Using a tube name that is 200 chars long returns INTERNAL_ERROR. The error should be reproducible with the following:
The error occurs at prot.c:343 and happens for one of two reasons, depending on your perspective.
Either prot.c:343 should use > instead of >=, like so:
if (r > LINE_BUF_SIZE) return reply_serr(c, MSG_INTERNAL_ERROR);
Or alternatively, LINE_BUF_SIZE could be increased from 208 to 209.
In my oppinion, prot.c:343 is the real issue. However, let me know what your preferred solution is and I can draft the appropriate pull request.
Fixed in 2279f18.