PosixProcessFeatures.cs

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using Microsoft.Extensions.Logging;
using Mono.Unix;
using Mono.Unix.Native;
using System;
using System.Globalization;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Tgstation.Server.Host.IO;

namespace Tgstation.Server.Host.System
{
    sealed class PosixProcessFeatures : IProcessFeatures
    {
        readonly IIOManager ioManager;

        readonly ILogger<PosixProcessFeatures> logger;

        public PosixProcessFeatures(IIOManager ioManager, ILogger<PosixProcessFeatures> logger)
        {
            this.ioManager = ioManager ?? throw new ArgumentNullException(nameof(ioManager));
            this.logger = logger ?? throw new ArgumentNullException(nameof(logger));
        }

        public void ResumeProcess(global::System.Diagnostics.Process process)
        {
            try
            {
                var result = Syscall.kill(process.Id, Signum.SIGCONT);
                if (result != 0)
                    throw new UnixIOException(result);
                logger.LogTrace("Resumed PID {0}", process.Id);
            }
            catch (Exception e)
            {
                logger.LogError(e, "Failed to resume PID {0}!", process.Id);
                throw;
            }
        }

        public void SuspendProcess(global::System.Diagnostics.Process process)
        {
            try
            {
                var result = Syscall.kill(process.Id, Signum.SIGSTOP);
                if (result != 0)
                    throw new UnixIOException(result);
                logger.LogTrace("Resumed PID {0}", process.Id);
            }
            catch (Exception e)
            {
                logger.LogError(e, "Failed to suspend PID {0}!", process.Id);
                throw;
            }
        }

        public async Task<string> GetExecutingUsername(global::System.Diagnostics.Process process, CancellationToken cancellationToken)
        {
            if (process == null)
                throw new ArgumentNullException(nameof(process));

            // Need to read /proc/[pid]/status
            // http://man7.org/linux/man-pages/man5/proc.5.html
            // https://unix.stackexchange.com/questions/102676/why-is-uid-information-not-in-proc-x-stat
            var pid = process.Id;
            var statusFile = ioManager.ConcatPath("/proc", pid.ToString(CultureInfo.InvariantCulture), "status");
            var statusBytes = await ioManager.ReadAllBytes(statusFile, cancellationToken).ConfigureAwait(false);
            var statusText = Encoding.UTF8.GetString(statusBytes);
            var splits = statusText.Split('\n', StringSplitOptions.RemoveEmptyEntries);
            var entry = splits.FirstOrDefault(x => x.Trim().StartsWith("Uid:", StringComparison.Ordinal));
            if (entry == default)
                return "UNKNOWN";

            return entry
                .Substring(4)
                .Split(' ', StringSplitOptions.RemoveEmptyEntries)
                .FirstOrDefault(x => !String.IsNullOrWhiteSpace(x))
                ?? "UNPARSABLE";
        }
    }
}