Failed to dial target host "localhost:8181": context deadline exceeded about grpcui HOT 3 CLOSED

I think the issue is that you may just wrapping the Connect handlers with h2c.NewHandler. If you instead wrap the root handler/mux for the server, then you would at least have gotten a 404 quickly instead of it timing out. When you say you removed the path prefix, I assume the result was h2c was indeed applied at the root.

This is necessary in order to properly support h2c, so the server will recognize and correctly handle the HTTP/2 preface. Otherwise, the server will decide the request is invalid and immediately hang up. The client doesn't know why the server hung up so treats it as a temporary error and just keeps re-trying until the connection timeout elapses. (This is closely related to fullstorydev/grpcurl#387, which mentions a possible improvement that could at least enable failing faster in these cases and providing a better error message to users.)

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I tried listening on a path with no prefixes and it's working now.

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That's exactly the case. Thank you very much for the clarification!

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