DGPS Message too large

Attempting to use rtklib's str2str to feed RTCM data from an NTRIP server to a GNSS module attached to a Pixhawk. The DGPS module reports 'DGPS: Message too large' at regular intervals. I have no problems feeding the same data stream using Mission Planner but due to the UDP requirement of DGPS, have used netcat to forward data from the TCP output of str2str to UDP. At least some correction data is making it through as the module can achieve float/fix. Looking at the DGPS module code, it is apparent that the incoming data is split into a maximum of 4 x 180byte messages. Any incoming data that is larger than 720bytes (=4x180) is dropped (with the error message described) I have not found any information as to why this limit is imposed. I have tried a limit of 6 and this appears to work but I am still not sure that all correction data is being passed through. I would have thought that using str2str with mavproxy for this purpose would have been quite common?

Start by tracing how MAVProxy handles the DGPS data path from str2str or netcat to the GNSS module, using the DGPS module code and the reported 4 x 180-byte limit. Determine why messages over 720 bytes are dropped and verify whether the forwarding path preserves all correction data. Done means the cause is established and oversized correction messages are handled without losing required data.

Written by the indexing model from the issue text.