Use h2c from x/net to handle h2c requests

Co-authored-by: Mathieu Lonjaret <mathieu.lonjaret@gmail.com>

vendor/golang.org/x/net/trace/trace.go

@@ -64,12 +64,14 @@ package trace // import "golang.org/x/net/trace"
 
 import (
 	"bytes"
+	"context"
 	"fmt"
 	"html/template"
 	"io"
 	"log"
 	"net"
 	"net/http"
+	"net/url"
 	"runtime"
 	"sort"
 	"strconv"
@@ -84,6 +86,12 @@ import (
 // FOR DEBUGGING ONLY. This will slow down the program.
 var DebugUseAfterFinish = false
 
+// HTTP ServeMux paths.
+const (
+	debugRequestsPath = "/debug/requests"
+	debugEventsPath   = "/debug/events"
+)
+
 // AuthRequest determines whether a specific request is permitted to load the
 // /debug/requests or /debug/events pages.
 //
@@ -110,10 +118,29 @@ var AuthRequest = func(req *http.Request) (any, sensitive bool) {
 }
 
 func init() {
+	_, pat := http.DefaultServeMux.Handler(&http.Request{URL: &url.URL{Path: debugRequestsPath}})
+	if pat == debugRequestsPath {
+		panic("/debug/requests is already registered. You may have two independent copies of " +
+			"golang.org/x/net/trace in your binary, trying to maintain separate state. This may " +
+			"involve a vendored copy of golang.org/x/net/trace.")
+	}
+
 	// TODO(jbd): Serve Traces from /debug/traces in the future?
 	// There is no requirement for a request to be present to have traces.
-	http.HandleFunc("/debug/requests", Traces)
-	http.HandleFunc("/debug/events", Events)
+	http.HandleFunc(debugRequestsPath, Traces)
+	http.HandleFunc(debugEventsPath, Events)
+}
+
+// NewContext returns a copy of the parent context
+// and associates it with a Trace.
+func NewContext(ctx context.Context, tr Trace) context.Context {
+	return context.WithValue(ctx, contextKey, tr)
+}
+
+// FromContext returns the Trace bound to the context, if any.
+func FromContext(ctx context.Context) (tr Trace, ok bool) {
+	tr, ok = ctx.Value(contextKey).(Trace)
+	return
 }
 
 // Traces responds with traces from the program.