/sync error Error: CORS request rejected

[dajohi]

When using https://riot.im/app logged into a third-party homeserver matrix.example.com (changed for sake of PR) with Firefox, hitting F5/refresh I see:

/sync error Error: CORS request rejected: https://matrix.example.com/_matrix/client/r0/sync?filter=2&timeout=30000&since=s1010070_41078931_376_3148196_408924_861_1044_174076_38 bundle.js:41:18094
    r https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:41
    _onSyncError https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:70
    e https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:70
    E https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    _invoke https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    t https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    c https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _promiseRejected https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _settlePromise https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _rejectPromises https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _settlePromises https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    p https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    d https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _drainQueues https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    drainQueues https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    a https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:63
    A https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:63
    u https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:41

Error: "CORS request rejected: https://matrix.example.com/_matrix/client/r0/sync?filter=2&timeout=30000&since=s1010070_41078931_376_3148196_408924_861_1044_174076_38"
    c https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    onreadystatechange https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
bundle.js:41:18094
    r https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:41
    _onSyncError https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:70
    e https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:70
    E https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    _invoke https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    t https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:23
    c https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _promiseRejected https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _settlePromise https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _rejectPromises https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _settlePromises https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    p https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    d https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    _drainQueues https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    drainQueues https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:1
    a https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:63
    A https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:63
    u https://riot.im/app/bundles/ffb4fa6e8a9bd1bedd9a/bundle.js:41

Does the third-party synapse server need to implement CORS?

[jryans]

Yes, servers are generally expected to set the CORS headers on responses.

If Synapse is not doing that for some request, please file an issue on that repo. If it's some other HS, they should likely change to set these headers.

This doesn't seem like Riot issue, so I'll close this, but please re-open if I misunderstood.