why resource timing api is giving the encoded , decoded and transfer size of some resources as 0?

Question

I am using resource timing api to capture the encoded, decoded and transfer size of all the resources of a page,but for some of the resources it is giving the zero for all the 3 keys. Please help me to solve this.

Answer 1

The Timing-Allow-Origin header is a response header. It can be zero due to the cross-origin restrictions.

You can check your browser header response section. Also, you want to share the timing data with a web site.

Timing-Allow-Origin: https://example.com

Or, you can specify a wild card, but it not recommended because it will open yourself up to cross-site timing attacks via the Web Resource Timing API.

Timing-Allow-Origin: *

Bonus: Twitter Silhouette Attack

Answer 2

it happens for the cross origin resources when the "Timing-Allow-Origin" header is not set by the server and hence wont expose the resource timing values please go through the specification here

hope this answers your question.