（OSX）用户单击浏览器中的电子邮件链接时，操作系统如何将电子邮件地址传送到默认邮件应用程序？

Question

My dad is annoyed that when he clicks an e-mail hyperlink, OSX tries to open Mail, which he has never used and doesn't want to learn. He'd like it to just open a browser window to his ISP-provided email service (bleh).

I'm trying to write a program that basically handles that interaction, but I cannot figure out how the e-mail address from the hyperlink is passed along to the application. Essentially... When I click a mailto hyperlink for foo@example.com, How does the OS tell Mail.app (or whatever the default client is) to compose a new e-mail to foo@example.com?

Answer 1

First, Mail.app passively tells Launch Services that it handles the "mailto" URL scheme by including the following in its Info.plist file:

<key>CFBundleURLTypes</key>
<array>
    <dict>
        <key>CFBundleURLName</key>
        <string>Email Address URL</string>
        <key>CFBundleURLSchemes</key>
        <array>
            <string>mailto</string>
        </array>
        <key>LSIsAppleDefaultForScheme</key>
        <true/>
    </dict>
    ...
</array>

Next, it sets up a handler for the kInternetEventClass / kAEGetURL Apple Event. In Cocoa, that looks something like:

NSAppleEventManager* appleEventManager = [NSAppleEventManager sharedAppleEventManager];
[appleEventManager setEventHandler:self andSelector:@selector(handleGetURLEvent:withReplyEvent:) forEventClass:kInternetEventClass andEventID:kAEGetURL];

You could implement the handler method like this:

- (BOOL)handleGetURLEvent:(NSAppleEventDescriptor*)event withReplyEvent:(NSAppleEventDescriptor*)replyEvent
{
    NSAppleEventDescriptor* directObjectDescriptor  = [event paramDescriptorForKeyword:keyDirectObject];
    NSString*               urlString               = [directObjectDescriptor stringValue];
    NSURL*                  url                     = [NSURL URLWithString:urlString];
    // ... do something with url ...
}

For a "mailto" URL, much of the parsing behavior of NSURL isn't effective because the URLs don't conform to RFC 1808 (the resource specifier doesn't start with "//"). You can really only get the scheme (mailto) and the resource specifier using the -resourceSpecifier method. Some mailto URLs might have query-like syntax, such as "?subject=Some%20subject%20text", on them, but NSURL won't help you pick that apart. So, you'll need to do that manually. (You might consider constructing a bogus URL by injecting "//" at the front of the resource specifier and having NSURL parse that.)