pub const ETAG: OptNumber;Expand description
ETag
generated from RFC7252 section 5.10.6
An entity-tag is intended for use as a resource-local identifier for differentiating between representations of the same resource that vary over time. It is generated by the server providing the resource, which may generate it in any number of ways including a version, checksum, hash, or time. An endpoint receiving an entity- tag MUST treat it as opaque and make no assumptions about its content or structure. (Endpoints that generate an entity-tag are encouraged to use the most compact representation possible, in particular in regards to clients and intermediaries that may want to store multiple ETag values.)
ETag as a Request Option
ETag as a Request Option
generated from RFC7252 section 5.10.6.2
In a GET request, an endpoint that has one or more representations previously obtained from the resource, and has obtained ETag response options with these, can specify an instance of the ETag Option for one or more of these stored responses.
A server can issue a 2.03 Valid response (Section 5.9.1.3) in place of a 2.05 Content response if one of the ETags given is the entity- tag for the current representation, i.e., is valid; the 2.03 Valid response then echoes this specific ETag in a response option.
In effect, a client can determine if any of the stored representations is current (see Section 5.6.2) without needing to transfer them again.
The ETag Option MAY occur zero, one, or multiple times in a request.
ETag as a Response Option
ETag as a Response Option
generated from RFC7252 section 5.10.6.1
The ETag Option in a response provides the current value (i.e., after the request was processed) of the entity-tag for the “tagged representation”. If no Location-* options are present, the tagged representation is the selected representation (Section 5.5.3) of the target resource. If one or more Location-* options are present and thus a location URI is indicated (Section 5.10.7), the tagged representation is the representation that would be retrieved by a GET request to the location URI.
An ETag response option can be included with any response for which there is a tagged representation (e.g., it would not be meaningful in a 4.04 or 4.00 response). The ETag Option MUST NOT occur more than once in a response.
There is no default value for the ETag Option; if it is not present in a response, the server makes no statement about the entity-tag for the tagged representation.