Add ModelContextProtocol.Core package (#428)
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Stephen Halter
GitHub
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1 changed files with 239 additions and 94 deletions
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using Microsoft.Extensions.Logging;
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using Microsoft.Extensions.Logging.Abstractions;
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using ModelContextProtocol.Protocol;
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using System.Diagnostics;
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using System.Runtime.InteropServices;
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using System.Text;
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using System.Text.RegularExpressions;
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#pragma warning disable CS1998 // Async method lacks 'await' operators and will run synchronously
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namespace ModelContextProtocol.Client;
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/// <summary>
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/// Provides a <see cref="IClientTransport"/> implemented via "stdio" (standard input/output).
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/// </summary>
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/// <remarks>
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/// <para>
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/// This transport launches an external process and communicates with it through standard input and output streams.
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/// It's used to connect to MCP servers launched and hosted in child processes.
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/// </para>
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/// <para>
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/// The transport manages the entire lifecycle of the process: starting it with specified command-line arguments
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/// and environment variables, handling output, and properly terminating the process when the transport is closed.
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/// </para>
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/// </remarks>
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public sealed partial class StdioClientTransport : IClientTransport
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{
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private readonly StdioClientTransportOptions _options;
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private readonly ILoggerFactory? _loggerFactory;
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/// <summary>
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/// Initializes a new instance of the <see cref="StdioClientTransport"/> class.
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/// </summary>
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/// <param name="options">Configuration options for the transport, including the command to execute, arguments, working directory, and environment variables.</param>
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/// <param name="loggerFactory">Logger factory for creating loggers used for diagnostic output during transport operations.</param>
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public StdioClientTransport(StdioClientTransportOptions options, ILoggerFactory? loggerFactory = null)
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{
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Throw.IfNull(options);
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_options = options;
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_loggerFactory = loggerFactory;
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Name = options.Name ?? $"stdio-{Regex.Replace(Path.GetFileName(options.Command), @"[\s\.]+", "-")}";
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}
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/// <inheritdoc />
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public string Name { get; }
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/// <inheritdoc />
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public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken = default)
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{
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string endpointName = Name;
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Process? process = null;
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bool processStarted = false;
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string command = _options.Command;
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IList<string>? arguments = _options.Arguments;
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if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows) &&
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!string.Equals(Path.GetFileName(command), "cmd.exe", StringComparison.OrdinalIgnoreCase))
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{
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// On Windows, for stdio, we need to wrap non-shell commands with cmd.exe /c {command} (usually npx or uvicorn).
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// The stdio transport will not work correctly if the command is not run in a shell.
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arguments = arguments is null or [] ? ["/c", command] : ["/c", command, ..arguments];
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command = "cmd.exe";
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}
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ILogger logger = (ILogger?)_loggerFactory?.CreateLogger<StdioClientTransport>() ?? NullLogger.Instance;
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try
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{
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LogTransportConnecting(logger, endpointName);
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UTF8Encoding noBomUTF8 = new(encoderShouldEmitUTF8Identifier: false);
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ProcessStartInfo startInfo = new()
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{
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FileName = command,
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RedirectStandardInput = true,
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RedirectStandardOutput = true,
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RedirectStandardError = true,
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UseShellExecute = false,
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CreateNoWindow = true,
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WorkingDirectory = _options.WorkingDirectory ?? Environment.CurrentDirectory,
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StandardOutputEncoding = noBomUTF8,
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StandardErrorEncoding = noBomUTF8,
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#if NET
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StandardInputEncoding = noBomUTF8,
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#endif
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};
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if (arguments is not null)
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{
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#if NET
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foreach (string arg in arguments)
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{
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startInfo.ArgumentList.Add(arg);
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}
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#else
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StringBuilder argsBuilder = new();
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foreach (string arg in arguments)
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{
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PasteArguments.AppendArgument(argsBuilder, arg);
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}
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startInfo.Arguments = argsBuilder.ToString();
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#endif
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}
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if (_options.EnvironmentVariables != null)
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{
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foreach (var entry in _options.EnvironmentVariables)
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{
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startInfo.Environment[entry.Key] = entry.Value;
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}
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}
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if (logger.IsEnabled(LogLevel.Trace))
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{
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LogCreateProcessForTransportSensitive(logger, endpointName, _options.Command,
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startInfo.Arguments,
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string.Join(", ", startInfo.Environment.Select(kvp => $"{kvp.Key}={kvp.Value}")),
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startInfo.WorkingDirectory);
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}
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else
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{
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LogCreateProcessForTransport(logger, endpointName, _options.Command);
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}
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process = new() { StartInfo = startInfo };
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// Set up stderr handling. Log all stderr output, and keep the last
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// few lines in a rolling log for use in exceptions.
