Function decompressPartialGzip

src/utils.ts:1588–1625

(
  fileBytes: Uint8Array,
  numBytes: number,
)

// Partially decompress a gzip-encoded Uint8Array, returning a Uint8Array of
// the specified numBytes from the start of the file.
export function decompressPartialGzip(
  fileBytes: Uint8Array,
  numBytes: number,
): Uint8Array {
  const chunks: Uint8Array[] = [];
  let totalBytes = 0;
  let result: Uint8Array | null = null;

  const gunzip = new Gunzip((data, final) => {
    chunks.push(data);
    totalBytes += data.length;
    if (final || totalBytes >= numBytes) {
      const allBytes = new Uint8Array(totalBytes);
      let offset = 0;
      for (const chunk of chunks) {
        allBytes.set(chunk, offset);
        offset += chunk.length;
      }
      result = allBytes.slice(0, numBytes);
    }
  });

  const CHUNK_SIZE = 1024;
  let offset = 0;
  while (result == null && offset < fileBytes.length) {
    const chunk = fileBytes.slice(offset, offset + CHUNK_SIZE);
    gunzip.push(chunk, false);
    offset += CHUNK_SIZE;
  }

  if (result == null) {
    gunzip.push(new Uint8Array(), true);
    if (result == null) {
      throw new Error("Failed to decompress partial gzip");
    }
  }
  return result;
}

export class GunzipReader {
  fileBytes: Uint8Array;