Handle errors from serving perfetto backend

Warn once if port 9001 is not avialable.

Remove the error return now that errors are handled and logged. This
removes one errcheckwarning where Serve is called as a goroutine.

runtime/perfetto/db.go

@@ -27,8 +27,10 @@ import (
  "fmt"
  "net"
  "net/http"
+ "os"
  "path/filepath"
  "strconv"
+ "sync"
  "time"
 
  "github.com/ServiceWeaver/weaver/internal/files"
@@ -487,7 +489,7 @@ func (d *DB) execDB(ctx context.Context, query string, args ...any) (sql.Result,
 //
 // Perfetto UI requires that the server runs on the local port 9001. For that
 // reason, this method will block until port 9001 becomes available.
-func (d *DB) Serve(ctx context.Context) error {
+func (d *DB) Serve(ctx context.Context) {
  mux := http.NewServeMux()
  mux.HandleFunc("/status", func(w http.ResponseWriter, _ *http.Request) {
  w.Write([]byte("OK")) //nolint:errcheck // response write error
@@ -513,16 +515,28 @@ func (d *DB) Serve(ctx context.Context) error {
  })
  server := http.Server{Handler: mux}
  ticker := time.NewTicker(time.Second)
+ var warnOnce sync.Once
  for {
  select {
  case <-ticker.C:
  lis, err := net.Listen("tcp", "localhost:9001")
- if err == nil {
- ticker.Stop()
- return server.Serve(lis)
+ if err != nil {
+ warnOnce.Do(func() {
+ fmt.Fprintf(os.Stderr, "Perfetto server failed to listen on port 9001: %v\n", err)
+ fmt.Fprintf(os.Stderr, "Perfetto server will retry until port 9001 is available\n")
+ })
+ continue
  }
+
+ ticker.Stop()
+ err = server.Serve(lis)
+ if !errors.Is(err, http.ErrServerClosed) {
+ fmt.Fprintf(os.Stderr, "Failed to serve perfetto backend: %v\n", err)
+ }
+ return
+
  case <-ctx.Done():
- return ctx.Err()
+ return
  }
  }
 }