cookbook sentry integration page

.travis.yml

@@ -160,10 +160,10 @@ script:
   - (cd "doc/cookbook/using-free-client" && cabal sdist)
   - echo -en 'travis_fold:end:sdist\\r'
   - echo Unpacking... && echo -en 'travis_fold:start:unpack\\r'
-  - mv "servant"/dist/servant-*.tar.gz "servant-client"/dist/servant-client-*.tar.gz "servant-client-core"/dist/servant-client-core-*.tar.gz "servant-docs"/dist/servant-docs-*.tar.gz "servant-foreign"/dist/servant-foreign-*.tar.gz "servant-server"/dist/servant-server-*.tar.gz "doc/tutorial"/dist/tutorial-*.tar.gz "doc/cookbook/basic-auth"/dist/cookbook-basic-auth-*.tar.gz "doc/cookbook/curl-mock"/dist/cookbook-curl-mock-*.tar.gz "doc/cookbook/db-postgres-pool"/dist/cookbook-db-postgres-pool-*.tar.gz "doc/cookbook/db-sqlite-simple"/dist/cookbook-db-sqlite-simple-*.tar.gz "doc/cookbook/file-upload"/dist/cookbook-file-upload-*.tar.gz "doc/cookbook/generic"/dist/cookbook-generic-*.tar.gz "doc/cookbook/https"/dist/cookbook-https-*.tar.gz "doc/cookbook/jwt-and-basic-auth"/dist/cookbook-jwt-and-basic-auth-*.tar.gz "doc/cookbook/pagination"/dist/cookbook-pagination-*.tar.gz "doc/cookbook/structuring-apis"/dist/cookbook-structuring-apis-*.tar.gz "doc/cookbook/using-custom-monad"/dist/cookbook-using-custom-monad-*.tar.gz "doc/cookbook/using-free-client"/dist/cookbook-using-free-client-*.tar.gz ${DISTDIR}/
+  - mv "servant"/dist/servant-*.tar.gz "servant-client"/dist/servant-client-*.tar.gz "servant-client-core"/dist/servant-client-core-*.tar.gz "servant-docs"/dist/servant-docs-*.tar.gz "servant-foreign"/dist/servant-foreign-*.tar.gz "servant-server"/dist/servant-server-*.tar.gz "doc/tutorial"/dist/tutorial-*.tar.gz "doc/cookbook/basic-auth"/dist/cookbook-basic-auth-*.tar.gz "doc/cookbook/db-postgres-pool"/dist/cookbook-db-postgres-pool-*.tar.gz "doc/cookbook/db-sqlite-simple"/dist/cookbook-db-sqlite-simple-*.tar.gz "doc/cookbook/file-upload"/dist/cookbook-file-upload-*.tar.gz "doc/cookbook/generic"/dist/cookbook-generic-*.tar.gz "doc/cookbook/https"/dist/cookbook-https-*.tar.gz "doc/cookbook/jwt-and-basic-auth"/dist/cookbook-jwt-and-basic-auth-*.tar.gz "doc/cookbook/pagination"/dist/cookbook-pagination-*.tar.gz "doc/cookbook/structuring-apis"/dist/cookbook-structuring-apis-*.tar.gz "doc/cookbook/using-custom-monad"/dist/cookbook-using-custom-monad-*.tar.gz "doc/cookbook/using-free-client"/dist/cookbook-using-free-client-*.tar.gz "doc/cookbook/sentry"/dist/cookbook-sentry-*.tar.gz "doc/cookbook/curl-mock"/dist/cookbook-curl-mock-*.tar.gz ${DISTDIR}/
   - cd ${DISTDIR} || false
   - find . -maxdepth 1 -name '*.tar.gz' -exec tar -xvf '{}' \;
-  - "printf 'packages: servant-*/*.cabal servant-client-*/*.cabal servant-client-core-*/*.cabal servant-docs-*/*.cabal servant-foreign-*/*.cabal servant-server-*/*.cabal tutorial-*/*.cabal cookbook-basic-auth-*/*.cabal cookbook-curl-mock-*/*.cabal cookbook-db-postgres-pool-*/*.cabal cookbook-db-sqlite-simple-*/*.cabal cookbook-file-upload-*/*.cabal cookbook-generic-*/*.cabal cookbook-https-*/*.cabal cookbook-jwt-and-basic-auth-*/*.cabal cookbook-pagination-*/*.cabal cookbook-structuring-apis-*/*.cabal cookbook-using-custom-monad-*/*.cabal cookbook-using-free-client-*/*.cabal\\n' > cabal.project"
+  - "printf 'packages: servant-*/*.cabal servant-client-*/*.cabal servant-client-core-*/*.cabal servant-docs-*/*.cabal servant-foreign-*/*.cabal servant-server-*/*.cabal tutorial-*/*.cabal cookbook-basic-auth-*/*.cabal cookbook-curl-mock-*/*.cabal cookbook-db-postgres-pool-*/*.cabal cookbook-db-sqlite-simple-*/*.cabal cookbook-file-upload-*/*.cabal cookbook-generic-*/*.cabal cookbook-https-*/*.cabal cookbook-jwt-and-basic-auth-*/*.cabal cookbook-pagination-*/*.cabal cookbook-structuring-apis-*/*.cabal cookbook-using-custom-monad-*/*.cabal cookbook-using-free-client-*/*.cabal cookbook-sentry-*/*.cabal\\n' > cabal.project"
   - "echo 'constraints: foundation >=0.0.14,memory <0.14.12 || >0.14.12' >> cabal.project"
   - "echo 'allow-newer: servant-auth-server:http-types,servant-auth-server:servant-server, servant-pagination:servant,servant-pagination:servant-server' >> cabal.project"
   - touch cabal.project.local

