node-tools: say whose words a refused event is (hq issue 276)

"plex did not take radarr.download.completed: Unexpected end of JSON input"
read as the runtime failing to parse the bundle's answer. It was plex's own
handler error, relayed. A bundle's error answer is now a launch.Refused, and
the line says the handler answered an error, quotes it, names the event id
and the delay before the next offer; the runtime's own failures (no answer
in time, bundle exited) are said as before.

The rule, unchanged and now tested: any mesh/event answer that is not an
error takes the event, whatever its result says, including none.

node-tools/internal/launch/event_answer_test.go

@@ -0,0 +1,89 @@
+package launch
+
+import (
+	"encoding/json"
+	"errors"
+	"os"
+	"path/filepath"
+	"sync"
+	"testing"
+	"time"
+)
+
+// A bundle that answers `mesh/event` as $ANSWER says: an error, a result, or an answer with neither.
+const answeringBundle = `#!/bin/sh
+while IFS= read -r line; do
+  id=$(printf '%s' "$line" | sed -n 's/.*"id":\([0-9]*\)[,}].*/\1/p')
+  case "$line" in
+    *'"method":"initialize"'*) printf '{"jsonrpc":"2.0","id":%s,"result":{}}\n' "$id" ;;
+    *'"method":"tools/list"'*)
+      printf '{"jsonrpc":"2.0","id":%s,"result":{"tools":[]}}\n' "$id"
+      printf '{"jsonrpc":"2.0","id":"s1","method":"mesh/subscribe","params":{"pattern":"#"}}\n' ;;
+    *'"method":"mesh/event"'*)
+      case "$ANSWER" in
+        error) printf '{"jsonrpc":"2.0","id":%s,"error":{"code":-32000,"message":"Unexpected end of JSON input"}}\n' "$id" ;;
+        result) printf '{"jsonrpc":"2.0","id":%s,"result":{}}\n' "$id" ;;
+        bare) printf '{"jsonrpc":"2.0","id":%s}\n' "$id" ;;
+      esac ;;
+  esac
+done
+`
+
+type subscribing struct {
+	mu      sync.Mutex
+	deliver func(json.RawMessage) error
+}
+
+func (b *subscribing) Publish(json.RawMessage) error                          { return nil }
+func (b *subscribing) Ask(json.RawMessage) (json.RawMessage, error)           { return nil, nil }
+func (b *subscribing) State(string, json.RawMessage) (json.RawMessage, error) { return nil, nil }
+func (b *subscribing) Watch(json.RawMessage, func(json.RawMessage) error) (func(), error) {
+	return func() {}, nil
+}
+func (b *subscribing) Subscribe(d func(json.RawMessage) error) error {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	b.deliver = d
+	return nil
+}
+
+func deliverTo(t *testing.T, answer string) error {
+	t.Helper()
+	entry := filepath.Join(t.TempDir(), "bundle")
+	if err := os.WriteFile(entry, []byte(answeringBundle), 0o755); err != nil {
+		t.Fatal(err)
+	}
+	b := &subscribing{}
+	l, err := Start("plex", entry, append(os.Environ(), "ANSWER="+answer), b, t.Logf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(l.Stop)
+	for i := 0; ; i++ {
+		b.mu.Lock()
+		d := b.deliver
+		b.mu.Unlock()
+		if d != nil {
+			return d(json.RawMessage(`{"key":"radarr.download.completed","body":{"title":"x"}}`))
+		}
+		if i > 100 {
+			t.Fatal("the bundle never subscribed")
+		}
+		time.Sleep(20 * time.Millisecond)
+	}
+}
+
+// An event is taken by any answer that is not an error, and not taken by an error, which reaches the
+// runtime as the bundle's own words — not as something the runtime failed to read (hq issue 276).
+func TestAnEventIsTakenByAnyAnswerThatIsNotAnError(t *testing.T) {
+	for _, answer := range []string{"result", "bare"} {
+		if err := deliverTo(t, answer); err != nil {
+			t.Errorf("an answer %q did not take the event: %v", answer, err)
+		}
+	}
+	err := deliverTo(t, "error")
+	var refused *Refused
+	if !errors.As(err, &refused) || refused.Method != "mesh/event" || refused.Message != "Unexpected end of JSON input" {
+		t.Fatalf("an error answer was not the bundle's refusal of mesh/event: %#v", err)
+	}
+}

node-tools/internal/launch/launch.go

@@ -65,6 +65,17 @@ type Bus interface {
 // EventTimeout bounds how long a bundle has to handle one event before it is offered again.
 var EventTimeout = 2 * time.Minute
 
+// Refused is a bundle's error answer to what the runtime asked it: the bundle's own words, as opposed
+// to the runtime not reaching it (not running, exited, no answer in time). For `mesh/event` it is the
+// one way a bundle says it did not take an event: any answer that is not an error — `{}`, `null`, no
+// result at all — takes it (mesh-sdk, "Taking an event"; novox/hq issue 276).
+type Refused struct {
+	Method  string
+	Message string
+}
+
+func (r *Refused) Error() string { return r.Message }
+
 // Restart backoff: a bundle that exits is started again at once, then after growing pauses while it
 // keeps exiting, back to at once once it has run a while.
 var (
@@ -144,6 +155,7 @@ func Start(module, entry string, env []string, mesh Bus, logf func(string, ...an
 		if c == nil {
 			return errors.New(module + "'s bundle is not running to take its events")
 		}
+		// Taken unless the answer is an error; what a result says is not read (see Refused).
 		_, err := c.ask(module, "mesh/event", map[string]any{"envelope": envelope}, EventTimeout)
 		return err
 	}
@@ -528,7 +540,7 @@ func (c *child) ask(module, method string, params any, timeout time.Duration) (j
 			if msg == "" {
 				msg = "the bundle refused the request"
 			}
-			return nil, errors.New(msg)
+			return nil, &Refused{Method: method, Message: msg}
 		}
 		return m.Result, nil
 	case <-c.dead: