Return error on JSON request failures

content/browser/tracing/tracing_ui.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/tracing/tracing_ui.h"
 
 #include <string>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 102 matching lines @@
 }
 
 void BeginReadingRecordingResult(
     const WebUIDataSource::GotDataCallback& callback,
     const base::FilePath& path) {
   BrowserThread::PostTask(
       BrowserThread::FILE, FROM_HERE,
       base::Bind(ReadRecordingResult, callback, path));
 }
 
-bool OnBeginRequest(const std::string& path,
-                    const WebUIDataSource::GotDataCallback& callback) {
+bool OnBeginJSONRequest(const std::string& path,
+                        const WebUIDataSource::GotDataCallback& callback) {
   if (path == "json/categories") {
-    TracingController::GetInstance()->GetCategories(
+    return TracingController::GetInstance()->GetCategories(
         base::Bind(OnGotCategories, callback));
-    return true;
   }
   const char* beginRecordingPath = "json/begin_recording?";
-  if (path.find(beginRecordingPath) == 0) {
+  if (StartsWithASCII(path, beginRecordingPath, true)) {
     std::string data = path.substr(strlen(beginRecordingPath));
     return OnBeginRecording(data, callback);
   }
   if (path == "json/get_buffer_percent_full") {
     return TracingController::GetInstance()->GetTraceBufferPercentFull(
         base::Bind(OnTraceBufferPercentFullResult, callback));
   }
   if (path == "json/end_recording") {
     return TracingController::GetInstance()->DisableRecording(
         base::FilePath(), base::Bind(BeginReadingRecordingResult, callback));
   }
-  if (StartsWithASCII(path, "json/", true))
-    LOG(ERROR) << "Unhandled request to " << path;
+  LOG(ERROR) << "Unhandled request to " << path;
   return false;
 }
 
+bool OnBeginRequest(const std::string& path,
+                    const WebUIDataSource::GotDataCallback& callback) {
+  if (StartsWithASCII(path, "json/", true)) {
+    if (!OnBeginJSONRequest(path, callback)) {
+      std::string error("##ERROR##");

[dsinclair, 2014/01/06 15:20:33]

Why not make this valid json? {"error": "invalid path"}?

[Xianzhu, 2014/01/06 17:11:27]

I didn't think of this, just randomly selected the error indicator. However in
JS UI code (https://codereview.appspot.com/47660043/), error condition is
checked in XHR handling before JSON decoding, so using a plain string seems more
convenient.

+      callback.Run(base::RefCountedString::TakeString(&error));
+    }
+    return true;
+  }
+  return false;
+}
+
 }  // namespace
 
 
 ////////////////////////////////////////////////////////////////////////////////
 //
 // TracingUI
 //
 ////////////////////////////////////////////////////////////////////////////////
 
 TracingUI::TracingUI(WebUI* web_ui) : WebUIController(web_ui) {
   // Set up the chrome://tracing/ source.
   BrowserContext* browser_context =
       web_ui->GetWebContents()->GetBrowserContext();
 
   WebUIDataSource* source = WebUIDataSource::Create(kChromeUITracingHost);
   source->SetJsonPath("strings.js");
   source->SetDefaultResource(IDR_TRACING_HTML);
   source->AddResourcePath("tracing.js", IDR_TRACING_JS);
   source->SetRequestFilter(base::Bind(OnBeginRequest));
   WebUIDataSource::Add(browser_context, source);
 }
 
 }  // namespace content