Want-Digest

The Want-Digest HTTP header is primarily used in a HTTP request, to ask the server to provide a digest of the requested resource using the Digest response header.

The header contains identifiers for one or more digest algorithms that the sender wishes the server to use to create the digest. The request may use quality values to indicate its preference/order for particular digest algorithms.

If Want-Digest does not include any digest algorithms that the server supports, the server may respond with:

  • a digest calculated using a different digest algorithm, or
  • a 400 Bad Request error, and include another Want-Digest header with that response, listing the algorithms that it does support.

See the page for the Digest header for more information.

Header type Request header, Response header
Forbidden header name no

Syntax

Want-Digest: <digest-algorithm>

// Multiple algorithms, weighted with the quality value syntax:
Want-Digest: <digest-algorithm><q-value>,<digest-algorithm><q-value>

Directives

<digest-algorithm>

Digest algorithms are defined in Digest Headers.

  • Permitted digest algorithms values include: unixsum, unixcksum, crc32c, sha-256 and sha-512, id-sha-256, id-sha-512
  • Deprecated algorithms values include: md5, sha, adler32.
<q-value>

The quality value to apply to that option.

Examples

Want-Digest: sha-256
Want-Digest: SHA-512;q=0.3, sha-256;q=1, md5;q=0

Basic operation

The sender provides a list of digests which it is prepared to accept, and the server uses one of them:

Request:

GET /item
Want-Digest: sha-256;q=0.3, sha;q=1

Response:

HTTP/1.1 200 Ok
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

Unsupported digests

The server does not support any of the requested digest algorithms, so uses a different algorithm:

Request:

GET /item
Want-Digest: sha;q=1

Response:

HTTP/1.1 200 Ok
Digest: sha-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=

The server does not support any of the requested digest algorithms. In this case it responds with a 400 error and includes another Want-Digest header, listing the algorithms that it does support:

Request:

GET /item
Want-Digest: sha;q=1

Response:

HTTP/1.1 400 Bad Request
Want-Digest: sha-256, sha-512

Specifications

Specification
Unknown specification
# section-4

Browser compatibility

BCD tables only load in the browser

See also