Snap.Types

snap-core-0.2.16: Snap: A Haskell Web Framework (Core)

Snap.Types

Contents

- The Snap Monad
  - Functions for control flow and early termination
  - Routing
  - Access to state
  - Logging
  - Grabbing/transforming request bodies
- HTTP Datatypes and Functions
  - Headers
  - Requests
  - Responses
    - Response I/O
- Iteratee
- HTTP utilities

Description

This module contains the core type definitions, class instances, and functions for HTTP as well as the `Snap` monad, which is used for web handlers.

Synopsis

- data Snap a
- runSnap :: Snap a -> (ByteString -> IO ()) -> Request -> Iteratee IO (Request, Response)
- data NoHandlerException = NoHandlerException
- finishWith :: Response -> Snap a
- pass :: Snap a
- method :: Method -> Snap a -> Snap a
- path :: ByteString -> Snap a -> Snap a
- dir :: ByteString -> Snap a -> Snap a
- ifTop :: Snap a -> Snap a
- route :: [(ByteString, Snap a)] -> Snap a
- routeLocal :: [(ByteString, Snap a)] -> Snap a
- getRequest :: Snap Request
- getResponse :: Snap Response
- putRequest :: Request -> Snap ()
- putResponse :: Response -> Snap ()
- modifyRequest :: (Request -> Request) -> Snap ()
- modifyResponse :: (Response -> Response) -> Snap ()
- localRequest :: (Request -> Request) -> Snap a -> Snap a
- withRequest :: (Request -> Snap a) -> Snap a
- withResponse :: (Response -> Snap a) -> Snap a
- logError :: ByteString -> Snap ()
- runRequestBody :: Iteratee IO a -> Snap a
- getRequestBody :: Snap ByteString
- transformRequestBody :: (forall a. Enumerator a) -> Snap ()
- data Request
- data Response
- type Headers = Map CIByteString [ByteString]
- class HasHeaders a where
  - updateHeaders :: (Headers -> Headers) -> a -> a
  - headers :: a -> Headers
- type Params = Map ByteString [ByteString]
- data Method
  - = GET
  - | HEAD
  - | POST
  - | PUT
  - | DELETE
  - | TRACE
  - | OPTIONS
  - | CONNECT
- data Cookie = Cookie {
  - cookieName :: !ByteString
  - cookieValue :: !ByteString
  - cookieExpires :: !(Maybe UTCTime)
  - cookieDomain :: !(Maybe ByteString)
  - cookiePath :: !(Maybe ByteString)
  }
- type HttpVersion = (Int, Int)
- addHeader :: HasHeaders a => CIByteString -> ByteString -> a -> a
- setHeader :: HasHeaders a => CIByteString -> ByteString -> a -> a
- getHeader :: HasHeaders a => CIByteString -> a -> Maybe ByteString
- deleteHeader :: HasHeaders a => CIByteString -> a -> a
- ipHeaderFilter :: Snap ()
- ipHeaderFilter' :: CIByteString -> Snap ()
- rqServerName :: Request -> ByteString
- rqServerPort :: Request -> Int
- rqRemoteAddr :: Request -> ByteString
- rqRemotePort :: Request -> Int
- rqLocalAddr :: Request -> ByteString
- rqLocalHostname :: Request -> ByteString
- rqIsSecure :: Request -> Bool
- rqContentLength :: Request -> Maybe Int
- rqMethod :: Request -> Method
- rqVersion :: Request -> HttpVersion
- rqCookies :: Request -> [Cookie]
- rqPathInfo :: Request -> ByteString
- rqContextPath :: Request -> ByteString
- rqURI :: Request -> ByteString
- rqQueryString :: Request -> ByteString
- rqParams :: Request -> Params
- rqParam :: ByteString -> Request -> Maybe [ByteString]
- getParam :: ByteString -> Snap (Maybe ByteString)
- rqModifyParams :: (Params -> Params) -> Request -> Request
- rqSetParam :: ByteString -> [ByteString] -> Request -> Request
- emptyResponse :: Response
- setResponseCode :: Int -> Response -> Response
- setResponseStatus :: Int -> ByteString -> Response -> Response
- rspStatus :: Response -> Int
- rspStatusReason :: Response -> ByteString
- setContentType :: ByteString -> Response -> Response
- addCookie :: Cookie -> Response -> Response
- setContentLength :: Int64 -> Response -> Response
- clearContentLength :: Response -> Response
- redirect :: ByteString -> Snap ()
- redirect' :: ByteString -> Int -> Snap ()
- setResponseBody :: (forall a. Enumerator a) -> Response -> Response
- modifyResponseBody :: (forall a. Enumerator a -> Enumerator a) -> Response -> Response
- addToOutput :: (forall a. Enumerator a) -> Snap ()
- writeBS :: ByteString -> Snap ()
- writeLazyText :: Text -> Snap ()
- writeText :: Text -> Snap ()
- writeLBS :: ByteString -> Snap ()
- sendFile :: FilePath -> Snap ()
- sendFilePartial :: FilePath -> (Int64, Int64) -> Snap ()
- type Enumerator a = Enumerator IO a
- data SomeEnumerator = SomeEnumerator (forall a. Enumerator a)
- formatHttpTime :: CTime -> IO ByteString
- parseHttpTime :: ByteString -> IO CTime
- urlEncode :: ByteString -> ByteString
- urlDecode :: ByteString -> Maybe ByteString

