For issue #48, add Gunzipper that relies on DecompressionStream('gzip').

Author: codedread

archive/decompress.js

@@ -319,6 +319,31 @@ export class Untarrer extends Unarchiver {
   getScriptFileName() { return './untar.js'; };
 }
 
+/**
+ * IMPORTANT NOTES for Gunzipper:
+ * 1) A Gunzipper will only ever emit one EXTRACT event, because a gzipped file only ever contains
+ *    a single file.
+ * 2) If the gzipped file does not include the original filename as a FNAME block, then the
+ *    UnarchivedFile in the UnarchiveExtractEvent will not include a filename. It will be up to the
+ *    client to re-assemble the filename (if needed).
+ * 3) update() is not supported on a Gunzipper, since the current implementation relies on runtime
+ *    support for DecompressionStream('gzip') which can throw hard-to-detect errors reading only
+ *    only part of a file.
+ * 4) PROGRESS events are not yet supported in Gunzipper.
+ */
+export class Gunzipper extends Unarchiver {
+  /**
+   * @param {ArrayBuffer} ab 
+   * @param {UnarchiverOptions} options 
+   */
+  constructor(ab, options = {}) {
+    super(ab, options);
+  }
+
+  getMIMEType() { return 'application/gzip'; }
+  getScriptFileName() { return './gunzip.js'; }
+}
+
 // TODO(2.0): When up-revving to a major new version, remove the string type for options.
 
 /**
@@ -344,6 +369,8 @@ export function getUnarchiver(ab, options = {}) {
     unarchiver = new Unrarrer(ab, options);
   } else if (mimeType === 'application/zip') { // PK (Zip)
     unarchiver = new Unzipper(ab, options);
+  } else if (mimeType === 'application/gzip') { // GZIP
+    unarchiver = new Gunzipper(ab, options);
   } else { // Try with tar
     unarchiver = new Untarrer(ab, options);
   }

