Messages in this thread Patch in this message | | | From | Askar Safin <> | Subject | TCP connections come in wrong order | Date | Mon, 02 Feb 2015 00:30:31 +0300 |
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Consider the following code:
// C99, No error checking for simplicity
#include <stdio.h> #include <stdlib.h> #include <string.h>
#include <sys/socket.h> #include <unistd.h> #include <netdb.h>
#include <err.h>
static int tcp_connect_loop (const char *host, const char *protocol, struct addrinfo *res) { for (; res != NULL; res = res->ai_next) { int result = socket (res->ai_family, res->ai_socktype, res->ai_protocol);
if (result != -1) { if (connect (result, res->ai_addr, res->ai_addrlen) == 0) { return result; }
close (result); } }
// SOMEDAY: печатать больше инфы (то же для tcp_listen_loop)? errx (EXIT_FAILURE, "sh_tcp_connect: [%s]:%s: all structs returned by getaddrinfo failed", host, protocol); }
int //@ sh_tcp_connect (const char *host, const char *protocol, int family)//@; { struct addrinfo hints = {};
hints.ai_family = family; hints.ai_socktype = SOCK_STREAM;
struct addrinfo *res;
getaddrinfo (host, protocol, &hints, &res);
// POSIX 2013 says that now 'res' list contains at least one item
int result;
result = tcp_connect_loop (host, protocol, res); freeaddrinfo (res);
return result; }
static int tcp_listen_loop (const char *protocol, struct addrinfo *res) { for (; res != NULL; res = res->ai_next) { int result = socket (res->ai_family, res->ai_socktype, res->ai_protocol);
if (result != -1) { const int on = 1;
if (setsockopt (result, SOL_SOCKET, SO_REUSEADDR, &on, sizeof (on)) != -1) { if (bind (result, res->ai_addr, res->ai_addrlen) == 0) { return result; } }
close (result); } }
errx (EXIT_FAILURE, "sh_tcp_listen: *:%s: all structs returned by getaddrinfo failed", protocol); }
int //@ sh_tcp_listen (const char *protocol, int family)//@; { struct addrinfo hints = {};
hints.ai_flags = AI_PASSIVE; hints.ai_family = family; hints.ai_socktype = SOCK_STREAM;
struct addrinfo *res;
getaddrinfo (NULL, protocol, &hints, &res);
int result;
result = tcp_listen_loop (protocol, res);
listen (result, 5); freeaddrinfo (res); return result; }
#ifndef N #define N 100000 #endif
int main (int argc, char *argv[]) { if (strcmp (argv[1], "-l") == 0) { int l = sh_tcp_listen (argv[2], AF_INET);
for (;;) { int s = accept (l, NULL, NULL); if (s == -1) { continue; } char buf[1000]; write (1, buf, read (s, buf, sizeof (buf))); close (s); } } else { for (int i = 0; i != N; ++i) { int s = sh_tcp_connect (argv[1], argv[2], AF_INET); dprintf (s, "%d\n", i); close (s); } } exit (EXIT_SUCCESS); }
Compile this code as, for example, /tmp/x (again: this is C99), then run:
/tmp/x -l 5555 > /tmp/ooo
This command will accept connections and write coming data to /tmp/ooo . Okey, then run in another terminal:
/tmp/x localhost 5555
This command will connect to localhost, write 0, then connect again, write 1, etc. Soon you will not have available ports, so /tmp/x will fail before it will perform all N connections, this is OK. When this command complete, go to the first terminal and kill the program using Ctrl-C. Then look in /tmp/ooo and notice the last line, let's assume this is 28290. Then compare /tmp/ooo with the right monotonic number sequence:
echo {0..28290} | tr ' ' '\n' | diff -ur - /tmp/ooo
With some luck you will notice that /tmp/ooo is wrong. For example, I got the following:
--- - 2015-02-02 00:24:35.606008461 +0300 +++ /tmp/ooo 2015-02-02 00:09:25.002694629 +0300 @@ -7391,8 +7391,6 @@ 7390 7391 7392 -7393 -7394 7395 7396 7397 @@ -7546,6 +7544,8 @@ 7545 7546 7547 +7393 +7394 7548 7549 7550 If 'diff' doesn't report difference, then try again and again.
Is this a bug? I think that this is a bug.
Linux ideal-os 3.16.0-4-amd64 #1 SMP Debian 3.16.7-ckt2-1 (2014-12-08) x86_64 GNU/Linux Debian 8.0 Jessie GNU C Library (Debian GLIBC 2.19-13) stable release version 2.19, by Roland McGrath et al. == Askar Safin http://vk.com/safinaskar Kazan, Russia | |