Go 1.27 goroutine leak profile (golang/go#74609): formats, HTTP, and a failing test. Run with GOEXPERIMENT=goroutineleakprofile

formats.go

// Goroutine leak profile, accepted for Go 1.27 (golang/go#74609).
// Run: GOEXPERIMENT=goroutineleakprofile go run formats.go
package main

import (
	"bytes"
	"fmt"
	"os"
	"runtime"
	"runtime/pprof"
)

func leakSend() {
	ch := make(chan int)
	go func() { ch <- 1 }() // nobody receives, the send blocks forever
}

func leakRange() {
	ch := make(chan int)
	go func() {
		for range ch { // ch is never closed, the range never ends
		}
	}()
}

func main() {
	leakSend()
	leakRange()
	runtime.Gosched() // let both goroutines reach their blocked state

	p := pprof.Lookup("goroutineleak")

	// Gotcha: Count() is 0 until a WriteTo runs the leak-detecting GC cycle.
	fmt.Println("Count() before WriteTo:", p.Count())

	var proto bytes.Buffer
	p.WriteTo(&proto, 0) // debug=0: gzipped pprof protobuf for `go tool pprof`
	fmt.Printf("debug=0: %d gzipped bytes\n", proto.Len())
	fmt.Println("Count() after WriteTo:", p.Count())

	fmt.Println("--- debug=1: leaked goroutines as text ---")
	p.WriteTo(os.Stdout, 1)

	fmt.Println("--- debug=2: full dump, leaked ones tagged (leaked) ---")
	p.WriteTo(os.Stdout, 2)
}

leak_test.go

// Fail a test on leaks the way uber-go/goleak does, but from the stdlib.
// Run: GOEXPERIMENT=goroutineleakprofile go test
package main

import (
	"bytes"
	"runtime"
	"runtime/pprof"
	"testing"
)

// verifyNone mirrors goleak.VerifyNone: fail the test on any leaked goroutine.
func verifyNone(t *testing.T) {
	var b bytes.Buffer
	p := pprof.Lookup("goroutineleak")
	p.WriteTo(&b, 1) // WriteTo runs detection; Count() reads 0 without it
	if p.Count() > 0 {
		t.Fatalf("leaked goroutines:\n%s", b.String())
	}
}

func TestRun(t *testing.T) {
	defer verifyNone(t) // like defer goleak.VerifyNone(t)

	ch := make(chan int)
	go func() { ch <- 1 }() // the code under test leaks a goroutine
	runtime.Gosched()
}

server.go

// Pull leaks from a running service over HTTP.
// Run:  GOEXPERIMENT=goroutineleakprofile go run server.go
// Then: curl 'localhost:6060/debug/pprof/goroutineleak?debug=1'
package main

import (
	"net/http"
	_ "net/http/pprof" // registers /debug/pprof/goroutineleak
)

func main() {
	ch := make(chan int)
	go func() { ch <- 1 }() // leak

	http.ListenAndServe("localhost:6060", nil)
}