Fix WiFiClientSecure::available() blocking on dropped connections (#6449)

* Fix WiFiClientSecure::available blocking

Added a check of WiFiClient::availableForWrite to prevent blocking writes when the _run_until blocking flag is false

* change availForWrite from int to size_t

* add timeout to _run_until loop

fixes #6464

* use polledTimeout with _timeout millis

Author: johnm545

libraries/ESP8266WiFi/src/WiFiClientSecureBearSSL.cpp

@@ -32,6 +32,7 @@ extern "C" {
 }
 #include "debug.h"
 #include "ESP8266WiFi.h"
+#include "PolledTimeout.h"
 #include "WiFiClient.h"
 #include "WiFiClientSecureBearSSL.h"
 #include "StackThunk.h"
@@ -437,12 +438,17 @@ int WiFiClientSecure::_run_until(unsigned target, bool blocking) {
     DEBUG_BSSL("_run_until: Not connected\n");
     return -1;
   }
-  for (int no_work = 0; blocking || no_work < 2;) {
-    if (blocking) {
-      // Only for blocking operations can we afford to yield()
-      optimistic_yield(100);
+  
+  esp8266::polledTimeout::oneShotMs loopTimeout(_timeout);
+  
+  for (int no_work = 0; blocking || no_work < 2;) {    
+    optimistic_yield(100);
+    
+    if (loopTimeout) {
+      DEBUG_BSSL("_run_until: Timeout\n");
+      return -1;
     }
-
+    
     int state;
     state = br_ssl_engine_current_state(_eng);
     if (state & BR_SSL_CLOSED) {
@@ -461,8 +467,19 @@ int WiFiClientSecure::_run_until(unsigned target, bool blocking) {
       unsigned char *buf;
       size_t len;
       int wlen;
+      size_t availForWrite;
 
       buf = br_ssl_engine_sendrec_buf(_eng, &len);
+      availForWrite = WiFiClient::availableForWrite();
+      
+      if (!blocking && len > availForWrite) {
+        /* 
+           writes on WiFiClient will block if len > availableForWrite()
+           this is needed to prevent available() calls from blocking
+           on dropped connections 
+        */
+        len = availForWrite;
+      }	  
       wlen = WiFiClient::write(buf, len);
       if (wlen <= 0) {
         /*