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const int MaxStderrLength = 10; // keep the last 10 lines of stderr
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Queue<string> stderrRollingLog = new(MaxStderrLength);
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process.ErrorDataReceived += (sender, args) =>
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{
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string? data = args.Data;
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if (data is not null)
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{
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lock (stderrRollingLog)
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{
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if (stderrRollingLog.Count >= MaxStderrLength)
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{
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stderrRollingLog.Dequeue();
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}
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stderrRollingLog.Enqueue(data);
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}
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LogReadStderr(logger, endpointName, data);
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}
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};
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// We need both stdin and stdout to use a no-BOM UTF-8 encoding. On .NET Core,
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// we can use ProcessStartInfo.StandardOutputEncoding/StandardInputEncoding, but
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// StandardInputEncoding doesn't exist on .NET Framework; instead, it always picks
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// up the encoding from Console.InputEncoding. As such, when not targeting .NET Core,
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// we temporarily change Console.InputEncoding to no-BOM UTF-8 around the Process.Start
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// call, to ensure it picks up the correct encoding.
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#if NET
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processStarted = process.Start();
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#else
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Encoding originalInputEncoding = Console.InputEncoding;
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try
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{
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Console.InputEncoding = noBomUTF8;
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processStarted = process.Start();
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}
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finally
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{
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Console.InputEncoding = originalInputEncoding;
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}
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#endif
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if (!processStarted)
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{
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LogTransportProcessStartFailed(logger, endpointName);
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throw new IOException("Failed to start MCP server process.");
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}
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LogTransportProcessStarted(logger, endpointName, process.Id);
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process.BeginErrorReadLine();
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return new StdioClientSessionTransport(_options, process, endpointName, stderrRollingLog, _loggerFactory);
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}
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catch (Exception ex)
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{
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LogTransportConnectFailed(logger, endpointName, ex);
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try
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{
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DisposeProcess(process, processStarted, _options.ShutdownTimeout, endpointName);
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}
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catch (Exception ex2)
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{
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LogTransportShutdownFailed(logger, endpointName, ex2);
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}
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throw new IOException("Failed to connect transport.", ex);
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}
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}
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internal static void DisposeProcess(
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Process? process, bool processRunning, TimeSpan shutdownTimeout, string endpointName)
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{
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if (process is not null)
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{
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try
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{
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processRunning = processRunning && !HasExited(process);
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if (processRunning)
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{
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// Wait for the process to exit.
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// Kill the while process tree because the process may spawn child processes
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// and Node.js does not kill its children when it exits properly.
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process.KillTree(shutdownTimeout);
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}
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}
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finally
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{
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process.Dispose();
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}
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}
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}
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/// <summary>Gets whether <paramref name="process"/> has exited.</summary>
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internal static bool HasExited(Process process)
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{
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try
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{
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return process.HasExited;
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}
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catch
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{
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return true;
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}
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}
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[LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} connecting.")]
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private static partial void LogTransportConnecting(ILogger logger, string endpointName);
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[LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} starting server process. Command: '{Command}'.")]
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private static partial void LogCreateProcessForTransport(ILogger logger, string endpointName, string command);
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[LoggerMessage(Level = LogLevel.Trace, Message = "{EndpointName} starting server process. Command: '{Command}', Arguments: {Arguments}, Environment: {Environment}, Working directory: {WorkingDirectory}.")]
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private static partial void LogCreateProcessForTransportSensitive(ILogger logger, string endpointName, string command, string? arguments, string environment, string workingDirectory);
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[LoggerMessage(Level = LogLevel.Warning, Message = "{EndpointName} failed to start server process.")]
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private static partial void LogTransportProcessStartFailed(ILogger logger, string endpointName);
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[LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} received stderr log: '{Data}'.")]
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private static partial void LogReadStderr(ILogger logger, string endpointName, string data);
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[LoggerMessage(Level = LogLevel.Information, Message = "{EndpointName} started server process with PID {ProcessId}.")]
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private static partial void LogTransportProcessStarted(ILogger logger, string endpointName, int processId);
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[LoggerMessage(Level = LogLevel.Warning, Message = "{EndpointName} connect failed.")]
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private static partial void LogTransportConnectFailed(ILogger logger, string endpointName, Exception exception);
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[LoggerMessage(Level = LogLevel.Warning, Message = "{EndpointName} shutdown failed.")]
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private static partial void LogTransportShutdownFailed(ILogger logger, string endpointName, Exception exception);
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}
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