Adds mailto: URL support to app launching.

ios/chrome/browser/web/mailto_handler.h

+// Copyright 2017 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.
+
+#ifndef _IOS_CHROME_BROWSER_WEB_MAILTO_HANDLER_H_
+#define _IOS_CHROME_BROWSER_WEB_MAILTO_HANDLER_H_
+
+#import <Foundation/Foundation.h>
+
+class GURL;
+
+// MailtoHandler is the base class for Mail client apps that can handle
+// mailto: URLs via custom URL schemes. To add support for Mail clients,
+// subclass from this and add it to MailtoURLRewriter class.
+@interface MailtoHandler : NSObject
+
+// Name of Mail client. This is a name that a user can recognize, e.g. @"Gmail".
+@property(nonatomic, readonly) NSString* appName;
+
+// The iOS App Store ID for the Mail client. This is usually a string of digits.
+@property(nonatomic, readonly) NSString* appStoreID;
+
+// Designated initializer that subclasses should call from -init.
+- (instancetype)initWithName:(NSString*)appName
+                  appStoreID:(NSString*)appStoreID;
+
+// Returns whether the Mail client app is installed.
+- (BOOL)isAvailable;

[jif, 2017/05/03 13:01:35]

I think the subclass should return the Mail client's scheme instead:
mailto:// for Apple Mail.
googlegmail:// for Gmail.

 This way, we'd avoid duplicating the 
"[[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:" logic.

Also, this information may allow us to check at runtime that the
LSApplicationQueriesSchemes section of the app's .plist contains the schemes.
This can be done in a separate CL.

[pkl (ping after 24h if needed), 2017/05/03 22:17:18]

May be I don't understand completely. Having this return the URL scheme does not
tell us whether Gmail is installed or not.
However, checking LSApplicationQUeriesSchemes section before calling
-canOpenURL: is a good idea. It is possible to DCHECK if the scheme is not
listed.

[jif, 2017/05/04 14:08:47]

Indeed it does not.
I'm suggesting factoring the code actually  doing the check out of the
subclasses,
to the base class.
Here's some pseudo code showing what I have in mind:




mailto_handler.mm would contain something like:

- (NSString*)applicationScheme {
  // This should be implemented by subclasses.
  return nil;
}

- (BOOL)isAvailable {
  NSString* scheme = [self applicationScheme];
  DCHECK( plist contains |scheme| );
  return [[UIApplication sharedApplication] canOpenURL:[NSURL
URLWithString:scheme]];
}




mailto_handler_system_mail.mm would contain something like:

- (NSString*)applicationScheme {
  return @"mailto://";
}




mailto_handler_gmail.mm would contain something like:

- (NSString*)applicationScheme {
  return @"googlemail://";
}

[jif, 2017/05/05 09:49:39]

Seems like you missed this reply (which is in the Patch Set 4 ).

+
+// Rewrites |gURL| into a URL with a different URL scheme that will cause a
+// native iOS app to be launched to handle the mailto: URL. Returns nil if
+// |gURL| is not a mailto: URL.
+// This method is intended to be an abstract interface for subclasses and is
+// not implemented for this class.
+- (NSString*)rewriteMailtoURL:(const GURL&)gURL;
+
+@end
+
+#endif  // _IOS_CHROME_BROWSER_WEB_MAILTO_HANDLER_H_