fork from https://github.com/mozilla/pdf.js.git

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 };