Improvements to the existing ETag implementation

libraries/ESP8266WebServer/src/ESP8266WebServer-impl.h

@@ -68,6 +68,13 @@ template <typename ServerType>
 void ESP8266WebServerTemplate<ServerType>::enableCORS(bool enable) {
   _corsEnabled = enable;
 }
+
+template <typename ServerType>
+void ESP8266WebServerTemplate<ServerType>::enableETag(bool enable, ETagFunction fn) {
+  _eTagEnabled = enable;
+  _eTagFunction = fn;
+}
+
 template <typename ServerType>
 void ESP8266WebServerTemplate<ServerType>::begin() {
   close();
@@ -264,10 +271,11 @@ void ESP8266WebServerTemplate<ServerType>::serveStatic(const char* uri, FS& fs,
     file.close();
   }
 
-  if(is_file)
+  if(is_file) {
     _addRequestHandler(new StaticFileRequestHandler<ServerType>(fs, path, uri, cache_header));
-  else
+  } else {
     _addRequestHandler(new StaticDirectoryRequestHandler<ServerType>(fs, path, uri, cache_header));  
+  }
 }
 
 template <typename ServerType>
@@ -436,6 +444,7 @@ void ESP8266WebServerTemplate<ServerType>::_prepareHeader(String& response, int
       sendHeader(String(F("Keep-Alive")), String(F("timeout=")) + HTTP_MAX_CLOSE_WAIT);
     }
 
+
     response += _responseHeaders;
     response += "\r\n";
     _responseHeaders = "";

libraries/ESP8266WebServer/src/ESP8266WebServer.h

@@ -114,6 +114,8 @@ class ESP8266WebServerTemplate
   void requestAuthentication(HTTPAuthMethod mode = BASIC_AUTH, const char* realm = NULL, const String& authFailMsg = String("") );
 
   typedef std::function<void(void)> THandlerFunction;
+  typedef std::function<String(FS &fs, const String &fName)> ETagFunction;
+
   void on(const Uri &uri, THandlerFunction handler);
   void on(const Uri &uri, HTTPMethod method, THandlerFunction fn);
   void on(const Uri &uri, HTTPMethod method, THandlerFunction fn, THandlerFunction ufn);
@@ -122,6 +124,7 @@ class ESP8266WebServerTemplate
   void onNotFound(THandlerFunction fn);  //called when handler is not assigned
   void onFileUpload(THandlerFunction fn); //handle file uploads
   void enableCORS(bool enable);
+  void enableETag(bool enable, ETagFunction fn = nullptr);
 
   const String& uri() const { return _currentUri; }
   HTTPMethod method() const { return _currentMethod; }
@@ -271,6 +274,9 @@ class ESP8266WebServerTemplate
     }
   }
 
+  bool             _eTagEnabled = false;
+  ETagFunction     _eTagFunction = nullptr;
+
 protected:
   void _addRequestHandler(RequestHandlerType* handler);
   void _handleRequest();

libraries/ESP8266WebServer/src/detail/RequestHandlersImpl.h

@@ -9,6 +9,25 @@
 
 namespace esp8266webserver {
 
+// calculate an eTag for a file in filesystem
+static String calcETag(FS &fs, const String path) {
+    String result;
+
+    // calculate eTag using md5 checksum
+    uint8_t md5_buf[16];
+    File f = fs.open(path, "r");
+    MD5Builder calcMD5;
+    calcMD5.begin();
+    calcMD5.addStream(f, f.size());
+    calcMD5.calculate();
+    calcMD5.getBytes(md5_buf);
+    f.close();
+    // create a minimal-length eTag using base64 byte[]->text encoding.
+    result = "\"" + base64::encode(md5_buf, 16, false) + "\"";
+    return(result);
+} // calcETag
+
+
 template<typename ServerType>
 class FunctionRequestHandler : public RequestHandler<ServerType> {
     using WebServerType = ESP8266WebServerTemplate<ServerType>;
@@ -92,6 +111,7 @@ class StaticRequestHandler : public RequestHandler<ServerType> {
 };
 
