Replace mk_payload with a Java utility

mk_payload was used to create a microdroid's payload metadata blob. It
was too verbose and inefficient to do it via external host tool
(mk_payload).

Bug: 269409253
Test: atest MicrodroidHostTestCases
Change-Id: Ic898e1958be528df2996fe2edb77b4c0b23f04fb
diff --git a/microdroid/payload/Android.bp b/microdroid/payload/Android.bp
index f77c037..da4e09d 100644
--- a/microdroid/payload/Android.bp
+++ b/microdroid/payload/Android.bp
@@ -36,6 +36,17 @@
     ],
 }
 
+java_library_host {
+    name: "microdroid_payload_metadata",
+    srcs: [
+        "src/**/*.java",
+        "metadata.proto",
+    ],
+    proto: {
+        type: "lite",
+    },
+}
+
 cc_binary_host {
     name: "mk_payload",
     srcs: [
diff --git a/microdroid/payload/metadata.proto b/microdroid/payload/metadata.proto
index c74c23b..6b999af 100644
--- a/microdroid/payload/metadata.proto
+++ b/microdroid/payload/metadata.proto
@@ -18,6 +18,9 @@
 
 package android.microdroid;
 
+option java_package = "com.android.virt";
+option java_outer_classname = "PayloadMetadataProtos";
+
 // Metadata is the body of the "metadata" partition
 message Metadata {
   uint32 version = 1;
diff --git a/microdroid/payload/src/com/android/virt/PayloadMetadata.java b/microdroid/payload/src/com/android/virt/PayloadMetadata.java
new file mode 100644
index 0000000..c2f0a7f
--- /dev/null
+++ b/microdroid/payload/src/com/android/virt/PayloadMetadata.java
@@ -0,0 +1,49 @@
+package com.android.virt;
+
+import java.io.DataOutputStream;
+import java.io.File;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+/** Provides utility to create/read/write PayloadMetadata */
+public class PayloadMetadata {
+    public static void write(PayloadMetadataProtos.Metadata metadata, File file)
+            throws IOException {
+        byte[] message = metadata.toByteArray();
+
+        try (DataOutputStream os = new DataOutputStream(new FileOutputStream(file))) {
+            // write length prefix (4-byte, big-endian)
+            os.writeInt(message.length);
+            // write the message
+            os.write(message);
+        }
+    }
+
+    public static PayloadMetadataProtos.Metadata metadata(
+            String configPath,
+            PayloadMetadataProtos.ApkPayload apk,
+            Iterable<? extends PayloadMetadataProtos.ApexPayload> apexes) {
+        return PayloadMetadataProtos.Metadata.newBuilder()
+                .setVersion(1)
+                .setConfigPath(configPath)
+                .setApk(apk)
+                .addAllApexes(apexes)
+                .build();
+    }
+
+    public static PayloadMetadataProtos.ApkPayload apk(String name) {
+        return PayloadMetadataProtos.ApkPayload.newBuilder()
+                .setName(name)
+                .setPayloadPartitionName("microdroid-apk")
+                .setIdsigPartitionName("microdroid-apk-idsig")
+                .build();
+    }
+
+    public static PayloadMetadataProtos.ApexPayload apex(String name) {
+        return PayloadMetadataProtos.ApexPayload.newBuilder()
+                .setName(name)
+                .setIsFactory(true)
+                .setPartitionName(name)
+                .build();
+    }
+}
diff --git a/tests/hostside/Android.bp b/tests/hostside/Android.bp
index 046a9d6..f1e5054 100644
--- a/tests/hostside/Android.bp
+++ b/tests/hostside/Android.bp
@@ -37,6 +37,7 @@
         "MicrodroidHostTestHelper",
         "compatibility-host-util",
         "cts-statsd-atom-host-test-utils",
+        "microdroid_payload_metadata",
     ],
     per_testcase_directory: true,
     data: [
@@ -57,7 +58,6 @@
         "initrd_bootconfig",
         "lpmake",
         "lpunpack",
-        "mk_payload",
         "sign_virt_apex",
         "simg2img",
     ],
diff --git a/tests/hostside/java/com/android/microdroid/test/MicrodroidHostTests.java b/tests/hostside/java/com/android/microdroid/test/MicrodroidHostTests.java
index 726fb4a..0be6a62 100644
--- a/tests/hostside/java/com/android/microdroid/test/MicrodroidHostTests.java
+++ b/tests/hostside/java/com/android/microdroid/test/MicrodroidHostTests.java
@@ -50,6 +50,7 @@
 import com.android.tradefed.util.FileUtil;
 import com.android.tradefed.util.RunUtil;
 import com.android.tradefed.util.xml.AbstractXmlParser;
+import com.android.virt.PayloadMetadata;
 
 import org.json.JSONArray;
 import org.json.JSONObject;
@@ -133,42 +134,14 @@
 
     private void createPayloadMetadata(List<ActiveApexInfo> apexes, File payloadMetadata)
             throws Exception {
-        // mk_payload's config
-        File configFile = new File(payloadMetadata.getParentFile(), "payload_config.json");
-        JSONObject config = new JSONObject();
-        config.put(
-                "apk",
-                new JSONObject(Map.of("name", "microdroid-apk", "path", "", "idsig_path", "")));
-        config.put("payload_config_path", "/mnt/apk/assets/vm_config.json");
-        config.put(
-                "apexes",
-                new JSONArray(
+        PayloadMetadata.write(
+                PayloadMetadata.metadata(
+                        "/mnt/apk/assets/vm_config.json",
+                        PayloadMetadata.apk("microdroid-apk"),
                         apexes.stream()
-                                .map(apex -> new JSONObject(Map.of("name", apex.name, "path", "")))
-                                .collect(toList())));
-        FileUtil.writeToFile(config.toString(), configFile);
-
-        RunUtil runUtil = new RunUtil();
-        String command =
-                String.join(
-                        " ",
-                        findTestFile("mk_payload").getAbsolutePath(),
-                        "--metadata-only",
-                        configFile.getAbsolutePath(),
-                        payloadMetadata.getAbsolutePath());
-        // mk_payload should run fast enough
-        CommandResult result = runUtil.runTimedCmd(5000, "/bin/bash", "-c", command);
-        String out = result.getStdout();
-        String err = result.getStderr();
-        assertWithMessage(
-                        "creating payload metadata failed:\n\tout: "
-                                + out
-                                + "\n\terr: "
-                                + err
-                                + "\n")
-                .about(command_results())
-                .that(result)
-                .isSuccess();
+                                .map(apex -> PayloadMetadata.apex(apex.name))
+                                .collect(toList())),
+                payloadMetadata);
     }
 
     private void resignVirtApex(