doc/cookbook/cabal.project

@@ -9,6 +9,7 @@ packages:
   structuring-apis/
   https/
   pagination/
+  sentry/
   ../../servant
   ../../servant-server
   ../../servant-client-core

doc/cookbook/index.rst

@@ -29,3 +29,4 @@ you name it!
   file-upload/FileUpload.lhs
   pagination/Pagination.lhs
   curl-mock/CurlMock.lhs
+  sentry/Sentry.lhs

doc/cookbook/sentry/Sentry.lhs

@@ -0,0 +1,116 @@
+# Error logging with Sentry
+
+In this recipe we will use [Sentry](https://sentry.io) to collect the runtime exceptions generated by our application. We will use the [raven-haskell](https://hackage.haskell.org/package/raven-haskell) package, which is a client for a Sentry event server. Mind that this package is not present on [Stackage](https://www.stackage.org/), so if we are using [Stack](https://docs.haskellstack.org) we’ll need to add it to our `extra-deps` section in the `stack.yaml` file.
+
+To exemplify this we will need the following imports
+
+```haskell
+{-# LANGUAGE DataKinds     #-}
+{-# LANGUAGE TypeOperators #-}
+
+import           Control.Exception                      (Exception,
+                                                         SomeException, throw)
+import           Data.ByteString.Char8                  (unpack)
+import           Network.Wai                            (Request, rawPathInfo,
+                                                         requestHeaderHost)
+import           Network.Wai.Handler.Warp               (defaultOnException,
+                                                         defaultSettings,
+                                                         runSettings,
+                                                         setOnException,
+                                                         setPort)
+import           Servant
+import           System.Log.Raven                       (initRaven, register,
+                                                         silentFallback)
+import           System.Log.Raven.Transport.HttpConduit (sendRecord)
+import           System.Log.Raven.Types                 (SentryLevel (Error),
+                                                         SentryRecord (..))
+```
+
+Just for the sake of the example we will use the following API which will throw an exception
+
+```haskell
+type API = "break" :> Get '[JSON] ()
+
+data MyException = MyException deriving (Show)
+
+instance Exception MyException
+
+server = breakHandler
+  where breakHandler :: Handler ()
+        breakHandler = do
+          throw MyException
+          return ()
+```
+
+First thing we need to do if we want to intercept and log this exception, we need to look in the section of our code where we run the `warp` application, and instead of using the simple `run` function from `warp`, we use the `runSettings` functions which allows to customise the handling of requests
+
+```haskell
+main :: IO ()
+main =
+  let
+    settings =
+      setPort 8080 $
+      setOnException sentryOnException $
+      defaultSettings
+  in
+    runSettings settings $ serve (Proxy :: Proxy API) server
+```
+
+The definition of the `sentryOnException` function could look as follows
+
+```haskell
+sentryOnException :: Maybe Request -> SomeException -> IO ()
+sentryOnException mRequest exception = do
+  sentryService <- initRaven
+    "https://username:password@senty.host/id"
+    id
+    sendRecord
+    silentFallback
+  register
+    sentryService
