Configure hosted stdio servers to log to stderr (#173)

* Configure hosted stdio servers to log to stderr

* Fix newline

* Use CreateApplicationBuilder where possible

* Address PR feedback

Author: halter73

README.md

@@ -83,13 +83,24 @@ It includes a simple echo tool as an example (this is included in the same file
 the employed overload of `WithTools` examines the current assembly for classes with the `McpServerToolType` attribute, and registers all methods with the
 `McpTool` attribute as tools.)
 
+```
+dotnet add package ModelContextProtocol --prerelease
+dotnet add package Microsoft.Extensions.Hosting
+```
+
 ```csharp
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
 using ModelContextProtocol.Server;
 using System.ComponentModel;
 
-var builder = Host.CreateEmptyApplicationBuilder(settings: null);
+var builder = Host.CreateApplicationBuilder(args);
+builder.Logging.AddConsole(consoleLogOptions =>
+{
+    // Configure all logs to go to stderr
+    consoleLogOptions.LogToStandardErrorThreshold = LogLevel.Trace;
+});
 builder.Services
     .AddMcpServer()
     .WithStdioServerTransport()

samples/QuickstartClient/Program.cs

@@ -5,7 +5,7 @@
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol.Transport;
 
-var builder = Host.CreateEmptyApplicationBuilder(settings: null);
+var builder = Host.CreateApplicationBuilder(args);
 
 builder.Configuration
     .AddEnvironmentVariables()

samples/QuickstartWeatherServer/Program.cs

@@ -1,13 +1,19 @@
 using Microsoft.Extensions.DependencyInjection;
 using Microsoft.Extensions.Hosting;
+using Microsoft.Extensions.Logging;
 using System.Net.Http.Headers;
 
-var builder = Host.CreateEmptyApplicationBuilder(settings: null);
+var builder = Host.CreateApplicationBuilder(args);
 
 builder.Services.AddMcpServer()
     .WithStdioServerTransport()
     .WithToolsFromAssembly();
 
+builder.Logging.AddConsole(options =>
+{
+    options.LogToStandardErrorThreshold = LogLevel.Trace;
+});
+
 builder.Services.AddSingleton(_ =>
 {
     var client = new HttpClient() { BaseAddress = new Uri("https://api.weather.gov") };

src/ModelContextProtocol/Logging/Log.cs

@@ -98,8 +98,8 @@ internal static partial class Log
     [LoggerMessage(Level = LogLevel.Information, Message = "Creating process for transport for {endpointName} with command {command}, arguments {arguments}, environment {environment}, working directory {workingDirectory}, shutdown timeout {shutdownTimeout}")]
     internal static partial void CreateProcessForTransport(this ILogger logger, string endpointName, string command, string? arguments, string environment, string workingDirectory, string shutdownTimeout);
 
-    [LoggerMessage(Level = LogLevel.Error, Message = "Transport for {endpointName} error: {data}")]
-    internal static partial void TransportError(this ILogger logger, string endpointName, string data);
+    [LoggerMessage(Level = LogLevel.Information, Message = "Transport for {endpointName} received stderr log: {data}")]
+    internal static partial void ReadStderr(this ILogger logger, string endpointName, string data);
 
     [LoggerMessage(Level = LogLevel.Information, Message = "Transport process start failed for {endpointName}")]
     internal static partial void TransportProcessStartFailed(this ILogger logger, string endpointName);

src/ModelContextProtocol/Protocol/Transport/StdioClientTransport.cs

@@ -85,7 +85,7 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
             process = new() { StartInfo = startInfo };
 
             // Set up error logging
-            process.ErrorDataReceived += (sender, args) => logger.TransportError(endpointName, args.Data ?? "(no data)");
+            process.ErrorDataReceived += (sender, args) => logger.ReadStderr(endpointName, args.Data ?? "(no data)");
 
             // We need both stdin and stdout to use a no-BOM UTF-8 encoding. On .NET Core,
             // we can use ProcessStartInfo.StandardOutputEncoding/StandardInputEncoding, but

tests/ModelContextProtocol.TestServer/Program.cs

@@ -24,6 +24,10 @@ private static ILoggerFactory CreateLoggerFactory()
 
         return LoggerFactory.Create(builder =>
         {
+            builder.AddConsole(options =>
+            {
+                options.LogToStandardErrorThreshold = LogLevel.Trace;
+            });
             builder.AddSerilog();
         });
     }