ESP8266WebServer - Drop inactive connection when another is waiting to improve page load time (esp8266#8216)

* ESP8266WebServer - drop current HC_WAIT_READ connection sooner when another has data

Safari sometimes opens two connections when loading a page and only
sends a request over the second one, resulting in a 5 second wait
(HTTP_MAX_DATA_WAIT) before the request is processed. This commit
drops the current connection after 30ms (HTTP_MAX_DATA_AVAILABLE_WAIT)
when there is a new connection with data available or the buffer of
pending TCP clients is full (currently 5).

Author: aWZHY0yQH81uOYvH

Diff for: doc/esp8266wifi/server-class.rst

@@ -49,6 +49,8 @@ Other Function Calls
 .. code:: cpp
 
     bool  hasClient () 
+    size_t  hasClientData () 
+    bool  hasMaxPendingClients ()
     bool  getNoDelay () 
     virtual size_t  write (const uint8_t *buf, size_t size) 
     uint8_t  status () 

Diff for: libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h

@@ -343,11 +343,18 @@ void ESP8266WebServerTemplate<ServerType>::handleClient() {
         } // switch _parseRequest()
       } else {
         // !_currentClient.available(): waiting for more data
-        if (millis() - _statusChange <= HTTP_MAX_DATA_WAIT) {
-          keepCurrentClient = true;
+        unsigned long timeSinceChange = millis() - _statusChange;
+        // Use faster connection drop timeout if any other client has data
+        // or the buffer of pending clients is full
+        if ((_server.hasClientData() || _server.hasMaxPendingClients())
+          && timeSinceChange > HTTP_MAX_DATA_AVAILABLE_WAIT)
+            DBGWS("webserver: closing since there's another connection to read from\n");
+        else {
+          if (timeSinceChange > HTTP_MAX_DATA_WAIT)
+            DBGWS("webserver: closing after read timeout\n");
+          else
+            keepCurrentClient = true;
         }
-        else
-          DBGWS("webserver: closing after read timeout\n");
         callYield = true;
       }
       break;

Diff for: libraries/ESP8266WebServer/src/ESP8266WebServer.h

@@ -59,6 +59,7 @@ enum HTTPAuthMethod { BASIC_AUTH, DIGEST_AUTH };
 #endif
 
 #define HTTP_MAX_DATA_WAIT 5000 //ms to wait for the client to send the request
+#define HTTP_MAX_DATA_AVAILABLE_WAIT 30 //ms to wait for the client to send the request when there is another client with data available
 #define HTTP_MAX_POST_WAIT 5000 //ms to wait for POST data to arrive
 #define HTTP_MAX_SEND_WAIT 5000 //ms to wait for data chunk to be ACKed
 #define HTTP_MAX_CLOSE_WAIT 2000 //ms to wait for the client to close the connection

Diff for: libraries/ESP8266WiFi/src/WiFiServer.cpp

@@ -109,6 +109,25 @@ bool WiFiServer::hasClient() {
     return false;
 }
 
+size_t WiFiServer::hasClientData() {
+    ClientContext *next = _unclaimed;
+    while (next) {
+        size_t s = next->getSize();
+        // return the amount of data available from the first connection that has any
+        if (s) return s;
+        next = next->next();
+    }
+    return 0;
+}
+
+bool WiFiServer::hasMaxPendingClients() {
+#if TCP_LISTEN_BACKLOG
+    return ((struct tcp_pcb_listen *)_listen_pcb)->accepts_pending >= MAX_PENDING_CLIENTS_PER_PORT;
+#else
+    return false;
+#endif
+}
+
 WiFiClient WiFiServer::available(byte* status) {
     (void) status;
     if (_unclaimed) {

Diff for: libraries/ESP8266WiFi/src/WiFiServer.h

@@ -82,6 +82,13 @@ class WiFiServer : public Server {
   virtual ~WiFiServer() {}
   WiFiClient available(uint8_t* status = NULL);
   bool hasClient();
+  // hasClientData():
+  // returns the amount of data available from the first client
+  // or 0 if there is none
+  size_t hasClientData();
+  // hasMaxPendingClients():
+  // returns true if the queue of pending clients is full
+  bool hasMaxPendingClients();
   void begin();
   void begin(uint16_t port);
   void begin(uint16_t port, uint8_t backlog);

Diff for: tests/host/common/MockWiFiServerSocket.cpp

@@ -99,7 +99,7 @@ void WiFiServer::begin ()
 		exit(EXIT_FAILURE);
 	}
 
-    	server.sin_family = AF_INET;
+	server.sin_family = AF_INET;
 	server.sin_port = htons(mockport);
 	server.sin_addr.s_addr = htonl(global_source_address);
 	if (bind(sock, (struct sockaddr*)&server, sizeof(server)) == -1)
@@ -150,3 +150,23 @@ void WiFiServer::stop ()
 {
     close();
 }
+
+size_t WiFiServer::hasClientData ()
+{
+    // Trivial Mocking:
+    // There is no waiting list of clients in this trivial mocking code,
+    // so the code has to act as if the tcp backlog list is full,
+    // and nothing is known about potential further clients.
+    // It could be implemented by accepting new clients and store their data until the current one is closed.
+    return 0;
+}
+
+bool WiFiServer::hasMaxPendingClients ()
+{
+    // Mocking code does not consider the waiting client list,
+    // so it will return ::hasClient() here meaning:
+    // - our waiting client list does not exist
+    // - we consider pending number is max if a new client is waiting
+    //   or not max if there's no new client.
+    return hasClient();
+}