Async Process

[Imran Geriskovan]

Below you can find async SubProcess class which
derives from Stream Class send previously.

Features:
1) Process Pipes (See Example)
2) ContextManager style usage (See Example)

I would like to hear your experiences regarding
SubProcess usage patterns. I'll be glad if a similar
approach is included in standard library.

Example:
This is a http handler which dumps Html formatted
man page into a chunked stream.
** Note the piping among processes.

async def manpage(stream, f):
async with await create_proc('groff -mandoc -Thtml -P -l -P -D -P
/tmp/', 'rw') as groff:
async with await create_proc('zcat ' + f, outstream=groff):
while 1:
r = await groff.readline()
if not r:
break
# Format links to other man pages
r = sub(b'<b>(.+?)</b>\\((.+?)\\)',
b'<b><a href="./\\1.\\2"
target=_blank>\\1</a>(\\2)</b>', r)
await stream.flushchunk(r)


Source:
from asyncio import create_subprocess_exec, get_event_loop
from asyncio.subprocess import PIPE

from lib.setup import bsize
from lib.stream import Stream

async def create_proc(cmd, mode='r', outstream=None):
stdin = PIPE if 'w' in mode else None
stdout = PIPE if outstream or ('r' in mode) else None
if type(cmd) is str:
clist = cmd.split()
else:
clist = cmd
aproc = await create_subprocess_exec(*clist, stdin=stdin,
stdout=stdout, limit=bsize)
return Proc(aproc, outstream)


class Proc(Stream):

def __init__(self, aproc, outstream):
Stream.__init__(self, aproc.stdout, aproc.stdin)
self.aproc = aproc
self.outstream = outstream

async def readwrite(self):
while 1:
r = await self.read(bsize)
if r:
self.outstream.write(r)
else:
break
self.outstream.close()

async def __aenter__(self):
if self.outstream:
get_event_loop().create_task(self.readwrite())
return self

async def __aexit__(self, *args):
if self.aproc.stdout:
await self.read() # ??
await self.aproc.wait()