feat: add message sequence number to comms protocol

Author: FUDCo

packages/SwingSet/src/vats/comms/delivery.js

@@ -5,7 +5,7 @@ import { parseLocalSlot, insistLocalType } from './parseLocalSlots';
 import { makeUndeliverableError } from '../../makeUndeliverableError';
 import { insistCapData } from '../../capdata';
 import { insistRemoteType } from './parseRemoteSlot';
-import { insistRemoteID } from './remote';
+import { insistRemoteID, getRemote } from './remote';
 
 const UNDEFINED = harden({
   body: JSON.stringify({ '@qclass': 'undefined' }),
@@ -132,14 +132,27 @@ export function makeDeliveryKit(state, syscall, transmit, clistKit, stateKit) {
       // changed to assert here that the result parameter is null or undefined.
       syscall.resolve([[result, false, UNDEFINED]]);
     }
-    const command = message.split(':', 1)[0];
+    // The message is preceded by an optional sequence number:
+    // `$seqnum:$actualMessage` or `:actualMessage`
+    const colon = message.indexOf(':');
+    assert(colon >= 0, X`received message ${message} lacks seqNum delimiter`);
+    const seqNum = message.substring(0, colon);
+    const remote = getRemote(state, remoteID);
+    assert(
+      seqNum === '' || seqNum === `${remote.nextExpectedRecvSeqNum}`,
+      X`unexpected recv seqNum ${seqNum}`,
+    );
+    remote.nextExpectedRecvSeqNum += 1;
+
+    const msgBody = message.substring(colon + 1);
+    const command = msgBody.split(':', 1)[0];
     if (command === 'deliver') {
-      return sendFromRemote(remoteID, message);
+      return sendFromRemote(remoteID, msgBody);
     }
     if (command === 'resolve') {
-      return resolveFromRemote(remoteID, message);
+      return resolveFromRemote(remoteID, msgBody);
     }
-    assert.fail(X`unrecognized '${command}' in received message ${message}`);
+    assert.fail(X`unrecognized '${command}' in received message ${msgBody}`);
   }
 
   function sendFromRemote(remoteID, message) {

packages/SwingSet/src/vats/comms/dispatch.js

@@ -18,7 +18,7 @@ export function buildCommsDispatch(
   _vatPowers,
   vatParameters = {},
 ) {
-  const { identifierBase = 0 } = vatParameters;
+  const { identifierBase = 0, sendExplicitSeqNums = true } = vatParameters;
   const state = makeState(identifierBase);
   const stateKit = makeStateKit(state);
   const clistKit = makeCListKit(state, syscall, stateKit);
@@ -27,7 +27,12 @@ export function buildCommsDispatch(
     const remote = getRemote(state, remoteID);
     // the vat-tp "integrity layer" is a regular vat, so it expects an argument
     // encoded as JSON
-    const args = harden({ body: JSON.stringify([msg]), slots: [] });
+    const seqNum = sendExplicitSeqNums ? remote.nextSendSeqNum : '';
+    const args = harden({
+      body: JSON.stringify([`${seqNum}:${msg}`]),
+      slots: [],
+    });
+    remote.nextSendSeqNum += 1;
     syscall.send(remote.transmitterID, 'transmit', args); // sendOnly
   }
 

packages/SwingSet/src/vats/comms/remote.js

@@ -50,6 +50,8 @@ export function addRemote(state, name, transmitterID) {
     nextResolverIndex: state.identifierBase + 30,
     nextPromiseIndex: state.identifierBase + 40,
     transmitterID,
+    nextSendSeqNum: 1,
+    nextExpectedRecvSeqNum: 1,
   });
   state.identifierBase += 1000;
   state.names.set(name, remoteID);

packages/SwingSet/test/test-comms.js

@@ -71,7 +71,7 @@ test('transmit', t => {
   t.deepEqual(sends.shift(), [
     transmitterID,
     'transmit',
-    encodeArgs('deliver:ro+23:foo:;argsbytes'),
+    encodeArgs('1:deliver:ro+23:foo:;argsbytes'),
   ]);
 
