Appendix A: Registering an Application to a URL Protocol

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To enable an application to handle a particular URL protocol, you must add a new key, with the appropriate keys and values, to the registry in HKEY_CLASSES_ROOT.

The new registry key must match the protocol scheme that is being added. For instance, to add the protocol note:, the key added to HKEY_CLASSES_ROOT should be note. Under this new key, the Default string value should be the name of the new protocol, and the URLProtocol string value should contain either protocol-specific information or an empty string. Also under the new key, a DefaultIcon key and a shell key should be added. The Default string value under the DefaultIcon key must be the file name to use as an icon for this new URL protocol. Under the shell key, a key using a verb (such as open) should be added. A command key and a DDEEXEC key can be added under the key using a verb. The values under the command and DDEEXEC keys are used to call the application.

The following example shows which registry values must be added to register a new application (notepad.exe in this example) to handle a new URL protocol (note:).

[HKEY_CLASSES_ROOT]
    [note]
        (Default) = "URL:Note Protocol"
        URL Protocol = ""
        [DefaultIcon]
            (Default) = "notepad.exe"
        [shell]
            [open]
                [command]
                    (Default) = "c:\windows\notepad.exe %1"

By adding these settings to the registry, attempts to navigate to URLs such as note:c:\myfile.txt would launch Notepad to edit the file c:\myfile.txt. Of course, all the commands supported under Shell\Open are supported, including DDEEXEC (in other words, "command" is not the only key you can put under the verb).