archive/gunzip.js

@@ -0,0 +1,125 @@
+/**
+ * gunzip.js
+ *
+ * Licensed under the MIT License
+ *
+ * Copyright(c) 2024 Google Inc.
+ *
+ * Reference Documentation:
+ *
+ * https://www.ietf.org/rfc/rfc1952.txt
+ */
+
+import { BitStream } from '../io/bitstream.js';
+import { ByteStream } from '../io/bytestream.js';
+
+/** @type {MessagePort} */
+let hostPort;
+
+/** @type {ByteStream} */
+let bstream = null;
+// undefined unless a FNAME block is present.
+let filename;
+
+const err = str => hostPort.postMessage({ type: 'error', msg: str });
+
+async function gunzip() {
+  const sig = bstream.readBytes(2);
+  if (sig[0] !== 0x1F || sig[1] !== 0x8B) {
+    const errMsg = `First two bytes not 0x1F, 0x8B: ${sig[0].toString(16)} ${sig[1].toString(16)}`;
+    err(errMsg);
+    return;
+  }
+  const compressionMethod = bstream.readNumber(1);
+  if (compressionMethod !== 8) {
+    const errMsg = `Compression method ${compressionMethod} not supported`;
+    err(errMsg);
+    return;
+  }
+
+  // Parse the GZIP header to see if we can find a filename (FNAME block).
+  const flags = new BitStream(bstream.readBytes(1).buffer);
+  flags.skip(1); // skip FTEXT bit
+  const fhcrc = flags.readBits(1);
+  const fextra = flags.readBits(1);
+  const fname = flags.readBits(1);
+  const fcomment = flags.readBits(1);
+
+  bstream.skip(4); // MTIME
+  bstream.skip(1); // XFL
+  bstream.skip(1); // OS
+
+  if (fextra) {
+    const xlen = bstream.readNumber(2);
+    bstream.skip(xlen);
+  }
+
+  if (fname) {
+    // Find the null-terminator byte.
+    let numBytes = 0;
+    const findNull = bstream.tee();
+    while (findNull.readNumber(1) !== 0) numBytes++;
+    filename = bstream.readString(numBytes);
+  }
+
+  if (fcomment) {
+    // Find the null-terminator byte.
+    let numBytes = 0;
+    const findNull = bstream.tee();
+    while (findNull.readNumber(1) !== 0) numBytes++;
+    bstream.skip(numBytes); // COMMENT
+  }
+
+  if (fhcrc) {
+    bstream.readNumber(2); // CRC16
+  }
+
+  // Now try to use native implementation of INFLATE, if supported by the runtime.
+  const blob = new Blob([bstream.bytes.buffer]);
+  const decompressedStream = blob.stream().pipeThrough(new DecompressionStream('gzip'));
+  const fileData = new Uint8Array(await new Response(decompressedStream).arrayBuffer());
+  const unarchivedFile = { filename, fileData };
+  hostPort.postMessage({ type: 'extract', unarchivedFile }, [fileData.buffer]);
+
+  // TODO: Supported chunked decompression?
+  // TODO: Fall through to non-native implementation via inflate() ?
+
+  hostPort.postMessage({ type: 'finish', metadata: {} });
+}
+
+// event.data.file has the first ArrayBuffer.
+const onmessage = async function (event) {
+  const bytes = event.data.file;
+
+  if (!bstream) {
+    bstream = new ByteStream(bytes);
+    bstream.setLittleEndian(true);
+  } else {
+    throw `Gunzipper does not calling update() with more bytes. Send the whole file with start().`
+  }
+
+  await gunzip();
+};
+
+/**
+ * Connect the host to the gunzip implementation with the given MessagePort.
+ * @param {MessagePort} port
+ */
+export function connect(port) {
+  if (hostPort) {
+    throw `connect(): hostPort already connected in gunzip.js`;
+  }
+
+  hostPort = port;
+  port.onmessage = onmessage;
+}
+
+export function disconnect() {
+  if (!hostPort) {
+    throw `disconnect(): hostPort was not connected in gunzip.js`;
+  }
+
+  hostPort = null;
+  bstream = null;
+  filename = undefined;
+}

tests/archive-decompress.spec.js

@@ -2,7 +2,7 @@ import * as fs from 'node:fs';
 import 'mocha';
 import { expect } from 'chai';
 
-import { Unarchiver, Unrarrer, Untarrer, Unzipper, getUnarchiver } from '../archive/decompress.js';
+import { Gunzipper, Unarchiver, getUnarchiver } from '../archive/decompress.js';
 
 const PATH = `tests/archive-testfiles/`;
 
@@ -69,4 +69,30 @@ describe('bitjs.archive.decompress', () => {
       expect(extractEvtFiredForOnExtract).equals(true);
     });
   }
+
+  describe('gunzip', () => {
+    it('can unzip a file', async () => {
+      const bufs = new Map(inputArrayBuffers);
+      const nodeBuf = fs.readFileSync(`${PATH}sample-1-slowest.txt.gz`);
+      const ab = nodeBuf.buffer.slice(nodeBuf.byteOffset, nodeBuf.byteOffset + nodeBuf.length);
+      let gunzipper = getUnarchiver(ab, {debug: true});
+      expect(gunzipper instanceof Gunzipper).equals(true);
+      let extractEvtFiredForOnExtract = false;
+
+      gunzipper.onExtract(evt => {
+        extractEvtFiredForOnExtract = true;
+        const {filename, fileData} = evt.unarchivedFile;
+        expect(filename).equals('sample-1.txt');
+
+        const ab = bufs.get('sample-1.txt');
+        expect(fileData.byteLength).equals(ab.byteLength);
+        for (let b = 0; b < fileData.byteLength; ++b) {
+          expect(fileData[b] === ab[b]);
+        }
+      });
+
+      await gunzipper.start();
+      expect(extractEvtFiredForOnExtract).equals(true);
+    });
+  });
 });