Halt} ->
	    disk_log_1:close(Halt#halt.fdc, L#log.filename, Mode);
	#log{format_type = wrap_int, mode = Mode, extra = Handle} ->
	    disk_log_1:mf_int_close(Handle, Mode);
	#log{format_type = halt_ext, extra = Halt} ->
	    disk_log_1:fclose(Halt#halt.fdc, L#log.filename);
	#log{format_type = wrap_ext, mode = Mode, extra = Handle} ->
	    disk_log_1:mf_ext_close(Handle, Mode);
        #log{type = rotate, extra = Handle} ->
            disk_log_1:rotate_ext_close(Handle)
    end,
    closed.

do_format_error({error, Module, Error}) ->
    Module:format_error(Error);
do_format_error({error, Reason}) ->
    do_format_error(Reason);
do_format_error({Node, Error = {error, _Reason}}) ->
    lists:append(io_lib:format("~p: ", [Node]), do_format_error(Error));
do_format_error({badarg, Arg}) ->
    io_lib:format("The argument ~p is missing, not recognized or "
		  "not wellformed~n", [Arg]);
do_format_error({size_mismatch, OldSize, ArgSize}) ->
    io_lib:format("The given size ~p does not match the size ~p found on "
		  "the disk log size file~n", [ArgSize, OldSize]);
do_format_error({read_only_mode, Log}) ->
    io_lib:format("The disk log ~tp has been opened read-only, but the "
		  "requested operation needs read-write access~n", [Log]);
do_format_error({format_external, Log}) ->
    io_lib:format("The requested operation can only be applied on internally "
		  "formatted disk logs, but ~tp is externally formatted~n",
		  [Log]);
do_format_error({blocked_log, Log}) ->
    io_lib:format("The blocked disk log ~tp does not queue requests, or "
		  "the log has been blocked by the calling process~n", [Log]);
do_format_error({full, Log}) ->
    io_lib:format("The halt log ~tp is full~n", [Log]);
do_format_error({not_blocked, Log}) ->
    io_lib:format("The disk log ~tp is not blocked~n", [Log]);
do_format_error({not_owner, Pid}) ->
    io_lib:format("The pid ~tp is not an owner of the disk log~n", [Pid]);
do_format_error({not_blocked_by_pid, Log}) ->
    io_lib:format("The disk log ~tp is blocked, but only the blocking pid "
		  "can unblock a disk log~n", [Log]);
do_format_error({new_size_too_small, Log, CurrentSize}) ->
    io_lib:format("The current size ~p of the halt log ~tp is greater than the "
		  "requested new size~n", [CurrentSize, Log]);
do_format_error({halt_log, Log}) ->
    io_lib:format("The halt log ~tp cannot be wrapped~n", [Log]);
do_format_error({same_file_name, Log}) ->
    io_lib:format("Current and new file name of the disk log ~tp "
		  "are the same~n", [Log]);
do_format_error({arg_mismatch, Option, FirstValue, ArgValue}) ->
    io_lib:format("The value ~tp of the disk log option ~p does not match "
		  "the current value ~tp~n", [ArgValue, Option, FirstValue]);
do_format_error({name_already_open, Log}) ->
    io_lib:format("The disk log ~tp has already opened another file~n", [Log]);
do_format_error({open_read_write, Log}) ->
    io_lib:format("The disk log ~tp has already been opened read-write~n", 
		  [Log]);
do_format_error({open_read_only, Log}) ->
    io_lib:format("The disk log ~tp has already been opened read-only~n", 
		  [Log]);
do_format_error({not_internal_wrap, Log}) ->
    io_lib:format("The requested operation cannot be applied since ~tp is not "
		  "an internally formatted disk log~n", [Log]);
do_format_error(no_such_log) ->
    io_lib:format("There is no disk log with the given name~n", []);
do_format_error(nonode) ->
    io_lib:format("There seems to be no node up that can handle "
		  "the request~n", []);
do_format_error(nodedown) ->
    io_lib:format("There seems to be no node up that can handle "
		  "the request~n", []);
do_format_error({corrupt_log_file, FileName}) ->
    io_lib:format("The disk log file \"~ts\" contains corrupt data~n", 
                  [FileName]);
do_format_error({need_repair, FileName}) ->
    io_lib:format("The disk log file \"~ts\" has not been closed properly and "
		  "needs repair~n", [FileName]);
do_format_error({not_a_log_file, FileName}) ->
    io_lib:format("The file \"~ts\" is not a wrap log file~n", [FileName]);
do_format_error({invalid_header, InvalidHeader}) ->
    io_lib:format("The disk log header is not wellformed: ~p~n", 
		  [InvalidHeader]);
do_format_error(end_of_log) ->
    io_lib:format("An attempt was made to step outside a not yet "
		  "full wrap log~n", []);
do_format_error({invalid_index_file, FileName}) ->
    io_lib:format("The wrap log index file \"~ts\" cannot be used~n",
		  [FileName]);
do_format_error({no_continuation, BadCont}) ->
    io_lib:format("The term ~p is not a chunk continuation~n", [BadCont]);
do_format_error({file_error, FileName, Reason}) ->
    io_lib:format("\"~ts\": ~tp~n", [FileName, file:format_error(Reason)]);
do_format_error(E) ->
    io_lib:format("~tp~n", [E]).

