Network.HTTP.Enumerator

Contents

Description

This module contains everything you need to initiate HTTP connections. Make sure to wrap your code with withHttpEnumerator. If you want a simple interface based on URLs, you can use simpleHttp. If you want raw power, http is the underlying workhorse of this package. Some examples:

 -- Just download an HTML document and print it.
 import Network.HTTP.Enumerator
 import qualified Data.ByteString.Lazy as L

 main = simpleHttp "http://www.haskell.org/" >>= L.putStr

This example uses interleaved IO to write the response body to a file in constant memory space. By using httpRedirect, it will automatically follow 3xx redirects.

 import Network.HTTP.Enumerator
 import Data.Enumerator.IO
 import System.IO

 main = withFile "google.html" WriteMode $ \handle -> do
     request <- parseUrl "http://google.com/"
     httpRedirect (\_ _ -> iterHandle handle) request

The following headers are automatically set by this module, and should not be added to requestHeaders:

Content-Length
Host
Accept-Encoding (not currently set, but client usage of this variable will cause breakage).

One last thing: there are two different backends available for the HTTPS support: the OpenSSL library and the tls package. The former requires some initialization, while the latter does not. Therefore, this module exports a withHttpEnumerator function to provide necessary initialization. Additionally, any network code on Windows requires some initialization, and the network library provides withSocketsDo to perform it. Therefore, proper usage of this library will always involve calling those two functions at some point. The best approach is to simply call them at the beginning of your main function, such as:

 import Network.HTTP.Enumerator
 import qualified Data.ByteString.Lazy as L
 import Network (withSocketsDo)

 main = withSocketsDo . withHttpEnumerator
      $ simpleHttp "http://www.haskell.org/" >>= L.putStr

Synopsis

Perform a request

simpleHttp :: (MonadIO m, Failure HttpException m) => String -> m ByteString Source

Download the specified URL, following any redirects, and return the response body.

This function will failure an HttpException for any response with a non-2xx status code. It uses parseUrl to parse the input. This function essentially wraps httpLbsRedirect.

httpLbs :: MonadIO m => Request -> m Response Source

Download the specified Request, returning the results as a Response.

This is a simplified version of http for the common case where you simply want the response data as a simple datatype. If you want more power, such as interleaved actions on the response body during download, you'll need to use http directly. This function is defined as:

httpLbs = http lbsIter

Please see lbsIter for more information on how the Response value is created.

httpLbsRedirect :: (MonadIO m, Failure HttpException m) => Request -> m Response Source

Download the specified Request, returning the results as a Response and automatically handling redirects.

This is a simplified version of httpRedirect for the common case where you simply want the response data as a simple datatype. If you want more power, such as interleaved actions on the response body during download, you'll need to use httpRedirect directly. This function is defined as:

httpLbsRedirect = httpRedirect lbsIter

Please see lbsIter for more information on how the Response value is created.

http :: MonadIO m => (Int -> Headers -> Iteratee ByteString m a) -> Request -> m aSource

The most low-level function for initiating an HTTP request.

The second argument to this function gives a full specification on the request: the host to connect to, whether to use SSL, headers, etc. Please see Request for full details.

The first argument specifies how the response should be handled. It's a function that takes two arguments: the first is the HTTP status code of the response, and the second is a list of all response headers. This module exports lbsIter, which generates a Response value.

Note that this allows you to have fully interleaved IO actions during your HTTP download, making it possible to download very large responses in constant memory.

httpRedirect :: (MonadIO m, Failure HttpException m) => (Int -> Headers -> Iteratee ByteString m a) -> Request -> m aSource

Same as http, but follows all 3xx redirect status codes that contain a location header.

Datatypes

data Request Source

All information on how to connect to a host and what should be sent in the HTTP request.

If you simply wish to download from a URL, see parseUrl.

Constructors

Request
Fields method :: ByteString HTTP request method, eg GET, POST. secure :: Bool Whether to use HTTPS (ie, SSL). host :: ByteString port :: Int path :: ByteString Everything from the host to the query string. queryString :: Headers Automatically escaped for your convenience. requestHeaders :: Headers requestBody :: ByteString

Instances

Eq Request
Data Request
Read Request
Show Request
Typeable Request

data Response Source

A simple representation of the HTTP response created by lbsIter.

Constructors

Response
Fields statusCode :: Int responseHeaders :: Headers responseBody :: ByteString

Instances

Eq Response
Data Response
Read Response
Show Response
Typeable Response

type Headers = [(ByteString, ByteString)]Source

Utility functions

parseUrl :: Failure HttpException m => String -> m Request Source

Convert a URL into a Request.

This defaults some of the values in Request, such as setting method to GET and requestHeaders to [].

Since this function uses Failure, the return monad can be anything that is an instance of Failure, such as IO or Maybe.

withHttpEnumerator :: IO a -> IO aSource

The OpenSSL library requires some initialization of variables to be used, and therefore you must call withOpenSSL before using any of its functions. As this library uses OpenSSL, you must use withOpenSSL as well. (As a side note, you'll also want to use the withSocketsDo function for network activity.)

To future-proof this package against switching to different SSL libraries, we re-export withOpenSSL under this name. You can call this function as early as you like; in fact, simply wrapping the do block of your main function is probably best.

lbsIter :: Monad m => Int -> Headers -> Iteratee ByteString m Response Source

Convert the HTTP response into a Response value.

Even though a Response contains a lazy bytestring, this function does not utilize lazy I/O, and therefore the entire response body will live in memory. If you want constant memory usage, you'll need to write your own iteratee and use http or httpRedirect directly.

Request bodies

urlEncodedBody :: Headers -> Request -> Request Source

Add url-encoded paramters to the Request.

This sets a new requestBody, adds a content-type request header and changes the method to POST.

Exceptions

data HttpException Source

Constructors

StatusCodeException Int ByteString
InvalidUrlException String String
TooManyRedirects
HttpParserException String

Instances

Show HttpException
Typeable HttpException
Exception HttpException