Updating M26 to accomodate socket id assignment

This modem is a special case. It uses a given socket ID value rather
than providing one. A naive solution here would be to directly map the
index of a CellularSocket object in the CellularSocket container. But
considering the case where there are multiple sockets being opened (some
sockets being already created at the modem and some yet not created), direct mapping
to indices will not work. As it can happen that the CellularSocket
object is allocated but the socket id is not assigned yet as it is not
actually created on the modem.

In such a case, we check the container and assign the socket id from the
pool if an empty slot was found.

Author: Hasnain Virk

features/cellular/framework/targets/QUECTEL/M26/QUECTEL_M26_CellularStack.cpp

@@ -302,6 +302,8 @@ nsapi_error_t QUECTEL_M26_CellularStack::socket_connect(nsapi_socket_t handle, c
 {
     CellularSocket *socket = (CellularSocket *)handle;
 
+    MBED_ASSERT(socket->id != -1);
+
     int modem_connect_id = -1;
     int request_connect_id = socket->id;
     int err = -1;
@@ -348,7 +350,6 @@ nsapi_error_t QUECTEL_M26_CellularStack::socket_connect(nsapi_socket_t handle, c
     _at.unlock();
 
     if ((ret_val == NSAPI_ERROR_OK) && (modem_connect_id == request_connect_id)) {
-        socket->created = true;
         socket->remoteAddress = address;
         socket->connected = true;
         return NSAPI_ERROR_OK;
@@ -359,7 +360,29 @@ nsapi_error_t QUECTEL_M26_CellularStack::socket_connect(nsapi_socket_t handle, c
 
 nsapi_error_t QUECTEL_M26_CellularStack::create_socket_impl(CellularSocket *socket)
 {
-    int request_connect_id = socket->id;
+    // This modem is a special case. It takes in the socket ID rather than spitting
+    // it out. So we will first try to use the index of the socket construct as the id
+    // but if another opened socket is already opened with that id we will pick the next
+    // id which is not in use
+    bool duplicate = false;
+    int potential_sid = -1;
+    int index = find_socket_index(socket);
+
+    for (int i = 0; i < get_max_socket_count(); i++) {
+        CellularSocket *sock = _socket[i];
+        if (sock && sock != socket && sock->id == index) {
+            duplicate = true;
+        } else if (duplicate && !sock) {
+            potential_sid = i;
+            break;
+        }
+    }
+
+    if (duplicate) {
+        index = potential_sid;
+    }
+
+    int request_connect_id = index;
     int modem_connect_id = request_connect_id;
     int err = -1;
     nsapi_error_t ret_val;
@@ -403,13 +426,15 @@ nsapi_error_t QUECTEL_M26_CellularStack::create_socket_impl(CellularSocket *sock
         }
 
         ret_val = _at.get_last_error();
-        socket->created = ((ret_val == NSAPI_ERROR_OK) && (modem_connect_id == request_connect_id));
+        if ((ret_val == NSAPI_ERROR_OK) && (modem_connect_id == request_connect_id)) {
+            socket->id = request_connect_id;
+        }
         return ret_val;
     } else {
         ret_val = NSAPI_ERROR_OK;
     }
 
-    tr_debug("QUECTEL_M26_CellularStack:%s:%u: END [%d,%d]", __FUNCTION__, __LINE__, socket->created, ret_val);
+    tr_debug("QUECTEL_M26_CellularStack:%s:%u: END [%d]", __FUNCTION__, __LINE__, ret_val);
     return ret_val;
 }
 
@@ -431,11 +456,11 @@ nsapi_size_or_error_t QUECTEL_M26_CellularStack::socket_sendto_impl(CellularSock
         return NSAPI_ERROR_PARAMETER;
     }
 
-    if (!socket->created) {
+    if (socket->id == -1) {
         socket->remoteAddress = address;
         socket->connected = true;
         nsapi_error_t ret_val = create_socket_impl(socket);
-        if ((ret_val != NSAPI_ERROR_OK) || (!socket->created)) {
+        if ((ret_val != NSAPI_ERROR_OK) || (socket->id == -1)) {
             tr_error("QUECTEL_M26_CellularStack:%s:%u:[NSAPI_ERROR_NO_SOCKET]", __FUNCTION__, __LINE__);
             return NSAPI_ERROR_NO_SOCKET;
         }