-doc false.
do_info(L, Cnt) ->
    #log{name = Name, type = Type, mode = Mode, filename = File, 
	 extra = Extra, status = Status, owners = Owners, users = Users,
	 format = Format, head = Head} = L,
    Size = case Type of
	       wrap ->
		   disk_log_1:get_wrap_size(Extra);
               rotate ->
                   disk_log_1:get_rotate_size(Extra);
	       halt ->
		   Extra#halt.size
	   end,
    RW = case Type of
	     wrap when Mode =:= read_write ->
		 #handle{curB = CurB, curF = CurF, 
			 cur_cnt = CurCnt, acc_cnt = AccCnt, 
			 noFull = NoFull, accFull = AccFull} = Extra,
		 NewAccFull = AccFull + NoFull,
		 NewExtra = Extra#handle{noFull = 0, accFull = NewAccFull},
		 put(log, L#log{extra = NewExtra}),
		 [{no_current_bytes, CurB},
		  {no_current_items, CurCnt},
		  {no_items, Cnt},
		  {no_written_items, CurCnt + AccCnt},
		  {current_file, CurF},
		  {no_overflows, {NewAccFull, NoFull}}
		 ];
             rotate when Mode =:= read_write ->
                 #rotate_handle{curB = CurB} = Extra,
		 [{no_current_bytes, CurB},
		  {no_items, Cnt}
		 ];
	     halt when Mode =:= read_write ->
		 IsFull = case get(is_full) of 
			      undefined -> false; 
			      _ -> true 
			  end,
		 [{full, IsFull},
		  {no_written_items, Cnt}
		 ];
	     _ when Mode =:= read_only ->
		 []
	 end,
    HeadL = case Mode of
		read_write ->
		    [{head, case Head of
                                {ok, H} -> H;
                                none -> Head;
                                {_M, _F, _A} -> Head
                            end}];
		read_only ->
		    []
	    end,
    Common = [{name, Name},
	      {file, File},
	      {type, Type},
	      {format, Format},
	      {size, Size},
	      {items, Cnt}, % kept for "backward compatibility" (undocumented)
	      {owners, Owners},
	      {users, Users}] ++
	     HeadL ++
	     [{mode, Mode},
	      {status, Status},
	      {node, node()}
	     ],
    Common ++ RW.

do_block(Pid, QueueLogRecs, L) ->
    L2 = L#log{status = {blocked, QueueLogRecs}, blocked_by = Pid},
    put(log, L2),
    case is_owner(Pid, L2) of
	{true, _Notify} ->
	    ok;
	false ->
	    link(Pid)
    end.

do_unblock(Pid, #log{blocked_by = Pid}=L, S) ->
    do_unblock(L, S);
do_unblock(_Pid, _L, S) ->
    S.

do_unblock(L, S) ->
    unblock_pid(L),
    L2 = L#log{blocked_by = none, status = ok},
    put(log, L2),
    %% Since the block request is synchronous, and the blocking
    %% process is the only process that can unblock, all requests in
    %% 'messages' will have been put in 'queue' before the unblock
    %% request is granted.
    [] = S#state.messages, % assertion
    S#state{queue = [], messages = lists:reverse(S#state.queue)}.

