changeset 49286:c6a3243567b6

chg: replace mercurial.util.recvfds() by simpler pure Python implementation On Python 3, we have socket.socket.recvmsg(). This makes it possible to receive FDs in pure Python code. The new code behaves like the previous implementations, except that it’s more strict about the format of the ancillary data. This works because we know in which format the FDs are passed. Because the code is (and always has been) specific to chg (payload is 1 byte, number of passed FDs is limited) and we now have only one implementation and the code is very short, I decided to stop exposing a function in mercurial.util. Note on terminology: The SCM_RIGHTS mechanism is used to share open file descriptions to another process over a socket. The sending side passes an array of file descriptors and the receiving side receives an array of file descriptors. The file descriptors are different in general on both sides but refer to the same open file descriptions. The two terms are often conflated, even in the official documentation. That’s why I used “FD” above, which could mean both “file descriptor” and “file description”.
author Manuel Jacob <me@manueljacob.de>
date Thu, 02 Jun 2022 23:57:56 +0200
parents 34020d1f1635
children 127d33e63d1a
files mercurial/cext/osutil.c mercurial/cext/osutil.pyi mercurial/chgserver.py mercurial/pure/osutil.py mercurial/util.py
diffstat 5 files changed, 11 insertions(+), 177 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/cext/osutil.c	Mon Jun 06 13:58:32 2022 +0400
+++ b/mercurial/cext/osutil.c	Thu Jun 02 23:57:56 2022 +0200
@@ -685,75 +685,6 @@
 	return NULL;
 }
 
