Network/Browser.hs

{- |

Module : Network.Browser
Copyright : (c) Warrick Gray 2002
License : BSD
 
Maintainer : Sigbjorn Finne <sigbjorn.finne@gmail.com>
Stability : experimental
Portability : non-portable (not tested)

Session-level interactions over HTTP.
 
The "Network.Browser" goes beyond the basic "Network.HTTP" functionality in 
providing support for more involved, and real, request/response interactions over 
HTTP. Additional features supported are:

* HTTP Authentication handling

* Transparent handling of redirects

* Cookie stores + transmission.

* Transaction logging

* Proxy-mediated connections.

Example use:

> do 
> rsp <- Network.Browser.browse $ do
> setAllowRedirects True -- handle HTTP redirects
> request $ getRequest "http://google.com/"
> fmap (take 100) (getResponseBody rsp)
 
-}
module Network.Browser 
 ( BrowserState
 , BrowserAction -- browser monad, effectively a state monad.
 , Proxy(..)
 
 , browse -- :: BrowserAction a -> IO a
 , request -- :: Request -> BrowserAction Response
 
 , getBrowserState -- :: BrowserAction t (BrowserState t)
 , withBrowserState -- :: BrowserState t -> BrowserAction t a -> BrowserAction t a
 
 , setAllowRedirects -- :: Bool -> BrowserAction t ()
 , getAllowRedirects -- :: BrowserAction t Bool

 , setMaxRedirects -- :: Int -> BrowserAction t ()
 , getMaxRedirects -- :: BrowserAction t (Maybe Int)
 
 , Authority(..)
 , getAuthorities
 , setAuthorities
 , addAuthority
 , Challenge(..)
 , Qop(..)
 , Algorithm(..)
 
 , getAuthorityGen
 , setAuthorityGen
 , setAllowBasicAuth
 , getAllowBasicAuth
 
 , setMaxErrorRetries -- :: Maybe Int -> BrowserAction t ()
 , getMaxErrorRetries -- :: BrowserAction t (Maybe Int)

 , setMaxAuthAttempts -- :: Maybe Int -> BrowserAction t ()
 , getMaxAuthAttempts -- :: BrowserAction t (Maybe Int)

 , setCookieFilter -- :: (URI -> Cookie -> IO Bool) -> BrowserAction t ()
 , getCookieFilter -- :: BrowserAction t (URI -> Cookie -> IO Bool)
 , defaultCookieFilter -- :: URI -> Cookie -> IO Bool
 , userCookieFilter -- :: URI -> Cookie -> IO Bool
 
 , Cookie(..)
 , getCookies -- :: BrowserAction t [Cookie]
 , setCookies -- :: [Cookie] -> BrowserAction t ()
 , addCookie -- :: Cookie -> BrowserAction t ()
 
 , setErrHandler -- :: (String -> IO ()) -> BrowserAction t ()
 , setOutHandler -- :: (String -> IO ()) -> BrowserAction t ()
 
 , setEventHandler -- :: (BrowserEvent -> BrowserAction t ()) -> BrowserAction t ()
 
 , BrowserEvent(..)
 , BrowserEventType(..)
 , RequestID
 
 , setProxy -- :: Proxy -> BrowserAction t ()
 , getProxy -- :: BrowserAction t Proxy

 , setCheckForProxy -- :: Bool -> BrowserAction t ()
 , getCheckForProxy -- :: BrowserAction t Bool

 , setDebugLog -- :: Maybe String -> BrowserAction t ()
 
 , getUserAgent -- :: BrowserAction t String
 , setUserAgent -- :: String -> BrowserAction t ()
 
 , out -- :: String -> BrowserAction t ()
 , err -- :: String -> BrowserAction t ()
 , ioAction -- :: IO a -> BrowserAction a

 , defaultGETRequest
 , defaultGETRequest_
 
 , formToRequest
 , uriDefaultTo
 
 -- old and half-baked; don't use:
 , Form(..)
 , FormVar
 ) where

import Network.URI
 ( URI(..)
 , URIAuth(..)
 , parseURI, parseURIReference, relativeTo
 )
import Network.StreamDebugger (debugByteStream)
import Network.HTTP hiding ( sendHTTP_notify )
import Network.HTTP.HandleStream ( sendHTTP_notify )
import Network.HTTP.Auth
import Network.HTTP.Cookie
import Network.HTTP.Proxy

import Network.Stream ( ConnError(..), Result )
import Network.BufferType

import Data.Char (toLower)
import Data.List (isPrefixOf)
import Data.Maybe (fromMaybe, listToMaybe, catMaybes )
import Control.Monad (filterM, liftM, when)

import qualified System.IO
 ( hSetBuffering, hPutStr, stdout, stdin, hGetChar
 , BufferMode(NoBuffering, LineBuffering)
 )
import System.Time ( ClockTime, getClockTime )


------------------------------------------------------------------
----------------------- Cookie Stuff -----------------------------
------------------------------------------------------------------

-- | @defaultCookieFilter@ is the initial cookie acceptance filter.
-- It welcomes them all into the store @:-)@
defaultCookieFilter :: URI -> Cookie -> IO Bool
defaultCookieFilter _url _cky = return True

