Validators & conditional requests
06A validator lets a client ask whether cached content is current or whether an edit would overwrite a newer version.
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Related RFCs and changes
“Updates” changes part of an earlier RFC. “Obsoletes” replaces it. This list shows selected related documents.
DIAGRAM§ 13 ↗
RFC 9110 · § 13EXAMPLE
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04
Protect a newer edit.
A stale condition fails instead of silently overwriting revision 8.
Protocol participantThreat or exceptionProtocol controlSimplified drawings · precise section references
Read the updated RFC section ↗
Attach a precondition before reading or changing state.
- If-None-Match can revalidate GET or HEAD; an unchanged representation can produce 304.
- If-Match uses strong comparison and can prevent overwriting a changed representation.
- Failed preconditions generally produce 412, with evaluation order defined in §13.2.
Weak validators can establish semantic equivalence for some uses; they do not prove byte-for-byte identity for every operation. A 304 has no response content.
Read the RFC section ↗Diagrams simplify the RFC. Read the linked sections for complete requirements.
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