Fix duplicate worker console output

src/main/kotlin/io/bazel/worker/IO.kt

@@ -23,13 +23,28 @@ import java.io.ByteArrayOutputStream
 import java.io.Closeable
 import java.io.InputStream
 import java.io.PrintStream
+import java.nio.charset.StandardCharsets
 
 class IO(
   val input: InputStream,
   val output: PrintStream,
-  val captured: ByteArrayOutputStream,
+  private val captured: ByteArrayOutputStream,
   private val restore: () -> Unit = {}
 ) : Closeable {
+
+  /**
+   * Reads the captured std out and err as a UTF-8 string and then resets the
+   * captured ByteArrayOutputStream.
+   *
+   * Resetting the ByteArrayOutputStream prevents the worker from returning
+   * the same console output multiple times
+   **/
+  fun readCapturedAsUtf8String(): String {
+    val out = captured.toByteArray().toString(StandardCharsets.UTF_8)
+    captured.reset()
+    return out
+  }
+
   companion object {
     fun capture(): IO {
       val stdErr = System.err

src/main/kotlin/io/bazel/worker/PersistentWorker.kt

@@ -102,7 +102,7 @@ class PersistentWorker(
       val response = WorkerProtocol.WorkResponse.newBuilder().apply {
         output = listOf(
           result.log.out.toString(),
-          io.captured.toByteArray().toString(UTF_8)
+          io.readCapturedAsUtf8String()
         ).filter { it.isNotBlank() }.joinToString("\n")
         exitCode = result.status.exit
         requestId = request.requestId

src/test/kotlin/io/bazel/worker/IOTest.kt

@@ -58,7 +58,19 @@ class IOTest {
     assertThat(captured.written()).isEmpty()
     IO.capture().use { io ->
       println("foo foo is on the loose")
-      assertThat(io.captured.written()).isEqualTo("foo foo is on the loose\n")
+      assertThat(io.readCapturedAsUtf8String()).isEqualTo("foo foo is on the loose\n")
+    }
+    assertThat(captured.written()).isEmpty()
+  }
+
+  @Test
+  fun captureDoesNotRepeatOutput() {
+    assertThat(captured.written()).isEmpty()
+    IO.capture().use { io ->
+      println("foo foo is on the loose")
+      assertThat(io.readCapturedAsUtf8String()).isEqualTo("foo foo is on the loose\n")
+      println("bar bar is on the loose")
+      assertThat(io.readCapturedAsUtf8String()).isEqualTo("bar bar is on the loose\n")
     }
     assertThat(captured.written()).isEmpty()
   }