What is the "X-iinfo" HTTP header?

Question

I've seen an HTTP header called X-iinfo. Her are some examples:

X-Iinfo: 5-17009424-17011001 PNNN RT(1388193526625 4677) q(0 0 0 -1) r(1 1) U10000

X-Iinfo:4-13055499-13055501 NNNN CT(182 -1 0) RT(1388193578304 0) q(0 0 1 4) r(6 6) U1

Parts of them (but not all) seem to change on refresh.

What is this header?

Answer 1

I can confirm that it is a incapsula CDN header and i talked with then about a cache and got this info about it:

X-Iinfo:9-49176764-0 0CNN RT(1426425483129 667) q(0 -1 -1 -1) r(0 -1)

The C letter in the 0CNN above indicates the the resource is served from cache.

X-Iinfo:4-152072-152074 PVNN RT(1415979066955 4498) q(0 0 0 -1) r(2 2)

The V letter in the PVNN indicates the same, plus, that the resource passed validation (in the backend servers) and it is fresh.

X-Iinfo:4-152072-152074 PNNN RT(1415979066955 4498) q(0 0 0 -1) r(2 2)

Any other letter on that field will indicate that the resource is not served from cache and was fetch directly from the backend

Answer 2

After I pointed out to Imperva that their WAF Cloud Security customers are relying on Stack Overflow to interpret their header they have now kindly now included it in their documentation:

https://docs.imperva.com/bundle/cloud-application-security/page/settings/caching.htm

Answer 3

It appears to be related to the Incapsula search engine. Every site I found that supplied the X-Iinfo header also supplied X-CDN: Incapsula.

I couldn't find documentation on what the numbers mean, but the first number after RT appears to be a date. The rest would require more investigation.