   // bob!bar(alice, bob)
@@ -84,7 +84,7 @@ test('transmit', t => {
   t.deepEqual(sends.shift(), [
     transmitterID,
     'transmit',
-    encodeArgs('deliver:ro+23:bar::ro-20:ro+23;argsbytes'),
+    encodeArgs('2:deliver:ro+23:bar::ro-20:ro+23;argsbytes'),
   ]);
   // the outbound ro-20 should match an inbound ro+20, both represent 'alice'
   t.is(getLocalForRemote(remoteID, 'ro+20'), aliceLocal);
@@ -98,7 +98,7 @@ test('transmit', t => {
   t.deepEqual(sends.shift(), [
     transmitterID,
     'transmit',
-    encodeArgs('deliver:ro+23:bar::ro-20:ro+23;argsbytes'),
+    encodeArgs('3:deliver:ro+23:bar::ro-20:ro+23;argsbytes'),
   ]);
 
   // bob!cat(alice, bob, ayana)
@@ -112,7 +112,7 @@ test('transmit', t => {
   t.deepEqual(sends.shift(), [
     transmitterID,
     'transmit',
-    encodeArgs('deliver:ro+23:cat::ro-20:ro+23:ro-21;argsbytes'),
+    encodeArgs('4:deliver:ro+23:cat::ro-20:ro+23:ro-21;argsbytes'),
   ]);
 });
 
@@ -143,7 +143,7 @@ test('receive', t => {
   d.deliver(
     receiverID,
     'receive',
-    encodeArgs(`deliver:${bobRemote}:foo:;argsbytes`),
+    encodeArgs(`1:deliver:${bobRemote}:foo:;argsbytes`),
     null,
   );
   t.deepEqual(sends.shift(), [bobKernel, 'foo', capdata('argsbytes')]);
@@ -152,7 +152,7 @@ test('receive', t => {
   d.deliver(
     receiverID,
     'receive',
-    encodeArgs(`deliver:${bobRemote}:bar::ro-20:${bobRemote};argsbytes`),
+    encodeArgs(`2:deliver:${bobRemote}:bar::ro-20:${bobRemote};argsbytes`),
     null,
   );
   const expectedAliceKernel = 'o+31';
@@ -168,10 +168,11 @@ test('receive', t => {
   t.is(getLocalForKernel(expectedAliceKernel), 'lo11');
 
   // bob!bar(alice, bob), again, to test stability
+  // also test absent sequence number
   d.deliver(
     receiverID,
     'receive',
-    encodeArgs(`deliver:${bobRemote}:bar::ro-20:${bobRemote};argsbytes`),
+    encodeArgs(`:deliver:${bobRemote}:bar::ro-20:${bobRemote};argsbytes`),
     null,
   );
   t.deepEqual(sends.shift(), [
@@ -185,7 +186,9 @@ test('receive', t => {
   d.deliver(
     receiverID,
     'receive',
-    encodeArgs(`deliver:${bobRemote}:cat::ro-20:${bobRemote}:ro-21;argsbytes`),
+    encodeArgs(
+      `4:deliver:${bobRemote}:cat::ro-20:${bobRemote}:ro-21;argsbytes`,
+    ),
     null,
   );
   t.deepEqual(sends.shift(), [
@@ -194,6 +197,18 @@ test('receive', t => {
     capdata('argsbytes', [expectedAliceKernel, bobKernel, expectedAyanaKernel]),
   ]);
 
+  // react to bad sequence number
+  t.throws(
+    () =>
+      d.deliver(
+        receiverID,
+        'receive',
+        encodeArgs(`47:deliver:${bobRemote}:bar::ro-20:${bobRemote};argsbytes`),
+        null,
+      ),
+    { message: /unexpected recv seqNum \(a string\)/ },
+  );
+
   // make sure comms can tolerate dropExports, even if it's a no-op
   d.dropExports([expectedAliceKernel, expectedAyanaKernel]);
 });