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Add the {active,N} socket option, where N is an integer in the range
-32768..32767, to allow a caller to specify the number of data messages to
be delivered to the controlling process. Once the socket's delivered
message count either reaches 0 or is explicitly set to 0 with
inet:setopts/2 or by including {active,0} as an option when the socket is
created, the socket transitions to passive ({active, false}) mode and the
socket's controlling process receives a message to inform it of the
transition. TCP sockets receive {tcp_passive,Socket}, UDP sockets receive
{udp_passive,Socket} and SCTP sockets receive {sctp_passive,Socket}.
The socket's delivered message counter defaults to 0, but it can be set
using {active,N} via any gen_tcp, gen_udp, or gen_sctp function that takes
socket options as arguments, or via inet:setopts/2. New N values are added
to the socket's current counter value, and negative numbers can be used to
reduce the counter value. Specifying a number that would cause the socket's
counter value to go above 32767 causes an einval error. If a negative
number is specified such that the counter value would become negative, the
socket's counter value is set to 0 and the socket transitions to passive
mode. If the counter value is already 0 and inet:setopts(Socket,
[{active,0}]) is specified, the counter value remains at 0 but the
appropriate passive mode transition message is generated for the socket.
This commit contains a modified preloaded prim_inet.beam due to changes in
prim_inet.erl.
Add tests for {active,N} mode for TCP, UDP, and SCTP sockets.
Add documentation for {active,N} mode for inet, gen_tcp, gen_udp, and
gen_sctp.
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If an IPv4 fd is opened as an IPv6 socket, unexpected behaviour can
occur. For example, if an IPv4 UDP socket is opened and passed into
Erlang as an IPv6 socket, the first 3 bytes (corresponding to 1 byte
representing the protocol family, 2 bytes set to the port) are stripped
from the payload. The cause of the UDP payload truncation happens in
inet_drv.c:packet_inet_input when a call to inet_get_address fails
silently because the family is set to PF_INET6 but the buffer len is
the size of an IPv4 struct sockaddr_in.
Prevent this behaviour by checking that the protocol family of the file
descriptor matches the family of the requested Erlang socket.
{ok, S1} = gen_udp:open(0, [binary, inet]),
{ok, FD} = inet:getfd(S1),
{ok, Port} = inet:port(S1),
{ok, S} = gen_udp:open(Port, [binary, {fd, FD}, inet6]),
{ok, C} = gen_udp:open(0, [binary]),
Msg = <<1,2,3,4,5>>,
gen_udp:send(C, "127.0.0.1", Port, Msg),
receive
{udp, S, _, _, Msg} -> ok;
{udp, S, _, _, NewMsg} -> {error, Msg, NewMsg}
end.
This test results in: {error,<<1,2,3,4,5>>,<<4,5>>}
Thanks to Andrew Tunnell-Jones for finding the bug and the test case!
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