Answered: ssh exec program

You are right, Rebex File Server doesn't support executing external commands. Its simplified virtual shell is mostly supposed to complement SFTP and SCP protocols and all the built-in commands only work with the virtual file system.

However, what you are trying to do is a very interesting scenario and it actually turned out that adding support for it is quite simple - we just had to enhance the internals a bit and make the inner streams accessible through SshConsole, which is passed with ShellCommand event arguments.

You can give this a try as well - just sent you a link to the current beta build.

We have not sufficiently tested this yet, but I was able to clone a 300 MB repository without any issues by running hg clone ssh://demo@localhost:8022/repository_name against this proof-of-concept server app:

using System;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;
using Rebex.Net;
using Rebex.Net.Servers;

namespace Rebex.Samples
{
    public class MercurialServer
    {
        // path to mercurial
        private const string MercurialPath = @"c:\Program Files\TortoiseHg\hg.exe";

        // path to a directory that contains the repositories
        private const string RepositoryRoot = @"c:\data\repository";

        // buffer size for data proxy
        private const int BufferSize = 32 * 1024;

        // log writer
        private static readonly ILogWriter LogWriter = new ConsoleLogWriter(LogLevel.Debug);

        // user name
        private const string UserName = "demo";

        // password
        private const string Password = "password";

        // server port
        private const int ServerPort = 8022;

        // server key
        private const string ServerKey = @"-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----
";

        public static void Main()
        {
            var server = new FileServer();

            // enable logging
            server.LogWriter = LogWriter;

            // bind SSH shell subsystem to the specified port
            server.Bind(ServerPort, FileServerProtocol.Shell);

            // use the embedded private key for the sake of simplicity
            server.Keys.Add(new SshPrivateKey(new MemoryStream(Encoding.ASCII.GetBytes(ServerKey)), "password"));

            // only one user is supported for now
            server.Users.Add(UserName, Password);

            // custom command handler
            server.ShellCommand += (sender, e) =>
            {
                switch (e.Command)
                {
                    case "hg":
                        // intercept "hg" command
                        e.Action = RunMercurial;
                        break;
                    default:
                        // reject all other commands (optional)
                        e.WriteLine("Command not supported.");
                        e.ExitCode = 127;
                        break;
                }
            };

            server.Start();

            Console.WriteLine("Server is running, press any key to stop it.");
            Console.ReadKey(true);
        }

        public static int RunMercurial(string[] args, SshConsole console)
        {
            // start Mercurial

            var info = new ProcessStartInfo(MercurialPath, PrepareArguments(args));
            info.WorkingDirectory = RepositoryRoot;
            info.CreateNoWindow = true;
            info.UseShellExecute = false;
            info.RedirectStandardInput = true;
            info.RedirectStandardOutput = true;
            info.RedirectStandardError = true;

            var process = Process.Start(info);

            // proxy stdin/stdout/stderr

            Stream consoleInput = console.GetInputStream();
            Stream consoleOutput = console.GetOutputStream();
            Stream consoleError = console.GetErrorStream() ?? Stream.Null; // error stream is only available in terminal-less mode

            Stream processInput = process.StandardInput.BaseStream;
            Stream processOutput = process.StandardOutput.BaseStream;
            Stream processError = process.StandardError.BaseStream;

            CopyAllAsync("stdin", consoleInput, processInput);
            CopyAllAsync("stderr", processError, consoleError);
            CopyAllAsync("stdout", processOutput, consoleOutput);

            // wait for the process to end
            process.WaitForExit();

            // return the exit code
            return process.ExitCode;
        }

        private static string PrepareArguments(string[] args)
        {
            // TODO: This method is supposed to convert the argument array into a string,
            // but it is not yet implemented properly - if any of the arguments contains whitespaces or quotes,
            // this produces wrong results.

            // TODO: But if the users are only supposed to have SSH access to Mercurial repositories,
            // we should only allow "-R REPO_NAME serve --stdio" or its variants anyway.

            return string.Join("", args);
        }

        private static Task CopyAllAsync(string name, Stream input, Stream output)
        {
            // TODO: Error handling is missing.

            return Task.Run(() =>
            {
                byte[] buffer = new byte[BufferSize];
                while (true)
                {
                    int n = input.Read(buffer, 0, buffer.Length);
                    //Console.WriteLine("{0}: {1} bytes", name, n);
                    if (n == 0)
                    {
                        output.Close();
                        break;
                    }
                    output.Write(buffer, 0, n);
                    output.Flush();
                }
            });
        }

    }
}