Network.HTTP.Conduit.Downloader

HTTP downloader tailored for web-crawler needs.

• Handles all possible http-client exceptions and returns human readable error messages.
• Handles some web server bugs (returning deflate data instead of gzip, invalid gzip encoding).
• Uses OpenSSL instead of tls package (since tls doesn't handle all sites and works slower than OpenSSL).
• Ignores invalid SSL sertificates.
• Receives data in 32k chunks internally to reduce memory fragmentation on many parallel downloads.
• Download timeout.
• Total download size limit.
• Returns HTTP headers for subsequent redownloads and handles Not modified results.
• Can be used with external DNS resolver (hsdns-cache for example).
• Keep-alive connections pool (thanks to http-client).

Typical workflow in crawler:

 withDnsCache $  c -> withDownloader $  d -> do
 ... -- got URL from queue
 ra <- resolveA c $ hostNameFromUrl url
 case ra of
     Left err -> ... -- uh oh, bad host
     Right ha -> do
         ... -- crawler politeness stuff (rate limits, queues)
         dr <- download d url (Just ha) opts
         case dr of
             DROK dat redownloadOptions ->
                 ... -- analyze data, save redownloadOpts for next download
             DRRedirect .. -> ...
             DRNotModified -> ...
             DRError e -> ...
 

It's highly recommended to use http://hackage.haskell.org/package/concurrent-dns-cache (preferably with single resolver pointing to locally running BIND) for DNS resolution since getAddrInfo used in http-client can be buggy and ineffective when it needs to resolve many hosts per second for a long time.

Download operations

urlGetContents :: String -> IO ByteString

Download single URL with default DownloaderSettings. Fails if result is not DROK.

urlGetContentsPost :: String -> ByteString -> IO ByteString

Post data and download single URL with default DownloaderSettings. Fails if result is not DROK.

download

Arguments

:: Downloader

-> String

URL

-> Maybe HostAddress

Optional resolved HostAddress

-> DownloadOptions

-> IO DownloadResult

Perform download

post :: Downloader -> String -> Maybe HostAddress -> ByteString -> IO DownloadResult

Perform HTTP POST.

downloadG

Arguments

:: (Request -> IO Request)

Function to modify Request (e.g. sign or make postRequest)

-> Downloader

-> String

URL

-> Maybe HostAddress

Optional resolved HostAddress

-> DownloadOptions

-> IO DownloadResult

Generic version of download with ability to modify http-client Request.

rawDownload

Arguments

:: (Request -> IO Request)

Function to modify Request (e.g. sign or make postRequest)

-> Downloader

-> String

URL

-> Maybe HostAddress

Optional resolved HostAddress

-> DownloadOptions

-> IO (DownloadResult, Maybe RawDownloadResult)

Even more generic version of download, which returns RawDownloadResult. RawDownloadResult is optional since it can not be determined on timeouts and connection errors.

data DownloadResult

Result of download operation.

Constructors

DROK ByteString DownloadOptions

Successful download with data and options for next download.

DRRedirect String

Redirect URL

DRError String

Error

DRNotModified

HTTP 304 Not Modified

Instances

Read DownloadResult

Defined in Network.HTTP.Conduit.Downloader

Methods

readsPrec :: Int -> ReadS DownloadResult

readList :: ReadS [DownloadResult]

readPrec :: ReadPrec DownloadResult

readListPrec :: ReadPrec [DownloadResult]

Show DownloadResult

Defined in Network.HTTP.Conduit.Downloader

Methods

showsPrec :: Int -> DownloadResult -> ShowS

show :: DownloadResult -> String

showList :: [DownloadResult] -> ShowS

Eq DownloadResult

Defined in Network.HTTP.Conduit.Downloader

Methods

(==) :: DownloadResult -> DownloadResult -> Bool

(/=) :: DownloadResult -> DownloadResult -> Bool

data RawDownloadResult

Result of rawDownload operation.

Constructors

RawDownloadResult

Fields

• rdrStatus :: Status
• rdrHttpVersion :: HttpVersion
• rdrHeaders :: ResponseHeaders
• rdrBody :: ByteString
• rdrCookieJar :: CookieJar

Instances

Show RawDownloadResult

Defined in Network.HTTP.Conduit.Downloader

Methods

showsPrec :: Int -> RawDownloadResult -> ShowS

show :: RawDownloadResult -> String

showList :: [RawDownloadResult] -> ShowS

type DownloadOptions = [String]

If-None-Match and/or If-Modified-Since headers.

Downloader

data DownloaderSettings

Settings used in downloader.

Constructors

DownloaderSettings

Fields

• dsUserAgent :: ByteString

  User agent string. Default: "Mozilla/5.0 (compatible; HttpConduitDownloader/1.0; +http://hackage.haskell.org/package/http-conduit-downloader)".

  Be a good crawler. Provide your User-Agent please.

• dsTimeout :: Int

  Download timeout. Default: 30 seconds.

• dsManagerSettings :: ManagerSettings

  Conduit Manager settings. Default: ManagerSettings with SSL certificate checks removed.

• dsMaxDownloadSize :: Int

  Download size limit in bytes. Default: 10MB.

Instances

Default DownloaderSettings

Defined in Network.HTTP.Conduit.Downloader

Methods

def :: DownloaderSettings

data Downloader

Keeps http-client Manager and DownloaderSettings.

withDownloader :: (Downloader -> IO a) -> IO a

Create a new Downloader, use it in the provided function, and then release it.

withDownloaderSettings :: DownloaderSettings -> (Downloader -> IO a) -> IO a

Create a new Downloader with provided settings, use it in the provided function, and then release it.

newDownloader :: DownloaderSettings -> IO Downloader

Create a Downloader with settings.

Utils

postRequest :: ByteString -> Request -> Request

Make HTTP POST request.