Point standard output at standard error while a one-head delivery check runs, so its answer is the only JSON (issue 1311)

cmd/mesh-controller/delivery.go

@@ -902,16 +902,14 @@ func deliveryCommand(ctx context.Context, args []string) error {
 		if *group == "" && len(members) == 1 {
 			// One head, checked again as the forge's announcement would have it (a recheck): the controller's
 			// own path for a pull request, run because the delivery's owner asked.
-			// Its prose goes to standard error: standard output is the answer's JSON alone, or the seat verb
+			return recheckOneHead(members[0].ID, answer, func() (string, error) {
-			// reads no answer from it (novox/hq issue 1311).
+				var asked string
-			var asked string
+				err := sayingOnTheBus(ctx, inv, func() (err error) {
-			if err := sayingOnTheBus(ctx, inv, func() (err error) {
+					asked, err = (following{open: open, oneShot: true}).pullUpdated(ctx, members[0].pull(), os.Stderr)
-				asked, err = (following{open: open, oneShot: true}).pullUpdated(ctx, members[0].pull(), os.Stderr)
+					return err
-				return err
+				})
-			}); err != nil {
+				return asked, err
-				return err
+			})
-			}
-			return answer(recheckAnswer(asked, members[0].ID))
 		}
 		if *group == "" || len(members) < 2 {
 			return errors.New("delivery check --group <id> --members <json> (two heads or more), or --members <one head>")
@@ -1388,3 +1386,19 @@ func overNATS(conn *nats.Conn) (link.Bus, error) {
 func recheckAnswer(asked, member string) map[string]any {
 	return map[string]any{"asked": asked, "rechecked": member}
 }
+
+// recheckOneHead runs a one-head `delivery check` and answers it as data. Standard output is the answer's JSON alone,
+// or the seat verb reads no answer from it (novox/hq issue 1311): while the check runs, whatever it prints to standard
+// output (the controller's own path prints its prose there, as do the stores it reads) goes to standard error.
+func recheckOneHead(member string, answer func(any) error, ask func() (string, error)) error {
+	real := os.Stdout
+	os.Stdout = os.Stderr
+	asked, err := func() (string, error) {
+		defer func() { os.Stdout = real }()
+		return ask()
+	}()
+	if err != nil {
+		return err
+	}
+	return answer(recheckAnswer(asked, member))
+}

cmd/mesh-controller/delivery_check_answer_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"context"
 	"encoding/json"
+	"fmt"
+	"os"
 	"strings"
 	"testing"
 
@@ -44,3 +46,40 @@ func TestSayCheckedWritesTheSameLineToItsWriter(t *testing.T) {
 		t.Fatalf("sayChecked said %q; want %q", w.String(), want)
 	}
 }
+
+// Whatever the check prints to standard output while it runs (checks.go namedForTheCheck, the inventory's pointer
+// repair) must not reach the answer's standard output: it is exactly one JSON document (novox/hq issue 1311).
+func TestOneHeadRecheckLeavesStandardOutputTheAnswerAlone(t *testing.T) {
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	e, ew, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	realOut, realErr := os.Stdout, os.Stderr
+	os.Stdout, os.Stderr = w, ew
+	runErr := recheckOneHead("novox/x@abc", func(v any) error { return json.NewEncoder(os.Stdout).Encode(v) },
+		func() (string, error) {
+			fmt.Println("  the earlier checks' builds could not be read, so the check builds")
+			fmt.Fprintln(os.Stdout, "repaired a pointer")
+			return "check-42", nil
+		})
+	os.Stdout, os.Stderr = realOut, realErr
+	w.Close()
+	ew.Close()
+	if runErr != nil {
+		t.Fatal(runErr)
+	}
+	var out, errOut bytes.Buffer
+	_, _ = out.ReadFrom(r)
+	_, _ = errOut.ReadFrom(e)
+	var doc map[string]any
+	if err := json.Unmarshal(out.Bytes(), &doc); err != nil || doc["asked"] != "check-42" || doc["rechecked"] != "novox/x@abc" {
+		t.Fatalf("standard output %q is not the answer alone (%v)", out.String(), err)
+	}
+	if !strings.Contains(errOut.String(), "repaired a pointer") {
+		t.Fatalf("the prose should be on standard error: %q", errOut.String())
+	}
+}