Function getHeaderAndRoot

js/src/index.ts:581–610

(
  source: Source,
  decompress: DecompressFunc
)

}

async function getHeaderAndRoot(
  source: Source,
  decompress: DecompressFunc
): Promise<[Header, [string, number, Entry[] | ArrayBuffer]?]> {
  const resp = await source.getBytes(0, 16384);

  const v = new DataView(resp.data);
  if (v.getUint16(0, true) !== 0x4d50) {
    throw new Error("Wrong magic number for PMTiles archive");
  }

  const headerData = resp.data.slice(0, HEADER_SIZE_BYTES);

  const header = bytesToHeader(headerData, resp.etag);

  // optimistically set the root directory
  // TODO check root bounds
  const rootDirData = resp.data.slice(
    header.rootDirectoryOffset,
    header.rootDirectoryOffset + header.rootDirectoryLength
  );
  const dirKey = `${source.getKey()}|${header.etag || ""}|${
    header.rootDirectoryOffset
  }|${header.rootDirectoryLength}`;

  const rootDir = deserializeIndex(
    await decompress(rootDirData, header.internalCompression)
  );
  return [header, [dirKey, rootDir.length, rootDir]];
}

async function getDirectory(
  source: Source,