-- | @userCookieFilter@ is a handy acceptance filter, asking the
-- user if he/she is willing to accept an incoming cookie before
-- adding it to the store.
userCookieFilter :: URI -> Cookie -> IO Bool
userCookieFilter url cky = do
 do putStrLn ("Set-Cookie received when requesting: " ++ show url)
 case ckComment cky of
 Nothing -> return ()
 Just x -> putStrLn ("Cookie Comment:\n" ++ x)
 let pth = maybe "" ('/':) (ckPath cky)
 putStrLn ("Domain/Path: " ++ ckDomain cky ++ pth)
 putStrLn (ckName cky ++ '=' : ckValue cky)
 System.IO.hSetBuffering System.IO.stdout System.IO.NoBuffering
 System.IO.hSetBuffering System.IO.stdin System.IO.NoBuffering
 System.IO.hPutStr System.IO.stdout "Accept [y/n]? "
 x <- System.IO.hGetChar System.IO.stdin
 System.IO.hSetBuffering System.IO.stdin System.IO.LineBuffering
 System.IO.hSetBuffering System.IO.stdout System.IO.LineBuffering
 return (toLower x == 'y')

-- | @addCookie c@ adds a cookie to the browser state, removing duplicates.
addCookie :: Cookie -> BrowserAction t ()
addCookie c = alterBS (\b -> b{bsCookies = c : filter (/=c) (bsCookies b) })

-- | @setCookies cookies@ replaces the set of cookies known to
-- the browser to @cookies@. Useful when wanting to restore cookies
-- used across 'browse' invocations.
setCookies :: [Cookie] -> BrowserAction t ()
setCookies cs = alterBS (\b -> b { bsCookies=cs })

-- | @getCookies@ returns the current set of cookies known to
-- the browser.
getCookies :: BrowserAction t [Cookie]
getCookies = getBS bsCookies

-- ...get domain specific cookies...
-- ... this needs changing for consistency with rfc2109...
-- ... currently too broad.
getCookiesFor :: String -> String -> BrowserAction t [Cookie]
getCookiesFor dom path =
 do cks <- getCookies
 return (filter cookiematch cks)
 where
 cookiematch :: Cookie -> Bool
 cookiematch = cookieMatch (dom,path)
 

-- | @setCookieFilter fn@ sets the cookie acceptance filter to @fn@.
setCookieFilter :: (URI -> Cookie -> IO Bool) -> BrowserAction t ()
setCookieFilter f = alterBS (\b -> b { bsCookieFilter=f })

-- | @getCookieFilter@ returns the current cookie acceptance filter.
getCookieFilter :: BrowserAction t (URI -> Cookie -> IO Bool)
getCookieFilter = getBS bsCookieFilter

------------------------------------------------------------------
----------------------- Authorisation Stuff ----------------------
------------------------------------------------------------------

{-

The browser handles 401 responses in the following manner:
 1) extract all WWW-Authenticate headers from a 401 response
 2) rewrite each as a Challenge object, using "headerToChallenge"
 3) pick a challenge to respond to, usually the strongest
 challenge understood by the client, using "pickChallenge"
 4) generate a username/password combination using the browsers
 "bsAuthorityGen" function (the default behaviour is to ask
 the user)
 5) build an Authority object based upon the challenge and user
 data, store this new Authority in the browser state
 6) convert the Authority to a request header and add this
 to a request using "withAuthority"
 7) send the amended request

Note that by default requests are annotated with authority headers
before the first sending, based upon previously generated Authority
objects (which contain domain information). Once a specific authority
is added to a rejected request this predictive annotation is suppressed.

407 responses are handled in a similar manner, except
 a) Authorities are not collected, only a single proxy authority
 is kept by the browser
 b) If the proxy used by the browser (type Proxy) is NoProxy, then
 a 407 response will generate output on the "err" stream and
 the response will be returned.


Notes:
 - digest authentication so far ignores qop, so fails to authenticate 
 properly with qop=auth-int challenges
 - calculates a1 more than necessary
 - doesn't reverse authenticate
 - doesn't properly receive AuthenticationInfo headers, so fails
 to use next-nonce etc

-}

-- | Return authorities for a given domain and path.
-- Assumes "dom" is lower case
getAuthFor :: String -> String -> BrowserAction t [Authority]
getAuthFor dom pth = getAuthorities >>= return . (filter match)
 where
 match :: Authority -> Bool
 match au@AuthBasic{} = matchURI (auSite au)
 match au@AuthDigest{} = or (map matchURI (auDomain au))

 matchURI :: URI -> Bool
 matchURI s = (uriToAuthorityString s == dom) && (uriPath s `isPrefixOf` pth)
 

-- | @getAuthorities@ return the current set of @Authority@s known
-- to the browser.
getAuthorities :: BrowserAction t [Authority]
getAuthorities = getBS bsAuthorities

-- @setAuthorities as@ replaces the Browser's known set
-- of 'Authority's to @as@.
setAuthorities :: [Authority] -> BrowserAction t ()
setAuthorities as = alterBS (\b -> b { bsAuthorities=as })

-- @addAuthority a@ adds 'Authority' @a@ to the Browser's
-- set of known authorities.
addAuthority :: Authority -> BrowserAction t ()
addAuthority a = alterBS (\b -> b { bsAuthorities=a:bsAuthorities b })

