Allow "encapsulated output" from the shell command

Since the ConsoleReader now controls the display of the prompt, there is no
longer any way for an external program interacting with the nomulus shell to
recognize when the last command issued has been completed.

To remedy this, we introduce an "--encapsulate_output" flag, which causes
standard output and standard error to be wrapped in a class that precedes
all normal lines of output with a prefix ("out: " or "err: ", accordingly)
and allows the command processor to insert a "SUCCESS" or "FAILURE"
line (with no special prefix) after completing the processing of a
command.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=196702338

javatests/google/registry/tools/ShellCommandTest.java

@@ -16,6 +16,7 @@ package google.registry.tools;
 
 import static com.google.common.truth.Truth.assertThat;
 import static google.registry.testing.JUnitBackports.assertThrows;
+import static java.nio.charset.StandardCharsets.UTF_8;
 import static org.mockito.Mockito.mock;
 import static org.mockito.Mockito.when;
 
@@ -28,12 +29,17 @@ import com.google.common.collect.ImmutableMap;
 import google.registry.testing.FakeClock;
 import google.registry.tools.ShellCommand.JCommanderCompletor;
 import java.io.BufferedReader;
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
 import java.io.IOException;
+import java.io.PrintStream;
 import java.util.ArrayDeque;
 import java.util.ArrayList;
 import java.util.List;
 import org.joda.time.DateTime;
 import org.joda.time.Duration;
+import org.junit.After;
+import org.junit.Before;
 import org.junit.Test;
 import org.junit.runner.RunWith;
 import org.junit.runners.JUnit4;
@@ -44,8 +50,23 @@ public class ShellCommandTest {
   CommandRunner cli = mock(CommandRunner.class);
   FakeClock clock = new FakeClock(DateTime.parse("2000-01-01TZ"));
 
+  PrintStream orgStdout;
+  PrintStream orgStderr;
+
   public ShellCommandTest() {}
 
+  @Before
+  public void setUp() {
+    orgStdout = System.out;
+    orgStderr = System.err;
+  }
+
+  @After
+  public void tearDown() {
+    System.setOut(orgStdout);
+    System.setErr(orgStderr);
+  }
+
   @Test
   public void testParsing() {
     assertThat(ShellCommand.parseCommand("foo bar 123 baz+ // comment \"string data\""))
@@ -226,6 +247,55 @@ public class ShellCommandTest {
         "testCommand --xorg ", 0, "", "Flag documentation: test organization\n  (PRIVATE, PUBLIC)");
   }
 
+  @Test
+  public void testEncapsulatedOutputStream_basicFuncionality() throws Exception {
+    ByteArrayOutputStream backing = new ByteArrayOutputStream();
+    PrintStream out = new PrintStream(new ShellCommand.EncapsulatingOutputStream(backing, "out: "));
+    out.println("first line");
+    out.print("second line\ntrailing data");
+    out.flush();
+    assertThat(backing.toString())
+        .isEqualTo("out: first line\nout: second line\nout: trailing data\n");
+  }
+
+  @Test
+  public void testEncapsulatedOutputStream_emptyStream() throws Exception {
+    ByteArrayOutputStream backing = new ByteArrayOutputStream();
+    PrintStream out = new PrintStream(new ShellCommand.EncapsulatingOutputStream(backing, "out: "));
+    out.flush();
+    assertThat(backing.toString()).isEqualTo("");
+  }
+
+  @Test
+  public void testEncapsulatedOutput_command() throws Exception {
+    RegistryToolEnvironment.ALPHA.setup();
+
+    // capture output (have to do this before the shell command is created)
+    ByteArrayOutputStream stdout = new ByteArrayOutputStream();
+    ByteArrayOutputStream stderr = new ByteArrayOutputStream();
+    System.setOut(new PrintStream(stdout));
+    System.setErr(new PrintStream(stderr));
+    System.setIn(new ByteArrayInputStream("command1\n".getBytes(UTF_8)));
+
+    ShellCommand shellCommand =
+        new ShellCommand(
+            args -> {
+              System.out.println("first line");
+              System.err.println("second line");
+              System.out.print("fragmented ");
+              System.err.println("surprise!");
+              System.out.println("line");
+            });
+    shellCommand.encapsulateOutput = true;
+
+    shellCommand.run();
+    assertThat(stderr.toString()).isEmpty();
+    assertThat(stdout.toString())
+        .isEqualTo(
+            "out: first line\nerr: second line\nerr: surprise!\nout: fragmented line\n"
+                + "SUCCESS\n");
+  }
+
   @Parameters(commandDescription = "Test command")
   static class TestCommand implements Command {
     enum OrgType {