# The Snap Monad

data Snap a

`Snap` is the `Monad` that user web handlers run in. `Snap` gives you:

1. stateful access to fetch or modify an HTTP `Request`
2. stateful access to fetch or modify an HTTP `Response`
3. failure / `Alternative` / `MonadPlus` semantics: a `Snap` handler can choose not to handle a given request, using `empty` or its synonym `pass`, and you can try alternative handlers with the `<|>` operator:

     a :: Snap String
     a = pass

     b :: Snap String
     b = return "foo"

     c :: Snap String
     c = a <|> b             -- try running a, if it fails then try b

1. convenience functions (`writeBS`, `writeLBS`, `writeText`, `writeLazyText`, `addToOutput`) for writing output to the `Response`:

     a :: (forall a . Enumerator a) -> Snap ()
     a someEnumerator = do
         writeBS "I'm a strict bytestring"
         writeLBS "I'm a lazy bytestring"
         addToOutput someEnumerator

1. early termination: if you call `finishWith`:

     a :: Snap ()
     a = do
       modifyResponse $ setResponseStatus 500 "Internal Server Error"
       writeBS "500 error"
       r <- getResponse
       finishWith r

then any subsequent processing will be skipped and supplied `Response` value will be returned from `runSnap` as-is.

1. access to the `IO` monad through a `MonadIO` instance:

     a :: Snap ()
     a = liftIO fireTheMissiles

Instances

Monad Snap |
Functor Snap |
Typeable1 Snap |
MonadPlus Snap |
Applicative Snap |
MonadCatchIO Snap |
Alternative Snap |
MonadIO Snap |

runSnap :: Snap a -> (ByteString -> IO ()) -> Request -> Iteratee IO (Request, Response)

Runs a `Snap` monad action in the 'Iteratee IO' monad.

data NoHandlerException

This exception is thrown if the handler you supply to `runSnap` fails.

Constructors

NoHandlerException |

Instances

Eq NoHandlerException |
Show NoHandlerException |
Typeable NoHandlerException |
Exception NoHandlerException |

## Functions for control flow and early termination

finishWith :: Response -> Snap a

Short-circuits a `Snap` monad action early, storing the given `Response` value in its state.

pass :: Snap a

Fails out of a `Snap` monad action. This is used to indicate that you choose not to handle the given request within the given handler.