-- | @getAuthorityGen@ returns the current authority generator
getAuthorityGen :: BrowserAction t (URI -> String -> IO (Maybe (String,String)))
getAuthorityGen = getBS bsAuthorityGen

-- | @setAuthorityGen genAct@ sets the auth generator to @genAct@.
setAuthorityGen :: (URI -> String -> IO (Maybe (String,String))) -> BrowserAction t ()
setAuthorityGen f = alterBS (\b -> b { bsAuthorityGen=f })

-- | @setAllowBasicAuth onOff@ enables\/disables HTTP Basic Authentication.
setAllowBasicAuth :: Bool -> BrowserAction t ()
setAllowBasicAuth ba = alterBS (\b -> b { bsAllowBasicAuth=ba })

getAllowBasicAuth :: BrowserAction t Bool
getAllowBasicAuth = getBS bsAllowBasicAuth

-- | @setMaxAuthAttempts mbMax@ sets the maximum number of authentication attempts
-- to do. If @Nothing@, rever to default max.
setMaxAuthAttempts :: Maybe Int -> BrowserAction t ()
setMaxAuthAttempts mb 
 | fromMaybe 0 mb < 0 = return ()
 | otherwise = alterBS (\ b -> b{bsMaxAuthAttempts=mb})

-- | @getMaxAuthAttempts@ returns the current max auth attempts. If @Nothing@,
-- the browser's default is used.
getMaxAuthAttempts :: BrowserAction t (Maybe Int)
getMaxAuthAttempts = getBS bsMaxAuthAttempts

-- | @setMaxErrorRetries mbMax@ sets the maximum number of attempts at
-- transmitting a request. If @Nothing@, rever to default max.
setMaxErrorRetries :: Maybe Int -> BrowserAction t ()
setMaxErrorRetries mb
 | fromMaybe 0 mb < 0 = return ()
 | otherwise = alterBS (\ b -> b{bsMaxErrorRetries=mb})

-- | @getMaxErrorRetries@ returns the current max number of error retries.
getMaxErrorRetries :: BrowserAction t (Maybe Int)
getMaxErrorRetries = getBS bsMaxErrorRetries

-- TO BE CHANGED!!!
pickChallenge :: Bool -> [Challenge] -> Maybe Challenge
pickChallenge allowBasic []
 | allowBasic = Just (ChalBasic "/") -- manufacture a challenge if one missing; more robust.
pickChallenge _ ls = listToMaybe ls

-- | Retrieve a likely looking authority for a Request.
anticipateChallenge :: Request ty -> BrowserAction t (Maybe Authority)
anticipateChallenge rq =
 let uri = rqURI rq in
 do { authlist <- getAuthFor (uriAuthToString $ reqURIAuth rq) (uriPath uri)
 ; return (listToMaybe authlist)
 }

-- | Asking the user to respond to a challenge
challengeToAuthority :: URI -> Challenge -> BrowserAction t (Maybe Authority)
challengeToAuthority uri ch
 | not (answerable ch) = return Nothing
 | otherwise = do
 -- prompt user for authority
 prompt <- getAuthorityGen
 userdetails <- ioAction $ prompt uri (chRealm ch)
 case userdetails of
 Nothing -> return Nothing
 Just (u,p) -> return (Just $ buildAuth ch u p)
 where
 answerable :: Challenge -> Bool
 answerable ChalBasic{} = True
 answerable chall = (chAlgorithm chall) == Just AlgMD5

 buildAuth :: Challenge -> String -> String -> Authority
 buildAuth (ChalBasic r) u p = 
 AuthBasic { auSite=uri
 , auRealm=r
 , auUsername=u
 , auPassword=p
 }

 -- note to self: this is a pretty stupid operation
 -- to perform isn't it? ChalX and AuthX are so very
 -- similar.
 buildAuth (ChalDigest r d n o _stale a q) u p =
 AuthDigest { auRealm=r
 , auUsername=u
 , auPassword=p
 , auDomain=d
 , auNonce=n
 , auOpaque=o
 , auAlgorithm=a
 , auQop=q
 }


------------------------------------------------------------------
------------------ Browser State Actions -------------------------
------------------------------------------------------------------


-- | @BrowserState@ is the (large) record type tracking the current
-- settings of the browser.
data BrowserState connection
 = BS { bsErr, bsOut :: String -> IO ()
 , bsCookies :: [Cookie]
 , bsCookieFilter :: URI -> Cookie -> IO Bool
 , bsAuthorityGen :: URI -> String -> IO (Maybe (String,String))
 , bsAuthorities :: [Authority]
 , bsAllowRedirects :: Bool
 , bsAllowBasicAuth :: Bool
 , bsMaxRedirects :: Maybe Int
 , bsMaxErrorRetries :: Maybe Int
 , bsMaxAuthAttempts :: Maybe Int
 , bsConnectionPool :: [connection]
 , bsCheckProxy :: Bool
 , bsProxy :: Proxy
 , bsDebug :: Maybe String
 , bsEvent :: Maybe (BrowserEvent -> BrowserAction connection ())
 , bsRequestID :: RequestID
 , bsUserAgent :: Maybe String
 }

instance Show (BrowserState t) where
 show bs = "BrowserState { " 
 ++ shows (bsCookies bs) ("\n"
 {- ++ show (bsAuthorities bs) ++ "\n"-}
 ++ "AllowRedirects: " ++ shows (bsAllowRedirects bs) "} ")