-/*
- * recvfds() simply does not release GIL during blocking io operation because
- * command server is known to be single-threaded.
- *
- * Old systems such as Solaris don't provide CMSG_LEN, msg_control, etc.
- * Currently, recvfds() is not supported on these platforms.
- */
-#ifdef CMSG_LEN
-
-static ssize_t recvfdstobuf(int sockfd, int **rfds, void *cbuf, size_t cbufsize)
-{
-	char dummy[1];
-	struct iovec iov = {dummy, sizeof(dummy)};
-	struct msghdr msgh = {0};
-	struct cmsghdr *cmsg;
-
-	msgh.msg_iov = &iov;
-	msgh.msg_iovlen = 1;
-	msgh.msg_control = cbuf;
-	msgh.msg_controllen = (socklen_t)cbufsize;
-	if (recvmsg(sockfd, &msgh, 0) < 0)
-		return -1;
-
-	for (cmsg = CMSG_FIRSTHDR(&msgh); cmsg;
-	     cmsg = CMSG_NXTHDR(&msgh, cmsg)) {
-		if (cmsg->cmsg_level != SOL_SOCKET ||
-		    cmsg->cmsg_type != SCM_RIGHTS)
-			continue;
-		*rfds = (int *)CMSG_DATA(cmsg);
-		return (cmsg->cmsg_len - CMSG_LEN(0)) / sizeof(int);
-	}
-
-	*rfds = cbuf;
-	return 0;
-}
-
-static PyObject *recvfds(PyObject *self, PyObject *args)
-{
-	int sockfd;
-	int *rfds = NULL;
-	ssize_t rfdscount, i;
-	char cbuf[256];
-	PyObject *rfdslist = NULL;
-
-	if (!PyArg_ParseTuple(args, "i", &sockfd))
-		return NULL;
-
-	rfdscount = recvfdstobuf(sockfd, &rfds, cbuf, sizeof(cbuf));
-	if (rfdscount < 0)
-		return PyErr_SetFromErrno(PyExc_OSError);
-
-	rfdslist = PyList_New(rfdscount);
-	if (!rfdslist)
-		goto bail;
-	for (i = 0; i < rfdscount; i++) {
-		PyObject *obj = PyLong_FromLong(rfds[i]);
-		if (!obj)
-			goto bail;
-		PyList_SET_ITEM(rfdslist, i, obj);
-	}
-	return rfdslist;
-
-bail:
-	Py_XDECREF(rfdslist);
-	return NULL;
-}
-
-#endif /* CMSG_LEN */
-
 /* allow disabling setprocname via compiler flags */
 #ifndef SETPROCNAME_USE_NONE
 #if defined(HAVE_SETPROCTITLE)
@@ -1285,10 +1216,6 @@
 	{"statfiles", (PyCFunction)statfiles, METH_VARARGS | METH_KEYWORDS,
 	 "stat a series of files or symlinks\n"
 "Returns None for non-existent entries and entries of other types.\n"},
-#ifdef CMSG_LEN
-	{"recvfds", (PyCFunction)recvfds, METH_VARARGS,
-	 "receive list of file descriptors via socket\n"},
-#endif
 #ifndef SETPROCNAME_USE_NONE
 	{"setprocname", (PyCFunction)setprocname, METH_VARARGS,
 	 "set process title (best-effort)\n"},
--- a/mercurial/cext/osutil.pyi	Mon Jun 06 13:58:32 2022 +0400
+++ b/mercurial/cext/osutil.pyi	Thu Jun 02 23:57:56 2022 +0200
@@ -18,7 +18,6 @@
 def listdir(path: bytes, st: bool, skip: bool) -> List[stat]: ...
 def posixfile(name: AnyStr, mode: bytes, buffering: int) -> IO: ...
 def statfiles(names: Sequence[bytes]) -> List[stat]: ...
-def recvfds(sockfd: int) -> List[int]: ...
 def setprocname(name: bytes) -> None: ...
 def getfstype(path: bytes) -> bytes: ...
 def getfsmountpoint(path: bytes) -> bytes: ...
--- a/mercurial/chgserver.py	Mon Jun 06 13:58:32 2022 +0400
+++ b/mercurial/chgserver.py	Thu Jun 02 23:57:56 2022 +0200
@@ -389,7 +389,17 @@
         # tell client to sendmsg() with 1-byte payload, which makes it
         # distinctive from "attachio\n" command consumed by client.read()
         self.clientsock.sendall(struct.pack(b'>cI', b'I', 1))
-        clientfds = util.recvfds(self.clientsock.fileno())
+
+        data, ancdata, msg_flags, address = self.clientsock.recvmsg(1, 256)
+        assert len(ancdata) == 1
+        cmsg_level, cmsg_type, cmsg_data = ancdata[0]
+        assert cmsg_level == socket.SOL_SOCKET
+        assert cmsg_type == socket.SCM_RIGHTS
+        # memoryview.cast() was added in typeshed 61600d68772a, but pytype
+        # still complains
+        # pytype: disable=attribute-error
+        clientfds = memoryview(cmsg_data).cast('i').tolist()
+        # pytype: enable=attribute-error
         self.ui.log(b'chgserver', b'received fds: %r\n', clientfds)
 
         ui = self.ui
--- a/mercurial/pure/osutil.py	Mon Jun 06 13:58:32 2022 +0400
+++ b/mercurial/pure/osutil.py	Thu Jun 02 23:57:56 2022 +0200
@@ -9,7 +9,6 @@
 import ctypes
 import ctypes.util
 import os
-import socket
 import stat as statmod
 
 from ..pycompat import getattr
@@ -71,102 +70,6 @@
 if not pycompat.iswindows:
     posixfile = open
 
