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%% @author Bob Ippolito <bob@mochimedia.com>
%% @copyright 2010 Mochi Media, Inc.
%% @doc Write newline delimited log files, ensuring that if a truncated
%% entry is found on log open then it is fixed before writing. Uses
%% delayed writes and raw files for performance.
-module(mochilogfile2).
-author('bob@mochimedia.com').
-export([open/1, write/2, close/1, name/1]).
%% @spec open(Name) -> Handle
%% @doc Open the log file Name, creating or appending as necessary. All data
%% at the end of the file will be truncated until a newline is found, to
%% ensure that all records are complete.
open(Name) ->
{ok, FD} = file:open(Name, [raw, read, write, delayed_write, binary]),
fix_log(FD),
{?MODULE, Name, FD}.
%% @spec name(Handle) -> string()
%% @doc Return the path of the log file.
name({?MODULE, Name, _FD}) ->
Name.
%% @spec write(Handle, IoData) -> ok
%% @doc Write IoData to the log file referenced by Handle.
write({?MODULE, _Name, FD}, IoData) ->
ok = file:write(FD, [IoData, $\n]),
ok.
%% @spec close(Handle) -> ok
%% @doc Close the log file referenced by Handle.
close({?MODULE, _Name, FD}) ->
ok = file:sync(FD),
ok = file:close(FD),
ok.
fix_log(FD) ->
{ok, Location} = file:position(FD, eof),
Seek = find_last_newline(FD, Location),
{ok, Seek} = file:position(FD, Seek),
ok = file:truncate(FD),
ok.
%% Seek backwards to the last valid log entry
find_last_newline(_FD, N) when N =< 1 ->
0;
find_last_newline(FD, Location) ->
case file:pread(FD, Location - 1, 1) of
{ok, <<$\n>>} ->
Location;
{ok, _} ->
find_last_newline(FD, Location - 1)
end.
%%
%% Tests
%%
-ifdef(TEST).
-include_lib("eunit/include/eunit.hrl").
name_test() ->
D = mochitemp:mkdtemp(),
FileName = filename:join(D, "open_close_test.log"),
H = open(FileName),
?assertEqual(
FileName,
name(H)),
close(H),
file:delete(FileName),
file:del_dir(D),
ok.
open_close_test() ->
D = mochitemp:mkdtemp(),
FileName = filename:join(D, "open_close_test.log"),
OpenClose = fun () ->
H = open(FileName),
?assertEqual(
true,
filelib:is_file(FileName)),
ok = close(H),
?assertEqual(
{ok, <<>>},
file:read_file(FileName)),
ok
end,
OpenClose(),
OpenClose(),
file:delete(FileName),
file:del_dir(D),
ok.
write_test() ->
D = mochitemp:mkdtemp(),
FileName = filename:join(D, "write_test.log"),
F = fun () ->
H = open(FileName),
write(H, "test line"),
close(H),
ok
end,
F(),
?assertEqual(
{ok, <<"test line\n">>},
file:read_file(FileName)),
F(),
?assertEqual(
{ok, <<"test line\ntest line\n">>},
file:read_file(FileName)),
file:delete(FileName),
file:del_dir(D),
ok.
fix_log_test() ->
D = mochitemp:mkdtemp(),
FileName = filename:join(D, "write_test.log"),
file:write_file(FileName, <<"first line good\nsecond line bad">>),
F = fun () ->
H = open(FileName),
write(H, "test line"),
close(H),
ok
end,
F(),
?assertEqual(
{ok, <<"first line good\ntest line\n">>},
file:read_file(FileName)),
file:write_file(FileName, <<"first line bad">>),
F(),
?assertEqual(
{ok, <<"test line\n">>},
file:read_file(FileName)),
F(),
?assertEqual(
{ok, <<"test line\ntest line\n">>},
file:read_file(FileName)),
ok.
-endif.
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