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This is used to track and display + a network graph of service dependencies. + -} + -> Version + {- ^ The version of the local program. -} + -> Set ServiceAddr + {- ^ The well-known set of urls where the discovery service lives. -} + -> Manager + {- ^ + The http manager used to manage communication to the discovery + service, and also for communication with any services accessed + via the 'withResponse' function. + -} + -> IO Discovery +connect name version urls manager = + D name version . LB manager <$> evenlyDistributed (return urls) + + +{- | + Run a registered service, making sure to unregister upon ternination. +-} +withService :: ServiceAddr -> Discovery -> IO a -> IO a +withService addy d = + bracket launchPing stopPing . const + where + launchPing :: IO (MVar ()) + launchPing = do + stop <- newEmptyMVar + void . forkIO $ + let + loop = + tryTakeMVar stop >>= \case + Nothing -> ping >> threadDelay tenSeconds >> loop + Just () -> return () + in loop + return stop + + stopPing :: MVar () -> IO () + stopPing stop = putMVar stop () + + ping :: IO () + ping = do + let + userAgent = encodeUtf8 + $ unName (dName d) <> "-" <> pack (display (dVersion d)) + req = def { + path = + "/v1/ping/" + <> urlEncode False (encodeUtf8 (unName (dName d))) + <> "/" + <> urlEncode False (encodeUtf8 (pack (display (dVersion d)))), + method = "POST", + requestHeaders = [("user-agent", userAgent)], + checkStatus = const . const . const $ Nothing, + requestBody = RequestBodyLBS . encode . object $ [ + "serviceAddress" .= unServiceAddr addy + ] + } + {- TODO figure out what we want to do when the ping failes. -} + withResponse req (dLb d) (const (return ())) + + tenSeconds :: Int + tenSeconds = 10000000 {- in microseconds. -} + + +{- | Query the discovery service. -} +query + :: Name + {- ^ The name of the service you are looking for. -} + -> VersionRange + {- ^ The range of service versions with which you are compatible. -} + -> Discovery + {- ^ A handle on the discovery service. -} + -> IO (Set ServiceAddr) +query name range d = do + let + userAgent = encodeUtf8 + $ unName (dName d) <> "-" <> pack (display (dVersion d)) + req = def { + path = + "/v1/services/" + <> urlEncode False (encodeUtf8 (unName name)) + <> "/" + <> urlEncode False (encodeUtf8 (pack (display range))), + method = "GET", + requestHeaders = [("user-agent", userAgent)], + checkStatus = const . const . const $ Nothing + } + withResponse req (dLb d) (\case + Nothing -> fail "No Discovery instances available." + Just resp -> do + body <- brConsume (responseBody resp) + case responseStatus resp of + status | statusIsSuccessful status -> + case eitherDecode (fromChunks body) of + Left err -> fail + $ "Couldn't decode Discovery response: " ++ show err + Right instances -> return ( + Set.fromList + (ServiceAddr <$> Map.keys (instances :: Map Text Value)) + ) + status -> fail $ "Bad response from Discovery:" ++ show (status, body) + ) + + +{- | The name of a service. -} +newtype Name = Name {unName :: Text} deriving (IsString) + + +{- | + The type of a service address. + + A 'ServiceAddr' is a wrapper around an unstructured text value. The + meaning of the text value is dependent on the registered service, + as it is the one responsible for publishing the service address. We + __highly__ recommend that registered services choose to publish a + fully qualified URL as their service address. +-} +newtype ServiceAddr = ServiceAddr {unServiceAddr :: Text} + deriving (IsString, Eq, Ord, Show) + + +{- | + Similar to 'C.withResponse', but automatically replaces the host, + port, and scheme portions with one obtained from the load balancer. + + If a 'Nothing' value is passed to the response handler, that means + that there are no available instances that match the query params that were + passed to 'newLB'. +-} +withResponse + :: Request + -> LBHttp + -> (Maybe (Response BodyReader) -> IO a) + -> IO a +withResponse r lb f = withResource (lbLb lb) (\case + Nothing -> f Nothing + Just url -> do + lbReq <- parseRequest (unpack (unServiceAddr url)) + let + req = r { + host = host lbReq, + secure = secure lbReq, + port = port lbReq + } + C.withResponse req (lbManager lb) (f . Just) + ) + + +{- | A handle on the load balancing context. -} +data LBHttp = LB { + lbManager :: Manager, + lbLb :: LoadBalanced ServiceAddr + } + + +{- | + Create a new load balanced http client, for use with 'withResponse'. +-} +newLB :: Discovery -> Name -> VersionRange -> IO LBHttp +newLB d n r = LB (lbManager (dLb d)) <$> evenlyDistributed (query n r d) + + diff --git a/test/Spec.hs b/test/Spec.hs new file mode 100644 --- /dev/null +++ b/test/Spec.hs @@ -0,0 +1,2 @@ +main :: IO () +main = putStrLn "Test suite not yet implemented"