Adds mailto: URL support to app launching.

ios/chrome/browser/web/mailto_url_rewriter.mm

+// 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.
+
+#import "ios/chrome/browser/web/mailto_url_rewriter.h"
+
+#import "base/logging.h"
+#import "ios/chrome/browser/web/mailto_handler.h"
+#import "ios/chrome/browser/web/mailto_handler_gmail.h"
+#import "ios/chrome/browser/web/mailto_handler_system_mail.h"
+
+#import <UIKit/UIKit.h>
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+namespace {
+// The key for NSUserDefaults to store the Mail client selected to handle
+// mailto: URL scheme. If this key is not set, user has not made an explicit
+// choice for default mailto: handler and system-provided Mail client app will
+// be used.
+NSString* const kMailtoDefaultHandlerKey = @"MailtoHandlerDefault";
+}  // namespace
+
+@interface MailtoURLRewriter ()
+
+// Dictionary keyed by the App Store ID of the Mail client and the value is
+// the MailtoHandler object that can rewrite a mailto: URL.
+@property(nonatomic, strong)
+    NSMutableDictionary<NSString*, MailtoHandler*>* handlers;
+
+// Private method for testing to clear the default state.
++ (void)resetDefaultHandlerID;
+
+// Private method to add one or more |handlerApp| objects to the list of known
+// Mail client apps.
+- (void)addMailtoApps:(NSArray<MailtoHandler*>*)handlerApps;
+
+// Custom logic to handle the migration from Google Native App Launcher options
+// to this simplified mailto: URL only system. This must be called after
+// -addMailtoApp: has been called to add all the known Mail client apps.
+// TODO(crbug.com/718601): At some point in the future when almost all users
+// have upgraded, this method can be removed.
+- (void)migrateLegacyOptions;
+
+@end
+
+@implementation MailtoURLRewriter
+@synthesize handlers = _handlers;
+
++ (NSString*)systemMailApp {
+  // This is the App Store ID for Apple Mail app.
+  // See https://itunes.apple.com/us/app/mail/id1108187098?mt=8
+  return @"1108187098";
+}
+
+- (instancetype)init {
+  self = [super init];
+  if (self) {
+    _handlers = [NSMutableDictionary dictionary];
+  }
+  return self;
+}
+
+- (instancetype)initWithStandardHandlers {
+  self = [self init];
+  if (self) {
+    [self addMailtoApps:@[
+      [[MailtoHandlerSystemMail alloc] init], [[MailtoHandlerGmail alloc] init]
+    ]];
+  }
+  return self;
+}
+
+- (NSArray<MailtoHandler*>*)defaultHandlers {
+  return [_handlers allValues];
+}
+
+- (NSString*)defaultHandlerID {
+  NSString* value = [[NSUserDefaults standardUserDefaults]
+      stringForKey:kMailtoDefaultHandlerKey];
+  return value ? value : [[self class] systemMailApp];
+}
+
+- (void)setDefaultHandlerID:(NSString*)appStoreID {
+  DCHECK([appStoreID length]);
+  [[NSUserDefaults standardUserDefaults] setObject:appStoreID
+                                            forKey:kMailtoDefaultHandlerKey];
+}
+
+- (NSString*)rewriteMailtoURL:(const GURL&)gURL {
+  NSString* value = [self defaultHandlerID];
+  if ([value length]) {
+    MailtoHandler* handler = _handlers[value];
+    if (handler) {
+      return [handler rewriteMailtoURL:gURL];
+    }
+  }
+  return nil;
+}
+
+#pragma mark - Private
+
++ (void)resetDefaultHandlerID {

[rohitrao (ping after 24h), 2017/05/10 00:09:18]

What code will call this function and reset the handler ID?  Can the user
trigger this operation somehow?

[pkl (ping after 24h if needed), 2017/05/10 01:04:14]

No. This is only used by unit tests. I renamed it to *ForTesting to make it
obvious.

