sveltesociety.dev/scripts/untar.js

// @ts-check
// Source: https://github.com/bluwy/publint/blob/master/site/src/utils/untar.js

export function untar(arrayBuffer) {
	const tarFileStream = new UntarFileStream(arrayBuffer);
	const files = [];
	while (tarFileStream.hasNext()) {
		const file = tarFileStream.next();
		files.push(file);
	}
	return files;
}

// Source: https://gist.github.com/pascaldekloe/62546103a1576803dade9269ccf76330
// Unmarshals an Uint8Array to string.
function decodeUTF8(bytes) {
	var s = '';
	var i = 0;
	while (i < bytes.length) {
		var c = bytes[i++];
		if (c > 127) {
			if (c > 191 && c < 224) {
				if (i >= bytes.length) throw 'UTF-8 decode: incomplete 2-byte sequence';
				c = ((c & 31) << 6) | (bytes[i] & 63);
			} else if (c > 223 && c < 240) {
				if (i + 1 >= bytes.length) throw 'UTF-8 decode: incomplete 3-byte sequence';
				c = ((c & 15) << 12) | ((bytes[i] & 63) << 6) | (bytes[++i] & 63);
			} else if (c > 239 && c < 248) {
				if (i + 2 >= bytes.length) throw 'UTF-8 decode: incomplete 4-byte sequence';
				c =
					((c & 7) << 18) | ((bytes[i] & 63) << 12) | ((bytes[++i] & 63) << 6) | (bytes[++i] & 63);
			} else
				throw 'UTF-8 decode: unknown multibyte start 0x' + c.toString(16) + ' at index ' + (i - 1);
			++i;
		}

		if (c <= 0xffff) s += String.fromCharCode(c);
		else if (c <= 0x10ffff) {
			c -= 0x10000;
			s += String.fromCharCode((c >> 10) | 0xd800);
			s += String.fromCharCode((c & 0x3ff) | 0xdc00);
		} else throw 'UTF-8 decode: code point 0x' + c.toString(16) + ' exceeds UTF-16 reach';
	}
	return s;
}

function PaxHeader(fields) {
	this._fields = fields;
}

PaxHeader.parse = function (buffer) {
	// https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxa500/paxex.htm
	// An extended header shall consist of one or more records, each constructed as follows:
	// "%d %s=%s\n", <length>, <keyword>, <value>

	// The extended header records shall be encoded according to the ISO/IEC10646-1:2000 standard (UTF-8).
	// The <length> field, <blank>, equals sign, and <newline> shown shall be limited to the portable character set, as
	// encoded in UTF-8. The <keyword> and <value> fields can be any UTF-8 characters. The <length> field shall be the
	// decimal length of the extended header record in octets, including the trailing <newline>.

	var bytes = new Uint8Array(buffer);
	var fields = [];

	while (bytes.length > 0) {
		// Decode bytes up to the first space character; that is the total field length
		var fieldLength = parseInt(decodeUTF8(bytes.subarray(0, bytes.indexOf(0x20))));
		var fieldText = decodeUTF8(bytes.subarray(0, fieldLength));
		var fieldMatch = fieldText.match(/^\d+ ([^=]+)=(.*)\n$/);

		if (fieldMatch === null) {
			throw new Error('Invalid PAX header data format.');
		}

		var fieldName = fieldMatch[1];
		var fieldValue = fieldMatch[2];

		if (fieldValue.length === 0) {
			fieldValue = null;
		} else if (fieldValue.match(/^\d+$/) !== null) {
			// If it's a integer field, parse it as int
			// @ts-expect-error code wasn't written in TS
			fieldValue = parseInt(fieldValue);
		}
		// Don't parse float values since precision is lost

		var field = {
			name: fieldName,
			value: fieldValue
		};

		fields.push(field);

		bytes = bytes.subarray(fieldLength); // Cut off the parsed field data
	}

	return new PaxHeader(fields);
};

PaxHeader.prototype = {
	applyHeader: function (file) {
		// Apply fields to the file
		// If a field is of value null, it should be deleted from the file
		// https://www.mkssoftware.com/docs/man4/pax.4.asp

		this._fields.forEach(function (field) {
			var fieldName = field.name;
			var fieldValue = field.value;

			if (fieldName === 'path') {
				// This overrides the name and prefix fields in the following header block.
				fieldName = 'name';

				if (file.prefix !== undefined) {
					delete file.prefix;
				}
			} else if (fieldName === 'linkpath') {
				// This overrides the linkname field in the following header block.
				fieldName = 'linkname';
			}

			if (fieldValue === null) {
				delete file[fieldName];
			} else {
				file[fieldName] = fieldValue;
			}
		});
	}
};

function UntarStream(arrayBuffer) {
	this._bufferView = new DataView(arrayBuffer);
	this._position = 0;
}

