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compression.ts
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import { promisify } from 'util';
import * as zlib from 'zlib';
import { LEGACY_HELLO_COMMAND } from '../../constants';
import { getSnappy, getZstdLibrary, type SnappyLib, type ZStandard } from '../../deps';
import { MongoDecompressionError, MongoInvalidArgumentError } from '../../error';
/** @public */
export const Compressor = Object.freeze({
none: 0,
snappy: 1,
zlib: 2,
zstd: 3
} as const);
/** @public */
export type Compressor = (typeof Compressor)[CompressorName];
/** @public */
export type CompressorName = keyof typeof Compressor;
export const uncompressibleCommands = new Set([
LEGACY_HELLO_COMMAND,
'saslStart',
'saslContinue',
'getnonce',
'authenticate',
'createUser',
'updateUser',
'copydbSaslStart',
'copydbgetnonce',
'copydb'
]);
const ZSTD_COMPRESSION_LEVEL = 3;
const zlibInflate = promisify(zlib.inflate.bind(zlib));
const zlibDeflate = promisify(zlib.deflate.bind(zlib));
let zstd: typeof ZStandard;
let Snappy: SnappyLib | null = null;
function loadSnappy() {
if (Snappy == null) {
const snappyImport = getSnappy();
if ('kModuleError' in snappyImport) {
throw snappyImport.kModuleError;
}
Snappy = snappyImport;
}
return Snappy;
}
// Facilitate compressing a message using an agreed compressor
export async function compress(
options: { zlibCompressionLevel: number; agreedCompressor: CompressorName },
dataToBeCompressed: Buffer
): Promise<Buffer> {
const zlibOptions = {} as zlib.ZlibOptions;
switch (options.agreedCompressor) {
case 'snappy': {
Snappy ??= loadSnappy();
return Snappy.compress(dataToBeCompressed);
}
case 'zstd': {
loadZstd();
if ('kModuleError' in zstd) {
throw zstd['kModuleError'];
}
return zstd.compress(dataToBeCompressed, ZSTD_COMPRESSION_LEVEL);
}
case 'zlib': {
if (options.zlibCompressionLevel) {
zlibOptions.level = options.zlibCompressionLevel;
}
return zlibDeflate(dataToBeCompressed, zlibOptions);
}
default: {
throw new MongoInvalidArgumentError(
`Unknown compressor ${options.agreedCompressor} failed to compress`
);
}
}
}
// Decompress a message using the given compressor
export async function decompress(compressorID: number, compressedData: Buffer): Promise<Buffer> {
if (
compressorID !== Compressor.snappy &&
compressorID !== Compressor.zstd &&
compressorID !== Compressor.zlib &&
compressorID !== Compressor.none
) {
throw new MongoDecompressionError(
`Server sent message compressed using an unsupported compressor. (Received compressor ID ${compressorID})`
);
}
switch (compressorID) {
case Compressor.snappy: {
Snappy ??= loadSnappy();
return Snappy.uncompress(compressedData, { asBuffer: true });
}
case Compressor.zstd: {
loadZstd();
if ('kModuleError' in zstd) {
throw zstd['kModuleError'];
}
return zstd.decompress(compressedData);
}
case Compressor.zlib: {
return zlibInflate(compressedData);
}
default: {
return compressedData;
}
}
}
/**
* Load ZStandard if it is not already set.
*/
function loadZstd() {
if (!zstd) {
zstd = getZstdLibrary();
}
}