bpo-17560: Too small type for struct.pack/unpack in mutliprocessing.Connection (GH-10305)

Allow sending more than 2 GB at once on a multiprocessing connection on non-Windows systems.

Lib/multiprocessing/connection.py

@@ -389,7 +389,14 @@ class Connection(_ConnectionBase):
 
     def _send_bytes(self, buf):
         n = len(buf)
-        # For wire compatibility with 3.2 and lower
+        if n > 0x7fffffff:
+            pre_header = struct.pack("!i", -1)
+            header = struct.pack("!Q", n)
+            self._send(pre_header)
+            self._send(header)
+            self._send(buf)
+        else:
+            # For wire compatibility with 3.7 and lower
             header = struct.pack("!i", n)
             if n > 16384:
                 # The payload is large so Nagle's algorithm won't be triggered
@@ -406,6 +413,9 @@ class Connection(_ConnectionBase):
     def _recv_bytes(self, maxsize=None):
         buf = self._recv(4)
         size, = struct.unpack("!i", buf.getvalue())
+        if size == -1:
+            buf = self._recv(8)
+            size, = struct.unpack("!Q", buf.getvalue())
         if maxsize is not None and size > maxsize:
             return None
         return self._recv(size)

Misc/NEWS.d/next/Library/2018-11-03-10-12-04.bpo-35152.xpqskp.rst

+Allow sending more than 2 GB at once on a multiprocessing connection on non-Windows systems.
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