+    "myLogger"
+    Error
+    (formatMessage mRequest exception)
+    (recordUpdate mRequest exception)
+  defaultOnException mRequest exception
+```
+
+It does three things. First it initializes the service which will communicate with Sentry. The parameters it receives are:
+
+- the Sentry `DSN`, which is obtained when creating a new project on Sentry
+- a default way to update sentry fields, where we use the identity function
+- an event trasport, which generally would be `sendRecord`, an HTTPS capable trasport which uses http-conduit
+- a fallback handler, which we choose to be `silentFallback` since later we are logging to the console anyway.
+
+In the second step it actually sends our message to Sentry with the `register` function. Its arguments are:
+
+- the configured Sentry service which we just created
+- the name of the logger
+- the error level (see [SentryLevel](https://hackage.haskell.org/package/raven-haskell-0.1.2.0/docs/System-Log-Raven-Types.html#t:SentryLevel) for the possible options)
+- the message we want to send
+- an update function to handle the specific `SentryRecord`
+
+Eventually it just delegates the error handling to the default warp mechanism.
+
+The function `formatMessage` simply uses the request and the exception to return a string with the error message.
+
+```haskell
+formatMessage :: Maybe Request -> SomeException -> String
+formatMessage Nothing exception        = "Exception before request could be parsed: " ++ show exception
+formatMessage (Just request) exception = "Exception " ++ show exception ++ " while handling request " ++ request
+```
+
+The only piece left now is the `recordUpdate` function which allows to decorate with other [attributes](https://docs.sentry.io/clientdev/attributes/) the default `SentryRecord`.
+
+```haskell
+recordUpdate :: Maybe Request -> SomeException -> SentryRecord -> SentryRecord
+recordUpdate Nothing exception record        = record
+recordUpdate (Just request) exception record = record
+  { srCulprit = Just $ unpack $ rawPathInfo request
+  , srServerName = fmap unpack $ requestHeaderHost request
+  }
+```
+
+In this examples we set the raw path as the culprit and we use the `Host` header to populate the server name field.
+
+You can try to run this code using the `cookbook-sentry` executable. You should obtain a `MyException` error in the console and, if you provided a valid Sentry DSN, you should also find your error in the Sentry interface.

doc/cookbook/sentry/sentry.cabal

@@ -0,0 +1,23 @@
+name:                cookbook-sentry
+version:             0.1
+synopsis:            Collecting runtime exceptions using Sentry
+homepage:            http://haskell-servant.readthedocs.org/
+license:             BSD3
+license-file:        ../../../servant/LICENSE
+author:              Servant Contributors
+maintainer:          haskell-servant-maintainers@googlegroups.com
+build-type:          Simple
+cabal-version:       >=1.10
+
+executable cookbook-sentry
+  main-is:             Sentry.lhs
+  build-depends:       base == 4.*
+                     , bytestring
+                     , markdown-unlit >= 0.4
+                     , raven-haskell >= 0.1.2
+                     , servant-server
+                     , warp >= 3.2
+                     , wai >= 3.2
+  default-language:    Haskell2010
+  ghc-options:         -Wall -pgmL markdown-unlit
+  build-tool-depends: markdown-unlit:markdown-unlit