test(gemini): verify cancel goroutine exits when Download returns

internal/protocol/gemini/gemini_test.go

@@ -16,6 +16,7 @@ import (
 	"net"
 	"net/url"
 	"os"
+	"runtime"
 	"strconv"
 	"strings"
 	"testing"
@@ -450,3 +451,81 @@ func TestSaveGeminiResumeNoop(t *testing.T) {
 		// Should not panic.
 	})
 }
+
+// TestGeminiCancelGoroutineExits verifies that the ctx-cancellation
+// goroutine spawned by Gemini downloadWithRedirects does not outlive
+// Download itself. The goroutine used to wait forever on <-ctx.Done()
+// when the parent context was never cancelled; the done-channel bound
+// must let every iteration return to the runtime goroutine pool.
+func TestGeminiCancelGoroutineExits(t *testing.T) {
+	cfg := testTLSConfig()
+	listener, err := tls.Listen("tcp", "127.0.0.1:0", cfg)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer listener.Close()
+	port := listener.Addr().(*net.TCPAddr).Port
+
+	go func() {
+		for {
+			conn, lerr := listener.Accept()
+			if lerr != nil {
+				return
+			}
+			go func(c net.Conn) {
+				defer c.Close()
+				r := bufio.NewReader(c)
+				r.ReadString('\n')
+				// Brief response that Gemini Download can chew
+				// through quickly, spawning the cancellation
+				// goroutine and returning. The goroutine must
+				// exit via the done channel on return.
+				c.Write([]byte("20 application/octet-stream\r\n"))
+				c.Write([]byte("hi"))
+			}(conn)
+		}
+	}()
+
+	// Warm up to settle the runtime goroutine pool (timer, GC, etc.).
+	proto := NewProtocol()
+	proto.TLSInsecure = true
+	u, _ := url.Parse("gemini://127.0.0.1:" + strconv.Itoa(port) + "/warmup")
+	if _, dlErr := proto.Download(context.Background(), &core.DownloadRequest{
+		URL:    u,
+		Writer: &stringWriter{&strings.Builder{}},
+	}); dlErr != nil {
+		t.Fatalf("warmup: %v", dlErr)
+	}
+
+	runtime.GC()
+	time.Sleep(50 * time.Millisecond)
+	runtime.GC()
+	baseline := runtime.NumGoroutine()
+
+	const iterations = 50
+	for i := 0; i < iterations; i++ {
+		u, _ := url.Parse("gemini://127.0.0.1:" + strconv.Itoa(port) + "/x")
+		if _, dlErr := proto.Download(context.Background(), &core.DownloadRequest{
+			URL:    u,
+			Writer: &stringWriter{&strings.Builder{}},
+		}); dlErr != nil {
+			t.Fatalf("download %d: %v", i, dlErr)
+		}
+	}
+
+	// After every successful Download returns, its cancellation
+	// goroutine must have exited. Allow a brief settle window for
+	// the runtime to reclaim them.
+	deadline := time.Now().Add(2 * time.Second)
+	for time.Now().Before(deadline) {
+		runtime.GC()
+		time.Sleep(50 * time.Millisecond)
+		// One tolerance for any incidental stdlib goroutine that
+		// the Go runtime occasionally spins up between calls.
+		if runtime.NumGoroutine() <= baseline+1 {
+			return
+		}
+	}
+	t.Fatalf("goroutine leak: baseline=%d, after %d downloads = %d",
+		baseline, iterations, runtime.NumGoroutine())
+}