delivery: the grants part's grant keys and the source the assigner reads (a1; issue 774)

Why: the grants part writes grants.<module>.<fp> in shadow beside the controller's; the assigner switches source only when the lease is handed away.

go/buscompose/buscompose_test.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	"git.novox.be/novox/mesh-sdk/go/announce"
+	"git.novox.be/novox/mesh-sdk/go/delivery"
 	"github.com/nats-io/nats.go/jetstream"
 	"os"
 	"path/filepath"
@@ -431,6 +432,11 @@ func TestTheCopiedComposerComposesAsTheControllers(t *testing.T) {
 			if on, why := LeaseHandedAway([]byte(row.raw), row.found, row.err); on != row.on || why == "" {
 				t.Errorf("%s: on %v (%s), want %v", row.name, on, why, row.on)
 			}
+			// The assigner's grants source follows it: the grants part's bucket only for a handed-away lease (issue 774).
+			on, _ := LeaseHandedAway([]byte(row.raw), row.found, row.err)
+			if bucket, _ := delivery.GrantSource(on); (bucket == delivery.PartGrantsBucket) != row.on {
+				t.Errorf("%s: the grants source is %s", row.name, bucket)
+			}
 		}
 		announced := map[string]announce.States{ControllerSeat: ControllerAnnouncement("novox")}
 		for reader, want := range map[string]bool{VaultSeat: true, GrantsModule: true, "mesh-delivery-view": false} {

go/delivery/assigner_test.go

@@ -298,6 +298,25 @@ func TestControllerGrant(t *testing.T) {
 	if _, err := EncodeControllerGrant(ControllerGrant{Accounts: []string{""}}); err == nil {
 		t.Errorf("a grant naming an empty account was accepted")
 	}
+	// The grants part's keys are the controller's: the same key round-trips; the source is the part's bucket only for a
+	// handed-away lease (issue 774).
+	if pk, err := PartGrantKey("mesh-delivery-assigner", fp); err != nil || pk != key {
+		t.Errorf("PartGrantKey = %q, %v, want the controller's %q", pk, err, key)
+	}
+	if m, f, err := ParsePartGrantKey(key); err != nil || m != "mesh-delivery-assigner" || f != fp {
+		t.Errorf("ParsePartGrantKey = %q, %q, %v", m, f, err)
+	}
+	for _, c := range []struct {
+		away         bool
+		bucket, read string
+	}{
+		{false, "mesh-controller_grants", "mesh-controller.grants"},
+		{true, "mesh-grants_grants", "mesh-grants.grants"},
+	} {
+		if b, r := GrantSource(c.away); b != c.bucket || r != c.read {
+			t.Errorf("GrantSource(%v) = %q, %q, want %q, %q", c.away, b, r, c.bucket, c.read)
+		}
+	}
 	g := ControllerGrant{Accounts: []string{"ace.mesh-build-go", "shanks.mesh-mail.reader"}}
 	for _, c := range []struct {
 		g            ControllerGrant

go/delivery/grants.go

@@ -90,3 +90,39 @@ func (g ControllerGrant) NamesNode(node, module string) bool {
 	}
 	return false
 }
+
+// **The grants part's grants** (novox/hq ADR 0547 §4, §5, ADR 0561 §2, §6; issue 774). The grants part writes the same
+// keys, with the same value, into its own state `grants` (the bucket PartGrantsBucket), beside the controller's: first in
+// shadow, which nobody reads, so a tool can compare the two before anything switches. The assigner reads the part's keys
+// only once the controller's lease is handed away (GrantSource), and the controller's until then.
+const (
+	// PartGrantsState is the grants part's state of issued credentials by fingerprint, as its manifest names it.
+	PartGrantsState = "grants"
+	// PartGrantsBucket is that state's bucket, `<owner module>_<name>`.
+	PartGrantsBucket = "mesh-grants_" + PartGrantsState
+	// PartGrantsRead is that state as a reader names it in `reads`.
+	PartGrantsRead = "mesh-grants." + PartGrantsState
+	// PartGrantsHistory is the revisions the bucket keeps per key.
+	PartGrantsHistory = ControllerGrantsHistory
+)
+
+// PartGrantKey is the key, in PartGrantsBucket, of a module's credential issued for a fingerprint: the layout of the
+// controller's key (ControllerGrantKey), so a key of one is the key of the other and a compare is by key.
+func PartGrantKey(module, fingerprint string) (string, error) {
+	return ControllerGrantKey(module, fingerprint)
+}
+
+// ParsePartGrantKey is the inverse of PartGrantKey.
+func ParsePartGrantKey(key string) (module, fingerprint string, err error) {
+	return ParseControllerGrantKey(key)
+}
+
+// GrantSource names the bucket the assigner reads grants from, and the `reads` name that grants it: the grants part's
+// once the controller's lease is handed away (buscompose.LeaseHandedAway, which refuses every other value of the lease,
+// an unreadable one included), the controller's in every other case.
+func GrantSource(leaseHandedAway bool) (bucket, read string) {
+	if leaseHandedAway {
+		return PartGrantsBucket, PartGrantsRead
+	}
+	return ControllerGrantsBucket, "mesh-controller.grants"
+}