closes bpo-25041: Document AF_PACKET socket address format. (GH-4092)

3 files changed, 39 insertions, 13 deletions

diff --git a/Doc/library/socket.rst b/Doc/library/socket.rst
index cea0175577..32e7c5e6c0 100644
--- a/Doc/library/socket.rst
+++ b/Doc/library/socket.rst
@@ -173,10 +173,25 @@ created.  Socket addresses are represented as follows:
 
   .. versionadded:: 3.7
 
-- Certain other address families (:const:`AF_PACKET`, :const:`AF_CAN`)
-  support specific representations.
-
-  .. XXX document them!
+- :const:`AF_PACKET` is a low-level interface directly to network devices.
+  The packets are represented by the tuple
+  ``(ifname, proto[, pkttype[, hatype[, addr]]])`` where:
+
+  - *ifname* - String specifying the device name.
+  - *proto* - An in network-byte-order integer specifying the Ethernet
+    protocol number.
+  - *pkttype* - Optional integer specifying the packet type:
+
+    - ``PACKET_HOST`` (the default) - Packet addressed to the local host.
+    - ``PACKET_BROADCAST`` - Physical-layer broadcast packet.
+    - ``PACKET_MULTIHOST`` - Packet sent to a physical-layer multicast address.
+    - ``PACKET_OTHERHOST`` - Packet to some other host that has been caught by
+      a device driver in promiscuous mode.
+    - ``PACKET_OUTGOING`` - Packet originating from the local host that is
+      looped back to a packet socket.
+  - *hatype* - Optional integer specifying the ARP hardware address type.
+  - *addr* - Optional bytes-like object specifying the hardware physical
+    address, whose interpretation depends on the device.
 
 If you use a hostname in the *host* portion of IPv4/v6 socket address, the
 program may show a nondeterministic behavior, as Python uses the first address
@@ -376,6 +391,16 @@ Constants
    .. versionadded:: 3.7
 
 
+.. data:: AF_PACKET
+          PF_PACKET
+          PACKET_*
+
+   Many constants of these forms, documented in the Linux documentation, are
+   also defined in the socket module.
+
+   Availability: Linux >= 2.2.
+
+
 .. data:: AF_RDS
           PF_RDS
           SOL_RDS
@@ -469,12 +494,12 @@ The following functions all create :ref:`socket objects <socket-objects>`.
 
    Create a new socket using the given address family, socket type and protocol
    number.  The address family should be :const:`AF_INET` (the default),
-   :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN` or :const:`AF_RDS`. The
-   socket type should be :const:`SOCK_STREAM` (the default),
-   :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other ``SOCK_``
-   constants. The protocol number is usually zero and may be omitted or in the
-   case where the address family is :const:`AF_CAN` the protocol should be one
-   of :const:`CAN_RAW`, :const:`CAN_BCM` or :const:`CAN_ISOTP`
+   :const:`AF_INET6`, :const:`AF_UNIX`, :const:`AF_CAN`, :const:`AF_PACKET`,
+   or :const:`AF_RDS`. The socket type should be :const:`SOCK_STREAM` (the
+   default), :const:`SOCK_DGRAM`, :const:`SOCK_RAW` or perhaps one of the other
+   ``SOCK_`` constants. The protocol number is usually zero and may be omitted
+   or in the case where the address family is :const:`AF_CAN` the protocol
+   should be one of :const:`CAN_RAW`, :const:`CAN_BCM` or :const:`CAN_ISOTP`.
 
    If *fileno* is specified, the values for *family*, *type*, and *proto* are
    auto-detected from the specified file descriptor.  Auto-detection can be
diff --git a/Misc/NEWS.d/next/Documentation/2017-10-23-13-41-12.bpo-25041.iAo2gW.rst b/Misc/NEWS.d/next/Documentation/2017-10-23-13-41-12.bpo-25041.iAo2gW.rst
new file mode 100644
index 0000000000..5bb6e25db9
--- /dev/null
+++ b/Misc/NEWS.d/next/Documentation/2017-10-23-13-41-12.bpo-25041.iAo2gW.rst
@@ -0,0 +1 @@
+Document ``AF_PACKET`` in the :mod:`socket` module.
diff --git a/Modules/socketmodule.c b/Modules/socketmodule.c
index 8aadc780ff..adaefad556 100644
--- a/Modules/socketmodule.c
+++ b/Modules/socketmodule.c
@@ -1901,7 +1901,7 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
         const char *interfaceName;
         int protoNumber;
         int hatype = 0;
-        int pkttype = 0;
+        int pkttype = PACKET_HOST;
         Py_buffer haddr = {NULL, NULL};
 
         if (!PyTuple_Check(args)) {
@@ -1943,7 +1943,7 @@ getsockaddrarg(PySocketSockObject *s, PyObject *args,
         if (protoNumber < 0 || protoNumber > 0xffff) {
             PyErr_Format(
                 PyExc_OverflowError,
-                "%s(): protoNumber must be 0-65535.", caller);
+                "%s(): proto must be 0-65535.", caller);
             PyBuffer_Release(&haddr);
             return 0;
         }
@@ -2979,7 +2979,7 @@ PyDoc_STRVAR(bind_doc,
 \n\
 Bind the socket to a local address.  For IP sockets, the address is a\n\
 pair (host, port); the host must refer to the local host. For raw packet\n\
-sockets the address is a tuple (ifname, proto [,pkttype [,hatype]])");
+sockets the address is a tuple (ifname, proto [,pkttype [,hatype [,addr]]])");
 
 
 /* s.close() method.