[1452] added consideration for the case where the acceptor dies before push.

we needed to ignore SIGPIPE in this case, so added that setup.  also test
of course.

src/lib/util/io/fd_share.cc

@@ -18,6 +18,7 @@
 #include <sys/types.h>
 #include <sys/socket.h>
 #include <sys/uio.h>
+#include <errno.h>
 #include <stdlib.h>             // for malloc and free
 #include "fd_share.h"
 
@@ -130,7 +131,9 @@ send_fd(const int sock, const int fd) {
     *(int*)CMSG_DATA(cmsg) = fd;
 
     const int ret = sendmsg(sock, &msghdr, 0);
+    const int e = errno;
     free(msghdr.msg_control);
+    errno = e;                  // recover errno in case free() changed it
     return (ret >= 0 ? 0 : FD_COMM_ERROR);
 }
 

src/lib/util/io/fd_share.h

@@ -46,7 +46,8 @@ int recv_fd(const int sock);
  * counterpart of recv_fd().
  *
  * \return FD_COMM_ERROR when there's error sending the socket, FD_OTHER_ERROR
- *     for all other possible errors.
+ *     for all other possible errors.  The global 'errno' variable indicates
+ *     the corresponding system error.
  * \param sock The unix domain socket to send to. Tested and it does not
  *     work with a pipe.
  * \param fd The file descriptor to send. It should work with any valid

src/lib/util/io/socketsession.cc

@@ -19,6 +19,7 @@
 #include <netinet/in.h>
 
 #include <errno.h>
+#include <signal.h>
 #include <stdint.h>
 #include <string.h>
 
@@ -53,6 +54,11 @@ struct SocketSessionForwarder::ForwarderImpl {
 SocketSessionForwarder::SocketSessionForwarder(const std::string& unix_file) :
     impl_(NULL)
 {
+    // We need to filter SIGPIPE for subsequent push().  See the description.
+    if (signal(SIGPIPE, SIG_IGN) == SIG_ERR) {
+        isc_throw(Unexpected, "Failed to filter SIGPIPE: " << strerror(errno));
+    }
+
     ForwarderImpl impl;
     if (sizeof(impl.sock_un_.sun_path) - 1 < unix_file.length()) {
         isc_throw(SocketSessionError,
@@ -139,9 +145,9 @@ SocketSessionForwarder::push(int sock, int family, int sock_type, int protocol,
                   << static_cast<int>(remote_end.sa_family) << " given");
     }
 
-    const int e = send_fd(impl_->fd_, sock);
-    if (e != 0) {
-        isc_throw(SocketSessionError, "FD passing failed: " << e);
+    if (send_fd(impl_->fd_, sock) != 0) {
+        isc_throw(SocketSessionError, "FD passing failed: " <<
+                  strerror(errno));
     }
 
     impl_->buf_.clear();

src/lib/util/io/socketsession.h

@@ -33,7 +33,11 @@ public:
 
 class SocketSessionForwarder : boost::noncopyable {
 public:
+    // Note about SIGPIPE.  Assuming this class is not often instantiated
+    // (so the overhead of signal setting should be marginal) and could also be
+    // instantiated by multiple threads, it always set the filter.
     explicit SocketSessionForwarder(const std::string& unix_file);
+
     ~SocketSessionForwarder();
 
     void connectToReceptor();

src/lib/util/tests/socketsession_unittest.cc

@@ -532,14 +532,15 @@ TEST_F(ForwarderTest, badPush) {
                                  TEST_DATA, sizeof(TEST_DATA)),
                  SocketSessionError);
 
-#if 0
+    // Close the acceptor before push.  It will result in SIGPIPE (should be
+    // ignored) and EPIPE, which will be converted to SocketSessionError.
     const int receptor_fd = acceptForwarder();
     close(receptor_fd);
-    forwarder_.push(1, AF_INET, SOCK_DGRAM, IPPROTO_UDP,
-                    *getSockAddr("192.0.2.1", "53").first,
-                    *getSockAddr("192.0.2.2", "53").first,
-                    TEST_DATA, sizeof(TEST_DATA));
-#endif
+    EXPECT_THROW(forwarder_.push(1, AF_INET, SOCK_DGRAM, IPPROTO_UDP,
+                                 *getSockAddr("192.0.2.1", "53").first,
+                                 *getSockAddr("192.0.2.2", "53").first,
+                                 TEST_DATA, sizeof(TEST_DATA)),
+                 SocketSessionError);
 }
 
 TEST(SocketSession, badValue) {