## Routing

method :: Method -> Snap a -> Snap a

Runs a `Snap` monad action only if the request's HTTP method matches the given method.

path

Arguments

:: ByteString | path to match against
-> Snap a | handler to run
-> Snap a |

Runs a `Snap` monad action only for requests where `rqPathInfo` is exactly equal to the given string. If the path matches, locally sets `rqContextPath` to the old value of `rqPathInfo`, sets `rqPathInfo`="", and runs the given handler.

dir

Arguments

:: ByteString | path component to match
-> Snap a | handler to run
-> Snap a |

Runs a `Snap` monad action only when the `rqPathInfo` of the request starts with the given path. For example,

     dir "foo" handler

Will fail if `rqPathInfo` is not "`/foo`" or "`/foo/...`", and will add `"foo/"` to the handler's local `rqContextPath`.

ifTop :: Snap a -> Snap a

Runs a `Snap` monad action only when `rqPathInfo` is empty.

route :: [(ByteString, Snap a)] -> Snap a

A web handler which, given a mapping from URL entry points to web handlers, efficiently routes requests to the correct handler.

The URL entry points are given as relative paths, for example:

     route [ ("foo/bar/quux", fooBarQuux) ]

If the URI of the incoming request is

     /foo/bar/quux

or

     /foo/bar/quux/...anything...

then the request will be routed to "`fooBarQuux`", with `rqContextPath` set to "`/foo/bar/quux/`" and `rqPathInfo` set to "`...anything...`".

A path component within an URL entry point beginning with a colon ("`:`") is treated as a variable capture; the corresponding path component within the request URI will be entered into the `rqParams` parameters mapping with the given name. For instance, if the routes were:

     route [ ("foo/:bar/baz", fooBazHandler) ]

Then a request for "`/foo/saskatchewan/baz`" would be routed to `fooBazHandler` with a mapping for:

     "bar" => "saskatchewan"

in its parameters table.

Longer paths are matched first, and specific routes are matched before captures. That is, if given routes:

     [ ("a", h1), ("a/b", h2), ("a/:x", h3) ]

a request for "`/a/b`" will go to `h2`, "`/a/s`" for any s will go to `h3`, and "`/a`" will go to `h1`.

The following example matches "`/article`" to an article index, "`/login`" to a login, and "`/article/...`" to an article renderer.

     route [ ("article",     renderIndex)
           , ("article/:id", renderArticle)
           , ("login",       method POST doLogin) ]

routeLocal :: [(ByteString, Snap a)] -> Snap a

The `routeLocal` function is the same as `route'`, except it doesn't change the request's context path. This is useful if you want to route to a particular handler but you want that handler to receive the `rqPathInfo` as it is.

## Access to state

getRequest :: Snap Request

Grabs the `Request` object out of the `Snap` monad.

getResponse :: Snap Response

Grabs the `Response` object out of the `Snap` monad.

putRequest :: Request -> Snap ()

Puts a new `Request` object into the `Snap` monad.

putResponse :: Response -> Snap ()

Puts a new `Response` object into the `Snap` monad.

modifyRequest :: (Request -> Request) -> Snap ()

Modifies the `Request` object stored in a `Snap` monad.

modifyResponse :: (Response -> Response) -> Snap ()

Modifes the `Response` object stored in a `Snap` monad.

localRequest :: (Request -> Request) -> Snap a -> Snap a

Runs a `Snap` action with a locally-modified `Request` state object. The `Request` object in the Snap monad state after the call to localRequest will be unchanged.

withRequest :: (Request -> Snap a) -> Snap a

Fetches the `Request` from state and hands it to the given action.

withResponse :: (Response -> Snap a) -> Snap a

Fetches the `Response` from state and hands it to the given action.

## Logging

logError :: ByteString -> Snap ()

Log an error message in the `Snap` monad

## Grabbing/transforming request bodies

runRequestBody :: Iteratee IO a -> Snap a

Sends the request body through an iteratee (data consumer) and returns the result.

getRequestBody :: Snap ByteString

Returns the request body as a bytestring.

transformRequestBody

Arguments

:: (forall a. Enumerator a) | the output `Iteratee` is passed to this `Enumerator`, and then the resulting `Iteratee` is fed the request body stream. Your `Enumerator` is responsible for transforming the input.
-> Snap () |

Normally Snap is careful to ensure that the request body is fully consumed after your web handler runs, but before the `Response` enumerator is streamed out the socket. If you want to transform the request body into some output in O(1) space, you should use this function.

