fix(v7): align default seq formula in v7Bytes with updateV7State (#965)

---------

Co-authored-by: JSap0914 <[email protected]>
Co-authored-by: Robert Kieffer <[email protected]>

src/test/v7.test.ts

@@ -173,7 +173,7 @@ describe('v7', () => {
         now: 2,
         expected: {
           msecs: 2, // time interval should update
-          seq: 0x6c318c4, // sequence should be randomized
+          seq: 0xcc318c4, // sequence should be randomized
         },
       },
       {
@@ -297,4 +297,40 @@ describe('v7', () => {
     assert.throws(() => v7({}, buf30, -1), RangeError);
     assert.throws(() => v7({}, buf30, 15), RangeError);
   });
+
+  test('default seq (no explicit seq option) is consistent with updateV7State formula', () => {
+    // When v7() is called with random bytes and msecs but no explicit seq, the
+    // default seq should use the same formula as updateV7State() –
+    // ((rnds[6] & 0x7f) << 24) | (rnds[7] << 16) | (rnds[8] << 8) | rnds[9].
+    //
+    // Regression: the formula was `(rnds[6] * 0x7f) << 24`, which should have
+    // been `(rnds[6] & 0x7f) << 24`, producing a seq inconsistent with
+    // updateV7State.
+    const rnds = Uint8Array.of(
+      0x02,
+      0x91,
+      0x56,
+      0xbe,
+      0xc4,
+      0xfb,
+      0x02,
+      0xc3,
+      0x18,
+      0xc4,
+      0x6c,
+      0x0c,
+      0x0c,
+      0x07,
+      0x39,
+      0x8f,
+    );
+    const state = updateV7State({}, RFC_MSECS, rnds);
+    const uuidWithExplicitSeq = v7({
+      random: rnds,
+      msecs: RFC_MSECS,
+      seq: state.seq,
+    });
+    const uuidWithDefaultSeq = v7({ random: rnds, msecs: RFC_MSECS });
+    assert.strictEqual(uuidWithDefaultSeq, uuidWithExplicitSeq);
+  });
 });

src/v7.ts

@@ -56,7 +56,7 @@ export function updateV7State(state: V7State, now: number, rnds: Uint8Array) {
 
   if (now > state.msecs) {
     // Time has moved on! Pick a new random sequence number
-    state.seq = (rnds[6] << 23) | (rnds[7] << 16) | (rnds[8] << 8) | rnds[9];
+    state.seq = v7Sequence(rnds);
     state.msecs = now;
   } else {
     // Bump sequence counter w/ 32-bit rollover
@@ -97,7 +97,7 @@ function v7Bytes(
 
   // Defaults
   msecs ??= Date.now();
-  seq ??= ((rnds[6] * 0x7f) << 24) | (rnds[7] << 16) | (rnds[8] << 8) | rnds[9];
+  seq ??= v7Sequence(rnds);
 
   // byte 0-5: timestamp (48 bits)
   buf[offset++] = (msecs / 0x10000000000) & 0xff;
@@ -132,4 +132,8 @@ function v7Bytes(
   return buf;
 }
 
+function v7Sequence(rnds: Uint8Array) {
+  return ((rnds[6] & 0x7f) << 24) | (rnds[7] << 16) | (rnds[8] << 8) | rnds[9];
+}
+
 export default v7;