TCPIP: make the return value of network_socket_accept_tcp more expressive

The network_socket_accept_tcp function can only return either a valid
sealed capability or an untagged nullptr, so the caller cannot distinguish
a timeout from an out-of-memory failure. Change it so that it can return
an invalid capability that encodes the error code.

Author: nding0405

include/NetAPI.h

@@ -235,8 +235,13 @@ Socket __cheri_compartment("NetAPI")
  * of the connected client.  These can be null if the caller is not interested
  * in the client's address or port.
  *
- * This returns a valid sealed capability to a connected socket on success, or
- * an untagged value on failure.
+ * This returns either a valid sealed socket type or an untagged capability that
+ * encodes the error code, and here are what each of them represent:
+ * - `-ENOMEM`: allocation of the wrapper timed out or does not have memory for now.
+ * - `-EINVAL`: The timeout pointer is invalid, or FreeRTOS_accept returns invalid
+ * 			socket, or fail to claim the socket poiting to mallocCapability,
+ * 			or fail to add socket to the socket reset list,
+ * - `-ETIMEDOUT`: timed out on FreeRTOS_accept.
  */
 Socket __cheri_compartment("TCPIP")
   network_socket_accept_tcp(Timeout            *timeout,

lib/tcpip/network_wrapper.cc

@@ -608,7 +608,8 @@ Socket network_socket_accept_tcp(Timeout            *timeout,
                                  uint16_t           *port)
 {
 	Socket socket = nullptr;
-	with_sealed_socket(
+	int    retVal = with_sealed_socket(
+	  timeout,
 	  [&](SealedSocket *listeningSocket) {
 		  if (!check_timeout_pointer(timeout))
 		  {
@@ -621,24 +622,39 @@ Socket network_socket_accept_tcp(Timeout            *timeout,
 		  if (socketWrapper == nullptr)
 		  {
 			  Debug::log("Failed to allocate socket wrapper.");
-			  return -EINVAL;
+			  return -ENOMEM;
 		  }
 
 		  socketWrapper->socketEpoch = currentSocketEpoch.load();
 
 		  struct freertos_sockaddr addressTmp;
 		  uint32_t                 addressLength = sizeof(addressTmp);
-		  auto                     rawSocket     = FreeRTOS_accept(
-		    listeningSocket->socket, &addressTmp, &addressLength);
-		  if (rawSocket == nullptr)
+		  FreeRTOS_Socket_t       *rawSocket     = nullptr;
+
+		  // acceptResult: 0 = valid socket || -EINVAL = FREERTOS_INVALID_SOCKET
+		  // || -ETIMEDOUT = timed out
+		  int acceptResult = with_freertos_timeout(
+		    timeout,
+		    listeningSocket->socket,
+		    FREERTOS_SO_RCVTIMEO,
+		    [&]() -> int {
+			    rawSocket = FreeRTOS_accept(
+			      listeningSocket->socket, &addressTmp, &addressLength);
+			    if (rawSocket == nullptr)
+			    {
+				    return -ETIMEDOUT;
+			    }
+			    if (rawSocket == FREERTOS_INVALID_SOCKET)
+			    {
+				    return -EINVAL;
+			    }
+			    return 0; // returns a valid socket
+		    });
+
+		  if (acceptResult != 0)
 		  {
-			  Debug::log("Failed to create socket.");
-			  // This cannot fail unless buggy - we know that we
-			  // successfully allocated the token with this malloc
-			  // capability. Same for other calls to `token_obj_destroy`
-			  // in this function.
 			  token_obj_destroy(mallocCapability, socket_key(), sealedSocket);
-			  return -EINVAL;
+			  return acceptResult;
 		  }
 		  socketWrapper->socket = rawSocket;
 
@@ -720,6 +736,15 @@ Socket network_socket_accept_tcp(Timeout            *timeout,
 		  return 0;
 	  },
 	  sealedListeningSocket);
+
+	if (retVal != 0)
+	{
+		__clang_ignored_warning_push("-Wcheri-capability-misuse");
+		auto errCode = reinterpret_cast<Socket>(retVal);
+		__clang_ignored_warning_pop();
+		return errCode;
+	}
+
 	return socket;
 }