webp parser/builder (sample)

webp.erl

-module(webp).

-export([parse/0, parse/1]).
-export([build/1]).

-include_lib("eunit/include/eunit.hrl").

-define(MAX_SIZE, 4294967274).

%% http://www-2.cs.cmu.edu/~chuck/lennapg/lena_std.tif
%% $ cwebp -q 80 lena_std.tif -o lena_std.webp
%% https://developers.google.com/speed/webp/docs/riff_container

%% Erlang/OTP 19 [erts-8.0.2] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:10] [hipe] [kernel-poll:false] [dtrace] [sharing-preserving]
%% 
%% Eshell V8.0.2  (abort with ^G)
%% 1> c(webp).
%% {ok,webp}
%% 2> webp:parse().
%% webp.erl:24:<0.57.0>: ChunkSize = 30214
%% webp.erl:25:<0.57.0>: Size = 30202
%% webp.erl:


parse() ->
    parse("lena_std.webp").

parse(Filename) ->
    {ok, Binary} = file:read_file(Filename),
    parse_header(Binary).


parse_header(<<"RIFF",
               ChunkSize:32/unsigned-little,
               "WEBP",
               "VP8 ",
               Size:32/unsigned-little,
               _Rest/binary>>) ->
    ?debugVal(ChunkSize),
    ?debugVal(Size),
    ?debugVal(byte_size(_Rest)),
    ok.


%% @mururu
-spec build(binary()) -> {ok, binary()} | {error, too_large_image}.
build(Binary) ->
    case byte_size(Binary) of
        Size when Size =< ?MAX_SIZE ->
            {ok, <<"RIFF",
                   (Size + 12):32/unsigned-little,
                   "WEBP",
                   "VP8 ",
                   Size:32/unsigned-little,
                   Binary/binary>>};
        _ ->
            {error, too_large_image}
    end.