Repr-Digest
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The Repr-Digest
response or request header provides a digest of the selected representation of the target resource. It is invariant under e.g., Content-Encoding
or Content-Range
, which do affect the Content-Digest
. Furthermore, Content Negotiation can result in different selected representations with different representation digests.
Header type | Representation header |
---|---|
Forbidden header name | no |
Syntax
Repr-Digest
describes an RFC8941 dictionary with its keys being names of digest algorithms and its values being the digest in bytes (or an integer digest for legacy digest algorithms).
Note: In contrast to earlier drafts of the specification, the standard-base64-encoded digest bytes are wrapped in colons (:
, ASCII 0x3A) as part of the dictionary syntax.
Directives
Digest algorithms
Only two digest algorithms are currently registered and not considered insecure: sha-512
and sha-256
.
The registered insecure digest algorithms are: md5
, sha
(SHA-1), unixsum
, unixcksum
, adler
(ADLER32) and crc32c
.
Usage of digest algorithms which are considered insecure is discouraged as collisions can realistically be forced, rendering the digest's usefulness weak. Unless when working with legacy systems (which is unlikely since most will expect the legacy Digest
header and not understand this specification), consider not emitting a Repr-Digest
instead of emitting one using an insecure digest algorithm.
Examples
HTTP response where Repr-Digest
and Content-Digest
coincide
An HTTP server may send content octets equivalent to the selected representation's octets:
...
Repr-Digest: sha-256=:AEGPTgUMw5e96wxZuDtpfm23RBU3nFwtgY5fw4NYORo=:
Content-Digest: sha-256=:AEGPTgUMw5e96wxZuDtpfm23RBU3nFwtgY5fw4NYORo=:
...
Content-Type: text/yaml
Content-Encoding: identity
Content-Length: 38054
Content-Range: 0-38053/38054
...
HTTP responses where Repr-Digest
and Content-Digest
diverge
A static file server may however choose to compress an HTML page, resulting in differing Content-Digest
and Repr-Digest
header values:
...
Repr-Digest: sha-256=:AEGPTgUMw5e96wxZuDtpfm23RBU3nFwtgY5fw4NYORo=:, sha-512=:U59TCCaZPA9Qio3CzHJVAgDnIAut53t5Sgkj2Gv4BvDd0b+OX9QpIdgWkzdXLmBsmvBrf3t5PBt+UrVK6k5dkw==:
Content-Digest: sha-256=:293wcr5IoFAsDCzdoDXR1Qppgf2yxOPO1bvQ3nZQtuI=:, unixsum=54809
...
Content-Type: text/html; charset=utf-8
Content-Encoding: br
...
...
...
Repr-Digest: sha-256=:AEGPTgUMw5e96wxZuDtpfm23RBU3nFwtgY5fw4NYORo=:, sha-512=:U59TCCaZPA9Qio3CzHJVAgDnIAut53t5Sgkj2Gv4BvDd0b+OX9QpIdgWkzdXLmBsmvBrf3t5PBt+UrVK6k5dkw==:
Content-Digest: sha-256=:rv9Jivc4TmcacLUshzN3OdX7Hz+ORnQRaiTaIKZQ0zk=:
...
Content-Type: text/html; charset=utf-8
Content-Encoding: deflate, deflate, deflate
...
...
Successful HTTP request-response employing Want-Repr-Digest
, Repr-Digest
, and Content-Digest
PUT /api/transact HTTP/1.1
Want-Repr-Digest: sha-256=8
Content-Type: text/json
...
HTTP/1.1 201 Created
Repr-Digest: sha-256=:W8oN3H3CmE/CBpV6ZPNozV2AIDzzQpWL7CCOXyDyDzI=:
Content-Encoding: br
Content-Digest: sha-256=:2IBI7hQn83oTCgB3Z/6apOl91WGoctRfRj/F9gkvVo8=:
...
Unsuccessful HTTP request-response employing Repr-Digest
GET /api/last-transaction HTTP/1.1
Accept: text/json
Repr-Digest: sha-256=:2IBI7hQn83oTCgB3Z/6apOl91WGoctRfRj/F9gkvVo8=:
...
HTTP/1.1 406 Not Acceptable
Repr-Digest: sha-256=:W8oN3H3CmE/CBpV6ZPNozV2AIDzzQpWL7CCOXyDyDzI=:
...
Specifications
Specification |
---|
Unknown specification |
Browser compatibility
BCD tables only load in the browser