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I had a problem with a custom HTTP SESSION_ID header not being transfered by nginx proxy.
I was told that underscores are prohibited according to the HTTP RFC.
Searching, I found that most servers like Apache or nginx define them as illegal in RFC2616 section 4.2, which says:
follow the same generic format as that given in Section 3.1 of RFC 822 [9]
RFC822 says:
The field-name must be composed of printable ASCII characters (i.e., characters that have values between 33. and 126., decimal, except colon)
Underscore is decimal character 95 in the ASCII table in the 33-126 range.
What am I missing?
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The value of the HTTP request header you want to set can only contain: Alphanumeric characters: a - z and A - Z. The following special characters: _ :;.,\/"'?!(){}[]@<>=-+*#$&`|~^%
You can, but you have to define a Header, then set its value. Like in the HttpWebRequest you can add any header, as long as its not one of the reserved ones.
HTTP headers let the client and the server pass additional information with an HTTP request or response. An HTTP header consists of its case-insensitive name followed by a colon ( : ), then by its value. Whitespace before the value is ignored.
HTTP headers are case insensitive. To simplify your code, URL Loading System canonicalizes certain header field names into their standard form. For example, if the server sends a content-length header, it's automatically adjusted to be Content-Length .
They are not forbidden, it's CGI legacy. See "Missing (disappearing) HTTP Headers".
If you do not explicitly set
underscores_in_headers on;, nginx will silently drop HTTP headers with underscores (which are perfectly valid according to the HTTP standard). This is done in order to prevent ambiguities when mapping headers to CGI variables, as both dashes and underscores are mapped to underscores during that process.
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Underscores in header fields are allowed per RFC 7230, sec. 3.2., but are uncommon.
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