SecondTransfer.Utils.HTTPHeaders

Utilities for working with headers.

Simple manipulation

These transformations are simple enough that don't require going away from the list representation (see type Headers)

lowercaseHeaders :: Headers -> Headers

HTTP headers are case-insensitive, so we can use lowercase versions everywhere

headersAreLowercase :: Headers -> Bool

Checks that headers are lowercase

headersAreLowercaseAtHeaderEditor :: HeaderEditor -> Bool

fetchHeader :: Headers -> ByteString -> Maybe ByteString

Looks for a given header

Transformations based on maps

Many operations benefit from transforming the list to a map with custom sorting and doing a set of operations on that representation.

data HeaderEditor

Abstract data-type. Use fromList to get one of these from Headers. The underlying representation admits better asymptotics.

Instances

Monoid HeaderEditor

type Headers = [Header]

List of headers. The first part of each tuple is the header name (be sure to conform to the HTTP/2 convention of using lowercase) and the second part is the headers contents. This list needs to include the special :method, :scheme, :authority and :path pseudo-headers for requests; and :status (with a plain numeric value represented in ascii digits) for responses.

Introducing and removing the HeaderEditor

fromList :: Headers -> HeaderEditor

O(n*log n) Builds the editor from a list.

toList :: HeaderEditor -> Headers

O(n) Takes the HeaderEditor back to Headers

Access to a particular header

headerLens :: ByteString -> Lens' HeaderEditor (Maybe ByteString)

headerLens header_name represents a lens into the headers, and you can use it then to add, alter and remove headers. It uses the same semantics than replaceHeaderValue

replaceHeaderValue :: HeaderEditor -> ByteString -> Maybe ByteString -> HeaderEditor

replaceHeaderValue headers header_name maybe_header_value looks for header_name. If header_name is found and maybe_header_value is nothing, it returns a new headers list with the header deleted. If header_name is found and header_value is Just new_value, it returns a new list with the header containing the new value. If header_name is not in headers and maybe_header_value is Nothing, it returns the original headers list. If header_name is not in headers and maybe_header_value is Just new_value, it returns a new list where the last element is (header_name, new_value)

HTTP utilities

replaceHostByAuthority :: HeaderEditor -> HeaderEditor

Replaces a "host" HTTP/1.1 header by an ":authority" HTTP/2 header. The list is expected to be already in lowercase, so nothing will happen if there the header name portion is "Host" instead of "host".

Notice that having a Host header in an HTTP/2 message is perfectly valid in certain circumstances, check Section 8.1.2.3 of the spec for details.

introduceDateHeader :: HeaderEditor -> IO HeaderEditor

Given a header editor, introduces a Date header. This function has a side-effect: to get the current time