Add an --output-file option to DAML Script (#5590)

This PR adds an --output-file option to DAML Script that writes the
result of a DAML Script to a file and complements the --input-file option.

changelog_begin

- [DAML Script] ``daml script`` now has a `--output-file`` option that
  can be used to specify a file the result of the script should be
  written to. Similar to ``--input-file`` the result will be output in
  the DAML-LF JSON encoding.

changelog_end

daml-assistant/integration-tests/src/DA/Daml/Assistant/IntegrationTests.hs

@@ -192,6 +192,41 @@ packagingTests = testGroup "packaging"
           , "setup' = setup"
           ]
         withCurrentDirectory (tmpDir </> "proj") $ callCommandSilent "daml build"
+     , testCase "DAML Script --input-file and --output-file" $ withTempDir $ \projDir -> do
+           writeFileUTF8 (projDir </> "daml.yaml") $ unlines
+               [ "sdk-version: " <> sdkVersion
+               , "name: proj"
+               , "version: 0.0.1"
+               , "source: ."
+               , "dependencies: [daml-prim, daml-stdlib, daml-script]"
+               ]
+           writeFileUTF8 (projDir </> "Main.daml") $ unlines
+               [ "module Main where"
+               , "import Daml.Script"
+               , "test : Int -> Script (Int, Int)"
+               , "test x = pure (x, x + 1)"
+               ]
+           withCurrentDirectory projDir $ do
+               callCommandSilent "daml build -o script.dar"
+               writeFileUTF8 (projDir </> "input.json") "0"
+               p :: Int <- fromIntegral <$> getFreePort
+               withDevNull $ \devNull ->
+                   withCreateProcess (shell $ unwords ["daml sandbox --port " <> show p]) { std_out = UseHandle devNull } $ \_ _ _ _ -> do
+                       waitForConnectionOnPort (threadDelay 100000) p
+                       callCommand $ unwords
+                           [ "daml script"
+                           ,"--wall-clock-time"
+                           , "--dar script.dar --script-name Main:test"
+                           , "--input-file input.json --output-file output.json"
+                           , "--ledger-host localhost --ledger-port " <> show p
+                           ]
+           contents <- readFileUTF8 (projDir </> "output.json")
+           lines contents @?=
+               [ "{"
+               , "  \"_1\": 0,"
+               , "  \"_2\": 1"
+               , "}"
+               ]
      , testCase "Run init-script" $ withTempDir $ \tmpDir -> do
         let projDir = tmpDir </> "init-script-example"
         createDirectoryIfMissing True (projDir </> "daml")

daml-script/runner/src/main/scala/com/digitalasset/daml/lf/engine/script/RunnerConfig.scala

@@ -20,6 +20,7 @@ case class RunnerConfig(
     timeProviderType: TimeProviderType,
     commandTtl: Duration,
     inputFile: Option[File],
+    outputFile: Option[File],
     accessTokenFile: Option[Path],
     tlsConfig: Option[TlsConfiguration],
     jsonApi: Boolean,
@@ -83,6 +84,12 @@ object RunnerConfig {
       }
       .text("Path to a file containing the input value for the script in JSON format.")
 
+    opt[File]("output-file")
+      .action { (t, c) =>
+        c.copy(outputFile = Some(t))
+      }
+      .text("Path to a file where the result of the script will be written to in JSON format.")
+
     opt[String]("access-token-file")
       .action { (f, c) =>
         c.copy(accessTokenFile = Some(Paths.get(f)))
@@ -159,6 +166,7 @@ object RunnerConfig {
         timeProviderType = null,
         commandTtl = Duration.ofSeconds(30L),
         inputFile = None,
+        outputFile = None,
         accessTokenFile = None,
         tlsConfig = None,
         jsonApi = false,

daml-script/runner/src/main/scala/com/digitalasset/daml/lf/engine/script/RunnerMain.scala

@@ -9,6 +9,7 @@ import akka.stream._
 import java.nio.file.Files
 import java.time.Instant
 import java.util.stream.Collectors
+import scala.collection.JavaConverters._
 import scala.concurrent.{Await, ExecutionContext, Future}
 import scala.concurrent.duration.Duration
 import scala.io.Source
@@ -116,7 +117,14 @@ object RunnerMain {
             )
             Runner.connect(participantParams, clientConfig)
           }
-          _ <- Runner.run(dar, scriptId, inputValue, clients, applicationId, timeProvider)
+          result <- Runner.run(dar, scriptId, inputValue, clients, applicationId, timeProvider)
+          _ <- Future {
+            config.outputFile.foreach { outputFile =>
+              val jsVal = LfValueCodec.apiValueToJsValue(
+                result.toValue.assertNoRelCid(rcoid => s"Unexpected relative contract id $rcoid"))
+              Files.write(outputFile.toPath, Seq(jsVal.prettyPrint).asJava)
+            }
+          }
         } yield ()
 
         flow.onComplete(_ =>

docs/source/daml-script/index.rst

@@ -191,6 +191,11 @@ We can then initialize our ledger passing in the json file via ``--input-file``.
 
 If you open Navigator, you can now see the contracts that have been created.
 
+While we will not use it here, there is also an ``--output-file``
+option that you can use to write the result of a script to a file
+using the DAML-LF JSON encoding. This is particularly useful if you need to consume
+the result from another program.
+
 .. _script-ledger-initialization:
 
 Using DAML Script for Ledger Initialization