+  [[NSUserDefaults standardUserDefaults]
+      removeObjectForKey:kMailtoDefaultHandlerKey];
+}
+
+- (void)addMailtoApps:(NSArray<MailtoHandler*>*)handlerApps {
+  for (MailtoHandler* app in handlerApps) {
+    if ([app isAvailable])
+      [_handlers setObject:app forKey:[app appStoreID]];
+  }
+  [self migrateLegacyOptions];
+}
+
+//
+// Implements the migration logic for users of previous versions of Google
+// Chrome which supports Google Native App Launcher. The goal is to preserve
+// the previous behavior and support user choice of non-system provided Mail
+// client apps. System-provided Mail client app will be referred to as
+// "System Mail". The migration goals are:
+// - If a user has not made a choice for preferred mailto: handler in the past,
+//   the behavior after upgrading to this version should not change.
+// - If a user had disabled Gmail app as the preferred mailto: handler in the
+//   past, System Mail should be selected as the default mailto: handler.
+// - If a user installs Gmail app after the installation of Chrome, Gmail app
+//   will be chosen as the default mailto: handler, preserving the previous
+//   behavior.
+// - If a user installs another 3rd party mail client app, assuming that the
+//   3rd party mail client app is explicitly supported in Chrome, the new 3rd
+//   party mail client app can be set as the default mailto: handler through
+//   Tools > Settings > Content Settings.
+//
+// Two NSUserDefaults keys are interpreted with the following meanings:
+// - kLegacyShouldAutoOpenKey: The existence of this key implies that the user
+//   has used Chrome in the past and had Gmail app installed. Gmail app may or
+//   may not be installed currently.
+// - kMailtoDefaultHandlerKey: If this key is not set, System Mail app is used
+//   to handle mailto: URLs. If this key is set, the value is a string that is
+//   the key to |_handlers| which maps to a MailtoHandler object.
+//
+- (void)migrateLegacyOptions {
+  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
+
+  // User previously had a selection made for opening mailto: links with Gmail,
+  // upgrade will set Gmail app to be the default mailto: handler. If user had
+  // opted out to using Gmail app (even when it was installed), migrate user
+  // to use system-provided Mail client.
+  // The key used in NSUserDefaults is from legacy code when Native App
+  // Launcher was still in use. The general format is a string prefix,
+  // underscore, then followed by the App Store ID of the application.
+  NSString* const kGmailAppStoreID = @"422689480";
+  NSString* const kLegacyShouldAutoOpenKey =
+      [NSString stringWithFormat:@"ShouldAutoOpenLinks_%@", kGmailAppStoreID];
+  NSNumber* legacyValue = [defaults objectForKey:kLegacyShouldAutoOpenKey];
+  if (legacyValue) {
+    switch ([legacyValue intValue]) {
+      case 0:
+      case 2: {
+        // If legacy user was using default (kAutoOpenLinksNotSet) or had
+        // explicitly chosen to use Gmail (kAutoOpenLinksYes), migrate to use
+        // Gmail app.
+        MailtoHandler* gmailHandler = _handlers[kGmailAppStoreID];
+        if ([gmailHandler isAvailable])
+          [defaults setObject:kGmailAppStoreID forKey:kMailtoDefaultHandlerKey];
+        else
+          [defaults removeObjectForKey:kMailtoDefaultHandlerKey];
+        break;
+      }
+      case 1:
+        // If legacy user was not using Gmail to handle mailto: links
+        // (kAutoOpenLinksNo), migrate to use system-provided Mail app.
+        [defaults removeObjectForKey:kMailtoDefaultHandlerKey];
+        break;
+      default:
+        NOTREACHED();
+        break;
+    }
+    [defaults removeObjectForKey:kLegacyShouldAutoOpenKey];
+    return;
+  }
+
+  // If a default handler for mailto: has already been registered, this means

[rohitrao (ping after 24h), 2017/05/10 00:09:18]

The rest of this function after this line isn't really related to migration at
all.  Perhaps it's worth moving to a separate function, something like
switchHandlerToGmailIfInstalled?

[pkl (ping after 24h if needed), 2017/05/10 01:04:14]

Done.

+  // that user had made a choice and no further migration should be done.
+  if ([defaults objectForKey:kMailtoDefaultHandlerKey])
+    return;
+
+  // For users who have not made an explict choice (kMailtoDefaultHandlerKey

[rohitrao (ping after 24h), 2017/05/09 23:52:20]

Typo: explicit.

[rohitrao (ping after 24h), 2017/05/09 23:52:21]

The absence of kMailtoDefaultHandlerKey could happen even if the user makes an
explicit choice to use system mail, right?

[pkl (ping after 24h if needed), 2017/05/10 00:02:19]

From Settings UI, user can set Mail app as the handler. That will go through
-setDefaultHandlerID: which sets kMailtoDefaultHandlerKey. This means that once
user has made an explicit choice through Settings UI, kMailtoDefaultHandler key
will never become unset.

[pkl (ping after 24h if needed), 2017/05/10 00:02:19]

Yes, will fix that.

+  // not set), if Gmail is detected, make an explicit choice for the user to

[rohitrao (ping after 24h), 2017/05/09 23:52:20]

If I choose to use system mail, then later install the Gmail app, we will change
the default mailto handler in response.  Is that the intended behavior?

Actually, does this make it impossible to use system mail when gmail is
installed?  Will we constantly change the pref to gmail on startup?

[pkl (ping after 24h if needed), 2017/05/10 00:02:19]

If user has made a choice, this migration code will early return on line 188.
So, no, user will not be reverted to Gmail every time.

+  // use Gmail app as the default mailto: handler.
+  MailtoHandler* gmailHandler = _handlers[kGmailAppStoreID];
+  if ([gmailHandler isAvailable])
+    [defaults setObject:kGmailAppStoreID forKey:kMailtoDefaultHandlerKey];
+}
+
+@end