A data race was introduced in #9919 when the old synchronous storage
API was replaced with an async storage API. The problem arises when
`fetchWithCache` is called a second time while it's still processing
another call. In this case, the `cachedFetch` object can become
stale while blocked waiting for a fetch response, and result in a cache
being overwritten unintentionally.
See this example (options omitted for simplicity, and assuming an empty
initial cache):
```
await Promise.all([
fetchWithCache('https://metamask.io/foo'),
fetchWithCache('https://metamask.io/bar'),
]
```
The order of events could be as follows:
1. Empty cache retrieved for `/foo` route
2. Empty cache retrieved for `/bar` route
3. Call made to `/foo` route
4. Call made to `/bar` route
5. `/foo` response is added to the empty cache object retrieved in
step 1, then is saved in the cache.
6. `/bar` response is added to the empty cache object retrieved in
step 2, then is saved in the cache.
In step 6, the cache object saved would not contain the `/foo`
response set in step 5. As a result, `/foo` would never be cached.
This problem was resolved by embedding the URL being cached directly in
the cache key. This prevents simultaneous responses from overwriting
each others caches.
Technically a data race still exists when handing simultaneous
responses to the same route, but the result would be that the last call
to finish would overwrite the previous. This seems acceptable.
A data race was introduced in #9919 when the old synchronous storage
API was replaced with an async storage API. The problem arises when
`fetchWithCache` is called a second time while it's still processing
another call. In this case, the `cachedFetch` object can become
stale while blocked waiting for a fetch response, and result in a cache
being overwritten unintentionally.
See this example (options omitted for simplicity, and assuming an empty
initial cache):
```
await Promise.all([
fetchWithCache('https://metamask.io/foo'),
fetchWithCache('https://metamask.io/bar'),
]
```
The order of events could be as follows:
1. Empty cache retrieved for `/foo` route
2. Empty cache retrieved for `/bar` route
3. Call made to `/foo` route
4. Call made to `/bar` route
5. `/foo` response is added to the empty cache object retrieved in
step 1, then is saved in the cache.
6. `/bar` response is added to the empty cache object retrieved in
step 2, then is saved in the cache.
In step 6, the cache object saved would not contain the `/foo`
response set in step 5. As a result, `/foo` would never be cached.
This problem was resolved by embedding the URL being cached directly in
the cache key. This prevents simultaneous responses from overwriting
each others caches.
Technically a data race still exists when handing simultaneous
responses to the same route, but the result would be that the last call
to finish would overwrite the previous. This seems acceptable.
* Use @metamask/eslint-config@1.1.0
* Use eslint-plugin-mocha@6.2.2
* Mark root ESLint config as root
* Update Mocha ESLint rules with shared ESLint config
The `fetch-with-cache` utility was failing to actually cache anything.
It would cache an object with cache time and URL, and would return that
instead of a valid response. This resulted in the error:
`TypeError: fourByteResponse.json is not a function`
The utility was updated to call `.json()` within itself, and cache the
JSON response. The function signature was updated as well, to expect an
options object instead of just the `cacheRefreshTime` option. The
timeout was added to this options object, which helped with testing.
The utility method now also handles unsuccessfull responses, and
incompatible `fetch` options.
Erik Marks
Mark Stacey
David Walsh
Brad Decker
Whymarrh Whitby