Design a packet reassembler API
Overview
This question evaluates API design, stream-oriented buffer management, stateful packet assembly, input validation, concurrency control, testing strategy, and time/space complexity reasoning.
Bloomberg
Sep 6, 2025, 12:00 AM
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Design a PacketAssembler API for Streaming Fragments
Context and Assumptions
- You are building a small component that assembles packets from a byte stream.
- Each packet begins with a 1-byte header that encodes the payload length N (0–255). The header byte is not part of the payload.
- The stream may arrive fragmented arbitrarily; a single call may contain parts of a packet or multiple full packets back-to-back.
Example interaction:
- packetit(0x04, 'a', 'b', 'c') -> no output (header 4 indicates a 4-byte payload; only 3 bytes arrived)
- packetit('d') -> 'abcd' (completes the prior packet)
Requirements
- Specify the class and method signatures of a PacketAssembler API.
- Describe state management: buffering, expected size, and how fragments are handled.
- Behavior when receiving multiple consecutive packets within one or many calls.
- Handling of invalid headers and oversized input (e.g., header value exceeds a configured maximum).
- Define when/how state resets after emission and on errors.
- Thread-safety considerations and options.
- Provide tests (unit-style examples) that exercise common and edge cases.
- Analyze time and space complexity.
Solution
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