Add support for Brotli decompression

For now, `BrotliDecode` hasn't been specified but it should be in a
close future.
So when it's possible we use the native `DecompressionStream` API
with "brotli" as argument.
If that fails or if we've to decompress in a sync context, we fallback
to `BrotliStream` which a pure js implementation (see README in external/brotli).

eslint.config.mjs

@@ -31,6 +31,7 @@ export default [
       "**/docs/",
       "**/node_modules/",
       "external/bcmaps/",
+      "external/brotli/",
       "external/builder/fixtures/",
       "external/builder/fixtures_babel/",
       "external/openjpeg/",

external/brotli/LICENSE_BROTLI

@@ -0,0 +1,19 @@
+Copyright (c) 2009, 2010, 2013-2016 by the Brotli Authors.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in
+all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+THE SOFTWARE.

external/brotli/README.md

@@ -0,0 +1,8 @@
+## Release
+
+In order to get the file `decoder.js`:
+* `gulp release-brotli --hash` followed by the git hash of the revision.
+
+## Licensing
+
+[brotli](https://github.com/google/brotli/) is under [MIT License](https://github.com/google/brotli/blob/master/LICENSE)

gulpfile.mjs

@@ -21,6 +21,7 @@ import { exec, execSync, spawn, spawnSync } from "child_process";
 import autoprefixer from "autoprefixer";
 import babel from "@babel/core";
 import crypto from "crypto";
+import { finished } from "stream/promises";
 import fs from "fs";
 import gulp from "gulp";
 import hljs from "highlight.js";
@@ -874,6 +875,28 @@ gulp.task("default", function (done) {
   done();
 });
 
+gulp.task("release-brotli", async function (done) {
+  const hashIndex = process.argv.indexOf("--hash");
+  if (hashIndex === -1 || hashIndex + 1 >= process.argv.length) {
+    throw new Error('Missing "--hash <commit-hash>" argument.');
+  }
+  console.log();
+  console.log("### Getting Brotli js file for release");
+
+  const OUTPUT_DIR = "./external/brotli/";
+  const hash = process.argv[hashIndex + 1];
+  const url = `https://raw.githubusercontent.com/google/brotli/${hash}/js/decode.js`;
+  const outputPath = OUTPUT_DIR + "decode.js";
+  const res = await fetch(url);
+  const fileStream = fs.createWriteStream(outputPath, { flags: "w" });
+  await finished(stream.Readable.fromWeb(res.body).pipe(fileStream));
+  fileStream.end();
+
+  console.log(`Brotli js file saved to: ${outputPath}`);
+
+  done();
+});
+
 function createBuildNumber(done) {
   console.log();
   console.log("### Getting extension build number");
@@ -1692,6 +1715,7 @@ function buildLib(defines, dir) {
     gulp.src("external/openjpeg/*.js", { base: "openjpeg/", encoding: false }),
     gulp.src("external/qcms/*.js", { base: "qcms/", encoding: false }),
     gulp.src("external/jbig2/*.js", { base: "jbig2/", encoding: false }),
+    gulp.src("external/brotli/*.js", { base: "brotli/", encoding: false }),
   ]);
 
   return buildLibHelper(bundleDefines, inputStream, dir);

src/core/brotli_stream.js

@@ -0,0 +1,86 @@
+/* Copyright 2026 Mozilla Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { BrotliDecode } from "../../external/brotli/decode.js";
+import { DecodeStream } from "./decode_stream.js";
+import { Stream } from "./stream.js";
+
+class BrotliStream extends DecodeStream {
+  #isAsync = true;
+
+  constructor(stream, maybeLength) {
+    super(maybeLength);
+
+    this.stream = stream;
+    this.dict = stream.dict;
+  }
+
+  readBlock() {
+    // TODO: add some telemetry to measure how often we fallback here.
+    // Get all bytes from the input stream
+    const bytes = this.stream.getBytes();
+    const decodedData = BrotliDecode(
+      new Int8Array(bytes.buffer, bytes.byteOffset, bytes.length)
+    );
+
+    this.buffer = new Uint8Array(
+      decodedData.buffer,
+      decodedData.byteOffset,
+      decodedData.length
+    );
+    this.bufferLength = this.buffer.length;
+    this.eof = true;
+  }
+
+  async getImageData(length, _decoderOptions) {
+    const data = await this.asyncGetBytes();
+    if (!data) {
+      return this.getBytes(length);
+    }
+    if (data.length <= length) {
+      return data;
+    }
+    return data.subarray(0, length);
+  }
+
+  async asyncGetBytes() {
+    const { decompressed, compressed } =
+      await this.asyncGetBytesFromDecompressionStream("brotli");
+    if (decompressed) {
+      return decompressed;
+    }
+    // DecompressionStream failed (for example because there are some extra
+    // bytes after the end of the compressed data), so we fallback to our
+    // decoder.
+    // We already get the bytes from the underlying stream, so we just reuse
+    // them to avoid get them again.
+
+    this.#isAsync = false;
+    this.stream = new Stream(
+      compressed,
+      0,
+      compressed.length,
+      this.stream.dict
+    );
+    this.reset();
+    return null;
+  }
+
+  get isAsync() {
+    return this.#isAsync;
+  }
+}
+
+export { BrotliStream };

src/core/decode_stream.js

@@ -110,6 +110,46 @@ class DecodeStream extends BaseStream {
     return this.decodeImage(data, decoderOptions);
   }
 
