Log external handler invocations to the console

Previously, failing to invoke an external protocol handler ('foo://bar')
would fail silently if the protocol was not registered or if the user
gesture requirement was not met. This limitation made it difficult for
web developers to troubleshoot such situations. This CL emits errors to
the Developer Tools console when the protocol handler is not registered,
is forbidden, or is temporarily blocked pending a user-gesture.
Similarly, if an external handler is launched, an informational log
entry is added.

Bug: 1096610
Change-Id: Ie562d0c030f138f7e5ac0a09576ba73a79de3971
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2252848Reviewed-by: Matt Giuca <mgiuca@chromium.org>
Commit-Queue: Eric Lawrence [MSFT] <ericlaw@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#782007}

chrome/browser/external_protocol/external_protocol_handler.cc

@@ -112,6 +112,19 @@ void RunExternalProtocolDialogWithDelegate(
                                         has_user_gesture, initiating_origin);
     return;
   }
+
+#if defined(OS_MACOSX) || defined(OS_WIN)
+  // If the Shell does not have a registered name for the protocol,
+  // attempting to invoke the protocol will fail.
+  if (shell_integration::GetApplicationNameForProtocol(url).empty()) {
+    web_contents->GetMainFrame()->AddMessageToConsole(
+        blink::mojom::ConsoleMessageLevel::kError,
+        "Failed to launch '" + url.possibly_invalid_spec() +
+            "' because the scheme does not have a registered handler.");
+    return;
+  }
+#endif
+
   ExternalProtocolHandler::RunExternalProtocolDialog(
       url, web_contents, page_transition, has_user_gesture, initiating_origin);
 }
@@ -130,6 +143,10 @@ void LaunchUrlWithoutSecurityCheckWithDelegate(
   if (!web_contents)
     return;
 
+  web_contents->GetMainFrame()->AddMessageToConsole(
+      blink::mojom::ConsoleMessageLevel::kInfo,
+      "Launched external handler for '" + url.possibly_invalid_spec() + "'.");
+
   platform_util::OpenExternal(
       Profile::FromBrowserContext(web_contents->GetBrowserContext()), url);
 
@@ -391,6 +408,11 @@ void ExternalProtocolHandler::LaunchUrl(
       escaped_url.scheme(), base::OptionalOrNullptr(initiating_origin),
       g_external_protocol_handler_delegate, profile);
   if (block_state == BLOCK) {
+    web_contents->GetMainFrame()->AddMessageToConsole(
+        blink::mojom::ConsoleMessageLevel::kError,
+        "Not allowed to launch '" + url.possibly_invalid_spec() + "'" +
+            (g_accept_requests ? "." : " because a user gesture is required."));
+
     if (g_external_protocol_handler_delegate)
       g_external_protocol_handler_delegate->BlockRequest();
     return;

chrome/browser/external_protocol/external_protocol_handler_browsertest.cc

@@ -71,3 +71,41 @@ IN_PROC_BROWSER_TEST_F(ExternalProtocolHandlerBrowserTest,
   observer.Wait();
   EXPECT_EQ(browser()->tab_strip_model()->count(), 1);
 }
+
+IN_PROC_BROWSER_TEST_F(ExternalProtocolHandlerBrowserTest,
+                       ProtocolLaunchEmitsConsoleLog) {
+#if defined(OS_WIN)
+  // On Win 7 the protocol is registered to be handled by Chrome and thus never
+  // reaches the ExternalProtocolHandler so we skip the test. For
+  // more info see installer/util/shell_util.cc:GetShellIntegrationEntries
+  if (base::win::GetVersion() < base::win::Version::WIN8)
+    return;
+#endif
+
+  content::WebContents* web_contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+
+  content::WebContentsConsoleObserver observer(web_contents);
+  observer.SetPattern("Launched external handler for 'mailto:test@site.test'.");
+  ASSERT_TRUE(
+      ExecJs(web_contents, "window.open('mailto:test@site.test', '_self');"));
+  observer.Wait();
+  ASSERT_EQ(1u, observer.messages().size());
+}
+
+IN_PROC_BROWSER_TEST_F(ExternalProtocolHandlerBrowserTest,
+                       ProtocolFailureEmitsConsoleLog) {
+// Only on Mac and Windows is there a way for Chromium to know whether a
+// protocol handler is registered ahead of time.
+#if defined(OS_MACOSX) || defined(OS_WIN)
+  content::WebContents* web_contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+
+  content::WebContentsConsoleObserver observer(web_contents);
+  observer.SetPattern("Failed to launch 'does.not.exist:failure'*");
+  ASSERT_TRUE(
+      ExecJs(web_contents, "window.open('does.not.exist:failure', '_self');"));
+  observer.Wait();
+  ASSERT_EQ(1u, observer.messages().size());
+#endif
+}