 
+// serve all files within a given directory
 template<typename ServerType>
 class StaticDirectoryRequestHandler : public StaticRequestHandler<ServerType> {
 
@@ -117,6 +137,7 @@ class StaticDirectoryRequestHandler : public StaticRequestHandler<ServerType> {
         DEBUGV("DirectoryRequestHandler::handle: request=%s _uri=%s\r\n", requestUri.c_str(), SRH::_uri.c_str());
 
         String path;
+        String eTagCode;
         path.reserve(SRH::_path.length() + requestUri.length() + 32);
         path = SRH::_path;
 
@@ -156,17 +177,37 @@ class StaticDirectoryRequestHandler : public StaticRequestHandler<ServerType> {
             return false;
         }
 
+        if (server._eTagEnabled) {
+            if (server._eTagFunction) {
+                eTagCode = (server._eTagFunction)(SRH::_fs, path);
+            } else {
+                eTagCode = esp8266webserver::calcETag(SRH::_fs, path);
+            }
+
+            if (server.header("If-None-Match") == eTagCode) {
+                server.send(304);
+                return true;
+            }
+        }
+
         if (SRH::_cache_header.length() != 0)
             server.sendHeader("Cache-Control", SRH::_cache_header);
 
+        if ((server._eTagEnabled) && (eTagCode.length() > 0)) {
+            server.sendHeader("ETag", eTagCode);
+        }
+
         server.streamFile(f, contentType, requestMethod);
+
         return true;
     }
 
 protected:
     size_t _baseUriLength;
 };
 
+
+// Serve a specific, single file
 template<typename ServerType>
 class StaticFileRequestHandler
     :
@@ -180,13 +221,6 @@ public StaticRequestHandler<ServerType> {
         :
     StaticRequestHandler<ServerType>{fs, path, uri, cache_header}
     {
-        File f = SRH::_fs.open(path, "r");
-        MD5Builder calcMD5;
-        calcMD5.begin();
-        calcMD5.addStream(f, f.size());
-        calcMD5.calculate();
-        calcMD5.getBytes(_ETag_md5);
-        f.close();
     }
 
     bool canHandle(HTTPMethod requestMethod, const String& requestUri) override  {
@@ -197,11 +231,17 @@ public StaticRequestHandler<ServerType> {
         if (!canHandle(requestMethod, requestUri))
             return false;
 
-        const String etag = "\"" + base64::encode(_ETag_md5, 16, false) + "\"";
-
-        if(server.header("If-None-Match") == etag){
-            server.send(304);
-            return true;
+        if (server._eTagEnabled) {
+            if (server._eTagFunction) {
+                _eTagCode = (server._eTagFunction)(SRH::_fs, SRH::_path);
+            } else  if (_eTagCode.isEmpty()) {
+                _eTagCode = esp8266webserver::calcETag(SRH::_fs, SRH::_path);
+            }
+
+            if (server.header("If-None-Match") == _eTagCode) {
+                server.send(304);
+                return true;
+            }
         }
 
         File f = SRH::_fs.open(SRH::_path, "r");
@@ -217,14 +257,16 @@ public StaticRequestHandler<ServerType> {
         if (SRH::_cache_header.length() != 0)
             server.sendHeader("Cache-Control", SRH::_cache_header);
 
-        server.sendHeader("ETag", etag);
+        if ((server._eTagEnabled) && (_eTagCode.length() > 0)) {
+            server.sendHeader("ETag", _eTagCode);
+        }
 
         server.streamFile(f, mime::getContentType(SRH::_path), requestMethod);
         return true;
     }
 
 protected:
-    uint8_t _ETag_md5[16];       
+    String _eTagCode; // eTag as used in http header for this single file
 };
 
 } // namespace