-- | @BrowserAction@ is the IO monad, but carrying along a 'BrowserState'.
data BrowserAction conn a 
 = BA { lift :: BrowserState conn -> IO (BrowserState conn,a) }

instance Monad (BrowserAction conn) where
 a >>= f = BA (\b -> do { (nb,v) <- lift a b ; lift (f v) nb})
 return x = BA (\b -> return (b,x))
 fail x = BA (\_ -> fail x)

instance Functor (BrowserAction conn) where
 fmap f = liftM f

-- | @browse act@ is the toplevel action to perform a 'BrowserAction'.
-- Example use: @browse (request (getRequest yourURL))@.
browse :: BrowserAction conn a -> IO a
browse act = do x <- lift act defaultBrowserState
 return (snd x)

-- | The default browser state has the settings 
defaultBrowserState :: BrowserState t
defaultBrowserState = res
 where
 res = BS
 { bsErr = putStrLn
 , bsOut = putStrLn
 , bsCookies = []
 , bsCookieFilter = defaultCookieFilter
 , bsAuthorityGen = \ _uri _realm -> do
 bsErr res "No action for prompting/generating user+password credentials \
 \ provided (use: setAuthorityGen); returning Nothing"
 return Nothing
 , bsAuthorities = []
 , bsAllowRedirects = True
 , bsAllowBasicAuth = False
 , bsMaxRedirects = Nothing
 , bsMaxErrorRetries = Nothing
 , bsMaxAuthAttempts = Nothing
 , bsConnectionPool = []
 , bsCheckProxy = defaultAutoProxyDetect
 , bsProxy = noProxy
 , bsDebug = Nothing 
 , bsEvent = Nothing
 , bsRequestID = 0
 , bsUserAgent = Nothing
 }

-- | Alter browser state
alterBS :: (BrowserState t -> BrowserState t) -> BrowserAction t ()
alterBS f = BA (\b -> return (f b,()))

getBS :: (BrowserState t -> a) -> BrowserAction t a
getBS f = BA (\b -> return (b,f b))

-- | @getBrowserState@ returns the current browser config. Useful
-- for restoring state across 'BrowserAction's.
getBrowserState :: BrowserAction t (BrowserState t)
getBrowserState = getBS id

-- | @withBrowserAction st act@ performs @act@ with 'BrowserState' @st@.
withBrowserState :: BrowserState t -> BrowserAction t a -> BrowserAction t a
withBrowserState bs act = BA $ \ _ -> lift act bs

-- | @nextRequest act@ performs the browser action @act@ as
-- the next request, i.e., setting up a new request context
-- before doing so.
nextRequest :: BrowserAction t a -> BrowserAction t a
nextRequest act = do
 let updReqID st = 
 let 
 rid = succ (bsRequestID st)
 in
 rid `seq` st{bsRequestID=rid}
 alterBS updReqID
 act

-- | Lifts an IO action into the 'BrowserAction' monad.
ioAction :: IO a -> BrowserAction t a
ioAction a = BA (\b -> a >>= \v -> return (b,v))

-- | @setErrHandler@ sets the IO action to call when
-- the browser reports running errors. To disable any
-- such, set it to @const (return ())@.
setErrHandler :: (String -> IO ()) -> BrowserAction t ()
setErrHandler h = alterBS (\b -> b { bsErr=h })

-- | @setErrHandler@ sets the IO action to call when
-- the browser chatters info on its running. To disable any
-- such, set it to @const (return ())@.
setOutHandler :: (String -> IO ()) -> BrowserAction t ()
setOutHandler h = alterBS (\b -> b { bsOut=h })

out, err :: String -> BrowserAction t ()
out s = do { f <- getBS bsOut ; ioAction $ f s }
err s = do { f <- getBS bsErr ; ioAction $ f s }

-- | @setAllowRedirects onOff@ toggles the willingness to
-- follow redirects (HTTP responses with 3xx status codes).
setAllowRedirects :: Bool -> BrowserAction t ()
setAllowRedirects bl = alterBS (\b -> b {bsAllowRedirects=bl})

-- | @getAllowRedirects@ returns current setting of the do-chase-redirects flag.
getAllowRedirects :: BrowserAction t Bool
getAllowRedirects = getBS bsAllowRedirects

-- | @setMaxRedirects maxCount@ sets the maxiumum number of forwarding hops
-- we are willing to jump through. A no-op if the count is negative; if zero,
-- the max is set to whatever default applies. Notice that setting the max
-- redirects count does /not/ enable following of redirects itself; use
-- 'setAllowRedirects' to do so.
setMaxRedirects :: Maybe Int -> BrowserAction t ()
setMaxRedirects c 
 | fromMaybe 0 c < 0 = return ()
 | otherwise = alterBS (\b -> b{bsMaxRedirects=c})

-- | @getMaxRedirects@ returns the current setting for the max-redirect count.
-- If @Nothing@, the "Network.Browser"'s default is used.
getMaxRedirects :: BrowserAction t (Maybe Int)
getMaxRedirects = getBS bsMaxRedirects

