lengthfollowed

Lengthfollowed is a design convention in data encoding and communication protocols in which each variable-length field is preceded by a length indicator that specifies the number of bytes that follow. This arrangement allows parsers to determine field boundaries without relying on delimiters or external separators, improving robustness and memory safety in both binary and text formats.

In practice, lengthfollowed overlaps with and is often part of length-prefixed schemes such as TLV (Type-Length-Value). A length field may be fixed-size (8, 16, 32 bits) or use a variable-length encoding. The essential aspect is the immediate, unambiguous coupling of length and payload data.

Examples: An 8-bit length prefix followed by payload where length indicates number of payload bytes. A protocol using a 4-byte big-endian length prefix before a message body. A string encoding that stores length then UTF-8 bytes. If the declared length exceeds a negotiated maximum, or the payload cannot be delivered, the parser must reject to prevent resource exhaustion.

Advantages include deterministic parsing, improved validation, and support for streaming parsing. Limitations include potential overhead, endianness handling, and the need for strict length validation to avoid vulnerabilities such as integer overflow or denial of service. Implementation details vary by protocol, but the core principle remains a length indicator that directly governs the size of the following data block.

See also: length-prefixed encoding, TLV, framing, streaming parser.