Comprehensive Explanation

messagepack

Definition

MessagePack (abbreviated as MGPK in KERI contexts) is a binary data interchange format designed to serialize simple data structures—specifically arrays and associative arrays (key-value mappings)—into compact binary representations. The format emphasizes two core design principles: compactness (minimizing serialized data size) and simplicity (straightforward implementation across programming languages). Unlike text-based formats such as JSON, MessagePack sacrifices human readability to achieve superior bandwidth efficiency and processing performance.

Context in KERI/ACDC

Within the KERI protocol suite, MessagePack serves as one of three primary serialization formats supported by CESR (Composable Event Streaming Representation), alongside JSON and CBOR. CESR's architecture enables interleaved serialization, allowing MGPK-encoded data to coexist within CESR streams through special count codes that mark serialization boundaries.

For ACDC (Authentic Chained Data Container) credentials, MessagePack provides a binary encoding option that maintains the same logical structure as JSON variants while reducing payload size. The version string mechanism in ACDC supports MGPK through format indicators embedded in the version field, enabling parsers to correctly interpret serialized data.

CESR's sniffer component can detect MGPK-encoded sections within streams by identifying MessagePack's binary signatures. When MGPK is detected, the parser uses regex patterns to locate the , extracts length information, and processes the bounded MGPK block before resuming stream parsing. This enables where parsers can recover from errors by re-synchronizing at MGPK boundaries.