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how to check third parameter of socket(2)?

From: Steffen Dettmer
Subject: how to check third parameter of socket(2)?
Date: Wed, 24 Mar 2010 13:23:53 +0100


to prepare a TCP socket, usually someone calls something like:

   int sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);

however, on older linux versions, for example 2.2.16, this
returns a socket on which bind(2) will fail with `address already
in use'. Here, the following works:

   int sockfd = socket(AF_INET, SOCK_STREAM, IPPROTO_IP);

from netinet/in.h:

   IPPROTO_IP = 0,      /* Dummy protocol for TCP.  */

however, we also have socket APIs that /require/ to use the first
form. So we have platforms that accept both (recent linux
versions), only the first form (3rd party socket APIs) and others
only the second form (older linux versions).

I have no idea how to handle this. Best would be to have some
#define set by some configure check, but there are problems:

  - it is not the socket calls that fails but a subsequent bind
  - the bind fails with exactly the same error that will happen
    when the test-port is really in use (e.g. by a running
  - and, last but not least, this requires to RUN the program,
    which cannot work for cross-compilation.

Is this topic known? I think it could be an almost-FAQ because of
`IPPROTO_IP == Dummy protocol for TCP' and that tutorials in the
internet tell to use IPPROTO_TCP instead, which seems to be more

Any proposals how to handle this issue?



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