BG96: Add segmentation to TCP socket send

Unlike some other cellular modem drivers which use
segmentation, the BG96 driver did not support sending of large
TCP packets, i.e. maximum TCP packet size was restricted to
1400 bytes. This adds segmentation to the send function, so
larger packets can be sent using the TCP socket.

Author: boraozgen

connectivity/drivers/cellular/QUECTEL/BG96/QUECTEL_BG96_CellularStack.cpp

@@ -335,10 +335,6 @@ nsapi_error_t QUECTEL_BG96_CellularStack::create_socket_impl(CellularSocket *soc
 nsapi_size_or_error_t QUECTEL_BG96_CellularStack::socket_sendto_impl(CellularSocket *socket, const SocketAddress &address,
                                                                      const void *data, nsapi_size_t size)
 {
-    if (size > BG96_MAX_SEND_SIZE) {
-        return NSAPI_ERROR_PARAMETER;
-    }
-
     if (_ip_ver_sendto != address.get_ip_version()) {
         _ip_ver_sendto =  address.get_ip_version();
         socket_close_impl(socket->id);
@@ -358,29 +354,59 @@ nsapi_size_or_error_t QUECTEL_BG96_CellularStack::socket_sendto_impl(CellularSoc
 
     // Send
     if (socket->proto == NSAPI_UDP) {
+        if (size > BG96_MAX_SEND_SIZE) {
+            return NSAPI_ERROR_PARAMETER;
+        }
         char ipdot[NSAPI_IP_SIZE];
         ip2dot(address, ipdot);
         _at.cmd_start_stop("+QISEND", "=", "%d%d%s%d", socket->id, size,
                            ipdot, address.get_port());
-    } else {
-        if (socket->tls_socket) {
-            _at.cmd_start_stop("+QSSLSEND", "=", "%d%d", socket->id, size);
-        } else {
-            _at.cmd_start_stop("+QISEND", "=", "%d%d", socket->id, size);
+        _at.resp_start(">");
+        _at.write_bytes((uint8_t *)data, size);
+        _at.resp_start();
+        _at.set_stop_tag("\r\n");
+        // Possible responses are SEND OK, SEND FAIL or ERROR.
+        char response[16];
+        response[0] = '\0';
+        _at.read_string(response, sizeof(response));
+        _at.resp_stop();
+        if (strcmp(response, "SEND OK") != 0) {
+            return NSAPI_ERROR_DEVICE_ERROR;
         }
-    }
+    } else {
+        const char *buf = (const char *)data;
+        nsapi_size_t blk = BG96_MAX_SEND_SIZE;
+        nsapi_size_t count = size;
 
-    _at.resp_start(">");
-    _at.write_bytes((uint8_t *)data, size);
-    _at.resp_start();
-    _at.set_stop_tag("\r\n");
-    // Possible responses are SEND OK, SEND FAIL or ERROR.
-    char response[16];
-    response[0] = '\0';
-    _at.read_string(response, sizeof(response));
-    _at.resp_stop();
-    if (strcmp(response, "SEND OK") != 0) {
-        return NSAPI_ERROR_DEVICE_ERROR;
+        while (count > 0) {
+            if (count < blk) {
+                blk = count;
+            }
+
+            if (socket->tls_socket) {
+                _at.cmd_start_stop("+QSSLSEND", "=", "%d%d", socket->id, blk);
+            }
+
+            else {
+                _at.cmd_start_stop("+QISEND", "=", "%d%d", socket->id, blk);
+            }
+
+            _at.resp_start(">");
+            _at.write_bytes((uint8_t *)buf, blk);
+            _at.resp_start();
+            _at.set_stop_tag("\r\n");
+            // Possible responses are SEND OK, SEND FAIL or ERROR.
+            char response[16];
+            response[0] = '\0';
+            _at.read_string(response, sizeof(response));
+            _at.resp_stop();
+            if (strcmp(response, "SEND OK") != 0) {
+                return NSAPI_ERROR_DEVICE_ERROR;
+            }
+
+            buf += blk;
+            count -= blk;
+        }
     }
 
     // Get the sent count after sending