Middleware.hs

{-|
Module      : PostgREST.Middleware
Description : Sets CORS policy. Also the PostgreSQL GUCs, role, search_path and pre-request function.
-}
{-# LANGUAGE BlockArguments  #-}
{-# LANGUAGE RecordWildCards #-}
module PostgREST.Middleware
  ( runPgLocals
  , optionalRollback
  ) where

import qualified Data.Aeson                        as JSON
import qualified Data.ByteString.Lazy.Char8        as LBS
import qualified Data.HashMap.Strict               as M
import qualified Data.Text                         as T
import qualified Data.Text.Encoding                as T
import qualified Hasql.Decoders                    as HD
import qualified Hasql.DynamicStatements.Snippet   as SQL hiding (sql)
import qualified Hasql.DynamicStatements.Statement as SQL
import qualified Hasql.Transaction                 as SQL
import qualified Network.Wai                       as Wai

import Control.Arrow ((***))

import Data.Scientific (FPFormat (..), formatScientific, isInteger)

import PostgREST.Config             (AppConfig (..))
import PostgREST.Config.PgVersion   (PgVersion (..), pgVersion140)
import PostgREST.Error              (Error, errorResponseFor)
import PostgREST.GucHeader          (addHeadersIfNotIncluded)
import PostgREST.Query.SqlFragment  (fromQi, intercalateSnippet,
                                     unknownEncoder)
import PostgREST.Request.ApiRequest (ApiRequest (..), Target (..))

import PostgREST.Request.Preferences

import Protolude

-- | Runs local(transaction scoped) GUCs for every request, plus the pre-request function
runPgLocals :: AppConfig   -> M.HashMap Text JSON.Value ->
               (ApiRequest -> ExceptT Error SQL.Transaction Wai.Response) ->
               ApiRequest  -> ByteString -> PgVersion -> ExceptT Error SQL.Transaction Wai.Response
runPgLocals conf claims app req jsonDbS actualPgVersion = do
  lift $ SQL.statement mempty $ SQL.dynamicallyParameterized
    ("select " <> intercalateSnippet ", " (searchPathSql : roleSql ++ claimsSql ++ [methodSql, pathSql] ++ headersSql ++ cookiesSql ++ appSettingsSql ++ specSql))
    HD.noResult (configDbPreparedStatements conf)
  lift $ traverse_ SQL.sql preReqSql
  app req
  where
    methodSql = setConfigLocal mempty ("request.method", iMethod req)
    pathSql = setConfigLocal mempty ("request.path", iPath req)
    headersSql = if usesLegacyGucs
                   then setConfigLocal "request.header." <$> iHeaders req
                   else setConfigLocalJson "request.headers" (iHeaders req)
    cookiesSql = if usesLegacyGucs
                   then setConfigLocal "request.cookie." <$> iCookies req
                   else setConfigLocalJson "request.cookies" (iCookies req)
    claimsWithRole =
      let anon = JSON.String . toS $ configDbAnonRole conf in -- role claim defaults to anon if not specified in jwt
      M.union claims (M.singleton "role" anon)
    claimsSql = if usesLegacyGucs
                  then setConfigLocal "request.jwt.claim." <$> [(toUtf8 c, toUtf8 $ unquoted v) | (c,v) <- M.toList claimsWithRole]
                  else [setConfigLocal mempty ("request.jwt.claims", LBS.toStrict $ JSON.encode claimsWithRole)]
    roleSql = maybeToList $ (\x -> setConfigLocal mempty ("role", toUtf8 $ unquoted x)) <$> M.lookup "role" claimsWithRole
    appSettingsSql = setConfigLocal mempty <$> (join bimap toUtf8 <$> configAppSettings conf)
    searchPathSql =
      let schemas = T.intercalate ", " (iSchema req : configDbExtraSearchPath conf) in
      setConfigLocal mempty ("search_path", toUtf8 schemas)
    preReqSql = (\f -> "select " <> fromQi f <> "();") <$> configDbPreRequest conf
    specSql = case iTarget req of
      TargetProc{tpIsRootSpec=True} -> [setConfigLocal mempty ("request.spec", jsonDbS)]
      _                             -> mempty
    usesLegacyGucs = configDbUseLegacyGucs conf && actualPgVersion < pgVersion140

    unquoted :: JSON.Value -> Text
    unquoted (JSON.String t) = t
    unquoted (JSON.Number n) =
      toS $ formatScientific Fixed (if isInteger n then Just 0 else Nothing) n
    unquoted (JSON.Bool b) = show b
    unquoted v = T.decodeUtf8 . LBS.toStrict $ JSON.encode v

-- | Set a transaction to eventually roll back if requested and set respective
-- headers on the response.
optionalRollback
  :: AppConfig
  -> ApiRequest
  -> ExceptT Error SQL.Transaction Wai.Response
  -> ExceptT Error SQL.Transaction Wai.Response
optionalRollback AppConfig{..} ApiRequest{..} transaction = do
  resp <- catchError transaction $ return . errorResponseFor
  when (shouldRollback || (configDbTxRollbackAll && not shouldCommit)) $ lift do
    SQL.sql "SET CONSTRAINTS ALL IMMEDIATE"
    SQL.condemn
  return $ Wai.mapResponseHeaders preferenceApplied resp
  where
    shouldCommit =
      configDbTxAllowOverride && iPreferTransaction == Just Commit
    shouldRollback =
      configDbTxAllowOverride && iPreferTransaction == Just Rollback
    preferenceApplied
      | shouldCommit =
          addHeadersIfNotIncluded
            [toAppliedHeader Commit]
      | shouldRollback =
          addHeadersIfNotIncluded
            [toAppliedHeader Rollback]
      | otherwise =
          identity

-- | Do a pg set_config(setting, value, true) call. This is equivalent to a SET LOCAL.
setConfigLocal :: ByteString -> (ByteString, ByteString) -> SQL.Snippet
setConfigLocal prefix (k, v) =
  "set_config(" <> unknownEncoder (prefix <> k) <> ", " <> unknownEncoder v <> ", true)"

-- | Starting from PostgreSQL v14, some characters are not allowed for config names (mostly affecting headers with "-").
-- | A JSON format string is used to avoid this problem. See https://github.com/PostgREST/postgrest/issues/1857
setConfigLocalJson :: ByteString -> [(ByteString, ByteString)] -> [SQL.Snippet]
setConfigLocalJson prefix keyVals = [setConfigLocal mempty (prefix, gucJsonVal keyVals)]
  where
    gucJsonVal :: [(ByteString, ByteString)] -> ByteString
    gucJsonVal = LBS.toStrict . JSON.encode . M.fromList . arrayByteStringToText
    arrayByteStringToText :: [(ByteString, ByteString)] -> [(Text,Text)]
    arrayByteStringToText keyVal = (T.decodeUtf8 *** T.decodeUtf8) <$> keyVal