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Module

x/compress/gzip/gzip.ts

compress and uncompress for Deno
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import { crc32 } from "../utils/crc32.ts";import { deflate, inflate } from "../deflate/mod.ts";
// magic numbers marking this file as GZIPconst ID1 = 0x1F;const ID2 = 0x8B;
const compressionMethods = { "deflate": 8,};const possibleFlags = { "FTEXT": 0x01, "FHCRC": 0x02, "FEXTRA": 0x04, "FNAME": 0x08, "FCOMMENT": 0x10,};// const osMap = {// "fat": 0, // FAT file system (DOS, OS/2, NT) + PKZIPW 2.50 VFAT, NTFS// "amiga": 1, // Amiga// "vmz": 2, // VMS (VAX or Alpha AXP)// "unix": 3, // Unix// "vm/cms": 4, // VM/CMS// "atari": 5, // Atari// "hpfs": 6, // HPFS file system (OS/2, NT 3.x)// "macintosh": 7, // Macintosh// "z-system": 8, // Z-System// "cplm": 9, // CP/M// "tops-20": 10, // TOPS-20// "ntfs": 11, // NTFS file system (NT)// "qdos": 12, // SMS/QDOS// "acorn": 13, // Acorn RISC OS// "vfat": 14, // VFAT file system (Win95, NT)// "vms": 15, // MVS (code also taken for PRIMOS)// "beos": 16, // BeOS (BeBox or PowerMac)// "tandem": 17, // Tandem/NSK// "theos": 18, // THEOS// };const os = { "darwin": 3, "linux": 3, "windows": 0,};
const osCode = os[Deno.build.os] ?? 255;export const DEFAULT_LEVEL = 6;
function putByte(n: number, arr: number[]) { arr.push(n & 0xFF);}
// LSB firstfunction putShort(n: number, arr: number[]) { arr.push(n & 0xFF); arr.push(n >>> 8);}
// LSB firstexport function putLong(n: number, arr: number[]) { putShort(n & 0xffff, arr); putShort(n >>> 16, arr);}
function putString(s: string, arr: number[]) { for (let i = 0, len = s.length; i < len; i += 1) { putByte(s.charCodeAt(i), arr); }}
function readByte(arr: number[]): number { return arr.shift()!;}
function readShort(arr: number[]) { return arr.shift()! | (arr.shift()! << 8);}
function readLong(arr: number[]) { let n1 = readShort(arr); let n2 = readShort(arr);
// JavaScript can't handle bits in the position 32 // we'll emulate this by removing the left-most bit (if it exists) // and add it back in via multiplication, which does work if (n2 > 32768) { n2 -= 32768;
return ((n2 << 16) | n1) + 32768 * Math.pow(2, 16); }
return (n2 << 16) | n1;}
function readString(arr: number[]) { const charArr = [];
// turn all bytes into chars until the terminating null while (arr[0] !== 0) { charArr.push(String.fromCharCode(arr.shift()!)); }
// throw away terminating null arr.shift();
// join all characters into a cohesive string return charArr.join("");}
function readBytes(arr: number[], n: number) { const ret = []; for (let i = 0; i < n; i += 1) { ret.push(arr.shift()); } return ret;}
interface Options { level?: number; timestamp?: number; name?: string;}
export function getHeader( options: Options = {},): Uint8Array { let flags: number = 0; let level: number = options.level ?? DEFAULT_LEVEL; const out: number[] = [];
putByte(ID1, out); putByte(ID2, out);
putByte(compressionMethods["deflate"], out);
if (options.name) { flags |= possibleFlags["FNAME"]; }
putByte(flags, out); putLong(options.timestamp || Math.floor(Date.now() / 1000), out);
// put deflate args (extra flags) if (level === 1) { // fastest algorithm putByte(4, out); } else if (level === 9) { // maximum compression (fastest algorithm) putByte(2, out); } else { putByte(0, out); }
// OS identifier putByte(osCode, out);
if (options.name) { // ignore the directory part putString(options.name.substring(options.name.lastIndexOf("/") + 1), out);
// terminating null putByte(0, out); }
return new Uint8Array(out);}
export function gzip( bytes: Uint8Array, options: Options = {},): Uint8Array { let flags: number = 0; let level: number = options.level ?? DEFAULT_LEVEL; const out: number[] = [];
putByte(ID1, out); putByte(ID2, out);
putByte(compressionMethods["deflate"], out);
if (options.name) { flags |= possibleFlags["FNAME"]; }
putByte(flags, out); putLong(options.timestamp || Math.floor(Date.now() / 1000), out);
// put deflate args (extra flags) if (level === 1) { // fastest algorithm putByte(4, out); } else if (level === 9) { // maximum compression (fastest algorithm) putByte(2, out); } else { putByte(0, out); }
// OS identifier putByte(osCode, out);
if (options.name) { // ignore the directory part putString(options.name.substring(options.name.lastIndexOf("/") + 1), out);
// terminating null putByte(0, out); }
deflate(bytes, level).forEach(function (byte) { putByte(byte, out); });
putLong(parseInt(crc32(bytes), 16), out); putLong(bytes.length, out);
return new Uint8Array(out);}
export function gunzip(bytes: Uint8Array): Uint8Array { const arr = Array.from(bytes);
checkHeader(arr);
// give deflate everything but the last 8 bytes // the last 8 bytes are for the CRC32 checksum and filesize let res: Uint8Array = inflate(new Uint8Array(arr.splice(0, arr.length - 8)));
// if (flags & possibleFlags["FTEXT"]) { // res = Array.prototype.map.call(res, function (byte) { // return String.fromCharCode(byte); // }).join(""); // }
let crc: number = readLong(arr) >>> 0; if (crc !== parseInt(crc32(res), 16)) { throw "Checksum does not match"; }
let size: number = readLong(arr); if (size !== res.length) { throw "Size of decompressed file not correct"; }
return res;}
export function checkHeader(arr: number[]) { // check the first two bytes for the magic numbers if (readByte(arr) !== ID1 || readByte(arr) !== ID2) { throw "Not a GZIP file"; } if (readByte(arr) !== 8) { throw "Unsupported compression method"; }
let flags: number = readByte(arr); readLong(arr); // mtime readByte(arr); // xFlags readByte(arr); // os, throw away
// just throw away the bytes for now if (flags & possibleFlags["FEXTRA"]) { let t: number = readShort(arr); readBytes(arr, t); }
// just throw away for now if (flags & possibleFlags["FNAME"]) { readString(arr); }
// just throw away for now if (flags & possibleFlags["FCOMMENT"]) { readString(arr); }
// just throw away for now if (flags & possibleFlags["FHCRC"]) { readShort(arr); }}
export function checkTail(arr: number[]) { const tail = arr.splice(arr.length - 8);
let crc32: number = readLong(tail) >>> 0; let size: number = readLong(tail);
return { crc32, size, };}