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% Copyright 2007, 2008 Damien Katz <damien_katz@yahoo.com>
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% Licensed under the Apache License, Version 2.0 (the "License");
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% you may not use this file except in compliance with the License.
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% You may obtain a copy of the License at
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% http://www.apache.org/licenses/LICENSE-2.0
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% Unless required by applicable law or agreed to in writing, software
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% distributed under the License is distributed on an "AS IS" BASIS,
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% WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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% See the License for the specific language governing permissions and
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% limitations under the License.
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-behaviour(gen_server).
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-export([open/2, close/1, pread/3, pwrite/3, expand/2, bytes/1, sync/1, truncate/2]).
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-export([append_term/2, pread_term/2]).
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-export([init/1, terminate/2, handle_call/3, handle_cast/2, code_change/3, handle_info/2]).
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%%----------------------------------------------------------------------
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%% Args: Valid Options are [create] and [create,overwrite].
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%% Files are opened in read/write mode.
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%% Returns: On success, {ok, Fd}
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%% or {error, Reason} if the file could not be opened.
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%%----------------------------------------------------------------------
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open(Filepath, Options) ->
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case gen_server:start_link(couch_file, {Filepath, Options, self()}, []) of
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% we got back an ok, but that doesn't really mean it was successful.
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% Instead the true status has been sent back to us as a message.
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% We do this because if the gen_server doesn't initialize properly,
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% it generates a crash report that will get logged. This avoids
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% that mess, because we don't want.
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%%----------------------------------------------------------------------
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%% Args: Pos is the offset from the beginning of the file, Bytes is
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%% is the number of bytes to read.
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%% Returns: {ok, Binary} where Binary is a binary data from disk
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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pread(Fd, Pos, Bytes) when Bytes > 0 ->
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gen_server:call(Fd, {pread, Pos, Bytes}).
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%%----------------------------------------------------------------------
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%% Args: Pos is the offset from the beginning of the file, Bin is
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%% is the binary to write
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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pwrite(Fd, Pos, Bin) ->
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gen_server:call(Fd, {pwrite, Pos, Bin}).
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%%----------------------------------------------------------------------
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%% Purpose: To append a segment of zeros to the end of the file.
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%% Args: Bytes is the number of bytes to append to the file.
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%% Returns: {ok, Pos} where Pos is the file offset to the beginning of
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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expand(Fd, Bytes) when Bytes > 0 ->
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gen_server:call(Fd, {expand, Bytes}).
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%%----------------------------------------------------------------------
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%% Purpose: To append an Erlang term to the end of the file.
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%% Args: Erlang term to serialize and append to the file.
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%% Returns: {ok, Pos} where Pos is the file offset to the beginning the
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%% serialized term. Use pread_term to read the term back.
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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append_term(Fd, Term) ->
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gen_server:call(Fd, {append_term, Term}).
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%%----------------------------------------------------------------------
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%% Purpose: Reads a term from a file that was written with append_term
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%% Args: Pos, the offset into the file where the term is serialized.
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%% Returns: {ok, Term}
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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pread_term(Fd, Pos) ->
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gen_server:call(Fd, {pread_term, Pos}).
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%%----------------------------------------------------------------------
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%% Purpose: The length of a file, in bytes.
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%% Returns: {ok, Bytes}
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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gen_server:call(Fd, bytes).
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%%----------------------------------------------------------------------
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%% Purpose: Truncate a file to the number of bytes.
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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gen_server:call(Fd, {truncate, Pos}).
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%%----------------------------------------------------------------------
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%% Purpose: Ensure all bytes written to the file are flushed to disk.
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%% or {error, Reason}.
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%%----------------------------------------------------------------------
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gen_server:call(Fd, sync).
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%%----------------------------------------------------------------------
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%% Purpose: Close the file. Is performed asynchronously.
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%%----------------------------------------------------------------------
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gen_server:cast(Fd, close).
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init_status_ok(ReturnPid, Fd) ->
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ReturnPid ! {self(), ok}, % signal back ok
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init_status_error(ReturnPid, Error) ->
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ReturnPid ! {self(), Error}, % signal back error status
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self() ! self_close, % tell ourself to close async
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init({Filepath, Options, ReturnPid}) ->
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case lists:member(create, Options) of
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filelib:ensure_dir(Filepath),
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case file:open(Filepath, [read, write, raw, binary]) of
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{ok, Length} = file:position(Fd, eof),
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% this means the file already exists and has data.
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% FYI: We don't differentiate between empty files and non-existant
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% files here. That could cause issues someday.
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case lists:member(overwrite, Options) of
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{ok, 0} = file:position(Fd, 0),
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ok = file:truncate(Fd),
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init_status_ok(ReturnPid, Fd);
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init_status_error(ReturnPid, {error, file_exists})
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init_status_ok(ReturnPid, Fd)
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init_status_error(ReturnPid, Error)
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% open in read mode first, so we don't create the file if it doesn't exist.
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case file:open(Filepath, [read, raw]) of
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{ok, Fd} = file:open(Filepath, [read, write, raw, binary]),
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ok = file:close(Fd_Read),
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init_status_ok(ReturnPid, Fd);
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init_status_error(ReturnPid, Error)
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terminate(_Reason, nil) ->
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terminate(_Reason, Fd) ->
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handle_call({pread, Pos, Bytes}, _From, Fd) ->
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{reply, file:pread(Fd, Pos, Bytes), Fd};
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handle_call({pwrite, Pos, Bin}, _From, Fd) ->
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{reply, file:pwrite(Fd, Pos, Bin), Fd};
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handle_call({expand, Num}, _From, Fd) ->
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{ok, Pos} = file:position(Fd, eof),
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{reply, {file:pwrite(Fd, Pos + Num - 1, <<0>>), Pos}, Fd};
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handle_call(bytes, _From, Fd) ->
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{reply, file:position(Fd, eof), Fd};
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handle_call(sync, _From, Fd) ->
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{reply, file:sync(Fd), Fd};
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handle_call({truncate, Pos}, _From, Fd) ->
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{ok, Pos} = file:position(Fd, Pos),
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{reply, file:truncate(Fd), Fd};
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handle_call({append_term, Term}, _From, Fd) ->
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Bin = term_to_binary(Term),
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Bin2 = <<TermLen:32, Bin/binary>>,
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{ok, Pos} = file:position(Fd, eof),
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{reply, {file:pwrite(Fd, Pos, Bin2), Pos}, Fd};
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handle_call({pread_term, Pos}, _From, Fd) ->
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= file:pread(Fd, Pos, 4),
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{ok, Bin} = file:pread(Fd, Pos + 4, TermLen),
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{reply, {ok, binary_to_term(Bin)}, Fd}.
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handle_cast(close, Fd) ->
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{stop,normal,Fd}. % causes terminate to be called
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code_change(_OldVsn, State, _Extra) ->
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handle_info(self_close, State) ->
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handle_info(_Info, State) ->
added
removed
src/CouchDB/couch_file.erl
