'use strict';
var utils = require('../../utils');
var idbConstants = require('./constants');
var DETECT_BLOB_SUPPORT_STORE = idbConstants.DETECT_BLOB_SUPPORT_STORE;
//
// Detect blob support. Chrome didn't support it until version 38.
// In version 37 they had a broken version where PNGs (and possibly
// other binary types) aren't stored correctly, because when you fetch
// them, the content type is always null.
//
// Furthermore, they have some outstanding bugs where blobs occasionally
// are read by FileReader as null, or by ajax as 404s.
//
// Sadly we use the 404 bug to detect the FileReader bug, so if they
// get fixed independently and released in different versions of Chrome,
// then the bug could come back. So it's worthwhile to watch these issues:
// 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, idb) {
return new utils.Promise(function (resolve, reject) {
var blob = utils.createBlob([''], {type: 'image/png'});
txn.objectStore(DETECT_BLOB_SUPPORT_STORE).put(blob, 'key');
txn.oncomplete = function () {
// have to do it in a separate transaction, else the correct
// content type is always returned
var blobTxn = idb.transaction([DETECT_BLOB_SUPPORT_STORE],
'readwrite');
var getBlobReq = blobTxn.objectStore(
DETECT_BLOB_SUPPORT_STORE).get('key');
getBlobReq.onerror = reject;
getBlobReq.onsuccess = function (e) {
var storedBlob = e.target.result;
var url = URL.createObjectURL(storedBlob);
utils.ajax({
url: url,
cache: true,
binary: true
}, function (err, res) {
if (err && err.status === 405) {
// firefox won't let us do that. but firefox doesn't
// have the blob type bug that Chrome does, so that's ok
resolve(true);
} else {
resolve(!!(res && res.type === 'image/png'));
if (err && err.status === 404) {
utils.explain404('PouchDB is just detecting blob URL support.');
}
}
URL.revokeObjectURL(url);
});
};
};
}).catch(function () {
return false; // error, so assume unsupported
});
}
module.exports = checkBlobSupport;
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