untar-worker.js

/* globals postMessage: false, DataView: false, self: false, window: false, ArrayBuffer: false, Uint8Array: false */

function UntarWorker() {

}

UntarWorker.prototype = {
	onmessage: function(msg) {
		try {
			if (msg.data.type === "extract") {
				this.untarBuffer(msg.data.buffer);
			} else {
				throw new Error("Unknown message type: " + msg.data.type);
			}
		} catch (err) {
			this.postError(err);
		}
	},

 	postError: function(err) {
 		//console.info("postError(" + err.message + ")" + " " + JSON.stringify(err));
		this.postMessage({ type: "error", data: { message: err.message } });
	},

	postLog: function(level, msg) {
 		//console.info("postLog");
 		this.postMessage({ type: "log", data: { level: level, msg: msg }});
	},

	untarBuffer: function(arrayBuffer) {
		try {
			var tarFileStream = new UntarFileStream(arrayBuffer);
			while (tarFileStream.hasNext()) {
				var file = tarFileStream.next();

				this.postMessage({ type: "extract", data: file }, [file.buffer]);
			}

			this.postMessage({ type: "complete" });
		} catch (err) {
			this.postError(err);
		}
	},

	postMessage: function(msg, transfers) {
 		//console.info("postMessage(" + msg + ", " + JSON.stringify(transfers) + ")");
		self.postMessage(msg, transfers);
	}
};

if (typeof self !== "undefined") {
	// We're running in a worker thread
	var worker = new UntarWorker();
	self.onmessage = function(msg) { worker.onmessage(msg); };
}

// 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
            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 TarFile() {

}

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), true);
			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 = new TarFile();
		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;
	}
};