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Modify the wpf to connect to the mcp server using the stdio method #694

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Modify the wpf to connect to the mcp server using the stdio method #694

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487adcc
We should check in advance whether we are using a console program. If…
Aug 11, 2025
8b0c55e
We should determine if it is a console program, and only set the enco…
Aug 11, 2025
ccf4340
Merge branch 'main' into main
xbo729 Aug 14, 2025
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29 changes: 18 additions & 11 deletions src/ModelContextProtocol.Core/Client/StdioClientTransport.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -156,20 +156,21 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
// up the encoding from Console.InputEncoding. As such, when not targeting .NET Core,
// we temporarily change Console.InputEncoding to no-BOM UTF-8 around the Process.Start
// call, to ensure it picks up the correct encoding.
#if NET
processStarted = process.Start();
#else
Comment on lines -159 to -161
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We should keep the simple #if NET (.NET Core) case which never sets Console.InputEncoding, so it cannot be the cause of your issues.


Encoding originalInputEncoding = Console.InputEncoding;
try
if (HasConsole())
{
Console.InputEncoding = StreamClientSessionTransport.NoBomUtf8Encoding;
processStarted = process.Start();
}
finally
{
Console.InputEncoding = originalInputEncoding;
try
{
Console.InputEncoding = StreamClientSessionTransport.NoBomUtf8Encoding;
}
finally
{
Console.InputEncoding = originalInputEncoding;
}
}
#endif

processStarted = process.Start();
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We need start the process before resetting back to the originalInputEncoding for it to matter.


if (!processStarted)
{
Expand Down Expand Up @@ -199,7 +200,13 @@ public async Task<ITransport> ConnectAsync(CancellationToken cancellationToken =
throw new IOException("Failed to connect transport.", ex);
}
}
[DllImport("kernel32.dll")]
private static extern IntPtr GetConsoleWindow();

private static bool HasConsole()
{
try { return GetConsoleWindow() != IntPtr.Zero; } catch { return false; }
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I'm very suspicious this is the best way to determine whether the Console.InputEncoding setter is going to throw a NotSupportedException.

If we're going to catch arbitrary exceptions anyway, it would be better to catch the NotSupportedException from the setter although I'm not sure that's the best approach either. I think #73 added this logic. I'm curious if @willibrandon or @stephentoub have alternatives.

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If we're going to catch arbitrary exceptions anyway, it would be better to catch the NotSupportedException from the setter

Yeah, I'd rather just catch/eat the exception from the actual operation being performed than have a separate IsXx method that does the exact same thing and that's then used as a guard. We're about to launch a whole process; I'm not particularly concerned at the overhead of an exception.

That said, I'm unclear about the originally stated problem. I just created a WPF app, set both Console.OutputEncoding and Console.InputEncoding, and it worked fine, no exceptions. The code for these properties in Console also just bails without exception for what I would have expected in these cases:
https://github.com/dotnet/runtime/blob/edb570cd9e75036b6c61b201a0a9a9f2301db276/src/libraries/System.Console/src/System/ConsolePal.Windows.cs#L135-L138

Can you share a repro of the issue?

}
internal static void DisposeProcess(
Process? process, bool processRunning, TimeSpan shutdownTimeout, string endpointName)
{
Expand Down