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MessagePack Ext

The MessagePack Ext type extends custom types with (type_code, data) pairs, letting the application layer serialize non-standard types.

Purpose

To support application-defined types (e.g., Date, BigInt, custom classes) in MessagePack while keeping binary efficiency.

Mechanism

An Ext type marker (fixext1/2/4/8/16 or ext8/16/32) is followed by a 1-byte type_code (0-127 application-defined) and the raw data. Decoders dispatch on the type_code to custom deserializers.

Use cases

  • Custom type serialization
  • Date/BigInt extensions
  • Application type preservation

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References