Handle HEAD requests for static files correctly (esp8266#6837)

* Handle HEAD requests for static files correctly

* Handle HEAD requests for static files correctly

Author: mathertel

libraries/ESP8266WebServer/src/ESP8266WebServer.h

@@ -151,10 +151,22 @@ class ESP8266WebServerTemplate
 
   static String urlDecode(const String& text);
 
+  // Handle a GET request by sending a response header and stream file content to response body 
   template<typename T>
   size_t streamFile(T &file, const String& contentType) {
+    return streamFile(file, contentType, HTTP_GET);
+  }
+
+  // Implement GET and HEAD requests for files.
+  // Stream body on HTTP_GET but not on HTTP_HEAD requests. 
+  template<typename T>
+  size_t streamFile(T &file, const String& contentType, HTTPMethod requestMethod) {
+    size_t contentLength = 0;
     _streamFileCore(file.size(), file.name(), contentType);
-    return _currentClient.write(file);
+    if (requestMethod == HTTP_GET) {
+      contentLength = _currentClient.write(file);
+    }
+    return contentLength;
   }
 
   static const String responseCodeToString(const int code);

libraries/ESP8266WebServer/src/detail/RequestHandlersImpl.h

@@ -76,7 +76,7 @@ class StaticRequestHandler : public RequestHandler<ServerType> {
     }
 
     bool canHandle(HTTPMethod requestMethod, String requestUri) override  {
-        if (requestMethod != HTTP_GET)
+        if ((requestMethod != HTTP_GET) && (requestMethod != HTTP_HEAD))
             return false;
 
         if ((_isFile && requestUri != _uri) || !requestUri.startsWith(_uri))
@@ -125,7 +125,7 @@ class StaticRequestHandler : public RequestHandler<ServerType> {
         if (_cache_header.length() != 0)
             server.sendHeader("Cache-Control", _cache_header);
 
-        server.streamFile(f, contentType);
+        server.streamFile(f, contentType, requestMethod);
         return true;
     }