-- | @setProxy p@ will disable proxy usage if @p@ is @NoProxy@.
-- If @p@ is @Proxy proxyURL mbAuth@, then @proxyURL@ is interpreted
-- as the URL of the proxy to use, possibly authenticating via 
-- 'Authority' information in @mbAuth@.
setProxy :: Proxy -> BrowserAction t ()
setProxy p =
 -- Note: if user _explicitly_ sets the proxy, we turn
 -- off any auto-detection of proxies.
 alterBS (\b -> b {bsProxy = p, bsCheckProxy=False})

-- | @getProxy@ returns the current proxy settings. If
-- the auto-proxy flag is set to @True@, @getProxy@ will
-- perform the necessary 
getProxy :: BrowserAction t Proxy
getProxy = do
 p <- getBS bsProxy
 case p of
 -- Note: if there is a proxy, no need to perform any auto-detect.
 -- Presumably this is the user's explicit and preferred proxy server.
 Proxy{} -> return p
 NoProxy{} -> do
 flg <- getBS bsCheckProxy
 if not flg
 then return p 
 else do
 np <- ioAction $ fetchProxy True{-issue warning on stderr if ill-formed...-}
 -- note: this resets the check-proxy flag; a one-off affair.
 setProxy np
 return np

-- | @setCheckForProxy flg@ sets the one-time check for proxy
-- flag to @flg@. If @True@, the session will try to determine
-- the proxy server is locally configured. See 'Network.HTTP.Proxy.fetchProxy'
-- for details of how this done.
setCheckForProxy :: Bool -> BrowserAction t ()
setCheckForProxy flg = alterBS (\ b -> b{bsCheckProxy=flg})

-- | @getCheckForProxy@ returns the current check-proxy setting.
-- Notice that this may not be equal to @True@ if the session has
-- set it to that via 'setCheckForProxy' and subsequently performed
-- some HTTP protocol interactions. i.e., the flag return represents
-- whether a proxy will be checked for again before any future protocol
-- interactions.
getCheckForProxy :: BrowserAction t Bool
getCheckForProxy = getBS bsCheckProxy

-- | @setDebugLog mbFile@ turns off debug logging iff @mbFile@
-- is @Nothing@. If set to @Just fStem@, logs of browser activity
-- is appended to files of the form @fStem-url-authority@, i.e.,
-- @fStem@ is just the prefix for a set of log files, one per host/authority.
setDebugLog :: Maybe String -> BrowserAction t ()
setDebugLog v = alterBS (\b -> b {bsDebug=v})

-- | @setUserAgent ua@ sets the current @User-Agent:@ string to @ua@. It
-- will be used if no explicit user agent header is found in subsequent requests.
setUserAgent :: String -> BrowserAction t ()
setUserAgent ua = alterBS (\b -> b{bsUserAgent=Just ua})

-- | @getUserAgent@ returns the current @User-Agent:@ default string.
getUserAgent :: BrowserAction t String
getUserAgent = do
 n <- getBS bsUserAgent
 return (maybe defaultUserAgent id n)

-- | @RequestState@ is an internal tallying type keeping track of various 
-- per-connection counters, like the number of authorization attempts and 
-- forwards we've gone through.
data RequestState 
 = RequestState
 { reqDenies :: Int -- ^ number of 401 responses so far
 , reqRedirects :: Int -- ^ number of redirects so far
 , reqRetries :: Int -- ^ number of retries so far
 , reqStopOnDeny :: Bool -- ^ whether to pre-empt 401 response
 }

type RequestID = Int -- yeah, it will wrap around.

nullRequestState :: RequestState
nullRequestState = RequestState
 { reqDenies = 0
 , reqRedirects = 0
 , reqRetries = 0
 , reqStopOnDeny = True
 }

-- | @BrowserEvent@ is the event record type that a user-defined handler, set
-- via 'setEventHandler', will be passed. It indicates various state changes
-- encountered in the processing of a given 'RequestID', along with timestamps
-- at which they occurred.
data BrowserEvent
 = BrowserEvent
 { browserTimestamp :: ClockTime
 , browserRequestID :: RequestID
 , browserRequestURI :: {-URI-}String
 , browserEventType :: BrowserEventType
 }

-- | 'BrowserEventType' is the enumerated list of events that the browser
-- internals will report to a user-defined event handler.
data BrowserEventType
 = OpenConnection
 | ReuseConnection
 | RequestSent
 | ResponseEnd ResponseData
 | ResponseFinish
{- not yet, you will have to determine these via the ResponseEnd event.
 | Redirect
 | AuthChallenge
 | AuthResponse
-}
 
-- | @setEventHandler onBrowserEvent@ configures event handling.
-- If @onBrowserEvent@ is @Nothing@, event handling is turned off;
-- setting it to @Just onEv@ causes the @onEv@ IO action to be
-- notified of browser events during the processing of a request
-- by the Browser pipeline.
setEventHandler :: Maybe (BrowserEvent -> BrowserAction ty ()) -> BrowserAction ty ()
setEventHandler mbH = alterBS (\b -> b { bsEvent=mbH})

buildBrowserEvent :: BrowserEventType -> {-URI-}String -> RequestID -> IO BrowserEvent
buildBrowserEvent bt uri reqID = do
 ct <- getClockTime
 return BrowserEvent 
 { browserTimestamp = ct
 , browserRequestID = reqID
 , browserRequestURI = uri
 , browserEventType = bt
 }

reportEvent :: BrowserEventType -> {-URI-}String -> BrowserAction t ()
reportEvent bt uri = do
 st <- getBrowserState
 case bsEvent st of
 Nothing -> return ()
 Just evH -> do
 evt <- ioAction $ buildBrowserEvent bt uri (bsRequestID st)
 evH evt -- if it fails, we fail.

