Safe Haskell	None
Language	GHC2021

Ecluse.Core.Server.Conditional

Contents

Our own ETag (transformed bodies)
Relaying validators (pass-through bodies)

Description

Conditional-GET and ETag handling, split by how the served body relates to upstream's.

A pass-through body (an artifact, unfiltered private metadata) is byte-identical to upstream's, so the client's validators are relayed upstream (forwardValidators) and an upstream 304 is passed back (isNotModified). A transformed body (every packument is merged and filtered) takes our own strong ETag instead, derived from the serve's inputs rather than hashed over its output. It can therefore be stale only in the safe direction, a spurious 200 and never a wrong 304, and a 304 costs no assembly at all.

Synopsis

data ETag
mkStrongETag :: Digest SHA256 -> ETag
renderETag :: ETag -> Text
etagHeader :: ETag -> Header
data Conditional
- = NotModified ETag
- | Modified ETag
evaluateETag :: RequestHeaders -> ETag -> Conditional
forwardValidators :: RequestHeaders -> RequestHeaders
isNotModified :: Status -> Bool

Our own ETag (transformed bodies)

data ETag Source #

A strong entity tag in the quoted wire form ("…") the ETag header carries. The 'newtype' keeps that quoted form from being confused with the bare digest.

Instances

Instances details

Show ETag Source #
Instance details Defined in Ecluse.Core.Server.Conditional Methods showsPrec :: Int -> ETag -> ShowS # show :: ETag -> String # showList :: [ETag] -> ShowS #
Eq ETag Source #
Instance details Defined in Ecluse.Core.Server.Conditional Methods (==) :: ETag -> ETag -> Bool # (/=) :: ETag -> ETag -> Bool #
Ord ETag Source #
Instance details Defined in Ecluse.Core.Server.Conditional Methods compare :: ETag -> ETag -> Ordering # (<) :: ETag -> ETag -> Bool # (<=) :: ETag -> ETag -> Bool # (>) :: ETag -> ETag -> Bool # (>=) :: ETag -> ETag -> Bool # max :: ETag -> ETag -> ETag # min :: ETag -> ETag -> ETag #

mkStrongETag :: Digest SHA256 -> ETag Source #

Quote a SHA-256 digest as a strong ETag, hex-encoded. The digest is whatever fingerprint the serving layer stands behind.

renderETag :: ETag -> Text Source #

The ETags wire form, the quoted opaque tag as it goes into the header.

etagHeader :: ETag -> Header Source #

The ETag response header carrying this validator.

data Conditional Source #

The conditional outcome for a transformed body: whether the client's validator already matches what we would serve.

Constructors

NotModified ETag	The served body is unchanged from the client's validator. Answer `304` with this `ETag` and no body.
Modified ETag	The served body differs, or no validator was sent. Serve `200` with this `ETag` header.

Instances

Instances details

Show Conditional Source #
Instance details Defined in Ecluse.Core.Server.Conditional Methods showsPrec :: Int -> Conditional -> ShowS # show :: Conditional -> String # showList :: [Conditional] -> ShowS #
Eq Conditional Source #
Instance details Defined in Ecluse.Core.Server.Conditional Methods (==) :: Conditional -> Conditional -> Bool # (/=) :: Conditional -> Conditional -> Bool #

evaluateETag :: RequestHeaders -> ETag -> Conditional Source #

Evaluate a conditional request against our own ETag. The comparison is weak (RFC 7232), and If-Modified-Since is not consulted: a merge has no single upstream timestamp.

Relaying validators (pass-through bodies)

forwardValidators :: RequestHeaders -> RequestHeaders Source #

The client's conditional validators to relay upstream for a pass-through body. Only these two are forwarded, so upstream answers 304 without receiving any other client header.

isNotModified :: Status -> Bool Source #

Whether an upstream response is a 304 Not Modified to pass straight back to the client. Used on the pass-through path, where upstream's own validator decided.