lib/adapters/idb/blobSupport.js

'use strict';

var createBlob = require('../../deps/binary/blob');
var Promise = require('../../deps/promise');
var idbConstants = require('./constants');
var DETECT_BLOB_SUPPORT_STORE = idbConstants.DETECT_BLOB_SUPPORT_STORE;

//
// Blobs are not supported in all versions of IndexedDB, notably
// Chrome <37 and Android <5. In those versions, storing a blob will throw.
//
// Various other blob bugs exist in Chrome v37-42 (inclusive).
// Detecting them is expensive and confusing to users, and Chrome 37-42
// is at very low usage worldwide, so we do a hacky userAgent check instead.
//
// content-type bug: https://code.google.com/p/chromium/issues/detail?id=408120
// 404 bug: https://code.google.com/p/chromium/issues/detail?id=447916
// FileReader bug: https://code.google.com/p/chromium/issues/detail?id=447836
//
function checkBlobSupport(txn) {
  return new Promise(function (resolve) {
    var blob = createBlob(['']);
    txn.objectStore(DETECT_BLOB_SUPPORT_STORE).put(blob, 'key');

    txn.onabort = function (e) {
      // If the transaction aborts now its due to not being able to
      // write to the database, likely due to the disk being full
      e.preventDefault();
      e.stopPropagation();
      resolve(false);
    };

    txn.oncomplete = function () {
      var matchedChrome = navigator.userAgent.match(/Chrome\/(\d+)/);
      var matchedEdge = navigator.userAgent.match(/Edge\//);
      // MS Edge pretends to be Chrome 42:
      // https://msdn.microsoft.com/en-us/library/hh869301%28v=vs.85%29.aspx
      resolve(matchedEdge || !matchedChrome ||
        parseInt(matchedChrome[1], 10) >= 43);
    };
  }).catch(function () {
    return false; // error, so assume unsupported
  });
}

module.exports = checkBlobSupport;