Note that upon calling this function, response processing finishes early as if you called `finishWith`. Make sure you set any content types, headers, cookies, etc. before you call this function.

# HTTP Datatypes and Functions

HTTP-related datatypes: `Request`, `Response`, `Cookie`, etc.

data Request

Contains all of the information about an incoming HTTP request.

Instances

Show Request |
HasHeaders Request |

data Response

Represents an HTTP response.

Instances

Show Response |
HasHeaders Response |

type Headers = Map CIByteString [ByteString]

A type alias for a case-insensitive key-value mapping.

class HasHeaders a where

A typeclass for datatypes which contain HTTP headers.

Methods

updateHeaders :: (Headers -> Headers) -> a -> a

Modify the datatype's headers.

headers :: a -> Headers

Retrieve the headers from a datatype that has headers.

Instances

HasHeaders Response |
HasHeaders Request |
HasHeaders Headers |

type Params = Map ByteString [ByteString]

A type alias for the HTTP parameters mapping. Each parameter key maps to a list of ByteString values; if a parameter is specified multiple times (e.g.: "`GET /foo?param=bar1&param=bar2`"), looking up "`param`" in the mapping will give you `["bar1", "bar2"]`.

data Method

Enumerates the HTTP method values (see http://tools.ietf.org/html/rfc2068.html#section-5.1.1).

Constructors

GET |
HEAD |
POST |
PUT |
DELETE |
TRACE |
OPTIONS |
CONNECT |

Instances

Eq Method |
Ord Method |
Read Method |
Show Method |

data Cookie

A datatype representing an HTTP cookie.

Constructors

Cookie |
Fields cookieName :: !ByteString The name of the cookie. cookieValue :: !ByteString The cookie's string value. cookieExpires :: !(Maybe UTCTime) The cookie's expiration value, if it has one. cookieDomain :: !(Maybe ByteString) The cookie's "domain" value, if it has one. cookiePath :: !(Maybe ByteString) The cookie path.

Instances

Eq Cookie |
Show Cookie |

type HttpVersion = (Int, Int)

## Headers

addHeader :: HasHeaders a => CIByteString -> ByteString -> a -> a

Adds a header key-value-pair to the `HasHeaders` datatype. If a header with the same name already exists, the new value is appended to the headers list.

setHeader :: HasHeaders a => CIByteString -> ByteString -> a -> a

Sets a header key-value-pair in a `HasHeaders` datatype. If a header with the same name already exists, it is overwritten with the new value.

getHeader :: HasHeaders a => CIByteString -> a -> Maybe ByteString

Gets a header value out of a `HasHeaders` datatype. If many headers came in with the same name, they will be catenated together.

deleteHeader :: HasHeaders a => CIByteString -> a -> a

Clears a header value from a `HasHeaders` datatype.

ipHeaderFilter :: Snap ()

Modifies the `Request` in the state to set the `rqRemoteAddr` field to the value in the X-Forwarded-For header. If the header is not present, this action has no effect.

This action should be used only when working behind a reverse http proxy that sets the X-Forwarded-For header. This is the only way to ensure the value in the X-Forwarded-For header can be trusted.

This is provided as a filter so actions that require the remote address can get it in a uniform manner. It has specifically limited functionality to ensure that its transformation can be trusted, when used correctly.

ipHeaderFilter' :: CIByteString -> Snap ()

Modifies the `Request` in the state to set the `rqRemoteAddr` field to the value from the header specified. If the header specified is not present, this action has no effect.

This action should be used only when working behind a reverse http proxy that sets the header being looked at. This is the only way to ensure the value in the header can be trusted.

This is provided as a filter so actions that require the remote address can get it in a uniform manner. It has specifically limited functionality to ensure that its transformation can be trusted, when used correctly.

