[Bug 212716] recv() with MSG_WAITALL doesn't always unblock on EOF

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=212716

            Bug ID: 212716
           Summary: recv() with MSG_WAITALL doesn't always unblock on EOF
           Product: Base System
           Version: 10.3-RELEASE
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Many People
          Priority: ---
         Component: kern
          Assignee: freebsd-bugs at FreeBSD.org
          Reporter: lew at perftech.com

We have a simple test program to illustrate the problem.

Run "server" on a machine, and then run "client" on the same machine.

Server creates a listening socket and loops accepting connections, sending a
little data, closing the socket, and then back to the top of the loop.

Client creates a socket, connects to the server, does a recv() with
MSG_WAITALL, closes the socket, and loops.

This runs anywhere from one to a few dozen times and then hangs.  The server
socket is in FIN_WAIT_2, and the client socket is in CLOSE_WAIT.  So the client
side is waiting for the application to close the socket, but it's still stuck
in the recv(), never being awakened by the EOF from the server closing the
socket.

The same code runs on Linux and QNX without any problem.

This seems ridiculously simple and far reaching.  Seems like we must be
overlooking something, but it's a really simple test case.

client.c:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <err.h>

int main (int argc, char *argv[])
{
   int c;
   bool verbose = false;
   char *addr = "127.0.0.1";

   signal(SIGPIPE, SIG_IGN);
   while ((c = getopt(argc, argv, "v")) != -1) {
      switch (c) {
         case 'v': ++verbose;    break;
         default:  return 1;     break;
         }
      }
   argc -= optind - 1;
   argv += optind - 1;

   if (argc > 1) addr = argv[1];

   for (int try = 1;; try++) {
      printf("Try %d\n", try);
      int s;
      if ((s = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
         err(1, "socket");

      struct sockaddr_in sa = { .sin_family = AF_INET, .sin_port = htons(79),
.sin_addr.s_addr = inet_addr(addr) };
      if (connect(s, (struct sockaddr *)&sa, sizeof sa) < 0)
         err(1, "connect");

      // get the response
      char rbuf [4096];
      int rcvLen;
      if ((rcvLen = recv(s, rbuf, sizeof rbuf, MSG_WAITALL)) < 0)
         err(1, "recv");
      if (verbose) printf("Received: '%.*s'\n", rcvLen, rbuf);
      close(s);
      }

   return 0;
   }


server.c:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>
#include <ctype.h>
#include <signal.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <err.h>

int main (int argc, char *argv[])
{
   int c;
   bool verbose = false;

   signal(SIGPIPE, SIG_IGN);
   while ((c = getopt(argc, argv, "v")) != -1) {
      switch (c) {
         case 'v': ++verbose;    break;
         default:  return 1;     break;
         }
      }
   argc -= optind - 1;
   argv += optind - 1;

   int s0;
   if ((s0 = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0)
      err(1, "socket");
   int on = true;
   if (setsockopt(s0, SOL_SOCKET, SO_REUSEPORT, &on, sizeof on) < 0)
      err(1, "setsockopt");
   struct sockaddr_in sa = { .sin_family = AF_INET, .sin_port = htons(79) };

   if (bind(s0, (struct sockaddr *)&sa, sizeof sa) < 0)
      err(1, "bind");
   if (listen(s0, 1000) < 0)
      err(1, "listen");

   printf("Listening\n");

   for (int try = 1;; try++) {
      socklen_t sl;
      int s = accept(s0, (struct sockaddr *)&sa, &sl);
      if (s < 0) err(1, "accept");
      printf("Try %d\n", try);

      // send the response
      static char sbuf [] = "Hello from server\n";
      if (send(s, sbuf, sizeof sbuf - 1, 0) < 0)
         err(1, "send");
      if (verbose) printf("Sent:     %s", sbuf);
      shutdown(s, SHUT_WR);
      close(s);
      }

   return 0;
   }

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