-- ------------------------------------------------------ -- -- Copyright © 2015 Lars Kuhtz <lakuhtz@gmail.com> -- Copyright © 2014 AlephCloud Systems, Inc. -- ------------------------------------------------------ -- {-# LANGUAGE UnicodeSyntax #-} {-# LANGUAGE OverloadedStrings #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE RecordWildCards #-} {-# LANGUAGE LambdaCase #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE PatternGuards #-} {-# LANGUAGE CPP #-} -- | An implemenation of Cross-Origin resource sharing (CORS) for WAI that -- aims to be compliant with <http://www.w3.org/TR/cors>. -- -- The function 'simpleCors' enables support of simple cross-origin requests. More -- advanced CORS policies can be enabled by passing a 'CorsResourcePolicy' to the -- 'cors' middleware. -- -- = Note On Security -- -- This implementation doens't include any server side enforcement. By -- complying with the CORS standard it enables the client (i.e. the web -- browser) to enforce the CORS policy. For application authors it is strongly -- recommended to take into account the security considerations in section 6.3 -- of <http://wwww.w3.org/TR/cors>. In particular the application should check -- that the value of the @Origin@ header matches it's expectations. -- -- = Websockets -- -- Websocket connections don't support CORS and are ignored by this CORS -- implementation. However Websocket requests usually (at least for some -- browsers) include the @Origin@ header. Applications are expected to check -- the value of this header and respond with an error in case that its content -- doesn't match the expectations. -- -- = Example -- -- The following is an example how to enable support for simple cross-origin requests -- for a <http://hackage.haskell.org/package/scotty scotty> application. -- -- > {-# LANGUAGE UnicodeSyntax #-} -- > {-# LANGUAGE OverloadedStrings #-} -- > -- > module Main -- > ( main -- > ) where -- > -- > import Network.Wai.Middleware.Cors -- > import Web.Scotty -- > -- > main ∷ IO () -- > main = scotty 8080 $ do -- > middleware simpleCors -- > matchAny "/" $ text "Success" -- -- The result of following curl command will include the HTTP response header -- @Access-Control-Allow-Origin: *@. -- -- > curl -i http://127.0.0.1:8888 -H 'Origin: 127.0.0.1' -v -- module Network.Wai.Middleware.Cors ( Origin , CorsResourcePolicy(..) , simpleCorsResourcePolicy , cors , simpleCors -- * Utils , isSimple , simpleResponseHeaders , simpleHeaders , simpleContentTypes , simpleMethods ) where #ifndef MIN_VESION_base #define MIN_VESION_base(x,y,z) 1 #endif #ifndef MIN_VESION_wai #define MIN_VESION_wai(x,y,z) 1 #endif #if ! MIN_VERSION_base(4,8,0) import Control.Applicative #endif import Control.Monad.Error.Class import Control.Monad.Trans.Except #if ! MIN_VERSION_wai(2,0,0) import Control.Monad.Trans.Resource #endif import qualified Data.Attoparsec.ByteString as AttoParsec import qualified Data.ByteString.Char8 as B8 import qualified Data.ByteString.Lazy.Char8 as LB8 import qualified Data.CaseInsensitive as CI import qualified Data.CharSet as CS import Data.List (intersect, (\\), union) import Data.Maybe (catMaybes) import Data.Monoid.Unicode import Data.String import qualified Network.HTTP.Types as HTTP import qualified Network.Wai as WAI import Prelude.Unicode import qualified Text.Parser.Char as P import qualified Text.Parser.Combinators as P #if MIN_VERSION_wai(2,0,0) type ReqMonad = IO #else type ReqMonad = ResourceT IO #endif -- | Origins are expected to be formated as described in RFC 6454 (section -- 6.2). In particular the string @*@ is not a valid origin (but the string -- @null@ is). -- type Origin = B8.ByteString data CorsResourcePolicy = CorsResourcePolicy { -- | HTTP origins that are allowed in CORS requests. -- -- A value of 'Nothing' indicates unrestricted cross-origin sharing and -- results in @*@ as value for the @Access-Control-Allow-Origin@ HTTP -- response header. -- -- A value other than 'Nothing' is a tuple that consists of a list of -- origins each with a Boolean flag that indicates if credentials are used -- to access the resource via CORS. -- -- Origins must be formated as described in RFC6454 (section 6.2). In -- particular the string @*@ is not a valid origin (but the string @null@ -- is). -- corsOrigins ∷ !