ESP8266: add a retry mechanism to avoid duplicate data sends

We are now checking if ESP8266 has confirmed receiving data over serial
port with an undocumented (but existing) "Recv x bytes" message. Next we
are explicitly waiting for an official "SEND OK".

Author: michalpasztamobica

components/wifi/esp8266-driver/ESP8266/ESP8266.cpp

@@ -615,6 +615,7 @@ bool ESP8266::dns_lookup(const char *name, char *ip)
 nsapi_error_t ESP8266::send(int id, const void *data, uint32_t amount)
 {
     nsapi_error_t ret = NSAPI_ERROR_DEVICE_ERROR;
+    unsigned int send_ack_retries = 3;
     // +CIPSEND supports up to 2048 bytes at a time
     // Data stream can be truncated
     if (amount > 2048 && _sock_i[id].proto == NSAPI_TCP) {
@@ -643,8 +644,10 @@ nsapi_error_t ESP8266::send(int id, const void *data, uint32_t amount)
         _parser.remove_oob("OK");
         if (_busy) {
             if (_ok_received) {
+                tr_debug("send(): _ok_received.");
                 goto RETRY;
             } else if (_parser.recv("OK")) {
+                tr_debug("send(): parser found OK");
                 goto RETRY;
             }
         }
@@ -655,7 +658,37 @@ nsapi_error_t ESP8266::send(int id, const void *data, uint32_t amount)
     _ok_received = false;
     _parser.remove_oob("OK");
 
-    if (_parser.write((char *)data, (int)amount) >= 0 && _parser.recv("SEND OK")) {
+    if (_parser.write((char *)data, (int)amount) < 0) {
+        tr_debug("Failed to write data");
+        ret = NSAPI_ERROR_DEVICE_ERROR;
+        goto END;
+    }
+
+    // The "Recv X bytes" is not documented.
+    int bytes_confirmed;
+    if (!_parser.recv("Recv %d bytes", &bytes_confirmed)) {
+        tr_debug("Bytes not confirmed.");
+        ret = NSAPI_ERROR_DEVICE_ERROR;
+        goto END;
+    } else if (bytes_confirmed != amount) {
+        tr_debug("Error: confirmed %d bytes, but expected %d.", bytes_confirmed, amount);
+        ret = NSAPI_ERROR_DEVICE_ERROR;
+        goto END;
+    }
+
+    send_ack_retries = 3;
+RETRY_SEND_ACK:
+    if (!_parser.recv("SEND OK")) {
+        send_ack_retries--;
+        if (_busy) {
+            _busy = false;
+            tr_debug("Busy, retry...");
+            goto RETRY_SEND_ACK;
+        } else if (send_ack_retries > 0) {
+            tr_debug("Not busy, but no SEND OK. %d retries left...", send_ack_retries);
+            goto RETRY_SEND_ACK;
+        }
+    } else {
         ret = NSAPI_ERROR_OK;
     }