Revert "Revert 8541 wifi client fix (#267)"

This reverts commit 419e0ac.

Author: Jason2866

.github/ISSUE_TEMPLATE/Issue-report.yml

@@ -41,8 +41,6 @@ body:
       options:
         - latest master (checkout manually)
         - latest development Release Candidate (RC-X)
-        - v2.0.13
-        - v2.0.12
         - v2.0.11
         - v2.0.10
         - v2.0.9

libraries/WiFi/src/WiFiClient.cpp

@@ -158,6 +158,13 @@ class WiFiClientRxBuffer {
     size_t available(){
         return _fill - _pos + r_available();
     }
+
+    void flush(){
+        if(r_available()){
+            fillBuffer();
+        }
+        _pos = _fill;
+    }
 };
 
 class WiFiClientSocketHandle {
@@ -529,26 +536,7 @@ int WiFiClient::available()
 // Though flushing means to send all pending data,
 // seems that in Arduino it also means to clear RX
 void WiFiClient::flush() {
-    int res;
-    size_t a = available(), toRead = 0;
-    if(!a){
-        return;//nothing to flush
-    }
-    uint8_t * buf = (uint8_t *)malloc(WIFI_CLIENT_FLUSH_BUFFER_SIZE);
-    if(!buf){
-        return;//memory error
-    }
-    while(a){
-        toRead = (a>WIFI_CLIENT_FLUSH_BUFFER_SIZE)?WIFI_CLIENT_FLUSH_BUFFER_SIZE:a;
-        res = recv(fd(), buf, toRead, MSG_DONTWAIT);
-        if(res < 0) {
-            log_e("fail on fd %d, errno: %d, \"%s\"", fd(), errno, strerror(errno));
-            stop();
-            break;
-        }
-        a -= res;
-    }
-    free(buf);
+    _rxBuffer->flush();
 }
 
 uint8_t WiFiClient::connected()