uvloop does not support original unix udp socketpair

import asyncio
import os, socket
import uvloop
asyncio.set_event_loop_policy(uvloop.EventLoopPolicy())

try:
    os.unlink("./tmp")
except:
    pass
try:
    os.unlink("./tmp1")
except:
    pass

socket_pair = socket.socketpair(socket.AF_UNIX, socket.SOCK_DGRAM, 0)

class WorkerConnection(asyncio.Protocol):
    def __init__(self):
        print("init connection in worker")
        self.aio_connection = None

    def connection_made(self, transport):
        self.aio_connection = transport

    def datagram_received(self, data: bytes, addr):
    	print(data)

class DispatcherConnection(asyncio.Protocol):
    def __init__(self):
        print("init connection in dispatcher")
        self.aio_connection = None

    def connection_made(self, transport):
        self.aio_connection = transport

    def datagram_received(self, data: bytes, addr):
    	print(data)

loop = uvloop.new_event_loop()
asyncio.set_event_loop(loop)

coros = loop.create_datagram_endpoint(WorkerConnection, sock=socket_pair[0])
(transport1, protocol1) = loop.run_until_complete(coros)

coros = loop.create_datagram_endpoint(DispatcherConnection, sock=socket_pair[1])
(transport2, protocol2) = loop.run_until_complete(coros)

transport1.sendto(b'transport1')
transport2.sendto(b'transport2')

loop.run_forever()

I initialize a unix udp socketpair, and try to use uvloop to manage both sockets.
The code above has the following err:

However, when I bind address to both sockets, the err disappears.

socket_pair[0].bind("./tmp")
socket_pair[1].bind("./tmp1")

It shows uvloop does not support the original unix udp socketpair.

@ZhuYuJin

This seems to be a low-level behavior:

#include <unistd.h>
#include <stdint.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/errno.h>
#include <sys/ioctl.h>


void do_send(int fd) {
    int32_t w_buf = 32;
    write(fd, &w_buf, sizeof(w_buf));
}

void do_recv(int fd) {
    // copied from uv__udp_recvmsg
    struct sockaddr_storage peer;
    struct msghdr h;
    ssize_t nread;
    struct iovec buf;
    int r;
    int nonblocking = 1;
    buf.iov_base = malloc((32) * sizeof(char));
    buf.iov_len = 32;

    memset(&h, 0, sizeof(h));
    memset(&peer, 0, sizeof(peer));
    h.msg_name = &peer;
    h.msg_namelen = sizeof(peer);
    h.msg_iov = (void*) &buf;
    h.msg_iovlen = 1;

    // copied from uv__nonblock_ioctl
    do
        r = ioctl(fd, FIONBIO, &nonblocking);
    while (r == -1 && errno == EINTR);
    if (r) {
        printf("ioctl errno: %d %s\n", r, strerror(errno));
    }

    nread = recvmsg(fd, &h, 0);
    if (nread == -1 || errno != 0) {
        printf("%ld %s\n", nread, strerror(errno));
    } else {
        printf("nread=%ld sa_family=%d msg_namelen=%d\n", nread, ((struct sockaddr *)&peer)->sa_family, h.msg_namelen);
    }
}

int main() {
    int socket_vector[2];

    // use either SOCK_DGRAM or SOCK_STREAM
    if(0 != socketpair(AF_UNIX, SOCK_DGRAM, 0, socket_vector)) {
        perror("cannot create socket pair");
        return 2;
    }

    do_send(socket_vector[0]);
    do_recv(socket_vector[1]);
}

OS	socketpair type	nonblocking	peer.sa_family	msg_namelen
Linux	SOCK_DGRAM	0	AF_UNSPEC	0
Linux	SOCK_DGRAM	1	AF_UNSPEC	0
Linux	SOCK_STREAM	0	AF_UNSPEC	0
Linux	SOCK_STREAM	1	AF_UNSPEC	0
macOS	SOCK_DGRAM	0	AF_UNIX	16
macOS	SOCK_DGRAM	1	AF_UNIX	16
macOS	SOCK_STREAM	0	AF_UNSPEC	0
macOS	SOCK_STREAM	1	AF_UNSPEC	0

And ((struct sockaddr_un *) &peer)->sun_path is always an empty string.

Related code:

https://github.com/libuv/libuv/blob/0ed9692a80b2f310ad52060a8cb400f2a963d09c/src/unix/udp.c#L285-L301
uvloop/uvloop/handles/udp.pyx

Line 335 in 2870219

pyaddr = __convert_sockaddr_to_pyaddr(addr)

uvloop/uvloop/dns.pyx

Lines 64 to 68 in 2870219

    
           elif addr.sa_family == uv.AF_UNIX: 
        
               addr_un = <system.sockaddr_un*>addr 
        
               return system.MakeUnixSockPyAddr(addr_un) 
        
           raise RuntimeError("cannot convert sockaddr into Python object")

@ZhuYuJin 's code fails because __convert_sockaddr_to_pyaddr doesn't support AF_UNSPEC. @1st1 shall we patch __convert_sockaddr_to_pyaddr so that it returns an empty string if the family is AF_UNSPEC like this (Solution A)?

diff --git a/uvloop/dns.pyx b/uvloop/dns.pyx
index a252a24..843b5d5 100644
--- a/uvloop/dns.pyx
+++ b/uvloop/dns.pyx
@@ -65,6 +67,9 @@ cdef __convert_sockaddr_to_pyaddr(const system.sockaddr* addr):
         addr_un = <system.sockaddr_un*>addr
         return system.MakeUnixSockPyAddr(addr_un)

+    elif addr.sa_family == uv.AF_UNSPEC:
+        return ""
+
     raise RuntimeError("cannot convert sockaddr into Python object")

