SlunkCrypt/gui/Process/PasswordGen.cs

/******************************************************************************/
/* SlunkCrypt, by LoRd_MuldeR <MuldeR2@GMX.de>                                */
/* This work has been released under the CC0 1.0 Universal license!           */
/******************************************************************************/

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.IO;
using System.Text;
using System.Threading.Tasks;

namespace com.muldersoft.slunkcrypt.gui.process
{
    public static class PasswordGen
    {
        private static readonly TimeSpan TIMEOUT_MSEC = TimeSpan.FromSeconds(90);

        private const string COMMAND_PASSWRD = "-p {0:D}";

        // =============================================================================
        // Exception classes
        // =============================================================================

        public class GenerationFailedException : IOException
        {
            public GenerationFailedException(string message, Exception innerException) : base(message, innerException)
            {
            }
        }

        // =============================================================================
        // Public methods
        // =============================================================================

        public static async Task<string> GeneratePassword(int length)
        {
            using (FileStream executableFile = ExecutableHelper.GetExecutableFile())
            {
                try
                {
                    string password = await StartProcess(executableFile, length);
                    if (IsWeakPassword(password))
                    {
                        throw new InvalidDataException("The generated password string is invalid!");
                    }
                    return password;
                }
                catch (Exception e)
                {
                    throw new GenerationFailedException("Failed to generate password string!", e);
                }
            }
        }

        public static bool IsWeakPassword(string password)
        {
            int flags = 0;
            if (!string.IsNullOrEmpty(password))
            {
                foreach (char c in password)
                {
                    if (char.IsLetter(c))
                    {
                        flags |= char.IsUpper(c) ? 0x2 : 0x1;
                    }
                    else
                    {
                        flags |= char.IsDigit(c) ? 0x8 : 0x4;
                    }
                }
            }
            return (flags != 0xF);
        }

        // =============================================================================
        // Internal methods
        // =============================================================================

        private static async Task<string> StartProcess(FileStream executableFile, int length)
        {
            using (Process process = new Process())
            {
                process.StartInfo.UseShellExecute = false;
                process.StartInfo.CreateNoWindow = true;
                process.StartInfo.RedirectStandardOutput = true;
                process.StartInfo.StandardOutputEncoding = Encoding.UTF8;
                process.StartInfo.FileName = executableFile.Name;
                process.StartInfo.Arguments = string.Format(COMMAND_PASSWRD, length);
                process.Start();

                Stack<string> outputLines = await WaitForExit(process, TIMEOUT_MSEC);

                if (process.ExitCode == 0)
                {
                    while (outputLines.Count > 0)
                    {
                        string line = outputLines.Pop();
                        if (line.Length >= length)
                        {
                            return line;
                        }
                    }
                }
                return string.Empty;
            }
        }

        private static async Task<Stack<string>> WaitForExit(Process process, TimeSpan timeout)
        {
            Task<Stack<string>> readTask;
            await Task.WhenAny(readTask = Task.Run(() => ReadOutput(process)), Task.Delay(timeout));
            if (!process.WaitForExit(125))
            {
                process.Kill();
                process.WaitForExit();
            }
            return await readTask;
        }

        private static Stack<string> ReadOutput(Process process)
        {
            Stack<string> result = new Stack<string>();
            using (StreamReader reader = process.StandardOutput)
            {
                string line;
                while ((line = reader.ReadLine()) != null)
                {
                    line = line.Trim();
                    if (line.Length != 0)
                    {
                        result.Push(line.Trim());
                    }
                }
            }
            return result;
        }
    }
}