megaphone VII: Parsing Packets

Previously...

• I coded up the put_data function
• I coded up the put_data function...again
• I fixed some problems with remove_waiter and wrote the notify_wait function.

After the amount of coding that I had to do for some of the other functions, the packet decoding stuff was kind of anti-climactic:

parse_packet(Data) ->

    {ok, Request, Remainder} = erlang:decode_packet(http, [], Data),

    parse_headers([Request], Remainder).

parse_headers(Headers, Data) ->

    case erlang:decode_packet(httph, [], Data) of

        { ok, http_eoh, Rest } -> { Headers ++ http_eoh, Rest };

        { ok, Header, Rest } -> parse_headers(Headers ++ Header, Rest)

    end.

Not having any error handling might have something to do with it, but cryptic messages filled with weird braces are the erlang way!  Seriously, I'm going to put a reminder in the parking lot to go back and do a better job at error handling for this.

The erlang decode_packet function expects the caller to maintain some state as to where the parse is at between calls.  Hence parse_packet makes the first call to decode_packet with the http argument.  Subsequent calls are made in parse_headers and the httph argument is used.

This loop continues until decode_packet returns http_eoh, at which point the only thing left is the actual body of the request.

Next time: some odds and ends.