sshpeer: return framed file object when needed Currently, wireproto.wirepeer has a default implementation of _submitbatch() and sshv1peer has a very similar implementation. The main difference is that sshv1peer is aware of the total amount of bytes it can read whereas the default implementation reads the stream until no more data is returned. The default implementation works for HTTP, since there is a known end to HTTP responses (either Content-Length or 0 sized chunk). This commit teaches sshv1peer to use our just-introduced "cappedreader" class for wrapping a file object to limit the number of bytes that can be read. We do this by introducing an argument to specify whether the response is framed. If set, we returned a cappedreader instance instead of the raw pipe. _call() always has framed responses. So we set this argument unconditionally and then .read() the entirety of the result. Strictly speaking, we don't need to use cappedreader in this case and can inline frame decoding/read logic. But I like when things are consistent. The overhead should be negligible. _callstream() and _callcompressable() are special: whether framing is used depends on the specific command. So, we define a set of commands that have framed response. It currently only contains "batch." As a result of this change, the one-off implementation of _submitbatch() in sshv1peer can be removed since it is now safe to .read() the response's file object until end of stream. cappedreader takes care of not overrunning the frame. Differential Revision: https://phab.mercurial-scm.org/D2380