How the new Edge will handle file:// URI ?

navijayvargiya sylvainrodrigue narutards rakova17 jpochedley 

So sorry everyone!   For some reason, I haven't been getting updates to replies/mentions in here so I didn't see any your followup mentions/questions.

Here are some bits of pieces of code we cobbled together to make this work...

SETUP INSTALLER

Below is a method inside a WinForms installer app that adds the new "localfile" entry to the registry and sets the associated command to execute the localfile handler executable (further below).

private void makeRegEntries(string handlerInstallationFolder)
{
    RegistryKey localfileKey = Registry.ClassesRoot.CreateSubKey("localfile");

    // Create three subkeys under HKEY_CLASSES_ROOT\localfile
    // The keys are disposed when execution exits the using statement.

    using (RegistryKey
        shellSubKey = localfileKey.CreateSubKey("shell"),
        openSubKey = shellSubKey.CreateSubKey("open"),
        commandSubKey = openSubKey.CreateSubKey("command"))
    {
        // Create data for the localfile key
        localfileKey.SetValue("", "URL:localfile");
        localfileKey.SetValue("URL Protocol", "");

        // Create data for the command subkey
        commandSubKey.SetValue("", "\"" + handlerInstallationFolder + "\" %1");
    }

    localfileKey.Close();
}

LOCALFILE HANDLER

This console app code is what the "localfile" protocol registry command runs.  It basically tells the OS to open the parameter passed in on the data parameter.

static void Main(string[] args)
{
    Console.WriteLine("Init");

    // Skip everything if there's no args
    foreach (string argument in args)
    {
        // Decode the string passed from the browser, and make it just a path.
        string formattedArgumentDecoded = System.Net.WebUtility.UrlDecode(argument).Replace(@"localfile://open/?data=", "");

        // For case-insensitive security checks
        string formattedArgument = formattedArgumentDecoded.ToLower();

        Console.WriteLine("Testing: {0}", formattedArgumentDecoded);

        // TIP: Add some blacklist checks here for unqualified file extensions etc. if needed.
        
        Process.Start("explorer.exe", formattedArgumentDecoded);
    }

    Environment.Exit(0);
}

HELPER METHODS

BTW, there are a number of other convenience methods we added too (called inside the installer).  For example, in Chrome there's a checkbox that allows the user to save this protocol association.  Chrome has this hidden feature for security, but it can be enabled via the Registry.  Same goes for IE and Edge/Chromium.  These are the methods that set those (hopefully they will be of some use):

private void enableChromeCheckbox()
        {
            RegistryKey softwareKey = Registry.LocalMachine.CreateSubKey("SOFTWARE");

            // Create three subkeys under HKEY_CLASSES_ROOT\localfile
            // The keys are disposed when execution exits the using statement.

            using (RegistryKey
                policiesKey = softwareKey.CreateSubKey("Policies"),
                googleSubKey = policiesKey.CreateSubKey("Google"),
                chromeSubKey = googleSubKey.CreateSubKey("Chrome"))
            {
                // Create data for the localfile key
                chromeSubKey.SetValue("ExternalProtocolDialogShowAlwaysOpenCheckbox", "1", RegistryValueKind.DWord);

            }

            softwareKey.Close();
        }

private void enableChromiumEdgeCheckbox()
        {
            RegistryKey softwareKey = Registry.LocalMachine.OpenSubKey("SOFTWARE", true);

            // Create three subkeys under HKEY_CLASSES_ROOT\localfile
            // The keys are disposed when execution exits the using statement.

            using (RegistryKey
                policiesKey = softwareKey.CreateSubKey("Policies"),
                msSubKey = policiesKey.CreateSubKey("Microsoft"),
                edgeSubKey = msSubKey.CreateSubKey("Edge"))
            {
                // Create data for the localfile key
                edgeSubKey.SetValue("ExternalProtocolDialogShowAlwaysOpenCheckbox", "1", RegistryValueKind.DWord);

            }

            softwareKey.Close();
        }

private void enableNoAskToOpenHtmlEdgeCheckbox()
        {
            using (var hklmHandle = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64))
            using (var localFileKey = hklmHandle.CreateSubKey(@"SOFTWARE\Microsoft\Internet Explorer\ProtocolExecute\localfile", writable: true))
            {
                if (localFileKey.GetValue("WarnOnOpen") == null)
                    localFileKey.SetValue("WarnOnOpen", "0", RegistryValueKind.DWord);
            }

            //Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ProtocolExecute\
        }

We did a lot of research on the topic to get this put together.  

https://support.shotgunsoftware.com/hc/en-us/articles/219031308-Launching-applications-using-custom-browser-protocols

All the best!

Jeff