read-excel-file/modules/zip/unzipFromArrayBuffer.js

Read `.xlsx` files in a web browser or in Node.js

// `fflate` uses "synchronous" decompressor on `.zip` files that're under `512KB`
// (or when the compression level is too low), and an "asynchronous" (web worker)
// decompressor otherwise, as it can be seen from the source code of the `unzip()` function.
// This is because using web workers comes with an overhead of
// both creating a new worker and sending data back and forth.
//
import { unzip } from 'fflate';
import { createUnzipError } from './UnzipError.js';

/**
 * Reads `*.zip` file contents. Ignores anything besides `.xml` or `.xml.rels` files.
 * @param  {ArrayBuffer} input
 * @return {Promise<Record<string,Uint8Array>>} Resolves to an object holding `*.zip` file entries.
 */
export default function unzipFromArrayBuffer(input, options) {
  return unzipFromArrayBufferUsingFunction(input, options, unzipAsync, true);
}

/**
 * Reads `*.zip` file contents. Ignores anything besides `.xml` or `.xml.rels` files.
 * @param  {ArrayBuffer} input
 * @param  {(ArrayBuffer) => Record<string, Uint8Array> | Promise<Record<string, Uint8Array>>} unzip
 * @param  {boolean} isAsync — Should be `true` when `unzip()` returns a `Promise`, `false` otherwise.
 * @return {Promise<Record<string,Uint8Array>> | Record<string,Uint8Array>} Resolves to an object holding `*.zip` file entries.
 */
export function unzipFromArrayBufferUsingFunction(input) {
  var _ref = arguments.length > 1 && arguments[1] !== undefined ? arguments[1] : {},
    _filter = _ref.filter;
  var unzip = arguments.length > 2 ? arguments[2] : undefined;
  var isAsync = arguments.length > 3 ? arguments[3] : undefined;
  // Read the `.zip` archive.
  // `result` is either `object` or `Promise<object>`
  return unzip(new Uint8Array(input), {
    // Ignore certain types of files.
    filter: function filter(file) {
      if (_filter) {
        return _filter({
          path: file.name
        });
      }
      return true;
    }
  }).then(function (result) {
    return result;
  }, function (error) {
    // If `fflate` throws its specific error then it implies that the `.zip` file is not valid.
    if (isFlateError(error)) {
      throw createUnzipError(error);
    } else {
      throw error;
    }
  });
}
function unzipAsync(archive) {
  return new Promise(function (resolve, reject) {
    // `unzip()` will resort to "synchronous" decompression in two edge cases:
    // * When the archive size is less than `512KB`.
    // * When the data is barely compressed, i.e. the compression ratio is less than 20% reduction in size.
    unzip(archive, function (error, files) {
      if (error) {
        reject(error);
      } else {
        resolve(files);
      }
    });
  });
}

// This function attempts to guess if a given `error` was thrown by `fflate`.
function isFlateError(error) {
  // `fflate` doesn't export a `FlateError` class.
  // https://github.com/101arrowz/fflate/issues/290
  // return error instanceof FlateError

  // Here, it attempts to guess if an `error` is a `FlateError` by checking if `error.code` is a `number`.
  return typeof error.code === 'number';
}
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