stream_file.erl

serve_file(Response, File) ->
    case file:open(File, [raw, binary]) of
        {ok, IoDevice} ->
            %% Set ChunkSize to an optimal value
            ChunkSize = 1024,
            Stream = iodevice_stream(IoDevice, ChunkSize),
            Response1 = setelement(4, Response, Stream),
            file:close(IoDevice),
            Response1;
        _ ->
            %% Respond with 404...
            setelement(2, Response, {404, "NOT FOUND"})
    end.

iodevice_stream(IoDevice, ChunkSize) ->
    fun() ->
            case file:read(IoDevice, ChunkSize) of
                eof ->
                    {};
                {ok, Data} ->
                    {Data, iodevice_stream(IoDevice, ChunkSize)}
            end
    end.