zlib

Zlib compression/decompression (RFC 1950) — DEFLATE + 2-byte header + Adler32. Used by PNG, HTTP, and many binary formats.

Module zlib | Source packages/front/fw/src/io/compress/zlib.js | Deps deflate, adler32 | Worker-safe yes

Resolve

const zlib = runtime.resolve('zlib');
// Returns: { zlibSync, unzlibSync, zlib, unzlib, ZlibStream, UnzlibStream }

API

Synchrone

const compressed   = zlib.zlibSync(uint8Array, opts?);    // → Uint8Array
const decompressed = zlib.unzlibSync(compressed, opts?);  // → Uint8Array

Asynchrone

const compressed   = await zlib.zlib(uint8Array, opts?);
const decompressed = await zlib.unzlib(compressed, opts?);

Streaming

// Compression
const parts = [];
const comp = new zlib.ZlibStream(opts?, (chunk) => parts.push(chunk));
comp.push(data1);
comp.push(lastChunk, true);

// Decompression
const output = [];
const decomp = new zlib.UnzlibStream(opts?, (chunk) => output.push(chunk));
decomp.push(zlibChunk);
decomp.push(lastZlibChunk, true);

Options

Compression (zlibSync, zlib, ZlibStream)

Decompression (unzlibSync, unzlib, UnzlibStream)

Internal format (RFC 1950)

[CMF 1B][FLG 1B] [DICTID 4B optional] [DEFLATE payload] [Adler32 4B big-endian]

CMF = 0x78 (CM=8 DEFLATE, CINFO=7 window 32K). FCHECK ensures (CMF×256 + FLG) % 31 === 0.

Error codes

Example

const zlib = runtime.resolve('zlib');

const data = new TextEncoder().encode('<svg>...</svg>'.repeat(200));

const compressed   = zlib.zlibSync(data, { level: 9 });
const decompressed = zlib.unzlibSync(compressed);

// With dictionary (optimized compression for similar data)
const dict = new TextEncoder().encode('<svg><path d="');
const c = zlib.zlibSync(data, { level: 9, dictionary: dict });
const d = zlib.unzlibSync(c, { dictionary: dict });

Worker Usage

const worker = fw.createWorker(
    function ({ libs, args }) {
        const zlib = libs.zlib;
        const compressed = zlib.zlibSync(args.data, { level: 6 });
        self.postMessage(compressed, [compressed.buffer]);
    },
    { dependencies: ['zlib'], args: { data: new Uint8Array(rawData) } }
);

Notes

• Integrity checksum: Adler-32 (RFC 1950) computed on the uncompressed data — distinct from gzip which uses CRC-32.
• The zlib dictionary must be identical on both the compressor and decompressor sides — a mismatch produces a checksum error during decompression.
• The zlib format (CMF+FLG header) is not the same as gzip (magic bytes 1f 8b) or raw deflate (no header) — use the correct module for the target format.

See also

• deflate — underlying engine
• gzip — gzip format (CRC32 instead of Adler32)
• zip — multi-file archiving
• adler32