[PATCH 2 of 3 side-word (+4)] sshpeer: use a 'bufferedinputpipe' for standard output of the ssh process

[Yuya Nishihara]

On Mon, 1 Jun 2015 08:01:55 +0900, Yuya Nishihara wrote:
> On Sun, 31 May 2015 12:51:32 -0700, Pierre-Yves David wrote:
> > On 05/31/2015 07:10 AM, Yuya Nishihara wrote:
> > > On Sun, 31 May 2015 00:22:33 -0700, Pierre-Yves David wrote:
> > The issue with the buffer+select is that we want to be able to perform 
> > such operation:
> > 
> >   0) ssh: write "datadata"
> >   1) hg:  select() -> hey! data to read
> >   2) hg:  read(4) -> "data"
> >   3) hg:  select() -> hey! data to read
> >   4) hg:  read(4) -> "data"
> > 
> > If you add the buffering, the 2) will actually read all available data 
> > in the buffer the second half. (3) will not see any data to read and 
> > block for ever (4) will never run (5) the internet kitten will never 
> > have his bowl filled.
> > 
> > You can see the select usage here:
> > http://42.netv6.net/marmoute-wip/mercurial/rev/b9213af62475

Just an idea: because doublepipe requires main channel is a bufferedinputpipe,
we won't need two file-like classes. They could be simpler if

 - bufferedinputpipe is a fifo of string, like deque, not file-like
 - and doublepipe is responsible for all read operations.

For example,

    class doublepipe(object):
        def _wait(self):
            if self._mainfifo:
                return (True, True)
            select()
            ...

        def _call(self, methname, ...):
            ...
            while True:
                mainready, sideready = self._wait()
                ...
                if len(self._mainfifo) >= size:  # methname == 'read'
                    return self._mainfifo.pop(size)
                if mainready:
                    s = os.read(self._main.fileno(), chunksize)
                    if not s:
                        return self._maininfo.pop()  # EOF
                    self._mainfifo.push(s)

This will slightly complicate doublepipe, so I'm not sure which is better.

Regards,