-doc false.
-spec do_log(#log{}, [binary()]) -> integer() | {'error', _, integer()}.

do_log(L, B) ->
    do_log(L, B, iolist_size(B)).

do_log(#log{type = halt}=L, B, BSz) ->
    #log{format = Format, extra = Halt} = L,
    #halt{curB = CurSize, size = Sz} = Halt,
    {Bs, BSize} = logl(B, Format, BSz),
    case get(is_full) of
	true ->
            {error, {error, {full, L#log.name}}, 0};
	undefined when Sz =:= infinity; CurSize + BSize =< Sz ->
	    halt_write(Halt, L, B, Bs, BSize);
	undefined ->
	    halt_write_full(L, B, Format, 0)
    end;
do_log(#log{format_type = wrap_int}=L, B, _BSz) ->
    case disk_log_1:mf_int_log(L#log.extra, B, L#log.head) of
	{ok, Handle, Logged, Lost, Wraps} ->
	    notify_owners_wrap(Wraps),
	    put(log, L#log{extra = Handle}),
	    Logged - Lost;
	{ok, Handle, Logged} ->
	    put(log, L#log{extra = Handle}),
	    Logged;
	{error, Error, Handle, Logged, Lost} ->
	    put(log, L#log{extra = Handle}),
	    {error, Error, Logged - Lost}
    end;
do_log(#log{format_type = wrap_ext}=L, B, _BSz) ->
    case disk_log_1:mf_ext_log(L#log.extra, B, L#log.head) of
	{ok, Handle, Logged, Lost, Wraps} ->
	    notify_owners_wrap(Wraps),
	    put(log, L#log{extra = Handle}),
	    Logged - Lost;
	{ok, Handle, Logged} ->
	    put(log, L#log{extra = Handle}),
	    Logged;
	{error, Error, Handle, Logged, Lost} ->
	    put(log, L#log{extra = Handle}),
	    {error, Error, Logged - Lost}
    end;
do_log(#log{type = rotate}=L, B, _BSz) ->
    {ok, Handle, Logged} = disk_log_1:rotate_ext_log(L#log.extra, B, L#log.head), %%error case here
    put(log, L#log{extra = Handle}),
    Logged.

logl(B, external, undefined) ->
    {B, iolist_size(B)};
logl(B, external, Sz) ->
    {B, Sz};
logl(B, internal, _Sz) ->
    disk_log_1:logl(B).

halt_write_full(L, [Bin | Bins], Format, N) ->
    B = [Bin],
    {Bs, BSize} = logl(B, Format, undefined),
    Halt = L#log.extra,
    #halt{curB = CurSize, size = Sz} = Halt,
    if 
	CurSize + BSize =< Sz ->
	    case halt_write(Halt, L, B, Bs, BSize) of
		N1 when is_integer(N1) ->
		    halt_write_full(get(log), Bins, Format, N+N1);
		Error ->
		    Error
	    end;
	true ->
	    halt_write_full(L, [], Format, N)
    end;
halt_write_full(L, _Bs, _Format, N) ->
    put(is_full, true),
    notify_owners(full),
    {error, {error, {full, L#log.name}}, N}.

halt_write(Halt, L, B, Bs, BSize) ->
    case disk_log_1:fwrite(Halt#halt.fdc, L#log.filename, Bs, BSize) of
	{ok, NewFdC} ->
	    NCurB = Halt#halt.curB + BSize,
	    NewHalt = Halt#halt{fdc = NewFdC, curB = NCurB},
	    put(log, L#log{extra = NewHalt}),
	    length(B);
	{Error, NewFdC} ->
	    put(log, L#log{extra = Halt#halt{fdc = NewFdC}}),
	    {error, Error, 0}
    end.

%% -> ok | Error
do_write_cache(#log{filename = FName, type = halt, extra = Halt} = Log) ->
    {Reply, NewFdC} = disk_log_1:write_cache(Halt#halt.fdc, FName),
    put(log, Log#log{extra = Halt#halt{fdc = NewFdC}}),
    Reply;
do_write_cache(#log{type = wrap, extra = Handle} = Log) ->
    {Reply, NewHandle} = disk_log_1:mf_write_cache(Handle),
    put(log, Log#log{extra = NewHandle}),
    Reply;
do_write_cache(#log{type = rotate, extra = Handle} = Log) ->
    {Reply, NewHandle} = disk_log_1:rotate_write_cache(Handle),
    put(log, Log#log{extra = NewHandle}),
    Reply.

