A byte stream needs framing

15-minute session: read for 3 minutes, trace for 3, experiment for 7, and complete the check for 2. Spend longer whenever you need.

A TCP read may return part of a message or several messages together. Define framing using a length, delimiter, or specified format. Validate maximum length before allocation and handle truncated input. The model parses a two-byte length prefix from fixed bytes; no network connection is made in the sandbox.

Practice and evidence: Predict the example or draw its state transitions. Change one assumption, test the boundary, and record the actual result. Explain what this small model does not establish about a production system.

packet=bytes([0,3])+b"cat"
length=int.from_bytes(packet[:2],"big")
assert length<=100 and len(packet)-2==length
print(packet[2:].decode())

Expected result: cat

Practice and evidence

Keep three notes: your prediction, the actual result, and why they match or differ. The completion check grades understanding; the practice task builds skill.