Error handling for stream with Twitter's API. (Blank lines and receive problems)

Question

I'm trying to modify the functionality in my teacher's module for saving tweets from Twitter's Streaming API. The problem is that if I keep the stream open for more than a minute, the API starts sending blank lines to the stream in order to verify its connection.

From what I've understood, the tweets are broken down and then reassembled, but this becomes a problem with the last function in the code below, pop_size.

Pop_size expects the argument to start with a text-representation of a number. So when the blank lines are sent, represented by <<"\r\n">>, the stream crashes with this message:

Error in process <0.118.0> with exit value: {function_clause,
[{twitterminer_source,pop_size,[<<2 bytes>>],[{file,"src/twitterminer_source.erl"}

If I add the line below, does anyone have any suggestions what I should try executing in it?

pop_size(<<"\r\n">>) ->  %%Code here!

To clarify: I want the blank line to be disregarded and the loop to continue checking for the next tweets. I'm quite over my head here, but I'll try to answer any follow-up questions as elaborate as I can.

Code: (Three functions)

% Get HTTP chunks and reassemble them into chunks that we get
% as a result of specifying delimited=length.
% https://dev.twitter.com/streaming/overview/processing
split_loop(Sink, Sender, Buffer) -> 
  case pop_size(Buffer) of
    {size, N, Rest} ->
      case buffer_pop_n(Rest, N, Sender) of
        {pop, Chunk, NewBuf}   ->
          Sink ! {message, Chunk},
          receive next -> ok end,
          split_loop(Sink, Sender, NewBuf);
        {incomplete, Chunk}    -> Sink ! {error, {incomplete, Chunk}};
        {terminate, _Chunk}    -> Sink ! terminate;
        {error, Reason, Chunk} -> Sink ! {error, {Reason, Chunk}}
      end;

    {more, L} ->
      case buffer_pop_n(Buffer, L, Sender) of
        {pop, Chunk, NewBuf}   ->
          split_loop(Sink, Sender, <<Chunk/binary, NewBuf/binary>>);
        {incomplete, <<>>}     -> Sink ! finished;
        {incomplete, Chunk}    -> Sink ! {error, {incomplete, Chunk}};
        {terminate, _Chunk}    -> Sink ! terminate;
        {error, Reason, Chunk} -> Sink ! {error, {Reason, Chunk}}
      end
  end.

% Get a chunk of N bytes from the buffer. If there is not enough data
% in the buffer, get more messages from the pipeline.
buffer_pop_n(B, N, Sender) ->
  if
    byte_size(B) < N -> 
      Sender ! next,
      receive
        {message, Part} ->
          Part2 = Part,
          buffer_pop_n(<<B/binary, Part2/binary>>, N, Sender);
        finished -> {incomplete, B};
        terminate -> {terminate, B};
        {error, Reason} -> {error, Reason, B}
      end;
    true -> {pop, binary:part(B, {0, N}), binary:part(B, {N, byte_size(B)-N})}
  end.

% We should also support discarding \r\n here
% (see 'blank lines' in https://dev.twitter.com/streaming/overview/messages-types)
pop_size(<<>>) -> {more, 1};
pop_size(<<A,Rest/binary>>) when A >= $0, A =< $9 ->
  pop_size((A - $0), 1, Rest);
pop_size(_N, L, <<>>) -> {more, L+1};
pop_size(_N, L, <<"\r">>) -> {more, L+2};
pop_size(N, L, <<A,Rest/binary>>) when A >= $0, A =< $9 ->
  pop_size(N * 10 + (A - $0), L+1, Rest);
pop_size(N, _L, <<"\r\n",Rest/binary>>) -> {size, N, Rest}.