- সারি
- ৩ আগস্ট, ২০২৬ এ ২:৩১ AM UTC
- লেখক
- Kamo
- মন্তব্য@ info: status
- 46af581
Resolves a correspondent's email address to a picture, working outward from what Kamo already knows: member photo, then a photo someone attached to a contact, then the tenant's connected Microsoft/Google directory, then the sender domain's BIMI mark, then its favicon, then Gravatar. Anything unresolved renders a monogram, so the chain always terminates locally. The directory tier is worth calling out: the connect flows here already request admin.directory.user (Google) and User.ReadWrite.All + Directory.Read.All (Microsoft) alongside the mail scopes, so for Workspace and 365 tenants this returns authoritative photos with no re-consent and no third party involved. It should beat anything on the public internet and usually will. Two phases, never one. A request reads cache only; unknowns go to a bounded worker with DiscardPolicy — running an overflowed task on the caller would hand a request thread to a third-party host, and a discarded resolve costs nothing because the next poll asks again. A full-miss chain is DNS plus four HTTP calls, and a page carries dozens of addresses; nothing about opening a folder may depend on third-party availability. Decoupling also keeps resolution from correlating with a human opening a message, which would make it a read receipt — the exact behaviour the mailbox already blocks by default for remote images. This is the platform's first fetcher whose target URL is chosen by an untrusted party: a BIMI record is DNS content published by whoever owns a sending domain, and anyone becomes a sending domain by emailing a tenant. There is no egress NetworkPolicy and no forward proxy, so the controls are in code. SafeImageFetcher pins DNS — a custom resolver hands OkHttp only the addresses that passed PublicHostGuard, closing the rebinding window that defeats a naive pre-flight check — refuses redirects, caps bytes as they stream rather than trusting Content-Length, and requires an image content-type. SvgSanitizer parses and re-serializes against an allowlist instead of rasterizing. Batik 1.17 resolves external resources by default, so handing it a hostile SVG would dereference <image **************** from inside the cluster after the URL check already passed. The Tiny PS profile forbidding that is a statement about conforming files, not about bytes fetched from an attacker's URL. Provider miss semantics are all different and all cache-poisoning if treated as hits: Gravatar is asked with d=404 because every other default returns 200 with a placeholder; Google's no-match is a 404 carrying a byte-identical globe, so it is rejected by content hash; DuckDuckGo returns 404 with a real image body, so status decides. Bytes are re-hosted under a random name — never one derived from the address, which would let anyone probe whether a given person corresponds with this platform — and served through an authenticated route. Redis holds metadata only. That instance is 2GB with allkeys-lru on an emptyDir, sharing a keyspace with every live session; caching image bytes there would evict sessions and sign users out at random.