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Merge pull request #558 from nolanlawson/simpler-blob-check

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refactor(localforage): simpler blob support check
This commit is contained in:
tofumatt ☕️ 2016-05-04 22:53:26 +01:00
commit aadd230688
1 changed files with 27 additions and 60 deletions
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87
src/drivers/indexeddb.js
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@ -25,75 +25,42 @@ function _binStringToArrayBuffer(bin) {
return buf;
}
// Fetch a blob using ajax. This reveals bugs in Chrome < 43.
// For details on all this junk:
// https://github.com/nolanlawson/state-of-binary-data-in-the-browser#readme
function _blobAjax(url) {
return new Promise(function(resolve, reject) {
var xhr = new XMLHttpRequest();
xhr.open('GET', url);
xhr.withCredentials = true;
xhr.responseType = 'arraybuffer';
xhr.onreadystatechange = function() {
if (xhr.readyState !== 4) {
return;
}
if (xhr.status === 200) {
return resolve({
response: xhr.response,
type: xhr.getResponseHeader('Content-Type')
});
}
reject({status: xhr.status, response: xhr.response});
};
xhr.send();
});
}
//
// 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.
// Blobs are not supported in all versions of IndexedDB, notably
// Chrome <37 and Android <5. In those versions, storing a blob will throw.
//
// Furthermore, they have some outstanding bugs where blobs occasionally
// are read by FileReader as null, or by ajax as 404s.
// 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.
//
// 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:
// 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 _checkBlobSupportWithoutCaching(idb) {
return new Promise(function(resolve, reject) {
var blob = createBlob([''], {type: 'image/png'});
var txn = idb.transaction([DETECT_BLOB_SUPPORT_STORE], 'readwrite');
// Code borrowed from PouchDB. See:
// https://github.com/pouchdb/pouchdb/blob/9c25a23/src/adapters/idb/blobSupport.js
//
function _checkBlobSupportWithoutCaching(txn) {
return new Promise(function(resolve) {
var blob = createBlob(['']);
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);
_blobAjax(url).then(function(res) {
resolve(!!(res && res.type === 'image/png'));
}, function() {
resolve(false);
}).then(function() {
URL.revokeObjectURL(url);
});
};
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);
};
txn.onerror = txn.onabort = reject;
}).catch(function() {
return false; // error, so assume unsupported
});