Issue #23804: Fix SSL zero-length recv() calls to not block and raise EOF

Lib/test/test_ssl.py

@@ -2793,20 +2793,13 @@ else:
                         # consume data
                         s.read()
 
-                data = b"data"
-
                 # read(-1, buffer) is supported, even though read(-1) is not
+                data = b"data"
                 s.send(data)
                 buffer = bytearray(len(data))
                 self.assertEqual(s.read(-1, buffer), len(data))
                 self.assertEqual(buffer, data)
 
-                # recv/read(0) should return no data
-                s.send(data)
-                self.assertEqual(s.recv(0), b"")
-                self.assertEqual(s.read(0), b"")
-                self.assertEqual(s.read(), data)
-
                 # Make sure sendmsg et al are disallowed to avoid
                 # inadvertent disclosure of data and/or corruption
                 # of the encrypted data stream
@@ -2822,6 +2815,26 @@ else:
 
                 s.close()
 
+        def test_recv_zero(self):
+            server = ThreadedEchoServer(CERTFILE)
+            server.__enter__()
+            self.addCleanup(server.__exit__, None, None)
+            s = socket.create_connection((HOST, server.port))
+            self.addCleanup(s.close)
+            s = ssl.wrap_socket(s, suppress_ragged_eofs=False)
+            self.addCleanup(s.close)
+
+            # recv/read(0) should return no data
+            s.send(b"data")
+            self.assertEqual(s.recv(0), b"")
+            self.assertEqual(s.read(0), b"")
+            self.assertEqual(s.read(), b"data")
+
+            # Should not block if the other end sends no data
+            s.setblocking(False)
+            self.assertEqual(s.recv(0), b"")
+            self.assertEqual(s.recv_into(bytearray()), 0)
+
         def test_nonblocking_send(self):
             server = ThreadedEchoServer(CERTFILE,
                                         certreqs=ssl.CERT_NONE,

Misc/NEWS

@@ -19,6 +19,9 @@ Core and Builtins
 Library
 -------
 
+- Issue #23804: Fix SSL zero-length recv() calls to not block and not raise
+  an error about unclean EOF.
+
 - Issue #27466: Change time format returned by http.cookie.time2netscape,
   confirming the netscape cookie format and making it consistent with
   documentation.

Modules/_ssl.c

@@ -1913,6 +1913,10 @@ _ssl__SSLSocket_read_impl(PySSLSocket *self, int len, int group_right_1,
         dest = PyBytes_FromStringAndSize(NULL, len);
         if (dest == NULL)
             goto error;
+        if (len == 0) {
+            Py_XDECREF(sock);
+            return dest;
+        }
         mem = PyBytes_AS_STRING(dest);
     }
     else {
@@ -1924,6 +1928,10 @@ _ssl__SSLSocket_read_impl(PySSLSocket *self, int len, int group_right_1,
                                 "maximum length can't fit in a C 'int'");
                 goto error;
             }
+            if (len == 0) {
+                count = 0;
+                goto done;
+            }
         }
     }