How to Build a Simple Binary Protocol Parser Mock in Python

Defines a mock binary protocol with field definitions, encoding, and decoding to simulate network packet parsing for A/B testing and experiment setup.

Easy Python 3.9+ Aug 9, 2026 A/B testing & experimentation 12 views 0 copies

binary protocol mock parsing

Python code

38 lines

Python 3.9+

class SimpleProtocol:
    def __init__(self, name, version):
        self.name = name
        self.version = version
        self.fields = []

    def add_field(self, field_name, field_size):
        self.fields.append((field_name, field_size))

    def parse(self, data):
        if len(data) != sum(size for _, size in self.fields):
            raise ValueError("Data length mismatch")
        offset = 0
        result = {}
        for field_name, field_size in self.fields:
            result[field_name] = int.from_bytes(data[offset:offset + field_size], byteorder="big")
            offset += field_size
        return result

    def build(self, values):
        data = b""
        for field_name, field_size in self.fields:
            value = values[field_name]
            data += value.to_bytes(field_size, byteorder="big")
        return data


if __name__ == "__main__":
    proto = SimpleProtocol("MockPacket", "1.0")
    proto.add_field("header", 1)
    proto.add_field("payload", 4)
    proto.add_field("checksum", 2)

    packet = proto.build({"header": 0xAB, "payload": 0x12345678, "checksum": 0xCDEF})
    print("Raw:", packet.hex())

    parsed = proto.parse(packet)
    print("Parsed:", parsed)

Output

stdout

Raw: ab12345678cdef
Parsed: {'header': 171, 'payload': 305419896, 'checksum': 52719}

How it works

The SimpleProtocol class stores field names and sizes, then uses int.from_bytes and int.to_bytes to encode/decode big-endian integers. The parse method validates the data length against the sum of field sizes to catch malformed inputs. This mock allows deterministic packet generation and parsing, which is essential for testing protocol logic without real network dependencies. The code is self-contained, relying only on the Python standard library, and is easily extended with more fields or different byte orders.

Common mistakes

Mismatching field sizes and data length, causing ValueError at parse time
Using the wrong byte order (e.g., little-endian when the protocol requires big-endian)
Assuming values fit within the specified field size, leading to OverflowError

Variations

Supporting little-endian by adding a byteorder parameter to __init__
Using struct.pack and struct.unpack for fixed-size fields instead of int.to_bytes

Real-world use cases

Mocking network packet generation for A/B testing message handling logic before deploying to production.
Simulating experiment event payloads in offline batch tests to validate decoder changes.
Creating deterministic test fixtures for performance benchmarks of binary serialization libraries.

How to Build a Simple Binary Protocol Parser Mock in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from A/B testing & experimentation

Tutorials

Quizzes

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from A/B testing & experimentation

Keep learning

Tutorials

Quizzes