Add access to the PostgREST version through SQL

CHANGELOG.md

@@ -20,6 +20,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
    + Completely optional, define the functions in the database and they will be used automatically everywhere
    + Data representations preserve the ability to write to the original column and require no extra storage or complex triggers (compared to using `GENERATED ALWAYS` columns)
    + Note: data representations require Postgres 10 (Postgres 11 if using `IN` predicates); data representations are not implemented for RPC
+ - #2647, Allow to verify the PostgREST version in SQL: `select distinct application_name from pg_stat_activity`. - @laurenceisla
 
 ### Fixed
 

src/PostgREST/AppState.hs

@@ -34,6 +34,7 @@ import qualified Hasql.Pool                 as SQL
 import qualified Hasql.Session              as SQL
 import qualified Hasql.Transaction.Sessions as SQL
 import qualified PostgREST.Error            as Error
+import           PostgREST.Version          (prettyVersion)
 
 import Control.AutoUpdate (defaultUpdateSettings, mkAutoUpdate,
                            updateAction)
@@ -47,6 +48,7 @@ import Data.Time          (ZonedTime, defaultTimeLocale, formatTime,
 import Data.Time.Clock    (UTCTime, getCurrentTime)
 
 import PostgREST.Config                  (AppConfig (..),
+                                          addFallbackAppName,
                                           readAppConfig)
 import PostgREST.Config.Database         (queryDbSettings,
                                           queryPgVersion,
@@ -136,7 +138,7 @@ initPool AppConfig{..} =
     (fromIntegral configDbPoolAcquisitionTimeout)
     (fromIntegral configDbPoolMaxLifetime)
     (fromIntegral configDbPoolMaxIdletime)
-    (toUtf8 configDbUri)
+    (toUtf8 $ addFallbackAppName prettyVersion configDbUri)
 
 -- | Run an action with a database connection.
 usePool :: AppState -> SQL.Session a -> IO (Either SQL.UsageError a)
@@ -418,7 +420,7 @@ listener appState = do
 
   -- forkFinally allows to detect if the thread dies
   void . flip forkFinally (handleFinally dbChannel) $ do
-    dbOrError <- acquire $ toUtf8 configDbUri
+    dbOrError <- acquire $ toUtf8 (addFallbackAppName prettyVersion configDbUri)
     case dbOrError of
       Right db -> do
         logWithZTime appState $ "Listening for notifications on the " <> dbChannel <> " channel"

src/PostgREST/Config.hs

@@ -24,6 +24,7 @@
   , readPGRSTEnvironment
   , toURI
   , parseSecret
+  , addFallbackAppName
   ) where
 
 import qualified Crypto.JOSE.Types      as JOSE
@@ -47,6 +48,8 @@
 import Data.List.NonEmpty      (fromList, toList)
 import Data.Maybe              (fromJust)
 import Data.Scientific         (floatingOrInteger)
+import Network.URI             (escapeURIString, isUnescapedInURI,
+                                parseURI, uriQuery)
 import Numeric                 (readOct, showOct)
 import System.Environment      (getEnvironment)
 import System.Posix.Types      (FileMode)
@@ -460,3 +463,34 @@
 readPGRSTEnvironment :: IO Environment
 readPGRSTEnvironment =
   M.map T.pack . M.fromList . filter (isPrefixOf "PGRST_" . fst) <$> getEnvironment
+
+-- | Adds a `fallback_application_name` value to the connection string. This allows querying the PostgREST version on pg_stat_activity.
+--
+-- >>> let ver = "11.1.0 (5a04ec7)"::ByteString
+--
+-- >>> addFallbackAppName ver "postgres://user:pass@host:5432/postgres"
+-- "postgres://user:pass@host:5432/postgres?fallback_application_name=PostgREST%2011.1.0%20(5a04ec7)"
+--
+-- >>> addFallbackAppName ver "postgres://user:pass@host:5432/postgres?"
+-- "postgres://user:pass@host:5432/postgres?fallback_application_name=PostgREST%2011.1.0%20(5a04ec7)"
+--
+-- >>> addFallbackAppName ver "postgres:///postgres?host=server&port=5432"
+-- "postgres:///postgres?host=server&port=5432&fallback_application_name=PostgREST%2011.1.0%20(5a04ec7)"
+--
+-- >>> addFallbackAppName ver "host=localhost port=5432 dbname=postgres"
+-- "host=localhost port=5432 dbname=postgres fallback_application_name='PostgREST 11.1.0 (5a04ec7)'"
+--
+-- >>> addFallbackAppName ver "postgresql://"
+-- "postgresql://?fallback_application_name=PostgREST%2011.1.0%20(5a04ec7)"
+addFallbackAppName :: ByteString -> Text -> Text
+addFallbackAppName version dbUri = dbUri <>
+  case uriQuery <$> parseURI (toS dbUri) of
+    Nothing  -> " " <> keyValFmt -- Assume key/value connection string if the uri is not valid
+    Just ""  -> "?" <> uriFmt
+    Just "?" -> uriFmt
+    _        -> "&" <> uriFmt
+  where
+    uriFmt = toS $ escapeURIString isUnescapedInURI $ toS (pKeyWord <> pgrstVer)
+    keyValFmt = pKeyWord <> "'" <> T.replace "'" "\\'" pgrstVer <> "'"
+    pKeyWord = "fallback_application_name="
+    pgrstVer = "PostgREST " <> T.decodeUtf8 version

test/doc/Main.hs

@@ -17,4 +17,5 @@ main =
     , "src/PostgREST/ApiRequest/QueryParams.hs"
     , "src/PostgREST/Error.hs"
     , "src/PostgREST/MediaType.hs"
+    , "src/PostgREST/Config.hs"
     ]

test/io/fixtures.sql

@@ -158,3 +158,12 @@ create or replace function migrate_function() returns void as $_$
   $$ language sql;
   notify pgrst, 'reload schema';
 $_$ language sql security definer;
+
+create or replace function get_pgrst_version() returns text
+  language sql
+as $$
+select application_name
+from pg_stat_activity
+where application_name ilike 'postgrest%'
+limit 1;
+$$

test/io/test_io.py

@@ -998,3 +998,32 @@ def test_openapi_in_big_schema(defaultenv):
     with run(env=env) as postgrest:
         response = postgrest.session.get("/")
         assert response.status_code == 200
+
+
+def test_get_pgrst_version_with_uri_connection_string(dburi, defaultenv):
+    "The fallback_application_name should be added to the db-uri if it has a URI format"
+    defaultenv_without_libpq = {
+        key: value
+        for key, value in defaultenv.items()
+        if key not in ["PGDATABASE", "PGHOST", "PGUSER"]
+    }
+    env = {**defaultenv_without_libpq, "PGRST_DB_URI": dburi.decode()}
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.post("/rpc/get_pgrst_version")
+        assert response.text.startswith('"PostgREST ')
+
+
+def test_get_pgrst_version_with_keyval_connection_string(dburi, defaultenv):
+    "The fallback_application_name should be added to the db-uri if it has a keyword/value format"
+    uri = f'dbname={defaultenv["PGDATABASE"]} host={defaultenv["PGHOST"]} user={defaultenv["PGUSER"]}'
+    defaultenv_without_libpq = {
+        key: value
+        for key, value in defaultenv.items()
+        if key not in ["PGDATABASE", "PGHOST", "PGUSER"]
+    }
+    env = {**defaultenv_without_libpq, "PGRST_DB_URI": uri}
+
+    with run(env=env) as postgrest:
+        response = postgrest.session.post("/rpc/get_pgrst_version")
+        assert response.text.startswith('"PostgREST ')