Update flatbuffers.js (#1249)

source/flatbuffers.js

@@ -329,14 +329,25 @@ flatbuffers.StreamReader = class extends flatbuffers.BinaryReader {
 
  constructor(stream) {
  super();
- this.length = stream.length;
+ this._length = stream.length;
  this._stream = stream;
- this._fill(0, Math.min(0x100000, stream.length));
+ this._size = 0x10000000;
+ this._offset = 0;
+ this._window = Math.min(0x1000, stream.length);
+ const buffer = this._stream.peek(this._window);
+ this._buffer = buffer;
+ this._view = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
+ this._chunk = -1;
+ }
+
+ get length() {
+ return this._length;
  }
 
  read(offset, length) {
- this._stream.seek(offset);
- return this._stream.read(length);
+ const buffer = new Uint8Array(length);
+ this._read(buffer, offset);
+ return buffer;
  }
 
  uint8(offset) {
@@ -388,15 +399,52 @@ flatbuffers.StreamReader = class extends flatbuffers.BinaryReader {
  if (offset + length > this._length) {
  throw new Error(`Expected ${offset + length - this._length} more bytes. The file might be corrupted. Unexpected end of file.`);
  }
- if (!this._buffer || offset < this._offset || offset + length > this._offset + this._buffer.length) {
- this._offset = offset;
- this._stream.seek(this._offset);
- const size = Math.min(0x10000000, this.length - this._offset);
- this._buffer = this._stream.read(size);
- this._view = new DataView(this._buffer.buffer, this._buffer.byteOffset, this._buffer.byteLength);
+ if (offset < this._offset || offset + length > this._offset + this._window) {
+ const remainder = offset % this. _size;
+ const last = this._last;
+ if (this._chunk !== -1) {
+ this._last = [this._chunk, this._buffer, this._view];
+ }
+ if (remainder + length > this._size) {
+ const buffer = new Uint8Array(length);
+ this._read(buffer, length);
+ this._chunk = -1;
+ this._offset = offset;
+ this._window = length;
+ this._buffer = buffer;
+ this._view = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
+ } else {
+ const chunk = Math.floor(offset / this._size);
+ this._offset = chunk * this._size;
+ this._window = Math.min(this._length - this._offset, this._size);
+ if (last && last[0] === chunk) {
+ [this._chunk, this._buffer, this._view] = last;
+ } else {
+ this._chunk = chunk;
+ this._stream.seek(this._offset);
+ const buffer = this._stream.read(this._window);
+ this._buffer = buffer;
+ this._view = new DataView(buffer.buffer, buffer.byteOffset, buffer.byteLength);
+ this._stream.seek(0);
+ }
+ }
  }
  return offset - this._offset;
  }
+
+ _read(buffer, offset) {
+ const length = buffer.length;
+ if (offset < this._offset || offset + length > this._offset + this._window) {
+ this._stream.seek(offset);
+ const data = this._stream.read(length);
+ buffer.set(data, 0);
+ this._stream.seek(0);
+ } else {
+ offset -= this._offset;
+ const data = this._buffer.subarray(offset, offset + length);
+ buffer.set(data, 0);
+ }
+ }
 };
 
 flatbuffers.TextReader = class {