-- | The default number of hops we are willing not to go beyond for 
-- request forwardings.
defaultMaxRetries :: Int
defaultMaxRetries = 4

-- | The default number of error retries we are willing to perform.
defaultMaxErrorRetries :: Int
defaultMaxErrorRetries = 4

-- | The default maximum HTTP Authentication attempts we will make for
-- a single request.
defaultMaxAuthAttempts :: Int
defaultMaxAuthAttempts = 2

-- | The default setting for auto-proxy detection.
-- You may change this within a session via 'setAutoProxyDetect'.
-- To avoid initial backwards compatibility issues, leave this as @False@.
defaultAutoProxyDetect :: Bool
defaultAutoProxyDetect = False

-- | @request httpRequest@ tries to submit the 'Request' @httpRequest@
-- to some HTTP server (possibly going via a /proxy/, see 'setProxy'.)
-- Upon successful delivery, the URL where the response was fetched from
-- is returned along with the 'Response' itself.
request :: HStream ty
 => Request ty
	-> BrowserAction (HandleStream ty) (URI,Response ty)
request req = nextRequest $ do
 res <- request' nullVal initialState req
 reportEvent ResponseFinish (show (rqURI req))
 case res of
 Right r -> return r
 Left e -> do
 let errStr = ("Network.Browser.request: Error raised " ++ show e)
 err errStr
 fail errStr
 where
 initialState = nullRequestState
 nullVal = buf_empty bufferOps

-- | Internal helper function, explicitly carrying along per-request 
-- counts.
request' :: HStream ty
 => ty
	 -> RequestState
	 -> Request ty
	 -> BrowserAction (HandleStream ty) (Result (URI,Response ty))
request' nullVal rqState rq = do
 let uri = rqURI rq
 let uria = reqURIAuth rq 
 -- add cookies to request
 cookies <- getCookiesFor (uriAuthToString uria) (uriPath uri)
{- Not for now:
 (case uriUserInfo uria of
 "" -> id
 xs ->
 case chopAtDelim ':' xs of
 (_,[]) -> id
	 (usr,pwd) -> withAuth
	 AuthBasic{ auUserName = usr
 , auPassword = pwd
			 , auRealm = "/"
			 , auSite = uri
			 }) $ do
-}
 when (not $ null cookies) 
 (out $ "Adding cookies to request. Cookie names: " ++ unwords (map ckName cookies))
 -- add credentials to request
 rq' <- 
 if not (reqStopOnDeny rqState) 
 then return rq 
 else do 
 auth <- anticipateChallenge rq
 case auth of
 Nothing -> return rq
 Just x -> return (insertHeader HdrAuthorization (withAuthority x rq) rq)
 let rq'' = insertHeaders (map cookieToHeader cookies) rq'
 p <- getProxy
 def_ua <- getBS bsUserAgent
 let defaultOpts = 
 case p of 
	 NoProxy -> defaultNormalizeRequestOptions{normUserAgent=def_ua}
	 Proxy _ ath ->
	 defaultNormalizeRequestOptions
	 { normForProxy = True
		, normUserAgent = def_ua
		, normCustoms = 
		 maybe []
		 (\ authS -> [\ _ r -> insertHeader HdrProxyAuthorization (withAuthority authS r) r])
			 ath
		}
 let final_req = normalizeRequest defaultOpts rq''
 out ("Sending:\n" ++ show final_req)
 e_rsp <- 
 case p of
 NoProxy -> dorequest (reqURIAuth rq'') final_req
 Proxy str _ath -> do
 let notURI 
	 | null pt || null hst = 
	 URIAuth{ uriUserInfo = ""
	 , uriRegName = str
			, uriPort = ""
			}
	 | otherwise = 
	 URIAuth{ uriUserInfo = ""
	 , uriRegName = hst
			, uriPort = pt
			}
 -- If the ':' is dropped from port below, dorequest will assume port 80. Leave it!
 where (hst, pt) = span (':'/=) str
 -- Proxy can take multiple forms - look for http://host:port first,
 -- then host:port. Fall back to just the string given (probably a host name).
 let proxyURIAuth =
 maybe notURI
 (\parsed -> maybe notURI id (uriAuthority parsed))
 (parseURI str)

