mochilogfile2 module

src/mochilogfile2.erl

@@ -0,0 +1,140 @@
+%% @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
+%%
+-include_lib("eunit/include/eunit.hrl").
+-ifdef(TEST).
+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.