Fix port selection in the db migration tests

Each test running in turn was using the same port.

However due to the SO_LINGER TCP socket option, the port remains in
use for a short time after the wallet server process exits.

lib/jormungandr/test/migration/migration-test.hs

@@ -65,7 +65,7 @@ import Data.Aeson
 import Data.Aeson.Lens
     ( key, values, _Integral, _String )
 import Data.Maybe
-    ( isNothing )
+    ( fromMaybe, isNothing )
 import Data.Text
     ( Text )
 import Network.Wreq
@@ -74,6 +74,8 @@ import System.Environment
     ( getArgs )
 import System.Exit
     ( ExitCode (..), exitFailure, exitWith )
+import Text.Read
+    ( readMaybe )
 
 import qualified Data.Text as T
 
@@ -83,19 +85,19 @@ main = do
 
     cfg <- defaultConfigStdout
     withTrace cfg "migration-test" $ \tr ->
-        testMain @('Testnet 0) tr 9090 testAction launchArgs >>= exitWith
+        testMain @('Testnet 0) tr testAction launchArgs >>= exitWith
 
 -- | Something to do while the server is running.
 type TestAction (t :: NetworkDiscriminant) = Trace IO Text -> ApiBase -> IO ExitCode
 
 testMain
     :: forall t. (DecodeAddress t, EncodeAddress t)
     => Trace IO Text
-    -> Int
     -> TestAction t
     -> [String]
     -> IO ExitCode
-testMain tr serverPort testAction launchArgs = do
+testMain tr testAction launchArgs = do
+    let serverPort = getServerPort launchArgs
     let apiBase = mkApiBase serverPort
     let cmd = Command "cardano-wallet-jormungandr" launchArgs (pure ()) Inherit Inherit
     res <- withBackendProcess (trMessageText tr) cmd $ do
@@ -113,6 +115,15 @@ testMain tr serverPort testAction launchArgs = do
             logError tr ("Process exited with status " <> T.pack (show st))
             pure (ExitFailure 14)
 
+-- | Scan through cardano-wallet server CLI arguments to find a port.
+-- Returns the default 8090 if none found.
+getServerPort :: [String] -> Int
+getServerPort = fromMaybe 8090 . portArg
+  where
+    portArg ("--port":port:_) = readMaybe port
+    portArg (_:args) = portArg args
+    portArg [] = Nothing
+
 -- | @run@ action
 doRun
     :: forall t. (DecodeAddress t, EncodeAddress t)

nix/launch-migration-test.sh

@@ -30,7 +30,14 @@ if [ -z "${configFile:-}" ]; then
   exit 1
 fi
 
+# Find an unused TCP port to run the test on.
+# Source: https://unix.stackexchange.com/a/132524
+find_unused_port() {
+  python -c 'import socket; s=socket.socket(); s.bind(("", 0)); print(s.getsockname()[1]); s.close()'
+}
+
+# Sanity-check versions
 cardano-wallet-jormungandr version
 jormungandr --version
 
-exec migration-test $1 launch --port 9090 --state-dir $stateDir --genesis-block $genesisDataDir/block0.bin -- --secret $genesisDataDir/secret.yaml --config $configFile
+exec migration-test $1 launch --port "$(find_unused_port)" --state-dir $stateDir --genesis-block $genesisDataDir/block0.bin -- --secret $genesisDataDir/secret.yaml --config $configFile

nix/migration-tests.nix

@@ -112,6 +112,7 @@ let
           migrationTest
           pkgs.bash
           pkgs.coreutils
+          pkgs.python3
         ]}
         export genesisDataDir=${latestRelease.src}/lib/jormungandr/test/data/jormungandr
         export configFile=${targetRelease.src}/lib/jormungandr/test/data/jormungandr/config.yaml