nip13: let minePow keep a caller-chosen created_at (NIP-59 wraps) (#552)

* nip13: let minePow keep a caller-chosen created_at

minePow refreshes created_at to the current second while it mines, which is
right for a plain note but wrong for anything that has already chosen its
timestamp: NIP-59 seals and gift wraps carry a randomized created_at up to
two days in the past, and callers mining those lost it. This adds an opt-in
keepCreatedAt option (default behaviour unchanged) with a test.

* Delete bun.lock

---------

Co-authored-by: Ronish Bhatt <16808243+sunmoonron@users.noreply.github.com>

nip13.test.ts

@@ -28,3 +28,23 @@ test('mines POW for an event', async () => {
 
   expect(getPow(event.id)).toBeGreaterThanOrEqual(difficulty)
 })
+
+test('keeps a caller-chosen created_at when asked', async () => {
+  const difficulty = 10
+  const createdAt = 1700000000 // a fixed, past timestamp, as NIP-59 wraps use
+
+  const event = minePow(
+    {
+      kind: 1,
+      tags: [],
+      content: 'Hello, world!',
+      created_at: createdAt,
+      pubkey: '79c2cae114ea28a981e7559b4fe7854a473521a8d22a66bbab9fa248eb820ff6',
+    },
+    difficulty,
+    { keepCreatedAt: true },
+  )
+
+  expect(event.created_at).toEqual(createdAt)
+  expect(getPow(event.id)).toBeGreaterThanOrEqual(difficulty)
+})

nip13.ts

@@ -38,11 +38,22 @@ function getPowFromBytes(hash: Uint8Array): number {
   return count
 }
 
+export type MinePowOptions = {
+  /**
+   * By default the miner refreshes `created_at` to the current second while it works and restarts the
+   * nonce whenever the second changes, so a long mining run still yields a fresh timestamp. Set this
+   * to `true` to leave `created_at` exactly as given. NIP-59 gift wraps and seals must carry a
+   * randomized timestamp (up to two days in the past), and any other caller that has already chosen a
+   * `created_at` needs it to survive mining.
+   */
+  keepCreatedAt?: boolean
+}
+
 /**
  * Mine an event with the desired POW. This function mutates the event.
  * Note that this operation is synchronous and should be run in a worker context to avoid blocking the main thread.
  */
-export function minePow(unsigned: UnsignedEvent, difficulty: number): Omit<Event, 'sig'> {
+export function minePow(unsigned: UnsignedEvent, difficulty: number, options: MinePowOptions = {}): Omit<Event, 'sig'> {
   let count = 0
 
   const event = unsigned as Omit<Event, 'sig'>
@@ -51,11 +62,13 @@ export function minePow(unsigned: UnsignedEvent, difficulty: number): Omit<Event
   event.tags.push(tag)
 
   while (true) {
-    const now = Math.floor(new Date().getTime() / 1000)
+    if (!options.keepCreatedAt) {
+      const now = Math.floor(new Date().getTime() / 1000)
 
-    if (now !== event.created_at) {
-      count = 0
-      event.created_at = now
+      if (now !== event.created_at) {
+        count = 0
+        event.created_at = now
+      }
     }
 
     tag[1] = (++count).toString()