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add a new is_readable method to SocketType (fix #760) #1137

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Jul 6, 2019
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add a new is_readable method to SocketType (fix #760) #1137

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317b09a
add a new is_readable method to SocketType (fix #760)
ziirish Jul 3, 2019
10cf005
rephrase and fix typos
ziirish Jul 5, 2019
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4 changes: 4 additions & 0 deletions docs/source/reference-io.rst
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Expand Up @@ -403,6 +403,10 @@ Socket objects
left in an unknown state – possibly open, and possibly
closed. The only reasonable thing to do is to close it.

.. method:: is_readable

Check whether the socket is readable or not.

.. method:: sendfile

`Not implemented yet! <https://github.com/python-trio/trio/issues/45>`__
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3 changes: 3 additions & 0 deletions newsfragments/760.feature.rst
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@@ -0,0 +1,3 @@
We added a new ``is_readable`` method to the ``trio.socket.SocketType``
object that allows you to check whether a socket is ready to be read
or not.
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The double-backticks are raw code; since we're referring to objects that have entries in the documentation, we can use single-backticks to link directly:

Trio sockets have a new method `~trio.socket.SocketType.is_readable`, that allows you
to check whether a socket is readable. This is useful for HTTP/1.1 clients.

(The tilde is a shorthand that means "make a link to trio.socket.SocketType.is_readable, but just render it as is_readable".)

12 changes: 11 additions & 1 deletion trio/_socket.py
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@@ -1,5 +1,6 @@
import os as _os
import sys as _sys
import select
import socket as _stdlib_socket
from functools import wraps as _wraps

Expand Down Expand Up @@ -289,7 +290,7 @@ def socket(

def _sniff_sockopts_for_fileno(family, type, proto, fileno):
"""Correct SOCKOPTS for given fileno, falling back to provided values.

"""
# Wrap the raw fileno into a Python socket object
# This object might have the wrong metadata, but it lets us easily call getsockopt
Expand Down Expand Up @@ -478,6 +479,15 @@ def shutdown(self, flag):
if flag in [_stdlib_socket.SHUT_WR, _stdlib_socket.SHUT_RDWR]:
self._did_shutdown_SHUT_WR = True

def is_readable(self):
# use select.select on Windows, and select.poll everywhere else
if _sys.platform == "win32":
rready, _, _ = select.select([self._sock], [], [], 0)
return bool(rready)
p = select.poll()
p.register(self._sock, select.POLLIN)
return bool(p.poll(0))

async def wait_writable(self):
await _core.wait_writable(self._sock)

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17 changes: 17 additions & 0 deletions trio/tests/test_socket.py
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Expand Up @@ -404,6 +404,23 @@ async def test_SocketType_simple_server(address, socket_type):
assert await client.recv(1) == b"x"


async def test_SocketTupe_is_readable():
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Typo: "SocketTupe" should be "SocketType"

listener = tsocket.socket(tsocket.AF_INET)
client = tsocket.socket(tsocket.AF_INET)
with listener, client:
await listener.bind(('127.0.0.1', 0))
listener.listen(20)
addr = listener.getsockname()[:2]
async with _core.open_nursery() as nursery:
nursery.start_soon(client.connect, addr)
server, client_addr = await listener.accept()
with server:
assert not client.is_readable()
await server.send(b"x")
assert client.is_readable()
assert await client.recv(1) == b"x"
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This can be simplified a lot by using socketpair, which directly returns a pair of connected sockets. Something like:

a, b = trio.socket.socketpair()
with a, b:
    assert not a.is_readable()
    await b.send(b"x")
    await _core.wait_readable(a)
    assert a.is_readable()
    assert await a.recv(1) == b"x"
    assert not a.is_readable()

I also added a call to wait_readable, just in case the operating system needs a moment to notice that writing to b makes a readable.



# On some macOS systems, getaddrinfo likes to return V4-mapped addresses even
# when we *don't* pass AI_V4MAPPED.
# https://github.com/python-trio/trio/issues/580
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