+  async asyncGetBytesFromDecompressionStream(name) {
+    this.stream.reset();
+    const bytes = this.stream.isAsync
+      ? await this.stream.asyncGetBytes()
+      : this.stream.getBytes();
+
+    try {
+      const { readable, writable } = new DecompressionStream(name);
+      const writer = writable.getWriter();
+      await writer.ready;
+
+      // We can't await writer.write() because it'll block until the reader
+      // starts which happens few lines below.
+      writer
+        .write(bytes)
+        .then(async () => {
+          await writer.ready;
+          await writer.close();
+        })
+        .catch(() => {});
+
+      const chunks = [];
+      let totalLength = 0;
+
+      for await (const chunk of readable) {
+        chunks.push(chunk);
+        totalLength += chunk.byteLength;
+      }
+      const data = new Uint8Array(totalLength);
+      let offset = 0;
+      for (const chunk of chunks) {
+        data.set(chunk, offset);
+        offset += chunk.byteLength;
+      }
+      return { decompressed: data, compressed: bytes };
+    } catch {
+      return { decompressed: null, compressed: bytes };
+    }
+  }
+
   reset() {
     this.pos = 0;
   }

src/core/flate_stream.js

@@ -163,57 +163,26 @@ class FlateStream extends DecodeStream {
   }
 
   async asyncGetBytes() {
-    this.stream.reset();
-    const bytes = this.stream.isAsync
-      ? await this.stream.asyncGetBytes()
-      : this.stream.getBytes();
-
-    try {
-      const { readable, writable } = new DecompressionStream("deflate");
-      const writer = writable.getWriter();
-      await writer.ready;
-
-      // We can't await writer.write() because it'll block until the reader
-      // starts which happens few lines below.
-      writer
-        .write(bytes)
-        .then(async () => {
-          await writer.ready;
-          await writer.close();
-        })
-        .catch(() => {});
-
-      const chunks = [];
-      let totalLength = 0;
-
-      for await (const chunk of readable) {
-        chunks.push(chunk);
-        totalLength += chunk.byteLength;
-      }
-      const data = new Uint8Array(totalLength);
-      let offset = 0;
-      for (const chunk of chunks) {
-        data.set(chunk, offset);
-        offset += chunk.byteLength;
-      }
-
-      return data;
-    } catch {
-      // DecompressionStream failed (for example because there are some extra
-      // bytes after the end of the compressed data), so we fallback to our
-      // decoder.
-      // We already get the bytes from the underlying stream, so we just reuse
-      // them to avoid get them again.
-      this.#isAsync = false;
-      this.stream = new Stream(
-        bytes,
-        2 /* = header size (see ctor) */,
-        bytes.length,
-        this.stream.dict
-      );
-      this.reset();
-      return null;
+    const { decompressed, compressed } =
+      await this.asyncGetBytesFromDecompressionStream("deflate");
+    if (decompressed) {
+      return decompressed;
     }
+    // DecompressionStream failed (for example because there are some extra
+    // bytes after the end of the compressed data), so we fallback to our
+    // decoder.
+    // We already get the bytes from the underlying stream, so we just reuse
+    // them to avoid get them again.
+
+    this.#isAsync = false;
+    this.stream = new Stream(
+      compressed,
+      2 /* = header size (see ctor) */,
+      compressed.length,
+      this.stream.dict
+    );
+    this.reset();
+    return null;
   }
 
   get isAsync() {

src/core/parser.js

@@ -29,6 +29,7 @@ import {
 import { NullStream, Stream } from "./stream.js";
 import { Ascii85Stream } from "./ascii_85_stream.js";
 import { AsciiHexStream } from "./ascii_hex_stream.js";
+import { BrotliStream } from "./brotli_stream.js";
 import { CCITTFaxStream } from "./ccitt_stream.js";
 import { FlateStream } from "./flate_stream.js";
 import { Jbig2Stream } from "./jbig2_stream.js";
@@ -822,6 +823,8 @@ class Parser {
           return new RunLengthStream(stream, maybeLength);
         case "JBIG2Decode":
           return new Jbig2Stream(stream, maybeLength, params);
+        case "BrotliDecode":
+          return new BrotliStream(stream, maybeLength);
       }
       warn(`Filter "${name}" is not supported.`);
       return stream;

test/pdfs/.gitignore

@@ -870,3 +870,4 @@
 !bug2009627.pdf
 !page_with_number.pdf
 !page_with_number_and_link.pdf
+!Brotli-Prototype-FileA.pdf

test/test_manifest.json

@@ -13929,5 +13929,12 @@
     "md5": "e515a9abb11ab74332e57e371bfae61e",
     "rounds": 1,
     "type": "eq"
+  },
+  {
+    "id": "Brotli-Prototype-FileA",
+    "file": "pdfs/Brotli-Prototype-FileA.pdf",
+    "md5": "9113370932798776ba91c807ce95082e",
+    "rounds": 1,
+    "type": "eq"
   }
 ]