BearSSL Max Fragment Length Negotation and Node.js server (#5929)

* Minor bug fixes in Maximum Fragment Length Negotation example, mainly giving background processes some time in fetch()

* Minor layout changes to pass travis tests

* Use PolledTimeout for timeout

Author: Jeroen88

libraries/ESP8266WiFi/examples/BearSSL_MaxFragmentLength/BearSSL_MaxFragmentLength.ino

@@ -5,6 +5,7 @@
 // Released to the public domain
 
 #include <ESP8266WiFi.h>
+#include <PolledTimeout.h>
 
 #ifndef STASSID
 #define STASSID "your-ssid"
@@ -17,17 +18,22 @@ const char *pass = STAPSK;
 void fetch(BearSSL::WiFiClientSecure *client) {
   client->write("GET / HTTP/1.0\r\nHost: tls.mbed.org\r\nUser-Agent: ESP8266\r\n\r\n");
   client->flush();
-  uint32_t to = millis() + 5000;
+  using oneShot = esp8266::polledTimeout::oneShot;
+  oneShot timeout(5000);
   do {
     char tmp[32];
-    memset(tmp, 0, 32);
     int rlen = client->read((uint8_t*)tmp, sizeof(tmp) - 1);
     yield();
     if (rlen < 0) {
       break;
     }
+    if (rlen == 0) {
+      delay(10); // Give background processes some time
+      continue;
+    }
+    tmp[rlen] = '\0';
     Serial.print(tmp);
-  } while (millis() < to);
+  } while (!timeout);
   client->stop();
   Serial.printf("\n-------\n");
 }
@@ -73,11 +79,11 @@ int fetchMaxFragmentLength() {
 
   BearSSL::WiFiClientSecure client;
   client.setInsecure();
-  bool mfln = client.probeMaxFragmentLength("tls.mbed.org", 443, 1024);
+  bool mfln = client.probeMaxFragmentLength("tls.mbed.org", 443, 512);
   Serial.printf("\nConnecting to https://tls.mbed.org\n");
   Serial.printf("MFLN supported: %s\n", mfln ? "yes" : "no");
   if (mfln) {
-    client.setBufferSizes(1024, 1024);
+    client.setBufferSizes(512, 512);
   }
   client.connect("tls.mbed.org", 443);
   if (client.connected()) {
@@ -125,6 +131,6 @@ void loop() {
   yield();
 
   Serial.printf("\n\n");
-  Serial.printf("Default SSL:        %d bytes used\n", a);
-  Serial.printf("1024 byte MFLN SSL: %d bytes used\n", b);
+  Serial.printf("Default SSL:       %d bytes used\n", a);
+  Serial.printf("512 byte MFLN SSL: %d bytes used\n", b);
 }