Adds mailto: URL support to app launching.

ios/chrome/browser/web/mailto_handler.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_handler.h"
+
+#import "base/strings/sys_string_conversions.h"
+#include "url/gurl.h"
+#include "url/url_constants.h"
+
+#import <UIKit/UIKit.h>
+
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
+@implementation MailtoHandler
+@synthesize appName = _appName;
+@synthesize appStoreID = _appStoreID;
+
+- (instancetype)initWithName:(NSString*)appName
+                  appStoreID:(NSString*)appStoreID {
+  self = [super init];
+  if (self) {
+    _appName = [appName copy];
+    _appStoreID = [appStoreID copy];
+  }
+  return self;
+}
+
+- (BOOL)isAvailable {
+  // This should be implemented by subclasses.
+  NOTREACHED();
+  return NO;
+}
+
+- (NSString*)beginningScheme {
+  // Subclasses should override this method.
+  return @"mailtohandler:/co?";
+}
+
+- (NSSet*)supportedHeaders {
+  return [NSSet setWithObjects:@"to", @"from", @"cc", @"subject", @"body", nil];
+}
+
+- (NSString*)rewriteMailtoURL:(const GURL&)gURL {
+  if (!gURL.SchemeIs(url::kMailToScheme))
+    return nil;
+  NSMutableArray* outParams = [NSMutableArray array];
+  NSString* recipient = base::SysUTF8ToNSString(gURL.path());
+  if ([recipient length]) {
+    [outParams addObject:[NSString stringWithFormat:@"to=%@", recipient]];
+  }
+  NSString* query = base::SysUTF8ToNSString(gURL.query());
+  for (NSString* keyvalue : [query componentsSeparatedByString:@"&"]) {
+    NSArray* pair = [keyvalue componentsSeparatedByString:@"="];
+    if ([pair count] == 0U || [pair count] > 2U)

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

Do we really want to handle the case where [pair count] == 1 ?

if the link is:
mailto:pkl@chromium.org?cc
do we really care about the presence of cc ?

[pkl (ping after 24h if needed), 2017/05/04 22:25:59]

Good point. Checked some mailto query params docs and there shouldn't be any
acceptable params that do not take a =.

+      continue;
+    if (![[self supportedHeaders] containsObject:pair[0]])
+      continue;
+    if ([pair count] == 1) {
+      [outParams addObject:pair[0]];
+    } else if ([pair count] == 2) {
+      [outParams
+          addObject:[NSString stringWithFormat:@"%@=%@", pair[0], pair[1]]];
+    }
+  }
+  return [NSString stringWithFormat:@"%@%@", [self beginningScheme],
+                                    [outParams componentsJoinedByString:@"&"]];
+}
+
+@end