## Requests

rqServerName :: Request -> ByteString

The server name of the request, as it came in from the request's `Host:` header.

rqServerPort :: Request -> Int

Returns the port number the HTTP server is listening on.

rqRemoteAddr :: Request -> ByteString

The remote IP address.

rqRemotePort :: Request -> Int

The remote TCP port number.

rqLocalAddr :: Request -> ByteString

The local IP address for this request.

rqLocalHostname :: Request -> ByteString

Returns the HTTP server's idea of its local hostname.

rqIsSecure :: Request -> Bool

Returns `True` if this is an `HTTPS` session (currently always `False`).

rqContentLength :: Request -> Maybe Int

Returns the `Content-Length` of the HTTP request body.

rqMethod :: Request -> Method

Returns the HTTP request method.

rqVersion :: Request -> HttpVersion

Returns the HTTP version used by the client.

rqCookies :: Request -> [Cookie]

Returns a list of the cookies that came in from the HTTP request headers.

rqPathInfo :: Request -> ByteString

Handlers can (will be; --ed) be hung on a `URI` "entry point"; this is called the "context path". If a handler is hung on the context path `"/foo/"`, and you request `"/foo/bar"`, the value of `rqPathInfo` will be `"bar"`.

rqContextPath :: Request -> ByteString

The "context path" of the request; catenating `rqContextPath`, and `rqPathInfo` should get you back to the original `rqURI`. The `rqContextPath` always begins and ends with a slash (`"/"`) character, and represents the path (relative to your component/snaplet) you took to get to your handler.

rqURI :: Request -> ByteString

Returns the `URI` requested by the client.

rqQueryString :: Request -> ByteString

Returns the HTTP query string for this `Request`.

rqParams :: Request -> Params

Returns the `Params` mapping for this `Request`. "Parameters" are automatically decoded from the query string and `POST` body and entered into this mapping.

rqParam

Arguments

:: ByteString | parameter name to look up
-> Request | HTTP request
-> Maybe [ByteString] |

Looks up the value(s) for the given named parameter. Parameters initially come from the request's query string and any decoded POST body (if the request's `Content-Type` is `application/x-www-form-urlencoded`). Parameter values can be modified within handlers using rqModifyParams.

getParam

Arguments

:: ByteString | parameter name to look up
-> Snap (Maybe ByteString) |

See `rqParam`. Looks up a value for the given named parameter in the `Request`. If more than one value was entered for the given parameter name, `getParam` gloms the values together with:

        intercalate " "

rqModifyParams :: (Params -> Params) -> Request -> Request

Modifies the parameters mapping (which is a `Map ByteString ByteString`) in a `Request` using the given function.

rqSetParam

Arguments

:: ByteString | parameter name
-> [ByteString] | parameter values
-> Request | request
-> Request |

Writes a key-value pair to the parameters mapping within the given request.

## Responses

emptyResponse :: Response

An empty `Response`.

setResponseCode

Arguments

:: Int | HTTP response integer code
-> Response | Response to be modified
-> Response |

Sets the HTTP response code.

setResponseStatus

Arguments

:: Int | HTTP response integer code
-> ByteString | HTTP response explanation
-> Response | Response to be modified
-> Response |

Sets the HTTP response status. Note: normally you would use `setResponseCode` unless you needed a custom response explanation.

rspStatus :: Response -> Int

Returns the HTTP status code.

rspStatusReason :: Response -> ByteString

Returns the HTTP status explanation string.

setContentType :: ByteString -> Response -> Response

Sets the `Content-Type` in the `Response` headers.

addCookie

Arguments

:: Cookie | cookie value
-> Response | response to modify
-> Response |

Adds an HTTP `Cookie` to the `Response` headers.

setContentLength :: Int64 -> Response -> Response

A note here: if you want to set the `Content-Length` for the response, Snap forces you to do it with this function rather than by setting it in the headers; the `Content-Length` in the headers will be ignored.

The reason for this is that Snap needs to look up the value of `Content-Length` for each request, and looking the string value up in the headers and parsing the number out of the text will be too expensive.

