| Safe Haskell | Safe-Inferred |
|---|---|
| Language | Haskell2010 |
WebGear.Core.Trait.Header
Contents
Description
Traits and middlewares to handle request and response headers.
There are a number of ways to extract a header value from a request:
The header middleware can extract a header value trait and invoke
another handler. An error handler is invoked if the header is missing
or the parsing fails.
The optionalHeader middleware is similar but will not invoke the
error handling in case the header is missing. Instead, the trait
value will be set to Nothing in that case.
The lenientHeader middleware requires the header to be present. But
the trait attribute will be set to Left msg if an error occurs
while parsing it to a Haskell value. Here msg will indicate the
error in parsing.
Finally, we have optionalLenientHeader which combines the behaviors
of optionalHeader and lenientHeader. In this case, the header
extraction never fails. Missing headers and parse errors are
indicated in the trait attribute passed to next handler.
A response header can be set using setHeader or setOptionalHeader
arrows. They accept a linked response and a header value and sets the
header in the response. You can generate an input response object
using functions from WebGear.Core.Trait.Status module.
Synopsis
- data Header (e :: Existence) (p :: ParseStyle) (name :: Symbol) (val :: Type) = Header
- data HeaderNotFound = HeaderNotFound
- newtype HeaderParseError = HeaderParseError Text
- type RequiredHeader = Header Required Strict
- type OptionalHeader = Header Optional Strict
- header :: forall name val h req. (Get h (Header Required Strict name val) Request, ArrowChoice h) => h (Linked req Request, Either HeaderNotFound HeaderParseError) Response -> Middleware h req (Header Required Strict name val ': req)
- optionalHeader :: forall name val h req. (Get h (Header Optional Strict name val) Request, ArrowChoice h) => h (Linked req Request, HeaderParseError) Response -> Middleware h req (Header Optional Strict name val ': req)
- lenientHeader :: forall name val h req. (Get h (Header Required Lenient name val) Request, ArrowChoice h) => h (Linked req Request, HeaderNotFound) Response -> Middleware h req (Header Required Lenient name val ': req)
- optionalLenientHeader :: forall name val h req. (Get h (Header Optional Lenient name val) Request, ArrowChoice h) => Middleware h req (Header Optional Lenient name val ': req)
- setHeader :: forall name val a h res. Set h (Header Required Strict name val) Response => h a (Linked res Response) -> h (val, a) (Linked (Header Required Strict name val ': res) Response)
- setOptionalHeader :: forall name val a h res. Set h (Header Optional Strict name val) Response => h a (Linked res Response) -> h (Maybe val, a) (Linked (Header Optional Strict name val ': res) Response)
Traits
data Header (e :: Existence) (p :: ParseStyle) (name :: Symbol) (val :: Type) Source #
A Trait for capturing an HTTP header of specified name and
converting it to some type val. The modifiers e and p determine
how missing headers and parsing errors are handled. The header name
is compared case-insensitively.
Constructors
| Header |
Instances
data HeaderNotFound Source #
Indicates a missing header
Constructors
| HeaderNotFound |
Instances
| Read HeaderNotFound Source # | |
Defined in WebGear.Core.Trait.Header Methods readsPrec :: Int -> ReadS HeaderNotFound # readList :: ReadS [HeaderNotFound] # | |
| Show HeaderNotFound Source # | |
Defined in WebGear.Core.Trait.Header Methods showsPrec :: Int -> HeaderNotFound -> ShowS # show :: HeaderNotFound -> String # showList :: [HeaderNotFound] -> ShowS # | |
| Eq HeaderNotFound Source # | |
Defined in WebGear.Core.Trait.Header Methods (==) :: HeaderNotFound -> HeaderNotFound -> Bool # (/=) :: HeaderNotFound -> HeaderNotFound -> Bool # | |
newtype HeaderParseError Source #
Error in converting a header
Constructors
| HeaderParseError Text |
Instances
| Read HeaderParseError Source # | |
Defined in WebGear.Core.Trait.Header Methods readsPrec :: Int -> ReadS HeaderParseError # readList :: ReadS [HeaderParseError] # | |
| Show HeaderParseError Source # | |
Defined in WebGear.Core.Trait.Header Methods showsPrec :: Int -> HeaderParseError -> ShowS # show :: HeaderParseError -> String # showList :: [HeaderParseError] -> ShowS # | |
| Eq HeaderParseError Source # | |
Defined in WebGear.Core.Trait.Header Methods (==) :: HeaderParseError -> HeaderParseError -> Bool # (/=) :: HeaderParseError -> HeaderParseError -> Bool # | |
Middlewares
Arguments
| :: forall name val h req. (Get h (Header Required Strict name val) Request, ArrowChoice h) | |
| => h (Linked req Request, Either HeaderNotFound HeaderParseError) Response | Error handler |
| -> Middleware h req (Header Required Strict name val ': req) |
Extract a header value and convert it to a value of type val.
The associated trait attribute has type val.
Example usage:
header @"Content-Length" @Integer errorHandler okHandler
Arguments
| :: forall name val h req. (Get h (Header Optional Strict name val) Request, ArrowChoice h) | |
| => h (Linked req Request, HeaderParseError) Response | Error handler |
| -> Middleware h req (Header Optional Strict name val ': req) |
Extract an optional header value and convert it to a value of type
val.
The associated trait attribute has type Maybe val; a Nothing
value indicates that the header is missing from the request.
Example usage:
optionalHeader @"Content-Length" @Integer errorHandler okHandler
Arguments
| :: forall name val h req. (Get h (Header Required Lenient name val) Request, ArrowChoice h) | |
| => h (Linked req Request, HeaderNotFound) Response | Error handler |
| -> Middleware h req (Header Required Lenient name val ': req) |
Extract a header value and convert it to a value of type val.
The associated trait attribute has type Either Text val. The
parsing is done leniently and any errors are reported in the trait
attribute.
Example usage:
lenientHeader @"Content-Length" @Integer errorHandler okHandler
optionalLenientHeader :: forall name val h req. (Get h (Header Optional Lenient name val) Request, ArrowChoice h) => Middleware h req (Header Optional Lenient name val ': req) Source #
Extract a header value and convert it to a value of type val.
The associated trait attribute has type Maybe (Either Text
val). The parsing is done leniently. Any parsing errors and
missing header are reported in the trait attribute.
Example usage:
optionalLenientHeader @"Content-Length" @Integer handler
setHeader :: forall name val a h res. Set h (Header Required Strict name val) Response => h a (Linked res Response) -> h (val, a) (Linked (Header Required Strict name val ': res) Response) Source #
Set a header value in a response.
Example usage:
response' <- setHeader @"Content-Length" -< (response, 42)
setOptionalHeader :: forall name val a h res. Set h (Header Optional Strict name val) Response => h a (Linked res Response) -> h (Maybe val, a) (Linked (Header Optional Strict name val ': res) Response) Source #
Set an optional header value in a response.
Setting the header to Nothing will remove it from the response if
it was previously set. The header will be considered as optional in
all relevant places (such as documentation).
Example usage:
response' <- setOptionalHeader @"Content-Length" -< (response, Just 42)