The HTTP Dictionary-ID request header references a dictionary that can be used in Compression Dictionary Transport to compress the server's response.

A server can indicate that a resource can be used as a dictionary by sending the Use-As-Dictionary header with the response. The server may include an id directive in the Use-As-Dictionary header, thus assigning an ID value to the dictionary. If the server does this, then when the browser requests a resource that can be compressed using the dictionary, the resource request must include the Dictionary-ID header, and its value must match the ID that was given in Use-As-Dictionary.

This allows the server to identify and find a dictionary that is referenced by some arbitrary key, rather than having to use the dictionary hash as a key (if that approach is used, the server will have to hash every response that includes the Use-As-Dictionary header just in case the resource might eventually be used as a dictionary).

Note that while the server can identify and locate the dictionary from its Dictionary-ID, it must still check the hash from the Available-Dictionary header to confirm that it is a correct match.

See the Compression Dictionary Transport guide for more information.

Syntax

Dictionary-ID: "<string-identifier>"

Directives

<string-identifier>

A string representing the dictionary's server-assigned ID.

Examples

For example, suppose the server has sent a Use-As-Dictionary header containing an id="dictionary-12345" directive:

Use-As-Dictionary: match="/js/app.*.js", id="dictionary-12345"

When the client requests a matching resource, it will include this id value in a Dictionary-ID header:

Accept-Encoding: gzip, br, zstd, dcb, dcz
Available-Dictionary: :pZGm1Av0IEBKARczz7exkNYsZb8LzaMrV7J32a2fFG4=:
Dictionary-ID: "dictionary-12345"

Specifications

Browser compatibility

See also

• Compression Dictionary Transport guide
• Available-Dictionary
• Use-As-Dictionary