If you don't set a content length in your response, HTTP keep-alive will be disabled for HTTP/1.0 clients, forcing a `Connection: close`. For HTTP/1.1 clients, Snap will switch to the chunked transfer encoding if `Content-Length` is not specified.

clearContentLength :: Response -> Response

Removes any `Content-Length` set in the `Response`.

redirect :: ByteString -> Snap ()

Performs a redirect by setting the `Location` header to the given target URL/path and the status code to 302 in the `Response` object stored in a `Snap` monad. Note that the target URL is not validated in any way. Consider using 'redirect\'' instead, which allows you to choose the correct status code.

redirect' :: ByteString -> Int -> Snap ()

Performs a redirect by setting the `Location` header to the given target URL/path and the status code (should be one of 301, 302, 303 or 307) in the `Response` object stored in a `Snap` monad. Note that the target URL is not validated in any way.

### Response I/O

setResponseBody

Arguments

:: (forall a. Enumerator a) | new response body enumerator
-> Response | response to modify
-> Response |

Sets an HTTP response body to the given `Enumerator` value.

modifyResponseBody :: (forall a. Enumerator a -> Enumerator a) -> Response -> Response

Modifies a response body.

addToOutput

Arguments

:: (forall a. Enumerator a) | output to add
-> Snap () |

Adds the output from the given enumerator to the `Response` stored in the `Snap` monad state.

writeBS :: ByteString -> Snap ()

Adds the given strict `ByteString` to the body of the `Response` stored in the `Snap` monad state.

Warning: This function is intentionally non-strict. If any pure exceptions are raised by the expression creating the `ByteString`, the exception won't actually be raised within the Snap handler.

writeLazyText :: Text -> Snap ()

Adds the given lazy `Text` to the body of the `Response` stored in the `Snap` monad state.

Warning: This function is intentionally non-strict. If any pure exceptions are raised by the expression creating the `ByteString`, the exception won't actually be raised within the Snap handler.

writeText :: Text -> Snap ()

Adds the given strict `Text` to the body of the `Response` stored in the `Snap` monad state.

Warning: This function is intentionally non-strict. If any pure exceptions are raised by the expression creating the `ByteString`, the exception won't actually be raised within the Snap handler.

writeLBS :: ByteString -> Snap ()

Adds the given lazy `ByteString` to the body of the `Response` stored in the `Snap` monad state.

Warning: This function is intentionally non-strict. If any pure exceptions are raised by the expression creating the `ByteString`, the exception won't actually be raised within the Snap handler.

sendFile :: FilePath -> Snap ()

Sets the output to be the contents of the specified file.

Calling `sendFile` will overwrite any output queued to be sent in the `Response`. If the response body is not modified after the call to `sendFile`, Snap will use the efficient `sendfile()` system call on platforms that support it.

If the response body is modified (using `modifyResponseBody`), the file will be read using `mmap()`.

sendFilePartial :: FilePath -> (Int64, Int64) -> Snap ()

Sets the output to be the contents of the specified file, within the given (start,end) range.

Calling `sendFilePartial` will overwrite any output queued to be sent in the `Response`. If the response body is not modified after the call to `sendFilePartial`, Snap will use the efficient `sendfile()` system call on platforms that support it.

If the response body is modified (using `modifyResponseBody`), the file will be read using `mmap()`.

# Iteratee

type Enumerator a = Enumerator IO a

data SomeEnumerator

An existential wrapper for the `Enumerator` type

Constructors

SomeEnumerator (forall a. Enumerator a) |

# HTTP utilities

formatHttpTime :: CTime -> IO ByteString

Converts a `CTime` into an HTTP timestamp.

parseHttpTime :: ByteString -> IO CTime

Converts an HTTP timestamp into a `CTime`.

urlEncode :: ByteString -> ByteString

URL-escapes a string (see http://tools.ietf.org/html/rfc2396.html#section-2.4)

urlDecode :: ByteString -> Maybe ByteString

Decodes an URL-escaped string (see http://tools.ietf.org/html/rfc2396.html#section-2.4)