 out $ "proxy uri host: " ++ uriRegName proxyURIAuth ++ ", port: " ++ uriPort proxyURIAuth
	 dorequest proxyURIAuth final_req
 mbMx <- getMaxErrorRetries
 case e_rsp of
 Left v 
 | (reqRetries rqState < fromMaybe defaultMaxErrorRetries mbMx) && 
 (v == ErrorReset || v == ErrorClosed) ->
 request' nullVal rqState{reqRetries=succ (reqRetries rqState)} rq
 | otherwise -> 
 return (Left v)
 Right rsp -> do 
 out ("Received:\n" ++ show rsp)
 -- add new cookies to browser state
 handleCookies uri (uriAuthToString $ reqURIAuth rq) 
 (retrieveHeaders HdrSetCookie rsp)
 mbMxAuths <- getMaxAuthAttempts
 case rspCode rsp of
 (4,0,1) -- Credentials not sent or refused.
 | reqDenies rqState > fromMaybe defaultMaxAuthAttempts mbMxAuths -> do
 out "401 - credentials again refused; exceeded retry count (2)"
	 return (Right (uri,rsp))
	| otherwise -> do
 out "401 - credentials not supplied or refused; retrying.."
 let hdrs = retrieveHeaders HdrWWWAuthenticate rsp
	 flg <- getAllowBasicAuth
 case pickChallenge flg (catMaybes $ map (headerToChallenge uri) hdrs) of
 Nothing -> do
	 out "no challenge"
	 return (Right (uri,rsp)) {- do nothing -}
 Just x -> do
 au <- challengeToAuthority uri x
 case au of
 Nothing -> do
		 out "no auth"
		 return (Right (uri,rsp)) {- do nothing -}
 Just au' -> do
 out "Retrying request with new credentials"
		 request' nullVal
			 rqState{ reqDenies = succ(reqDenies rqState)
			 , reqStopOnDeny = False
				 }
 (insertHeader HdrAuthorization (withAuthority au' rq) rq)

 (4,0,7) -- Proxy Authentication required
 | reqDenies rqState > fromMaybe defaultMaxAuthAttempts mbMxAuths -> do
 out "407 - proxy authentication required; max deny count exceeeded (2)"
 return (Right (uri,rsp))
 | otherwise -> do
 out "407 - proxy authentication required"
 let hdrs = retrieveHeaders HdrProxyAuthenticate rsp
	 flg <- getAllowBasicAuth
 case pickChallenge flg (catMaybes $ map (headerToChallenge uri) hdrs) of
 Nothing -> return (Right (uri,rsp)) {- do nothing -}
 Just x -> do
 au <- challengeToAuthority uri x
 case au of
 Nothing -> return (Right (uri,rsp)) {- do nothing -}
 Just au' -> do
 pxy <- getBS bsProxy
 case pxy of
 NoProxy -> do
 err "Proxy authentication required without proxy!"
 return (Right (uri,rsp))
 Proxy px _ -> do
 out "Retrying with proxy authentication"
 setProxy (Proxy px (Just au'))
 request' nullVal
			 rqState{ reqDenies = succ(reqDenies rqState)
			 , reqStopOnDeny = False
				 }
			 rq

 (3,0,x) | x /= 5 -> do
 out ("30" ++ show x ++ " - redirect")
	allow_redirs <- allowRedirect rqState
	case allow_redirs of
	 False -> return (Right (uri,rsp))
	 _ -> do
 case retrieveHeaders HdrLocation rsp of
 [] -> do 
	 err "No Location: header in redirect response"
 return (Right (uri,rsp))
 (Header _ u:_) -> 
	 case parseURIReference u of
 Nothing -> do
 err ("Parse of Location: header in a redirect response failed: " ++ u)
 return (Right (uri,rsp))
 Just newURI
		| {-uriScheme newURI_abs /= uriScheme uri && -}(not (supportedScheme newURI_abs)) -> do
		 err ("Unable to handle redirect, unsupported scheme: " ++ show newURI_abs)
		 return (Right (uri, rsp))
 | otherwise -> do		 
 	 out ("Redirecting to " ++ show newURI_abs ++ " ...") 
 
 -- Redirect using GET request method, depending on
 -- response code.
 let toGet = x `elem` [2,3]
 method = if toGet then GET else rqMethod rq
 rq1 = rq { rqMethod=method, rqURI=newURI_abs }
 rq2 = if toGet then (replaceHeader HdrContentLength "0") (rq1 {rqBody = nullVal}) else rq1
 
 request' nullVal
			 rqState{ reqDenies = 0
			 , reqRedirects = succ(reqRedirects rqState)
				 , reqStopOnDeny = True
				 }
 rq2
 where
 newURI_abs = maybe newURI id (newURI `relativeTo` uri)

 (3,0,5) ->
 case retrieveHeaders HdrLocation rsp of
 [] -> do 
	 err "No Location header in proxy redirect response."
 return (Right (uri,rsp))
 (Header _ u:_) -> 
	 case parseURIReference u of
 Nothing -> do
 err ("Parse of Location header in a proxy redirect response failed: " ++ u)
 return (Right (uri,rsp))
 Just newuri -> do
 out ("Retrying with proxy " ++ show newuri ++ "...")
 setProxy (Proxy (uriToAuthorityString newuri) Nothing)
 request' nullVal rqState{ reqDenies = 0
	 , reqRedirects = 0
				 , reqRetries = succ (reqRetries rqState)
				 , reqStopOnDeny = True
				 }
				 rq
 (3,_,_) -> redirect uri rsp
 _ -> return (Right (uri,rsp))

 where 
 redirect uri rsp = do
 rd <- getAllowRedirects
 mbMxRetries <- getMaxRedirects
 if not rd || reqRedirects rqState > fromMaybe defaultMaxRetries mbMxRetries
 then return (Right (uri,rsp))
	else do
 case retrieveHeaders HdrLocation rsp of
 [] -> do 
	 err "No Location header in redirect response."
 return (Right (uri,rsp))
 (Header _ u:_) -> 
	 case parseURIReference u of
 Just newURI -> do
 let newURI_abs = maybe newURI id (newURI `relativeTo` uri)
 out ("Redirecting to " ++ show newURI_abs ++ " ...") 
 request' nullVal
		 rqState{ reqDenies = 0
			 , reqRedirects = succ (reqRedirects rqState)
			 , reqStopOnDeny = True
				}
		 rq{rqURI=newURI_abs}
 Nothing -> do
 err ("Parse of Location header in a redirect response failed: " ++ u)
 return (Right (uri,rsp))