(Maybe ([Origin], Bool)) -- | HTTP methods that are allowed in CORS requests. -- , corsMethods ∷ ![HTTP.Method] -- | Field names of HTTP request headers that are allowed in CORS requests. -- Header names that are included in 'simpleHeaders', except for -- @content-type@, are implicitely included an thus optional in this list. -- , corsRequestHeaders ∷ ![HTTP.HeaderName] -- | Field names of HTTP headers that are exposed on the client. -- , corsExposedHeaders ∷ !(Maybe [HTTP.HeaderName]) -- | Number of seconds that the response may be cached by the client. -- , corsMaxAge ∷ !(Maybe Int) -- | If the resource is shared by multiple origins but -- @Access-Control-Allow-Origin@ is not set to @*@ this may be set to -- 'True'. -- , corsVaryOrigin ∷ !Bool -- | If this is 'True' and the request does not include an @Origin@ header -- the response has HTTP status 400 (bad request) and the body contains -- a short error message. -- -- If this is 'False' and the request does not include an @Origin@ header -- the request is passed on unchanged to the application. -- -- @since 0.2 , corsRequireOrigin ∷ !Bool -- | In the case that -- -- * the request contains an @Origin@ header and -- -- * the client does not conform with the CORS protocol -- (/request is out of scope/) -- -- then -- -- * the request is passed on unchanged to the application if this field is -- 'True' or -- -- * an response with HTTP status 400 (bad request) and short -- error message is returned if this field is 'False'. -- -- @since 0.2 -- , corsIgnoreFailures ∷ !Bool } deriving (Show,Read,Eq,Ord) -- | A 'CorsResourcePolicy' that supports /simple cross-origin requests/ as defined -- in <http://www.w3.org/TR/cors/>. -- -- * The HTTP header @Access-Control-Allow-Origin@ is set to @*@. -- -- * Request methods are constraint to /simple methods/ (@GET@, @HEAD@, @POST@). -- -- * Request headers are constraint to /simple request headers/ -- (@Accept@, @Accept-Language@, @Content-Language@, @Content-Type@). -- -- * If the request is a @POST@ request the content type is constraint to -- /simple content types/ -- (@application/x-www-form-urlencoded@, @multipart/form-data@, @text/plain@), -- -- * Only /simple response headers/ may be exposed on the client -- (@Cache-Control@, @Content-Language@, @Content-Type@, @Expires@, @Last-Modified@, @Pragma@) -- -- * The @Vary-Origin@ header is left unchanged (possibly unset). -- -- * If the request doesn't include an @Origin@ header the request is passed unchanged to -- the application. -- -- * If the request includes an @Origin@ header but does not conform to the CORS -- protocol (/request is out of scope/) an response with HTTP status 400 (bad request) -- and a short error message is returned. -- -- For /simple cross-origin requests/ a preflight request is not required. However, if -- the client chooses to make a preflight request it is answered in accordance with -- the policy for /simple cross-origin requests/. -- simpleCorsResourcePolicy ∷ CorsResourcePolicy simpleCorsResourcePolicy = CorsResourcePolicy { corsOrigins = Nothing , corsMethods = simpleMethods , corsRequestHeaders = [] , corsExposedHeaders = Nothing , corsMaxAge = Nothing , corsVaryOrigin = False , corsRequireOrigin = False , corsIgnoreFailures = False } -- | A Cross-Origin resource sharing (CORS) middleware. -- -- The middleware is given a function that serves as a pattern to decide -- whether a requested resource is available for CORS. If the match fails with -- 'Nothing' the request is passed unmodified to the inner application. -- -- The current version of this module does only aim at compliance with the CORS -- protocol as specified in <http://www.w3.org/TR/cors/>. In accordance with -- that standard the role of the server side is to support the client to -- enforce CORS restrictions. This module does not implement any enforcement of -- authorization policies that are possibly implied by the -- 'CorsResourcePolicy'. It is up to the inner WAI application to enforce such -- policy and make sure that it is in accordance with the configuration of the -- 'cors' middleware. -- -- Matches are done as follows: @*@ matches every origin. For all other cases a -- match succeeds if and only if the ASCII serializations (as described in -- RCF6454 section 6.2) are equal. -- -- The OPTIONS method may return options for resources that are not actually -- available. In particular for preflight requests the implementation returns -- for the HTTP response headers @Access-Control-Allow-Headers@ and -- @Access-Control-Allow-Methods@ all values specified in the -- 'CorsResourcePolicy' together with the respective values for simple requests -- (except @content-type@). This does not imply that the application actually -- supports the respective values are for the requested resource. Thus, -- depending on the application, an actual request may still fail with 404 even -- if the preflight request /supported/ the usage of the HTTP method with CORS. -- -- The implementation does not distinguish between simple requests and requests -- that require preflight. The client is free to omit a preflight request or do -- a preflight request in cases when it wouldn't be required. -- -- For application authors it is strongly recommended to take into account the -- security considerations in section 6.3 of <http://wwww.w3.org/TR/cors>. -- -- /TODO/ -- -- * We may consider adding optional enforcment aspects to this module: we may -- check if a request respects our origin restrictions and we may check that a -- CORS request respects the restrictions that we publish in the preflight -- responses. -- -- * Even though slightly out of scope we may (optionally) check if -- host header matches the actual host of the resource, since clients -- using CORS may expect this, since this check is recommended in -- <http://www.w3.org/TR/cors>. -- -- * We may consider integrating CORS policy handling more closely with the -- handling of the source, for instance by integrating with 'ActionM' from -- scotty. -- cors ∷ (WAI.Request → Maybe CorsResourcePolicy) -- ^ A value of 'Nothing' indicates that the resource is not available for CORS → WAI.Middleware #if MIN_VERSION_wai(3,0,0) cors policyPattern app r respond #else cors policyPattern app r #endif -- We don't handle websockets, even if they include an @Origin@ header | isWebSocketsReq r = runApp | Just policy ← policyPattern r = case hdrOrigin of -- No origin header: requect request Nothing → if corsRequireOrigin policy then res $ corsFailure "Origin header is missing" else runApp -- Origin header: apply CORS policy to request Just origin → applyCorsPolicy policy origin | otherwise = runApp where #if MIN_VERSION_wai(3,0,0) res = respond runApp = app r respond #else res = return runApp = app r #endif -- Lookup the HTTP origin request header -- hdrOrigin = lookup "origin" (WAI.requestHeaders r) -- Process a CORS request -- applyCorsPolicy policy origin = do -- The error continuation let err e = if corsIgnoreFailures policy then runApp else res $ corsFailure (B8.pack e) -- Match request origin with corsOrigins from policy let respOrigin = case corsOrigins policy of Nothing → return Nothing Just (originList, withCreds) → if origin `elem` originList then Right $ Just (origin, withCreds) else Left $ "Unsupported origin: " ⊕ B8.unpack origin case respOrigin of Left e → err e Right respOrigin → do -- Determine headers that are common to actuall responses and preflight responses let ch = commonCorsHeaders respOrigin (corsVaryOrigin policy) case WAI.requestMethod r of -- Preflight CORS request "OPTIONS" → runExceptT (preflightHeaders policy) >>= \case Left e → err e Right headers → res $ WAI.responseLBS HTTP.ok200 (ch ⊕ headers) "" -- Actual CORS request #if MIN_VERSION_wai(3,0,0) _ → addHeaders (ch ⊕ respCorsHeaders policy) app r respond #else _ → addHeaders (ch ⊕ respCorsHeaders policy) app r #endif -- Compute HTTP response headers for a preflight request -- preflightHeaders ∷ (Functor μ, Monad μ) ⇒ CorsResourcePolicy → ExceptT String μ HTTP.ResponseHeaders preflightHeaders policy = concat <$> sequence [ hdrReqMethod policy , hdrRequestHeader policy , hdrMaxAge policy ] hdrMaxAge ∷ Monad μ ⇒ CorsResourcePolicy → ExceptT String μ HTTP.ResponseHeaders hdrMaxAge policy = case corsMaxAge policy of Nothing → return [] Just secs → return [("Access-Control-Max-Age", sshow secs)] hdrReqMethod ∷ Monad μ ⇒ CorsResourcePolicy → ExceptT String μ HTTP.ResponseHeaders hdrReqMethod policy = case lookup "Access-Control-Request-Method" (WAI.requestHeaders r) of Nothing → throwError "Access-Control-Request-Method header is missing in CORS preflight request" Just x → if x `elem` supportedMethods then return [("Access-Control-Allow-Methods", hdrL supportedMethods)] else throwError $ "Method requested in Access-Control-Request-Method of CORS request is not supported; requested: " ⊕ B8.unpack x ⊕ "; supported are " ⊕ B8.unpack (hdrL supportedMethods) ⊕ "." where supportedMethods = corsMethods policy `union` simpleMethods hdrRequestHeader ∷ Monad μ ⇒ CorsResourcePolicy → ExceptT String μ HTTP.ResponseHeaders hdrRequestHeader policy = case lookup "Access-Control-Request-Headers" (WAI.requestHeaders r) of Nothing → return [] Just hdrsBytes → do hdrs ← either throwError return $ AttoParsec.parseOnly httpHeaderNameListParser hdrsBytes if hdrs `isSubsetOf` supportedHeaders then return [("Access-Control-Allow-Headers", hdrLI supportedHeaders)] else throwError $ "HTTP header requested in Access-Control-Request-Headers of CORS request is not supported; requested: " ⊕ B8.unpack (hdrLI hdrs) ⊕ "; supported are " ⊕ B8.unpack (hdrLI supportedHeaders) ⊕ "." where supportedHeaders = corsRequestHeaders policy `union` simpleHeadersWithoutContentType simpleHeadersWithoutContentType = simpleHeaders \\ ["content-type"] -- HTTP response headers that are common to normal and preflight CORS responses -- commonCorsHeaders ∷ Maybe (Origin, Bool) → Bool → HTTP.ResponseHeaders commonCorsHeaders Nothing True = [("Access-Control-Allow-Origin", "*"), ("Vary", "Origin")] commonCorsHeaders Nothing False = [("Access-Control-Allow-Origin", "*")] commonCorsHeaders (Just (o, False)) _ = [("Access-Control-Allow-Origin", o)] commonCorsHeaders (Just (o, True)) _ = [("Access-Control-Allow-Origin", o), ("Access-Control-Allow-Credentials", "true")] -- HTTP response headers that are only used with normal CORS responses -- respCorsHeaders ∷ CorsResourcePolicy → HTTP.ResponseHeaders respCorsHeaders policy = catMaybes [ fmap (\x → ("Access-Control-Expose-Headers", hdrLI x)) (corsExposedHeaders policy) ] -- | A CORS middleware that supports simple cross-origin requests for all -- resources. -- -- This middleware does not check if the resource corresponds to the -- restrictions for simple requests. This is in accordance with -- <http://www.w3.org/TR/cors/>. The client (user-agent) is supposed to -- enforcement CORS policy. The role of the server is to provide the client -- with the respective policy constraints. -- -- It is out of the scope of the this module if the server chooses to -- enforce rules on its resources in relation to CORS policy itself. -- simpleCors ∷ WAI.Middleware simpleCors = cors (const $ Just simpleCorsResourcePolicy) -- -------------------------------------------------------------------------- -- -- Definition from Standards -- | Simple HTTP response headers as defined in <http://www.w3.org/TR/cors/> -- simpleResponseHeaders ∷ [HTTP.HeaderName] simpleResponseHeaders = [ "Cache-Control" , "Content-Language" , "Content-Type" , "Expires" , "Last-Modified" , "Pragma" ] simpleHeaders ∷ [HTTP.HeaderName] simpleHeaders = [ "Accept" , "Accept-Language" , "Content-Language" , "Content-Type" ] simpleContentTypes ∷ [CI.CI B8.ByteString] simpleContentTypes = [ "application/x-www-form-urlencoded" , "multipart/form-data" , "text/plain" ] -- | Simple HTTP methods as defined in <http://www.w3.org/TR/cors/> -- simpleMethods ∷ [HTTP.Method] simpleMethods = [ "GET" , "HEAD" , "POST" ] isSimple ∷ HTTP.Method → HTTP.RequestHeaders → Bool isSimple method headers = method `elem` simpleMethods ∧ map fst headers `isSubsetOf` simpleHeaders ∧ case (method, lookup "content-type" headers) of ("POST", Just x) → CI.mk x `elem` simpleContentTypes _ → True -- | Valid characters for HTTP header names according to RFC2616 (section 4.2) -- httpHeaderNameCharSet ∷ CS.CharSet httpHeaderNameCharSet = CS.range (toEnum 33) (toEnum 126) CS.\\ CS.fromList "()<>@,;:\\\"/[]?={}" httpHeaderNameParser ∷ P.CharParsing μ ⇒ μ HTTP.HeaderName httpHeaderNameParser = fromString <$> P.some (P.oneOfSet httpHeaderNameCharSet) P.<?> "HTTP Header Name" -- -------------------------------------------------------------------------- -- -- Generic Tools httpHeaderNameListParser ∷ P.CharParsing μ ⇒ μ [HTTP.HeaderName] httpHeaderNameListParser = P.spaces *> P.sepBy (httpHeaderNameParser <* P.spaces) (P.char ',') <* P.spaces sshow ∷ (IsString α, Show β) ⇒ β → α sshow = fromString ∘ show isSubsetOf ∷ Eq α ⇒ [α] → [α] → Bool isSubsetOf l1 l2 = intersect l1 l2 ≡ l1 -- | Add HTTP headers to a WAI response -- #if MIN_VERSION_wai(3,0,0) addHeaders ∷ HTTP.ResponseHeaders → WAI.Middleware addHeaders hdrs app req respond = app req $ \response → do let (st, headers, streamHandle) = WAI.responseToStream response streamHandle $ \streamBody → respond $ WAI.responseStream st (headers ⊕ hdrs) streamBody #elif MIN_VERSION_wai(2,0,0) addHeaders ∷ HTTP.ResponseHeaders → WAI.Middleware addHeaders hdrs app req = do (st, headers, src) ← WAI.responseToSource <$> app req WAI.responseSource st (headers ⊕ hdrs) <$> src return #else addHeaders ∷ HTTP.ResponseHeaders → WAI.Middleware addHeaders hdrs app req = do (st, headers, src) ← WAI.responseSource <$> app req return $ WAI.ResponseSource st (headers ⊕ hdrs) src #endif -- | Format a list of 'HTTP.HeaderName's such that it can be used as -- an HTTP header value -- hdrLI ∷ [HTTP.HeaderName] → B8.ByteString hdrLI l = B8.intercalate ", " (map CI.original l) -- | Format a list of 'B8.ByteString's such that it can be used as -- an HTTP header value -- hdrL ∷ [B8.ByteString] → B8.ByteString hdrL l = B8.intercalate ", " l corsFailure ∷ B8.ByteString -- ^ body → WAI.Response corsFailure msg = WAI.responseLBS HTTP.status400 [("Content-Type", "text/html; charset-utf-8")] (LB8.fromStrict msg) -- Copied from the [wai-websocket package](https://github.com/yesodweb/wai/blob/master/wai-websockets/Network/Wai/Handler/WebSockets.hs#L21) -- isWebSocketsReq ∷ WAI.Request → Bool isWebSocketsReq req = fmap CI.mk (lookup "upgrade" $ WAI.requestHeaders req) == Just "websocket"