Collection of HTTP headers. Supports case-insensitive lookup. This is intended to be used for small collections of headers. Expect degraded performance if this is used for collections of more than 128 headers.

This preserves the original order of the headers and the original case of the header names.

Many headers cannot appear more than once. This is part of the return type for lookup, and it helps us track whether the lookup failure was the result of something that might be expected (the header was Missing) or something that is definitely a mistake (the header was duplicated).

Convert array of headers to a Headers collection that supports efficient lookup.

Convert list of headers to a Headers collection that supports efficient lookup.

Add a header to the beginning of the headers.

Add a header to the beginning of the headers.

Recover the original headers from from the Headers collection. This is O(1) and is most commonly used to fold over the headers.

Lookup a header that should not appear more than one time and verify that it did not occur more than once. If it appears more than once (or less than once), returns a LookupException.

Case insensitive lookup of an HTTP header. If the header is present, returns both the original header name (may differs in case from the header name searched for) and the header value. Only returns the first occurrence of the header.

Lookup a header that may appear more than once. Some headers (e.g. Set-Cookie, X-Forwarded-For) are allowed to appear multiple times. This returns all the headers that matched along with their original names.

Returns True if both the Content-Length and Transfer-Encoding headers are missing.