A node's own want names no composition from the second milestone: the node composes its own (issue 1126, ADR 0547 §2)

go/delivery/assigner.go

@@ -322,10 +322,13 @@ type NodeWant struct {
 	Words    string `json:"words,omitempty"`
 }
 
-// EncodeNodeWant is w as JSON at Version; it refuses a digest not of the sha256 form.
+// EncodeNodeWant is w as JSON at Version; it refuses a digest not of the sha256 form. From ADR 0547's second milestone
+// the node composes its own composition (§2) and its own want names none: an empty Composed is that want.
 func EncodeNodeWant(w NodeWant) ([]byte, error) {
-	if err := checkDigest(w.Composed, "the node's own want's composition digest"); err != nil {
-		return nil, err
+	if w.Composed != "" {
+		if err := checkDigest(w.Composed, "the node's own want's composition digest"); err != nil {
+			return nil, err
+		}
 	}
 	w.V = Version
 	return json.Marshal(w)
@@ -343,8 +346,10 @@ func DecodeNodeWant(data []byte) (NodeWant, error) {
 	if err := d.Decode(&w); err != nil {
 		return NodeWant{}, fmt.Errorf("delivery: a node's own want does not fit its shape: %w", err)
 	}
-	if err := checkDigest(w.Composed, "the node's own want's composition digest"); err != nil {
-		return NodeWant{}, err
+	if w.Composed != "" {
+		if err := checkDigest(w.Composed, "the node's own want's composition digest"); err != nil {
+			return NodeWant{}, err
+		}
 	}
 	return w, nil
 }

go/delivery/want_composed_test.go

@@ -90,11 +90,17 @@ func TestTheNodesOwnWant(t *testing.T) {
 	if err != nil || back != w {
 		t.Errorf("node want came back %+v, %v", back, err)
 	}
-	for _, bad := range []NodeWant{{}, {Composed: "sha256:1"}} {
+	for _, bad := range []NodeWant{{Composed: "sha256:1"}} {
 		if _, err := EncodeNodeWant(bad); err == nil {
 			t.Errorf("EncodeNodeWant(%+v) accepted", bad)
 		}
 	}
+	// ADR 0547 §2 (issue 1126): from the second milestone the node composes its own composition, and its want names none.
+	if raw, err := EncodeNodeWant(NodeWant{Words: "the node composes its own"}); err != nil {
+		t.Errorf("a node want naming no composition: %v", err)
+	} else if back, err := DecodeNodeWant(raw); err != nil || back.Composed != "" {
+		t.Errorf("a node want naming no composition came back %+v, %v", back, err)
+	}
 	if _, err := DecodeNodeWant([]byte(`{"v":1,"composed":"` + hashOf('2') + `","fp":"` + fp2of('a') + `"}`)); err == nil {
 		t.Errorf("a node want naming a fingerprint was read")
 	}