RFC 5988 是否允许在 HTTP Link header 中使用空格？

Question

RFC 5988 的第 5 节定义 Link header 的语法如下：

Link           = "Link" ":" #link-value
link-value     = "<" URI-Reference ">" *( ";" link-param )

本规范使用 RFC 822 中定义的扩充 Backus-Naur 形式 (BNF)。

如果正确理解 BNF，规范不允许分号 (;) 和 link-param 之间有空格。但是，在第 5 节中出现的示例中，两个元素之间有空格：

Link: <http://example.com/TheBook/chapter2>; rel="previous";
      title="previous chapter"

Link: </>; rel="http://example.net/foo"

我还在 Link header 和 Github 的 API 中观察到空白，我认为这是更多 standard-compliant APIs:

$ curl -s -I https://api.github.com/users/mitsuhiko/repos
...
Link: <https://api.github.com/user/7396/repos?page=2>; rel="next", <https://api.github.com/user/7396/repos?page=7>; rel="last"

空格应该是允许的吗？除了这些例子之外，我找不到任何可以提供证据的东西。

Answer 1

这是允许的； RFC 5988 使用 RFC 2616 定义的 ABNF，它对线性白色 space 有特殊规则。见 https://www.greenbytes.de/tech/webdav/rfc5988.html#rfc.section.2.p.2 and https://www.greenbytes.de/tech/webdav/rfc2616.html#rfc.section.2.1:

The grammar described by this specification is word-based. Except where noted otherwise, linear white space (LWS) can be included between any two adjacent words (token or quoted-string), and between adjacent words and separators, without changing the interpretation of a field. At least one delimiter (LWS and/or separators) MUST exist between any two tokens (for the definition of "token" below), since they would otherwise be interpreted as a single token.

FWIW，无论如何，RFC 5988 几个月前就已经过时了；请参阅 RFC 8288 (https://www.greenbytes.de/tech/webdav/rfc8288.html) 了解最新和最好的（特别是第 3 节）。

RFC 5988 是否允许在 HTTP Link header 中使用空格？

Does RFC 5988 allow whitespace in the HTTP Link header?

http

http-headers

bnf

rfc822

rfc5988