Add some extra checks on cheap heartbeats

ledger/apply/heartbeat.go

@@ -42,11 +42,24 @@ func Heartbeat(hb transactions.HeartbeatTxnFields, header transactions.Header, b
 		if header.Fee.Raw > 0 {
 			kind = "cheap"
 		}
+
+		// These first checks are a little draconian. The idea is not let these
+		// free transactions do anything except their exact intended purpose.
+		if len(header.Note) > 0 {
+			return fmt.Errorf("%s heartbeat is not allowed to have a note", kind)
+		}
+		if header.Lease != [32]byte{} {
+			return fmt.Errorf("%s heartbeat is not allowed to have a lease", kind)
+		}
+		if !header.RekeyTo.IsZero() {
+			return fmt.Errorf("%s heartbeat is not allowed to rekey", kind)
+		}
+
 		if account.Status != basics.Online {
 			return fmt.Errorf("%s heartbeat is not allowed for %s %+v", kind, account.Status, hb.HbAddress)
 		}
 		if !account.IncentiveEligible {
-			return fmt.Errorf("%s heartbeat is not allowed for ineligible %+v", kind, hb.HbAddress)
+			return fmt.Errorf("%s heartbeat is not allowed when not IncentiveEligible %+v", kind, hb.HbAddress)
 		}
 		ch := FindChallenge(proto.Payouts, round, provider, ChRisky)
 		if ch.round == 0 {

ledger/apply/heartbeat_test.go

@@ -110,22 +110,28 @@ func TestCheapRules(t *testing.T) {
 		addrStart        byte
 		status           basics.Status
 		incentiveEligble bool
+		note             []byte
+		lease            [32]byte
+		rekey            [32]byte
 		err              string
 	}
-
+	empty := [32]byte{}
 	// Grace period is 200. For the second half of the grace period (1101-1200),
 	// the heartbeat is free for online, incentive eligible, challenged accounts.
 	cases := []tcase{
 		// test of range
-		{1100, 0x01, basics.Online, true, "no challenge"},
-		{1101, 0x01, basics.Online, true, ""},
-		{1200, 0x01, basics.Online, true, ""},
-		{1201, 0x01, basics.Online, true, "no challenge"},
+		{1100, 0x01, basics.Online, true, nil, empty, empty, "no challenge"},
+		{1101, 0x01, basics.Online, true, nil, empty, empty, ""},
+		{1200, 0x01, basics.Online, true, nil, empty, empty, ""},
+		{1201, 0x01, basics.Online, true, nil, empty, empty, "no challenge"},
 
 		// test of the other requirements
-		{1101, 0xf1, basics.Online, true, "not challenged by"},
-		{1101, 0x01, basics.Offline, true, "not allowed for Offline"},
-		{1101, 0x01, basics.Online, false, "not allowed for ineligible"},
+		{1101, 0x01, basics.Online, true, []byte("note"), empty, empty, "not allowed to have a note"},
+		{1101, 0x01, basics.Online, true, nil, [32]byte{'l', 'e', 'a', 's', 'e'}, empty, "not allowed to have a lease"},
+		{1101, 0x01, basics.Online, true, nil, empty, [32]byte{'r', 'e', 'k', 'e', 'y'}, "not allowed to rekey"},
+		{1101, 0xf1, basics.Online, true, nil, empty, empty, "not challenged by"},
+		{1101, 0x01, basics.Offline, true, nil, empty, empty, "not allowed for Offline"},
+		{1101, 0x01, basics.Online, false, nil, empty, empty, "not allowed when not IncentiveEligible"},
 	}
 	for _, tc := range cases {
 		const keyDilution = 777
@@ -164,6 +170,9 @@ func TestCheapRules(t *testing.T) {
 			Fee:        basics.MicroAlgos{Raw: 1},
 			FirstValid: tc.rnd - 10,
 			LastValid:  tc.rnd + 10,
+			Lease:      tc.lease,
+			Note:       tc.note,
+			RekeyTo:    tc.rekey,
 			HbAddress:  voter,
 			HbProof:    otss.Sign(id, seed),
 			HbSeed:     seed,