Standard library / zlib · on the one-page reference

zlib

Experimental — new, manually tested rather than conformance-suite covered.

A practical subset of Node's zlib module: one-shot gzip and raw-deflate compress/ decompress. Static functions, not Node's zlib.createGzip() transform-stream style — there's no stream/Buffer object in the language yet, and one-shot whole-buffer compression covers the common case (config blobs, already-buffered HTTP bodies, small payloads). Buffer-less v1 shape: Lumen's string is []const u8 — raw bytes, not validated UTF-8 (the same property crypto.randomBytes/sha256 already rely on) — so compressed binary output flows through string directly rather than a dedicated byte-buffer type, which doesn't exist yet.

gzipSync gunzipSync deflateSync inflateSync

`zlib.gzipSync(data)`

string → string — compresses data's bytes into a real gzip container (RFC 1952: 10-byte header, deflate body, CRC32 + size footer). The result is genuine gzip framing, not a private format — verified by writing it to a .gz file and decoding it with the system gunzip.

const input = "hello hello hello hello hello";
const gz = zlib.gzipSync(input);
console.log(gz.length < input.length); // true

`zlib.gunzipSync(data)`

string → string — inverse of gzipSync. Deviation from Node: on any decode error (bad header, truncated stream, checksum mismatch, or plain non-gzip garbage) returns "" rather than throwing — the same fallback-don't-crash shape every other fallible builtin here uses. A real gzip stream never decodes to "" in-band, so this is unambiguous as an error sentinel.

const input = "round trip me";
const back = zlib.gunzipSync(zlib.gzipSync(input));
console.log(back == input); // true
console.log(zlib.gunzipSync("not gzip data") == ""); // true

`zlib.deflateSync(data)`

string → string — raw deflate body only (RFC 1951), no gzip/zlib header or footer. 18 bytes smaller than gzipSync's output on the same input (the gzip container's 10-byte header + 8-byte footer).

const input = "hello hello hello hello hello";
console.log(zlib.deflateSync(input).length < zlib.gzipSync(input).length); // true

`zlib.inflateSync(data)`

string → string — inverse of deflateSync; same ""-on-error fallback as gunzipSync.

const input = "round trip me";
console.log(zlib.inflateSync(zlib.deflateSync(input)) == input); // true

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