-- | The internal request handling state machine.
dorequest :: (HStream ty)
 => URIAuth
	 -> Request ty
	 -> BrowserAction (HandleStream ty)
	 (Result (Response ty))
dorequest hst rqst = do
 pool <- getBS bsConnectionPool
 conn <- ioAction $ filterM (\c -> c `isTCPConnectedTo` uriAuthToString hst) pool
 rsp <- 
 case conn of
 [] -> do 
 out ("Creating new connection to " ++ uriAuthToString hst)
 let uPort = uriAuthPort Nothing{-ToDo: feed in complete URL-} hst
	reportEvent OpenConnection (show (rqURI rqst))
 c <- ioAction $ openStream (uriRegName hst) uPort
	updateConnectionPool c
	dorequest2 c rqst
 (c:_) -> do
 out ("Recovering connection to " ++ uriAuthToString hst)
	reportEvent ReuseConnection (show (rqURI rqst))
 dorequest2 c rqst
 case rsp of 
 Right (Response a b c _) -> 
 reportEvent (ResponseEnd (a,b,c)) (show (rqURI rqst)) ; _ -> return ()
 return rsp
 where
 dorequest2 c r = do
 dbg <- getBS bsDebug
 st <- getBrowserState
 let 
 onSendComplete =
 maybe (return ())
 (\evh -> do
	 x <- buildBrowserEvent RequestSent (show (rqURI r)) (bsRequestID st)
		(lift (evh x)) st
		return ())
 (bsEvent st)
 ioAction $ 
 maybe (sendHTTP_notify c r onSendComplete)
 (\ f -> do
 c' <- debugByteStream (f++'-': uriAuthToString hst) c
	 sendHTTP_notify c' r onSendComplete)
	 dbg

updateConnectionPool :: HStream hTy
 => HandleStream hTy
		 -> BrowserAction (HandleStream hTy) ()
updateConnectionPool c = do
 pool <- getBS bsConnectionPool
 let len_pool = length pool
 when (len_pool > maxPoolSize)
 (ioAction $ close (last pool))
 let pool' 
	| len_pool > maxPoolSize = init pool
	| otherwise = pool
 alterBS (\b -> b { bsConnectionPool=c:pool' })
 return ()
 
-- | Maximum number of open connections we are willing to have active.
maxPoolSize :: Int
maxPoolSize = 5

handleCookies :: URI -> String -> [Header] -> BrowserAction t ()
handleCookies _ _ [] = return () -- cut short the silliness.
handleCookies uri dom cookieHeaders = do
 when (not $ null errs)
 (err $ unlines ("Errors parsing these cookie values: ":errs))
 when (not $ null newCookies)
 (out $ foldl (\x y -> x ++ "\n " ++ show y) "Cookies received:" newCookies)
 filterfn <- getCookieFilter
 newCookies' <- ioAction (filterM (filterfn uri) newCookies)
 when (not $ null newCookies')
 (out $ "Accepting cookies with names: " ++ unwords (map ckName newCookies'))
 mapM_ addCookie newCookies'
 where
 (errs, newCookies) = processCookieHeaders dom cookieHeaders

------------------------------------------------------------------
----------------------- Miscellaneous ----------------------------
------------------------------------------------------------------

allowRedirect :: RequestState -> BrowserAction t Bool
allowRedirect rqState = do
 rd <- getAllowRedirects
 mbMxRetries <- getMaxRedirects
 return (rd && (reqRedirects rqState <= fromMaybe defaultMaxRetries mbMxRetries))

-- | Return @True@ iff the package is able to handle requests and responses
-- over it.
supportedScheme :: URI -> Bool
supportedScheme u = uriScheme u == "http:"

-- | @uriDefaultTo a b@ returns a URI that is consistent with the first
-- argument URI @a@ when read in the context of the second URI @b@.
-- If the second argument is not sufficient context for determining
-- a full URI then anarchy reins.
uriDefaultTo :: URI -> URI -> URI
uriDefaultTo a b = maybe a id (a `relativeTo` b)


-- This form junk is completely untested...

type FormVar = (String,String)

data Form = Form RequestMethod URI [FormVar]

formToRequest :: Form -> Request_String
formToRequest (Form m u vs) =
 let enc = urlEncodeVars vs
 in case m of
 GET -> Request { rqMethod=GET
 , rqHeaders=[ Header HdrContentLength "0" ]
 , rqBody=""
 , rqURI=u { uriQuery= '?' : enc } -- What about old query?
 }
 POST -> Request { rqMethod=POST
 , rqHeaders=[ Header HdrContentType "application/x-www-form-urlencoded",
 Header HdrContentLength (show $ length enc) ]
 , rqBody=enc
 , rqURI=u
 }
 _ -> error ("unexpected request: " ++ show m)