The Cursor at the End of Time — Python Bug Hunt

Briefing

Inspired by the API-pagination crashes that greet every client's FIRST request: the opaque cursor is decoded unconditionally — and the first page has no cursor at all. int("") says hello.

cursor.py encodes/decodes offset cursors of the form "off:<n>".

Bug report

BUG-PAGE1 · Priority: High · Reported by: API consumers

• decode(cursor): None or "" -> offset 0; "off:<n>" -> n; anything else -> raise ValueError
• encode(offset) -> "off:<n>"; round-trips exactly

Observed: the very first request (no cursor) throws, and junk cursors return offset 0 silently, restarting angry clients from page one.

Logs

[api] GET /items -> 500 ValueError: invalid literal for int()

The code as shipped

src/api/cursor.py (editable)

# Opaque pagination cursors: "off:<n>".

def encode(offset):
    return "off:" + str(offset)

def decode(cursor):
    return int(cursor.split(":")[1])