-    _SCM_RIGHTS = 0x01
-    _socklen_t = ctypes.c_uint
-
-    if pycompat.sysplatform.startswith(b'linux'):
-        # socket.h says "the type should be socklen_t but the definition of
-        # the kernel is incompatible with this."
-        _cmsg_len_t = ctypes.c_size_t
-        _msg_controllen_t = ctypes.c_size_t
-        _msg_iovlen_t = ctypes.c_size_t
-    else:
-        _cmsg_len_t = _socklen_t
-        _msg_controllen_t = _socklen_t
-        _msg_iovlen_t = ctypes.c_int
-
-    class _iovec(ctypes.Structure):
-        _fields_ = [
-            (u'iov_base', ctypes.c_void_p),
-            (u'iov_len', ctypes.c_size_t),
-        ]
-
-    class _msghdr(ctypes.Structure):
-        _fields_ = [
-            (u'msg_name', ctypes.c_void_p),
-            (u'msg_namelen', _socklen_t),
-            (u'msg_iov', ctypes.POINTER(_iovec)),
-            (u'msg_iovlen', _msg_iovlen_t),
-            (u'msg_control', ctypes.c_void_p),
-            (u'msg_controllen', _msg_controllen_t),
-            (u'msg_flags', ctypes.c_int),
-        ]
-
-    class _cmsghdr(ctypes.Structure):
-        _fields_ = [
-            (u'cmsg_len', _cmsg_len_t),
-            (u'cmsg_level', ctypes.c_int),
-            (u'cmsg_type', ctypes.c_int),
-            (u'cmsg_data', ctypes.c_ubyte * 0),
-        ]
-
-    _libc = ctypes.CDLL(ctypes.util.find_library(u'c'), use_errno=True)
-    _recvmsg = getattr(_libc, 'recvmsg', None)
-    if _recvmsg:
-        _recvmsg.restype = getattr(ctypes, 'c_ssize_t', ctypes.c_long)
-        _recvmsg.argtypes = (
-            ctypes.c_int,
-            ctypes.POINTER(_msghdr),
-            ctypes.c_int,
-        )
-    else:
-        # recvmsg isn't always provided by libc; such systems are unsupported
-        def _recvmsg(sockfd, msg, flags):
-            raise NotImplementedError(b'unsupported platform')
-
-    def _CMSG_FIRSTHDR(msgh):
-        if msgh.msg_controllen < ctypes.sizeof(_cmsghdr):
-            return
-        cmsgptr = ctypes.cast(msgh.msg_control, ctypes.POINTER(_cmsghdr))
-        return cmsgptr.contents
-
-    # The pure version is less portable than the native version because the
-    # handling of socket ancillary data heavily depends on C preprocessor.
-    # Also, some length fields are wrongly typed in Linux kernel.
-    def recvfds(sockfd):
-        """receive list of file descriptors via socket"""
-        dummy = (ctypes.c_ubyte * 1)()
-        iov = _iovec(ctypes.cast(dummy, ctypes.c_void_p), ctypes.sizeof(dummy))
-        cbuf = ctypes.create_string_buffer(256)
-        msgh = _msghdr(
-            None,
-            0,
-            ctypes.pointer(iov),
-            1,
-            ctypes.cast(cbuf, ctypes.c_void_p),
-            ctypes.sizeof(cbuf),
-            0,
-        )
-        r = _recvmsg(sockfd, ctypes.byref(msgh), 0)
-        if r < 0:
-            e = ctypes.get_errno()
-            raise OSError(e, os.strerror(e))
-        # assumes that the first cmsg has fds because it isn't easy to write
-        # portable CMSG_NXTHDR() with ctypes.
-        cmsg = _CMSG_FIRSTHDR(msgh)
-        if not cmsg:
-            return []
-        if (
-            cmsg.cmsg_level != socket.SOL_SOCKET
-            or cmsg.cmsg_type != _SCM_RIGHTS
-        ):
-            return []
-        rfds = ctypes.cast(cmsg.cmsg_data, ctypes.POINTER(ctypes.c_int))
-        rfdscount = (
-            cmsg.cmsg_len - _cmsghdr.cmsg_data.offset
-        ) // ctypes.sizeof(ctypes.c_int)
-        return [rfds[i] for i in pycompat.xrange(rfdscount)]
-
 
 else:
     import msvcrt
--- a/mercurial/util.py	Mon Jun 06 13:58:32 2022 +0400
+++ b/mercurial/util.py	Thu Jun 02 23:57:56 2022 +0200
@@ -156,11 +156,6 @@
 SERVERROLE = compression.SERVERROLE
 CLIENTROLE = compression.CLIENTROLE
 
-try:
-    recvfds = osutil.recvfds
-except AttributeError:
-    pass
-
 # Python compatibility
 
 _notset = object()