%% -> ok | Error
-doc false.
do_sync(#log{filename = FName, type = halt, extra = Halt} = Log) ->
    {Reply, NewFdC} = disk_log_1:sync(Halt#halt.fdc, FName),
    put(log, Log#log{extra = Halt#halt{fdc = NewFdC}}),
    Reply;
do_sync(#log{type = Type, extra = Handle} = Log) when Type == wrap orelse Type == rotate->
    {Reply, NewHandle} = disk_log_1:mf_sync(Handle),
    put(log, Log#log{extra = NewHandle}),
    Reply.

%% -> ok | Error | throw(Error)
do_trunc(#log{type = halt}=L, Head) ->
    #log{filename = FName, extra = Halt} = L,
    FdC = Halt#halt.fdc,
    {Reply1, FdC2} = 
        case L#log.format of
            internal ->
                disk_log_1:truncate(FdC, FName, Head);
            external ->
		case disk_log_1:truncate_at(FdC, FName, bof) of
		    {ok, NFdC} when Head =:= none ->
                        {ok, NFdC};
		    {ok, NFdC} ->
			{ok, H} = Head,
                        disk_log_1:fwrite(NFdC, FName, H, byte_size(H));
		    R -> 
			R
		end
        end,
    {Reply, NewHalt} = 
    case disk_log_1:position(FdC2, FName, cur) of
	{ok, NewFdC, FileSize} when Reply1 =:= ok ->
	    {ok, Halt#halt{fdc = NewFdC, curB = FileSize}};
	{Reply2, NewFdC} ->
	    {Reply2, Halt#halt{fdc = NewFdC}};
	{ok, NewFdC, _} ->
	    {Reply1, Halt#halt{fdc = NewFdC}}
    end,
    put(log, L#log{extra = NewHalt}),
    Reply;
do_trunc(#log{type = wrap}=L, Head) ->
    Handle = L#log.extra,
    OldHead = L#log.head,
    {MaxB, MaxF} = disk_log_1:get_wrap_size(Handle),
    ok = do_change_size(L, {MaxB, 1}),
    NewLog = trunc_wrap((get(log))#log{head = Head}),
    %% Just to remove all files with suffix > 1:
    NewLog2 = trunc_wrap(NewLog),
    NewHandle = (NewLog2#log.extra)#handle{noFull = 0, accFull = 0},
    do_change_size(NewLog2#log{extra = NewHandle, head = OldHead}, 
		   {MaxB, MaxF});
do_trunc(#log{type = rotate, head = Head, extra = Handle}=L, none) ->
    Handle1 = disk_log_1:do_rotate(Handle, Head),
    disk_log_1:remove_files(rotate, Handle1#rotate_handle.file, 0, Handle1#rotate_handle.maxF),
    put(log, L#log{extra = Handle1}),
    ok.

trunc_wrap(L) ->
    case do_inc_wrap_file(L) of
	{ok, L2, _Lost} ->
	    L2;
	{error, Error, _L2} ->
	    throw(Error)
    end.

do_chunk(#log{format_type = halt_int, extra = Halt} = L, Pos, B, N) ->
    FdC = Halt#halt.fdc,
    {NewFdC, Reply} = 
        case L#log.mode of
            read_only ->
                disk_log_1:chunk_read_only(FdC, L#log.filename, Pos, B, N);
            read_write ->
                disk_log_1:chunk(FdC, L#log.filename, Pos, B, N)
        end,
    put(log, L#log{extra = Halt#halt{fdc = NewFdC}}),
    Reply;
do_chunk(#log{format_type = wrap_int, mode = read_only, 
	      extra = Handle} = Log, Pos, B, N) ->
    {NewHandle, Reply} = disk_log_1:mf_int_chunk_read_only(Handle, Pos, B, N),
    put(log, Log#log{extra = NewHandle}),
    Reply;
do_chunk(#log{format_type = wrap_int, extra = Handle} = Log, Pos, B, N) ->
    {NewHandle, Reply} = disk_log_1:mf_int_chunk(Handle, Pos, B, N),
    put(log, Log#log{extra = NewHandle}),
    Reply;
do_chunk(Log, _Pos, _B, _) ->
    {error, {format_external, Log#log.name}}.

do_chunk_step(#log{format_type = wrap_int, extra = Handle}, Pos, N) ->
    disk_log_1:mf_int_chunk_step(Handle, Pos, N);
do_chunk_step(Log, _Pos, _N) ->
    {error, {not_internal_wrap, Log#log.name}}.

