fix: sort event parents (#41)

Ensures event blocks are deterministic.

Author: alanshaw

src/clock/index.js

@@ -94,12 +94,30 @@ export class EventFetcher {
  * @returns {Promise<API.EventBlockView<T>>}
  */
 export const encodeEventBlock = async (value) => {
-  // TODO: sort parents
-  const { cid, bytes } = await encode({ value, codec: cbor, hasher: sha256 })
+  if (typeof value.data === 'undefined' || !Array.isArray(value.parents)) {
+    throw new Error('invalid event block structure')
+  }
+  const { data } = value
+  const parents = [...value.parents].sort((a, b) => compareBytes(a.bytes, b.bytes))
+  const { cid, bytes } = await encode({ value: { data, parents }, codec: cbor, hasher: sha256 })
   // @ts-expect-error
   return new Block({ cid, value, bytes })
 }
 
+/**
+ * @param {Uint8Array} a
+ * @param {Uint8Array} b
+ */
+const compareBytes = (a, b) => {
+  for (let i = 0; i < a.byteLength; i++) {
+    if (a[i] < b[i]) return -1
+    if (a[i] > b[i]) return 1
+  }
+  if (a.byteLength > b.byteLength) return 1
+  if (a.byteLength < b.byteLength) return -1
+  return 0
+}
+
 /**
  * @template T
  * @param {Uint8Array} bytes

test/clock.test.js

@@ -292,4 +292,12 @@ describe('clock', () => {
     assert.equal(head[0].toString(), event3.cid.toString())
     assert.equal(count - before, 8, 'The number of traversals should be 8 with optimization')
   })
+
+  it('sorts event links', async () => {
+    const parent0 = await EventBlock.create(await randomEventData())
+    const parent1 = await EventBlock.create(await randomEventData())
+    const child0 = await EventBlock.create({}, [parent0.cid, parent1.cid])
+    const child1 = await EventBlock.create({}, [parent1.cid, parent0.cid])
+    assert.deepEqual(child0.bytes, child1.bytes)
+  })
 })