Allow to override User-Agent and Host HTTP headers (#1426)

* Allow to override User-Agent and Host HTTP headers

Fixes #1410

Idea borrowed from (unmerged) #1157

* Do not send port for host header for default ports

app/http/httpclient.c

@@ -181,7 +181,6 @@ static void ICACHE_FLASH_ATTR http_connect_callback( void * arg )
 	HTTPCLIENT_DEBUG( "Connected\n" );
 	struct espconn	* conn	= (struct espconn *) arg;
 	request_args_t	* req	= (request_args_t *) conn->reverse;
-	int len;
 	espconn_regist_recvcb( conn, http_receive_callback );
 	espconn_regist_sentcb( conn, http_send_callback );
 
@@ -198,37 +197,55 @@ static void ICACHE_FLASH_ATTR http_connect_callback( void * arg )
 		req->headers[0] = '\0';
 	}
 
-	char buf[69 + strlen( req->method ) + strlen( req->path ) + strlen( req->hostname ) +
-		 strlen( req->headers ) + strlen( post_headers )];
+	char ua_header[32] = "";
+    int ua_len = 0;
+    if (os_strstr( req->headers, "User-Agent:" ) == NULL && os_strstr( req->headers, "user-agent:" ) == NULL)
+    {
+        os_sprintf( ua_header, "User-Agent: %s\r\n", "ESP8266" );
+        ua_len = strlen(ua_header);
+    }
 
+	char host_header[32] = "";
+    int host_len = 0;
+    if ( os_strstr( req->headers, "Host:" ) == NULL && os_strstr( req->headers, "host:" ) == NULL)
+    {
         if ((req->port == 80) || ((req->port == 443) && ( req->secure )))
         {
-		len = os_sprintf( buf,
-		  		"%s %s HTTP/1.1\r\n"
-			    "Host: %s\r\n"
-			    "Connection: close\r\n"
-			    "User-Agent: ESP8266\r\n"
-			    "%s"
-			    "%s"
-			    "\r\n",
-			    req->method, req->path, req->hostname, req->headers, post_headers );
-	} else {
-		len = os_sprintf( buf,
-				"%s %s HTTP/1.1\r\n"
-				"Host: %s:%d\r\n"
-				"Connection: close\r\n"
-				"User-Agent: ESP8266\r\n"
-				"%s"
-				"%s"
-				"\r\n",
-				req->method, req->path, req->hostname, req->port, req->headers, post_headers );
+            os_sprintf( host_header, "Host: %s\r\n", req->hostname );
         }
-	if ( req->secure )
-		espconn_secure_send( conn, (uint8_t *) buf, len );
         else
+        {
+            os_sprintf( host_header, "Host: %s:%d\r\n", req->hostname, req->port );
+        }
+        host_len = strlen(host_header);
+    }
+
+    char buf[69 + strlen( req->method ) + strlen( req->path ) + host_len +
+           strlen( req->headers ) + ua_len + strlen( post_headers )];
+    int len = os_sprintf( buf,
+            "%s %s HTTP/1.1\r\n"
+            "%s" // Host (if not provided in the headers from Lua)
+            "Connection: close\r\n"
+            "%s" // Headers from Lua (optional)
+            "%s" // User-Agent (if not provided in the headers from Lua)
+            "%s" // Content-Length
+            "\r\n",
+            req->method, req->path, host_header, req->headers, ua_header, post_headers );
+
+    if (req->secure)
+    {
+        espconn_secure_send( conn, (uint8_t *) buf, len );
+    }
+    else
+    {
         espconn_send( conn, (uint8_t *) buf, len );
+    }
+
     if (req->headers != NULL)
+    {
         os_free( req->headers );
+    }
+
     req->headers = NULL;
     HTTPCLIENT_DEBUG( "Sending request header\n" );
 }

docs/en/modules/http.md

@@ -11,13 +11,7 @@ Basic HTTP *client* module that provides an interface to do GET/POST/PUT/DELETE
 
 Each request method takes a callback which is invoked when the response has been received from the server. The first argument is the status code, which is either a regular HTTP status code, or -1 to denote a DNS, connection or out-of-memory failure, or a timeout (currently at 10 seconds).
 
-For each operation it is also possible to include custom headers. Note that following headers *can not* be overridden however:
-
-- Host
-- Connection
-- User-Agent
-
-The `Host` header is taken from the URL itself, the `Connection` is always set to `close`, and the `User-Agent` is `ESP8266`.
+For each operation it is possible to provide custom HTTP headers or override standard headers. By default the `Host` header is deduced from the URL and `User-Agent` is `ESP8266`. Note, however, that the `Connection` header *can not* be overridden! It is always set to `close`.
 
 **SSL/TLS support**