%% Inlined.
replies(Pids, Reply) ->
    M = {disk_log, self(), Reply},
    send_reply(Pids, M).

send_reply(Pid, M) when is_pid(Pid) ->
    Pid ! M,
    ok;
send_reply([Pid | Pids], M) ->
    Pid ! M,
    send_reply(Pids, M);
send_reply([], _M) ->
    ok.

reply(To, Reply, S) ->
    To ! {disk_log, self(), Reply},
    loop(S).

req(Log, R) ->
    case disk_log_server:get_log_pid(Log) of
	undefined ->
	    {error, no_such_log};
	Pid ->
	    monitor_request(Pid, R)
    end.

monitor_request(Pid, Req) ->
    Ref = erlang:monitor(process, Pid),
    Pid ! {self(), Req},
    receive 
	{'DOWN', Ref, process, Pid, _Info} ->
	    {error, no_such_log};
	{disk_log, Pid, Reply} when not is_tuple(Reply) orelse
                                    element(2, Reply) =/= disk_log_stopped ->
	    erlang:demonitor(Ref, [flush]),
	    Reply
    end.

req2(Pid, R) ->
    monitor_request(Pid, R).

merge_head(none, Head) ->
    Head;
merge_head(Head, _) ->
    Head.

%% -> List of extensions of existing files (no dot included) | throw(FileError)
wrap_file_extensions(File) ->
    {_CurF, _CurFSz, _TotSz, NoOfFiles} =
	disk_log_1:read_index_file(File),
    Fs = if 
	     NoOfFiles >= 1 ->
		 lists:seq(1, NoOfFiles);
	     NoOfFiles =:= 0 ->
		 []
	 end,
    Fun = fun(Ext) ->
		  case file:read_file_info(add_ext(File, Ext)) of
		      {ok, _} ->
			  true;
		      _Else ->
			  false
		  end
	  end,
    lists:filter(Fun, ["idx", "siz" | Fs]).

rotate_file_extensions(File, MaxF) ->
    rotate_file_extensions(File, MaxF, 0, []).

rotate_file_extensions(_File, MaxF, MaxF, Res) ->
    Res;
rotate_file_extensions(File, MaxF, N, Res) ->
    Ext = integer_to_list(N) ++ ".gz", 
    case file:read_file_info(add_ext(File, Ext)) of
        {ok, _} -> rotate_file_extensions(File, MaxF, N+1, [Ext|Res]);
	_ -> rotate_file_extensions(File, MaxF, N+1, Res)
    end.

add_ext(File, Ext) ->
    lists:concat([File, ".", Ext]).

notify(Log, R) ->
    case disk_log_server:get_log_pid(Log) of
	undefined ->
	    {error, no_such_log};
	Pid ->
	    Pid ! R,
	    ok
    end.

notify_owners_wrap([]) ->
    ok;
notify_owners_wrap([N | Wraps]) ->
    notify_owners({wrap, N}),
    notify_owners_wrap(Wraps).

notify_owners(Note) ->
    L = get(log),
    Msg = {disk_log, node(), L#log.name, Note},
    lists:foreach(fun({Pid, true}) -> Pid ! Msg;
		     (_) -> ok
		  end, L#log.owners).

cache_error(#state{cache_error=Error}=S, Pids) ->
    ok = replies(Pids, Error),
    state_err(S#state{cache_error = ok}, Error).

state_ok(S) ->
    state_err(S, ok).

-spec state_err(#state{}, dlog_state_error()) -> #state{}.

state_err(S, Err) when S#state.error_status =:= Err -> S;
state_err(S, Err) ->
    notify_owners({error_status, Err}),
    S#state{error_status = Err}.