UntarStream.prototype = {
	readString: function (charCount) {
		//console.log("readString: position " + this.position() + ", " + charCount + " chars");
		var charSize = 1;
		var byteCount = charCount * charSize;

		var charCodes = [];

		for (var i = 0; i < charCount; ++i) {
			var charCode = this._bufferView.getUint8(this.position() + i * charSize);
			if (charCode !== 0) {
				charCodes.push(charCode);
			} else {
				break;
			}
		}

		this.seek(byteCount);

		return String.fromCharCode.apply(null, charCodes);
	},

	readBuffer: function (byteCount) {
		var buf;

		if (typeof ArrayBuffer.prototype.slice === 'function') {
			buf = this._bufferView.buffer.slice(this.position(), this.position() + byteCount);
		} else {
			buf = new ArrayBuffer(byteCount);
			var target = new Uint8Array(buf);
			var src = new Uint8Array(this._bufferView.buffer, this.position(), byteCount);
			target.set(src);
		}

		this.seek(byteCount);
		return buf;
	},

	seek: function (byteCount) {
		this._position += byteCount;
	},

	peekUint32: function () {
		return this._bufferView.getUint32(this.position(), true);
	},

	position: function (newpos) {
		if (newpos === undefined) {
			return this._position;
		} else {
			this._position = newpos;
		}
	},

	size: function () {
		return this._bufferView.byteLength;
	}
};

function UntarFileStream(arrayBuffer) {
	this._stream = new UntarStream(arrayBuffer);
	this._globalPaxHeader = null;
}

UntarFileStream.prototype = {
	hasNext: function () {
		// A tar file ends with 4 zero bytes
		return this._stream.position() + 4 < this._stream.size() && this._stream.peekUint32() !== 0;
	},

	next: function () {
		return this._readNextFile();
	},

	_readNextFile: function () {
		var stream = this._stream;
		var file = {};
		var isHeaderFile = false;
		var paxHeader = null;

		var headerBeginPos = stream.position();
		var dataBeginPos = headerBeginPos + 512;

		// Read header
		file.name = stream.readString(100);
		file.mode = stream.readString(8);
		file.uid = parseInt(stream.readString(8));
		file.gid = parseInt(stream.readString(8));
		file.size = parseInt(stream.readString(12), 8);
		file.mtime = parseInt(stream.readString(12), 8);
		file.checksum = parseInt(stream.readString(8));
		file.type = stream.readString(1);
		file.linkname = stream.readString(100);
		file.ustarFormat = stream.readString(6);

		if (file.ustarFormat.indexOf('ustar') > -1) {
			file.version = stream.readString(2);
			file.uname = stream.readString(32);
			file.gname = stream.readString(32);
			file.devmajor = parseInt(stream.readString(8));
			file.devminor = parseInt(stream.readString(8));
			file.namePrefix = stream.readString(155);

			if (file.namePrefix.length > 0) {
				file.name = file.namePrefix + '/' + file.name;
			}
		}

		stream.position(dataBeginPos);

		// Derived from https://www.mkssoftware.com/docs/man4/pax.4.asp
		// and https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.3.0/com.ibm.zos.v2r3.bpxa500/pxarchfm.htm
		switch (file.type) {
			case '0': // Normal file is either "0" or "\0".
			case '': // In case of "\0", readString returns an empty string, that is "".
				file.buffer = stream.readBuffer(file.size);
				break;
			case '1': // Link to another file already archived
				// TODO Should we do anything with these?
				break;
			case '2': // Symbolic link
				// TODO Should we do anything with these?
				break;
			case '3': // Character special device (what does this mean??)
				break;
			case '4': // Block special device
				break;
			case '5': // Directory
				break;
			case '6': // FIFO special file
				break;
			case '7': // Reserved
				break;
			case 'g': // Global PAX header
				isHeaderFile = true;
				this._globalPaxHeader = PaxHeader.parse(stream.readBuffer(file.size));
				break;
			case 'x': // PAX header
				isHeaderFile = true;
				paxHeader = PaxHeader.parse(stream.readBuffer(file.size));
				break;
			default: // Unknown file type
				break;
		}

		if (file.buffer === undefined) {
			file.buffer = new ArrayBuffer(0);
		}

		var dataEndPos = dataBeginPos + file.size;

		// File data is padded to reach a 512 byte boundary; skip the padded bytes too.
		if (file.size % 512 !== 0) {
			dataEndPos += 512 - (file.size % 512);
		}

		stream.position(dataEndPos);

		if (isHeaderFile) {
			file = this._readNextFile();
		}

		if (this._globalPaxHeader !== null) {
			this._globalPaxHeader.applyHeader(file);
		}

		if (paxHeader !== null) {
			paxHeader.applyHeader(file);
		}

		return file;
	}
};