add nip-13: proof of work

Author: jeffthibault

nostr/pow.py

@@ -0,0 +1,43 @@
+import time
+from .event import Event
+
+def zero_bits(b: int) -> int:
+    n = 0
+
+    if b == 0:
+        return 8
+
+    while b >> 1:
+        b = b >> 1
+        n += 1
+
+    return 7 - n
+
+def count_leading_zero_bits(event_id: str) -> int:
+    total = 0
+    for i in range(0, len(event_id) - 2, 2):
+        bits = zero_bits(int(event_id[i:i+2], 16))
+        total += bits
+
+        if bits != 8:
+            break
+
+    return total
+
+def mine_event(content: str, difficulty: int, public_key: str, kind: int, tags: list=[]) -> Event:
+    all_tags = [["nonce", "1", str(difficulty)]]
+    all_tags.extend(tags)
+
+    created_at = int(time.time())
+    event_id = Event.compute_id(public_key, created_at, kind, all_tags, content)
+    num_leading_zero_bits = count_leading_zero_bits(event_id)
+
+    attempts = 1
+    while num_leading_zero_bits < difficulty:
+        attempts += 1
+        all_tags[0][1] = str(attempts)
+        created_at = int(time.time())
+        event_id = Event.compute_id(public_key, created_at, kind, all_tags, content)
+        num_leading_zero_bits = count_leading_zero_bits(event_id)
+
+    return Event(public_key, content, created_at, kind, all_tags, event_id)