WiFiClientSecure::lastError() method (#945)

* Added a lastError method to WiFiClientSecure so that a connection error from mbedTLS can be retrieved if connection fails (and then presented to a user).

* Changed to dos CRLF

* Made buffer size a const\nMore cleanup to match source

libraries/WiFiClientSecure/src/WiFiClientSecure.cpp

@@ -103,6 +103,7 @@ int WiFiClientSecure::connect(IPAddress ip, uint16_t port, const char *_CA_cert,
 int WiFiClientSecure::connect(const char *host, uint16_t port, const char *_CA_cert, const char *_cert, const char *_private_key)
 {
     int ret = start_ssl_client(sslclient, host, port, _CA_cert, _cert, _private_key);
+    _lastError = ret;
     if (ret < 0) {
         log_e("lwip_connect_r: %d", errno);
         stop();
@@ -187,3 +188,13 @@ void WiFiClientSecure::setPrivateKey (const char *private_key)
     _private_key = private_key;
 }
 
+int WiFiClientSecure::lastError(char *buf, const size_t size)
+{
+    if (!_lastError) {
+        return 0;
+    }
+    char error_buf[100];
+    mbedtls_strerror(_lastError, error_buf, 100);
+    snprintf(buf, size, "%s", error_buf);
+    return _lastError;
+}

libraries/WiFiClientSecure/src/WiFiClientSecure.h

@@ -29,7 +29,8 @@ class WiFiClientSecure : public WiFiClient
 {
 protected:
     sslclient_context *sslclient;
-
+ 
+    int _lastError = 0;
     const char *_CA_cert;
     const char *_cert;
     const char *_private_key;
@@ -55,7 +56,7 @@ public:
     void flush() {}
     void stop();
     uint8_t connected();
-
+    int lastError(char *buf, const size_t size);
     void setCACert(const char *rootCA);
     void setCertificate(const char *client_ca);
     void setPrivateKey (const char *private_key);