Module length 

The EN 50221 length_field — the ASN.1-style length used by every PDU at the Transport, Session and Application layers — ETSI EN 50221 §7, Table 1 (PDF p. 11).

Coding:

• the first (MSB) bit is the size_indicator;
• size_indicator == 0: the data-field length is the remaining 7 bits — any length 0..=127 fits in one byte;
• size_indicator == 1: the remaining 7 bits (length_field_size) code how many subsequent bytes carry the length, MSB-first. The spec caps any length at 65535, i.e. at most three length bytes.

The indefinite-length ASN.1 form is NOT used.

Constants

SIZE_INDICATOR_MASK

The size_indicator bit (the MSB of the first length_field byte): set when the field is the multi-byte form.

Functions

decode

Decode a length_field from the front of bytes.

encode_into

Encode value as a length_field into buf, returning the bytes written.

encoded_len

Number of bytes encode_into will write for value.