MATLAB: Setting callbacks to respond to incoming messages on a LightStreamer channel.

lightstreamerurlread2

I want to read an open channel from LightStreamer, in particular the LightStreamer service from IG.
LS operates in two modes: streaming and polling (streaming being preferred). I have quite successfully written a lot of code to handle a polling connection (setting LS_polling=true on /lightstreamer/create_session.txt ; false is the default) but handling a stream connection would be much more efficient and simplify the process quite considerably.
I've been using Jim Hokanson's excellent URLREAD2 function for polling but this appears to hang if I try it in a streaming mode, on line 263 of the following, if that's helpful to anyone.
260 byteArrayOutputStream = java.io.ByteArrayOutputStream;
261 % This StreamCopier is unsupported and may change at any time. OH GREAT :/
262 isc = InterruptibleStreamCopier.getInterruptibleStreamCopier;
263 isc.copyStream(inputStream,byteArrayOutputStream);
264 inputStream.close;
265 byteArrayOutputStream.close;
I'm wondering if some modification to URLREAD2 might be possible that would open the connection and allow the setting of callbacks to handle incoming messages?

Best Answer

This is somewhat like having a conversation with myself (it happens). Anyway, as I started I'll continue. It turns out not to be as complicated as I thought it would be. I can strip out much of URLREAD2 for this dedicated situation, and then decoding the stream is very well defined. All that's left is to cast this into the classdef and handle the events.
function output = urlreadls(url,body,varargin)
% + URL
try
    protocol = url(1:find(url==':',1)-1);
    handler = sun.net.www.protocol.(protocol).Handler;
    url = java.net.URL([],url,handler);
    urlConnection = url.openConnection;
    urlConnection.setRequestMethod('POST');
catch ME
    % TODO


    rethrow(ME)
end
% + BODY
try
    body = unicode2native(body,'');
    urlConnection.setRequestProperty('Content-Length',int2str(length(body)));
    urlConnection.setDoOutput(true);
catch ME
    % TODO
    rethrow(ME)
end
% + POST
try
    outputStream = urlConnection.getOutputStream;
    outputStream.write(body);
    outputStream.close;
catch ME
    % TODO
    rethrow(ME)
end
% + STEAM
inputStream = urlConnection.getInputStream;
% Read the first line; it will be either "ERROR", "OK", 
% or possibly HTTP error 500.
line = linereader(inputStream);
switch line
    case 'ERROR'
        % There will be 2 more lines only; then close the stream.
        output.ERROR.err_code = linereader(inputStream);
        output.ERROR.err_msg = linereader(inputStream);
        inputStream.close;
      case 'OK'
          % There will be between 3 and 6 lines following in the form:
          % "ParamName:" + ParamValue + "\r\n", followed finally by a blank
          % line. The blank line marks the start of the push phase.
          line = linereader(inputStream);
          while ~isempty(line)
              param = regexp(line,':','split');
              output.OK.(param{1}) = param{2};
              line = linereader(inputStream);
          end
          % Handle the push phase.
          try
              while true
                  line = linereader(inputStream);
                  disp(line)
              end
          catch ME
          end
      otherwise
          % Probably HTTP 500; I don't know exactly what this looks like
          % until I see one. TODO: confirm it's a 500 or handle seperately.
          output.ERROR.err_code = '500';
          output.ERROR.err_msg = line;
          save errorline line
          inputStream.close;
  end
function line = linereader(inputStream)
byteArray(1) = inputStream.read; % <--- 'O'
byteArray(2) = inputStream.read; % <--- 'K'
while ~isequal(byteArray(end-1:end),[13 10])
    byteArray(end+1) = inputStream.read;
end
line = char(byteArray(1:end-2));
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