CODEWITHSUNDEEP
httphttp-headersvary
WASD42
WASD42

Reputation: 2379

Multiple Vary HTTP headers or one combined?

Question: What is the best way to send Vary HTTP header when server accept gzip/deflate connections AND serve a different content for mobile clients?

I see two possible variants but I cannot find any useful information whether they are correct and/or supported by most proxies and search engines:

  1. Combine variants to a single line: Vary: Accept-Encoding,User-Agent
  2. Send two separate headers:

Vary: Accept-Encoding

Vary: User-Agent

Any information or link to appropriate W3C standard are welcome :)

Upvotes: 15

Views: 5251

Answers (2)

Daniel W.
Daniel W.

Reputation: 32260

Multiple header fields with the same name are allowed for two cases:

  1. Set-Cookie

  2. All header fields where value is always a list (values seperated by commas)

Examples: Accept-Encoding, Vary, ...

RFC 7230 - 3.2.2

A sender MUST NOT generate multiple header fields with the same field name in a message unless either the entire field value for that header field is defined as a comma-separated list [i.e., #(values)] or the header field is a well-known exception (as noted below).

A recipient MAY combine multiple header fields with the same field name into one "field-name: field-value" pair, without changing the
semantics of the message, by appending each subsequent field value to the combined field value in order, separated by a comma. The order
in which header fields with the same field name are received is
therefore significant to the interpretation of the combined field
value; a proxy MUST NOT change the order of these field values when
forwarding a message.

Note: In practice, the "Set-Cookie" header field ([RFC6265]) often appears multiple times in a response message and does not use the list syntax, violating the above requirements on multiple header fields with the same name. Since it cannot be combined into a single field-value, recipients ought to handle "Set-Cookie" as a special case while processing header fields. (See Appendix A.2.3 of [Kri2001] for details.)

Upvotes: 2

Julian Reschke
Julian Reschke

Reputation: 41997

Both are valid (and mean the same thing).

And no, the W3C isn't relevant here. You will need to look into the IETF RFCs 7230 and 7231.

Upvotes: 17

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