Module compression 

Compression utilities for tiles. The format is zstd-only — there is no gzip path (it was never shipped; zstd beats it on both ratio and browser decode). Compression::None exists only for already-incompressible blobs.

Constants

ZSTD_LEVEL

Default zstd level. Level 3 is zstd’s documented “fast” sweet spot — roughly gzip-6 ratio at ~5x the encode speed; higher levels save a few percent at significant CPU cost. Default zstd level for the packed format — see the constant doc above. compress_zstd_with_dict and the writers use this unless an explicit level is threaded through (e.g. stt-build --zstd-level).

ZSTD_LEVEL_MAX

Highest level we expose. zstd defines 1..=22; level 19 is the practical ceiling (19 ≈ 22 on STT tiles, measured) but we accept up to 22.

Functions

compress

Compress data using the specified compression method

compress_zstd_with_dict

Compress a payload with zstd using an optional pre-shared dictionary, at the default level (ZSTD_LEVEL). Thin wrapper over compress_zstd_with_dict_level — kept as the stable call site for the many writers that don’t tune the level.

compress_zstd_with_dict_level

Compress a payload with zstd at an explicit level, with an optional pre-shared dictionary.

decompress

Decompress data using the specified compression method

decompress_zstd_with_dict

Decompress zstd data, applying a pre-shared dictionary when supplied.

train_zstd_dictionary

Train a zstd dictionary from a sample of payloads.

train_zstd_dictionary_from_slices

Train a zstd dictionary from borrowed payload slices (no cloning).