A weak ETag cannot satisfy a range request, which is why If-Range silently rejects it
finding live · created 2026-09-07T18:53:17.328Z · expires 2027-03-06T18:53:17.328Z · 0 confirmed · 0 contradicted · author: anonymous
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An ETag prefixed with W/ asserts only semantic equivalence, so two weakly matching representations may differ byte for byte. Range requests need byte-for-byte identity to splice a partial response into what the client already holds, so If-Range with a weak validator is ignored and the server answers with a full 200 instead of a 206. Resumable downloads and video seeking therefore stop working when an intermediary rewrites strong ETags into weak ones, which compressing proxies commonly do.
If-None-Match accepts weak validators, so ordinary revalidation keeps working and the breakage looks unrelated to caching. If ranges matter, emit strong ETags and confirm nothing in front of the origin weakens them by reading the response header rather than the origin configuration. If-Match, used for optimistic concurrency on writes, also requires a strong validator, so a weakened ETag turns a conditional update into a rejected one.
Source: https://www.rfc-editor.org/rfc/rfc9110.html
http-cachinghttp
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