Alternatively, we could patch udp.pyx to handle it like this (Solution B):

diff --git a/uvloop/handles/udp.pyx b/uvloop/handles/udp.pyx
index 675407d..5a0f225 100644
--- a/uvloop/handles/udp.pyx
+++ b/uvloop/handles/udp.pyx
@@ -330,6 +330,8 @@ cdef void __uv_udp_on_receive(uv.uv_udp_t* handle,

     if addr is NULL:
         pyaddr = None
+    elif addr.sa_family == uv.AF_UNSPEC:
+        pyaddr = ""
     else:
         try:
             pyaddr = __convert_sockaddr_to_pyaddr(addr)

Or less efficiently but support potential future changes to __convert_sockaddr_to_pyaddr (Solution C):

diff --git a/uvloop/handles/udp.pyx b/uvloop/handles/udp.pyx
index 675407d..16aced6 100644
--- a/uvloop/handles/udp.pyx
+++ b/uvloop/handles/udp.pyx
@@ -334,8 +334,11 @@ cdef void __uv_udp_on_receive(uv.uv_udp_t* handle,
         try:
             pyaddr = __convert_sockaddr_to_pyaddr(addr)
         except BaseException as exc:
-            udp._error(exc, False)
-            return
+            if addr.sa_family == uv.AF_UNSPEC:
+                pyaddr = ""
+            else:
+                udp._error(exc, False)
+                return

     if nread < 0:
         exc = convert_error(nread)

@fantix

@fantix It should solve the problem.
However, I specify a unix socket pair. Why does it become a AF_UNSPEC?
This code performs well in Mac OS.

Yeah, I think it is from Linux kernel - I tried to track it down but it's a lot of code to read, so we might want to work it around in uvloop first.

C or B would work. How does CPython deal with this btw?

That's a really good point - let me check.

Looks like it'll just return None:

https://github.com/python/cpython/blob/87502ddd710eb1f030b8ff5a60b05becea3f474f/Modules/socketmodule.c#L1335-L1341

static PyObject *
makesockaddr(SOCKET_T sockfd, struct sockaddr *addr, size_t addrlen, int proto)
{
    if (addrlen == 0) {
        /* No address -- may be recvfrom() from known socket */
        Py_RETURN_NONE;
    }

Guess solution D would be to update __convert_sockaddr_to_pyaddr to include this logic.

Guess solution D would be to update __convert_sockaddr_to_pyaddr to include this logic.

Yep!

@ZhuYuJin

Bad news: libuv didn't provide the addrlen (the msg_namelen below as a value-result argument) for callbacks (I'll file an issue in libuv):

https://github.com/libuv/libuv/blob/16910d23a34b8b8c313d24824fd85383aa8a8d40/src/unix/udp.c#L180-L200

static void uv__udp_recvmsg(uv_udp_t* handle) {
  struct sockaddr_storage peer;
  struct msghdr h;
  ...
    memset(&h, 0, sizeof(h));
    memset(&peer, 0, sizeof(peer));
    h.msg_name = &peer;
    h.msg_namelen = sizeof(peer);
    ...
      handle->recv_cb(handle, nread, &buf, (const struct sockaddr*) &peer, flags);

And I don't think it is a reliable way to check if the first byte is \0 as an equivalent to checking addrlen == 0 in __convert_sockaddr_to_pyaddr, because we don't know for sure what addr->sa_family is.

In this case, I would go for solution B if no objections.

By the way, @ZhuYuJin 's code doesn't work with vanilla asyncio - it uses sendto if peername is not set:

https://github.com/python/cpython/blob/515fce4fc4bb0d2db97b17df275cf90640017f56/Lib/asyncio/selector_events.py#L1043-L1046

    def sendto(self, data, addr=None):
        ...
                if self._extra['peername']:
                    self._sock.send(data)
                else:
                    self._sock.sendto(data, addr)

But the peername is always empty for a socketpair:

import socket

s1, s2 = socket.socketpair(socket.AF_UNIX, socket.SOCK_DGRAM, 0)
print("peername:", repr(s1.getpeername()))
s1.sendto(b'xxx', None)
s1.sendto(b'xxx', b'')

peername: ''
Traceback (most recent call last):
  File "t304.py", line 5, in <module>
    s1.sendto(b'xxx', None)
TypeError: a bytes-like object is required, not 'NoneType'

Traceback (most recent call last):
  File "t304.py", line 5, in <module>
    s1.sendto(b'xxx', b'')
OSError: [Errno 56] Socket is already connected

Should we consider this a bug in CPython asyncio and fix it there too?

Yeah, let's to B.

Bad news: libuv didn't provide the addrlen (the msg_namelen below as a value-result argument) for callbacks (I'll file an issue in libuv):

I think I also encountered this limitation myself one time, so resolving this at the libuv level would be great. IIRC I also had problems with dealing with abstract unix sockets in libuv, and maybe it was somehow related to this, I don't remember now.

Accept empty addr in UDP on_receive

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uvloop does not support original unix udp socketpair #304

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	elif addr.sa_family == uv.AF_UNIX:
	addr_un = <system.sockaddr_un*>addr
	return system.MakeUnixSockPyAddr(addr_un)

	raise RuntimeError("cannot convert sockaddr into Python object")

uvloop does not support original unix udp socketpair #304

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fantix commented on Apr 4, 2020

ZhuYuJin commented on Apr 17, 2020

fantix commented on Apr 17, 2020

1st1 commented on Apr 17, 2020

fantix commented on Apr 17, 2020

fantix commented on Apr 17, 2020

1st1 commented on Apr 22, 2020

fantix commented on Apr 25, 2020

1st1 commented on Apr 26, 2020

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