[Android Downloads] Long-press menu item "Download Link" should delegate job to OfflinePages backen…

chrome/browser/android/offline_pages/downloads/resource_throttle.cc

+// Copyright 2015 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 "chrome/browser/android/offline_pages/downloads/resource_throttle.h"

[asanka, 2016/12/07 16:37:40]

You could use the SaveLinkAsReferrerPolicyOrigin test in
//chrome/browser/download/download_browsertest.cc as a template to build a test
for this.

+
+#include "base/logging.h"
+#include "chrome/browser/android/offline_pages/offline_page_utils.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/resource_controller.h"
+#include "content/public/browser/resource_request_info.h"
+#include "content/public/browser/web_contents.h"
+#include "net/base/mime_util.h"
+
+ namespace {

[asanka, 2016/12/07 16:37:40]

Nit: whitespace. Perhaps run this through 'git cl format'.

+ // Mime type of download resource that should trigger handoff to OfflinePages
+ // backend for full page load and snapshot.
+const char kHTMLMimeType[] = "text/html";

[asanka, 2016/12/07 16:37:40]

SavePackage considers both text/html and application/xhtml+xml as HTML (see
https://cs.chromium.org/chromium/src/content/browser/download/save_package.cc...).

+
+void WillStartOfflineRequestOnUIThread(
+    const GURL& url,
+    const content::ResourceRequestInfo::WebContentsGetter& contents_getter) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
+  content::WebContents* web_contents = contents_getter.Run();
+  if (!web_contents)
+    return;
+  offline_pages::OfflinePageUtils::StartOfflinePageDownload(
+      web_contents->GetBrowserContext(), url);
+}
+}  // namespace
+
+namespace offline_pages {
+namespace downloads {
+
+ResourceThrottle::ResourceThrottle(const net::URLRequest* request)
+    : request_(request) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+}
+
+ResourceThrottle::~ResourceThrottle() {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+}
+
+void ResourceThrottle::WillProcessResponse(bool* defer) {
+  DCHECK_CURRENTLY_ON(content::BrowserThread::IO);
+  std::string mime_type;
+  request_->GetMimeType(&mime_type);
+  if (net::MatchesMimeType(kHTMLMimeType, mime_type)) {
+    controller()->Cancel();

[asanka, 2016/12/07 16:37:40]

Let's defer the Cancel() call until after you're done accessing request_ and its
ResourceRequestInfo. Doing so makes the code robust against state changes that
would happen as a result of the Cancel() call.

The cancellation is currently always asynchronous and doesn't affect the
lifetime of |*this|, |request_| and its ResourceRequestInfo, but that depends on
behavior deep in the guts of //net.

+
+    const content::ResourceRequestInfo* info =
+        content::ResourceRequestInfo::ForRequest(request_);
+    if (!info)
+      return;
+    content::BrowserThread::PostTask(
+      content::BrowserThread::UI, FROM_HERE,
+      base::Bind(&WillStartOfflineRequestOnUIThread,
+                 request_->url(),
+                 info->GetWebContentsGetterForRequest()));
+  }
+}
+
+const char* ResourceThrottle::GetNameForLogging() const {
+  return "offline_pages::downloads::ResourceThrottle";
+}
+
+}  // namespace downloads
+}  // namespace offline_pages
+