Issue #7749: ensure that request parameters are parsed only once

In WebController, CgiParser::parse is used once in handleRequest, and
once in requestDataReceived. requestDataReceived is called repeatedly
as uploads come in. This would cause a constant accumulation of duplicate
values for parameters, and cause a race condition if the value is being
updated while updateResourceProgress is being handled. This is most
noticeable when the upload is coming in very fast (e.g. on localhost).

Author: RockinRoel

src/web/CgiParser.C

@@ -194,6 +194,12 @@ void CgiParser::parse(WebRequest& request, ReadOption readOption)
 
   std::string queryString = request.queryString();
 
+  LOG_DEBUG("queryString (len=" << len << "): " << queryString);
+
+  if (!queryString.empty() && request_->parameters_.empty()) {
+    Http::Request::parseFormUrlEncoded(queryString, request_->parameters_);
+  }
+
   // XDomainRequest cannot set a contentType header, we therefore pass it
   // as a request parameter
   if (readOption != ReadHeadersOnly &&
@@ -222,17 +228,19 @@ void CgiParser::parse(WebRequest& request, ReadOption readOption)
 
     // This is a special Wt feature, I do not think it standard.
     // For POST, parameters in url-encoded URL are still parsed.
-    if (!queryString.empty())
-      queryString += '&';
 
-    queryString += buf;
+    std::string formQueryString = buf;
     delete[] buf;
-  }
-
-  LOG_DEBUG("queryString (len=" << len << "): " << queryString);
 
-  if (!queryString.empty())
-    Http::Request::parseFormUrlEncoded(queryString, request_->parameters_);
+    LOG_DEBUG("formQueryString (len=" << len << "): " << formQueryString);
+    if (!formQueryString.empty()) {
+      Http::Request::parseFormUrlEncoded(formQueryString, request_->parameters_);
+    }
+    Http::ParameterMap::const_iterator it = request_->parameters_.find("Wt-params");
+    if (it != request_->parameters_.end() && it->second.size() == 1) {
+      Http::Request::parseFormUrlEncoded(it->second[0], request_->parameters_);
+    }
+  }
 
   if (readOption != ReadHeadersOnly &&
       type && strstr(type, "multipart/form-data") == type) {
@@ -253,11 +261,6 @@ void CgiParser::parse(WebRequest& request, ReadOption readOption)
       }
     }
   }
-
-  Http::ParameterMap::const_iterator it = request_->parameters_.find("Wt-params");
-  if (it != request_->parameters_.end() && it->second.size() == 1) {
-    Http::Request::parseFormUrlEncoded(it->second[0], request_->parameters_);
-  }
 }
 
 void CgiParser::readMultipartData(WebRequest& request,