Added naive content length to upload struct (#5142)

Content length provides context into the size of the upload, it's not
the exact form body size it's off by the request header info, but it was
already parsed by the library and provides little to no additional
overhead to pass on for use in request handlers.

Author: RickeyWard

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

@@ -55,8 +55,9 @@ typedef struct {
   String  filename;
   String  name;
   String  type;
-  size_t  totalSize;    // file size
+  size_t  totalSize;    // total size of uploaded file so far
   size_t  currentSize;  // size of data currently in buf
+  size_t  contentLength; // size of entire post request, file size + headers and other request data.
   uint8_t buf[HTTP_UPLOAD_BUFLEN];
 } HTTPUpload;
 

Diff for: libraries/ESP8266WebServer/src/Parsing.cpp

@@ -468,6 +468,7 @@ bool ESP8266WebServer::_parseForm(WiFiClient& client, const String& boundary, ui
             _currentUpload->type = argType;
             _currentUpload->totalSize = 0;
             _currentUpload->currentSize = 0;
+            _currentUpload->contentLength = len;
 #ifdef DEBUG_ESP_HTTP_SERVER
             DEBUG_OUTPUT.print("Start File: ");
             DEBUG_OUTPUT.print(_currentUpload->filename);