WebServer: Allow client to send many requests on the same connection (#7414)

* WebServer: Allow client to send many requests on the same connection

* WebServer: Keep the connection alive with a client by default

* WebServer: Use the request's HTTP version and Connection header to set the default keep alive value

* Fix a typo in a comment

libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h

@@ -49,6 +49,7 @@ ESP8266WebServerTemplate<ServerType>::ESP8266WebServerTemplate(IPAddress addr, i
 , _currentVersion(0)
 , _currentStatus(HC_NONE)
 , _statusChange(0)
+, _keepAlive(false)
 , _currentHandler(nullptr)
 , _firstHandler(nullptr)
 , _lastHandler(nullptr)
@@ -327,6 +328,10 @@ void ESP8266WebServerTemplate<ServerType>::handleClient() {
   bool callYield = false;
 
   if (_currentClient.connected() || _currentClient.available()) {
+    if (_currentClient.available() && _keepAlive) {
+      _currentStatus = HC_WAIT_READ;
+    }
+
     switch (_currentStatus) {
     case HC_NONE:
       // No-op to avoid C++ compiler warning
@@ -431,7 +436,14 @@ void ESP8266WebServerTemplate<ServerType>::_prepareHeader(String& response, int
     if (_corsEnabled) {
       sendHeader(String(F("Access-Control-Allow-Origin")), String("*"));
     }
-    sendHeader(String(F("Connection")), String(F("close")));
+
+    if (_keepAlive && _server.hasClient()) { // Disable keep alive if another client is waiting.
+      _keepAlive = false;
+    }
+    sendHeader(String(F("Connection")), String(_keepAlive ? F("keep-alive") : F("close")));
+    if (_keepAlive) {
+      sendHeader(String(F("Keep-Alive")), String(F("timeout=")) + HTTP_MAX_CLOSE_WAIT);
+    }
 
     response += _responseHeaders;
     response += "\r\n";

libraries/ESP8266WebServer/src/ESP8266WebServer.h

@@ -168,6 +168,14 @@ public:
     sendContent(emptyString);
   }
 
+  // Whether other requests should be accepted from the client on the
+  // same socket after a response is sent.
+  // This will automatically configure the "Connection" header of the response.
+  // Defaults to true when the client's HTTP version is 1.1 or above, otherwise it defaults to false.
+  // If the client sends the "Connection" header, the value given by the header is used.
+  void keepAlive(bool keepAlive) { _keepAlive = keepAlive; }
+  bool keepAlive() { return _keepAlive; }
+
   static String credentialHash(const String& username, const String& realm, const String& password);
 
   static String urlDecode(const String& text);
@@ -224,6 +232,7 @@ protected:
   uint8_t     _currentVersion;
   HTTPClientStatus _currentStatus;
   unsigned long _statusChange;
+  bool _keepAlive;
 
   RequestHandlerType*  _currentHandler;
   RequestHandlerType*  _firstHandler;

libraries/ESP8266WebServer/src/Parsing-impl.h

@@ -114,6 +114,9 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
   }
   _currentMethod = method;
 
+  _keepAlive = _currentVersion > 0; // Keep the connection alive by default
+                                    // if the protocol version is greater than HTTP 1.0
+
 #ifdef DEBUG_ESP_HTTP_SERVER
   DEBUG_OUTPUT.print("method: ");
   DEBUG_OUTPUT.print(methodStr);
@@ -144,7 +147,7 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
     while(1){
       req = client.readStringUntil('\r');
       client.readStringUntil('\n');
-      if (req.isEmpty()) break;//no moar headers
+      if (req.isEmpty()) break; //no more headers
       int headerDiv = req.indexOf(':');
       if (headerDiv == -1){
         break;
@@ -177,6 +180,8 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
         contentLength = headerValue.toInt();
       } else if (headerName.equalsIgnoreCase(F("Host"))){
         _hostHeader = headerValue;
+      } else if (headerName.equalsIgnoreCase(F("Connection"))){
+        _keepAlive = headerValue.equalsIgnoreCase(F("keep-alive"));
       }
     }
 
@@ -241,6 +246,8 @@ bool ESP8266WebServerTemplate<ServerType>::_parseRequest(ClientType& client) {
 
       if (headerName.equalsIgnoreCase(F("Host"))){
         _hostHeader = headerValue;
+      } else if (headerName.equalsIgnoreCase(F("Connection"))){
+        _keepAlive = headerValue.equalsIgnoreCase(F("keep-alive"));
       }
     }
     _parseArguments(searchStr);