Help with echo server

[anderspitman]

I think I have some fundamental misunderstandings about how to use this library. I'm trying to get a simple echo server running. The following is a self-contained example (uses certmagic to automatically get Let's Encrypt certs):

package main

import (
	"context"
	"crypto/tls"
	"fmt"
	"io"
	"log"
	"net/http"

	"github.com/caddyserver/certmagic"
	"github.com/quic-go/quic-go"
	"github.com/quic-go/quic-go/http3"
	"github.com/quic-go/webtransport-go"
)

func main() {
	go runServer()
	runClient()
}

func runServer() {

	tlsConfig := getTlsConfig()

	ctx := context.Background()

	wtServer := webtransport.Server{
		H3: http3.Server{
			Addr:       ":443",
			TLSConfig:  tlsConfig,
			QuicConfig: &quic.Config{},
		},
	}

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {

		wtSession, err := wtServer.Upgrade(w, r)
		if err != nil {
			fmt.Println(err)
			return
		}

		stream, err := wtSession.AcceptStream(ctx)
		if err != nil {
			fmt.Println(err)
			return
		}

		bytes, err := io.ReadAll(stream)
		if err != nil {
			fmt.Println(err)
			return
		}

		fmt.Println(string(bytes))

		stream.Write(bytes)

		err = stream.Close()
		if err != nil {
			fmt.Println(err)
			return
		}
	})

	log.Fatal(wtServer.ListenAndServe())
}

func runClient() {
	ctx := context.Background()

	var d webtransport.Dialer
	_, wtSession, err := d.Dial(ctx, "https://example.com", nil)
	if err != nil {
		panic(err)
	}

	stream, err := wtSession.OpenStreamSync(ctx)
	if err != nil {
		panic(err)
	}

	stream.Write([]byte("Hi there"))
	stream.CancelWrite(0)

	bytes, err := io.ReadAll(stream)
	if err != nil {
		panic(err)
	}

	fmt.Println(string(bytes))
}

func getTlsConfig() *tls.Config {
	certmagic.DefaultACME.DisableHTTPChallenge = true
	certmagic.DefaultACME.Agreed = true

	certmagic.Default.OnDemand = &certmagic.OnDemandConfig{
		DecisionFunc: func(ctx context.Context, name string) error {
			return nil
		},
	}
	certConfig := certmagic.NewDefault()

	tlsConfig := &tls.Config{
		GetCertificate: certConfig.GetCertificate,
		NextProtos:     []string{"h3", "http/1.1", "acme-tls/1"},
	}

	return tlsConfig
}

I'm never seeing anything printed, either on the client or server side. Interestingly, if I sleep for a second before stream.CancelWrite(0) then I get an error log: "stream canceled with error code 0". I think I'm incorrectly assuming that EOF will be sent after a call to CancelWrite. Is that not the case? If not, is there a correct way to signal end of stream from the writer side?

[anderspitman]

I believe I've solved the problem. My misunderstanding is that I was assuming CancelWrite() was the correct way to close the send side of a stream. But according to the go-quic docs here, calling Close is the way to do it. I had assumed that would also close the receive side, but that's not the case. After sawpping CancelWrite for Close my code appears to be working.

[anderspitman]

@marten-seemann would you be interested in a PR that adds an examples directory and a simple echo server example, or is that not something you want in the repo?

Looks like I'm not the first to struggle with this: #103

[marten-seemann]

Sure, sounds like a good idea! Want to create a PR?

[anderspitman]

Submitted #122