Fix test failure on Windows

The send{,to,msg} and recv{,from,msg} functions have been updated to
delegate to WriteFile and ReadFile when appropriate, due to the fact
that socketpair(AF_UNIX) is implemented using kFdFile.

Thanks @fabriziobertocci for writing the test that caught this.

See #148 and #122

libc/sock/recvfrom.c

@@ -50,10 +50,19 @@ ssize_t recvfrom(int fd, void *buf, size_t size, uint32_t flags,
       sockaddr2linux(opt_out_srcaddr);
     }
     return got;
-  } else if (__isfdkind(fd, kFdSocket)) {
-    return sys_recvfrom_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1,
-                           flags, opt_out_srcaddr, opt_inout_srcaddrsize);
   } else {
-    return ebadf();
+    if (__isfdopen(fd)) {
+      if (__isfdkind(fd, kFdSocket)) {
+        return sys_recvfrom_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1,
+                               flags, opt_out_srcaddr, opt_inout_srcaddrsize);
+      } else if (__isfdkind(fd, kFdFile) && !opt_out_srcaddr) { /* socketpair */
+        if (flags) return einval();
+        return sys_read_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, -1);
+      } else {
+        return enotsock();
+      }
+    } else {
+      return ebadf();
+    }
   }
 }

libc/sock/recvmsg.c

@@ -38,17 +38,34 @@
  * @asyncsignalsafe
  */
 ssize_t recvmsg(int fd, struct msghdr *msg, int flags) {
+  ssize_t got;
   if (!IsWindows()) {
-    ssize_t got = sys_recvmsg(fd, msg, flags);
+    got = sys_recvmsg(fd, msg, flags);
     /* An address was provided, convert from BSD form */
     if (msg->msg_name && IsBsd() && got != -1) {
       sockaddr2linux(msg->msg_name);
     }
     return got;
-  } else if (__isfdkind(fd, kFdSocket)) {
-    return sys_recvfrom_nt(&g_fds.p[fd], msg->msg_iov, msg->msg_iovlen, flags,
-                           msg->msg_name, &msg->msg_namelen);
   } else {
-    return ebadf();
+    if (__isfdopen(fd)) {
+      if (msg->msg_control) return einval(); /* control msg not supported */
+      if (__isfdkind(fd, kFdSocket)) {
+        return sys_recvfrom_nt(&g_fds.p[fd], msg->msg_iov, msg->msg_iovlen,
+                               flags, msg->msg_name, &msg->msg_namelen);
+      } else if (__isfdkind(fd, kFdFile) && !msg->msg_name) { /* socketpair */
+        if (flags) return einval();
+        if ((got = sys_read_nt(&g_fds.p[fd], msg->msg_iov, msg->msg_iovlen,
+                               -1)) != -1) {
+          msg->msg_flags = 0;
+          return got;
+        } else {
+          return -1;
+        }
+      } else {
+        return enotsock();
+      }
+    } else {
+      return ebadf();
+    }
   }
 }

libc/sock/sendmsg.c

@@ -29,7 +29,7 @@
  * Sends a message on a socket.
  *
  * @param fd is the file descriptor returned by socket()
- * @param msg is a pointer to a struct msghdr containing all the required 
+ * @param msg is a pointer to a struct msghdr containing all the required
  *            parameters (the destination address, buffers, ...)
  * @param flags MSG_OOB, MSG_DONTROUTE, MSG_PARTIAL, MSG_NOSIGNAL, etc.
  * @return number of bytes transmitted, or -1 w/ errno
@@ -54,11 +54,19 @@ ssize_t sendmsg(int fd, const struct msghdr *msg, int flags) {
     }
     /* else do the syscall */
     return sys_sendmsg(fd, msg, flags);
-  } else if (__isfdkind(fd, kFdSocket)) {
-    if (msg->msg_control != NULL) return einval();  /* Control msg not supported */
-    return sys_sendto_nt(&g_fds.p[fd], msg->msg_iov, msg->msg_iovlen, flags,
-                         msg->msg_name, msg->msg_namelen);
   } else {
-    return ebadf();
+    if (__isfdopen(fd)) {
+      if (msg->msg_control) return einval(); /* control msg not supported */
+      if (__isfdkind(fd, kFdSocket)) {
+        return sys_sendto_nt(&g_fds.p[fd], msg->msg_iov, msg->msg_iovlen, flags,
+                             msg->msg_name, msg->msg_namelen);
+      } else if (__isfdkind(fd, kFdFile)) {
+        return sys_write_nt(&g_fds.p[fd], msg->msg_iov, msg->msg_iovlen, -1);
+      } else {
+        return enotsock();
+      }
+    } else {
+      return ebadf();
+    }
   }
 }

libc/sock/sendto.c

@@ -51,16 +51,27 @@ ssize_t sendto(int fd, const void *buf, size_t size, uint32_t flags,
     if (!IsBsd() || !opt_addr) {
       return sys_sendto(fd, buf, size, flags, opt_addr, addrsize);
     } else {
-      char addr2[sizeof(struct sockaddr_un_bsd)]; /* sockaddr_un_bsd is the largest */
+      char addr2[sizeof(
+          struct sockaddr_un_bsd)]; /* sockaddr_un_bsd is the largest */
       if (addrsize > sizeof(addr2)) return einval();
       memcpy(&addr2, opt_addr, addrsize);
       sockaddr2bsd(&addr2[0]);
       return sys_sendto(fd, buf, size, flags, &addr2[0], addrsize);
     }
-  } else if (__isfdkind(fd, kFdSocket)) {
-    return sys_sendto_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, flags,
-                         opt_addr, addrsize);
   } else {
-    return ebadf();
+    if (__isfdopen(fd)) {
+      if (__isfdkind(fd, kFdSocket)) {
+        return sys_sendto_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1,
+                             flags, opt_addr, addrsize);
+      } else if (__isfdkind(fd, kFdFile)) { /* e.g. socketpair() */
+        if (flags) return einval();
+        if (opt_addr) return eisconn();
+        return sys_write_nt(&g_fds.p[fd], (struct iovec[]){{buf, size}}, 1, -1);
+      } else {
+        return enotsock();
+      }
+    } else {
+      return ebadf();
+    }
   }
 }