diff --git a/microdroid/payload/metadata.cc b/microdroid/payload/metadata.cc
new file mode 100644
index 0000000..07083e9
--- /dev/null
+++ b/microdroid/payload/metadata.cc
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2021 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include "microdroid/metadata.h"
+
+#include <android-base/endian.h>
+#include <android-base/file.h>
+
+using android::base::ErrnoError;
+using android::base::Error;
+using android::base::Result;
+
+namespace android {
+namespace microdroid {
+
+Result<Metadata> ReadMetadata(const std::string& path) {
+    std::string content;
+    if (!base::ReadFileToString(path, &content)) {
+        return ErrnoError() << "Failed to read " << path;
+    }
+
+    // read length prefix (4-byte, big-endian)
+    uint32_t size;
+    const size_t length_prefix_bytes = sizeof(size);
+    if (content.size() < length_prefix_bytes) {
+        return Error() << "Invalid metadata: size == " << content.size();
+    }
+    size = be32toh(*reinterpret_cast<uint32_t*>(content.data()));
+    if (content.size() < length_prefix_bytes + size) {
+        return Error() << "Invalid metadata: size(" << size << ") mimatches to the content size("
+                       << content.size() - length_prefix_bytes << ")";
+    }
+    content = content.substr(length_prefix_bytes, size);
+
+    // parse content
+    Metadata metadata;
+    if (!metadata.ParseFromString(content)) {
+        return Error() << "Can't parse Metadata from " << path;
+    }
+    return metadata;
+}
+
+Result<void> WriteMetadata(const Metadata& metadata, std::ostream& out) {
+    // prepare content
+    std::string content;
+    if (!metadata.SerializeToString(&content)) {
+        return Error() << "Failed to write protobuf.";
+    }
+
+    // write length prefix (4-byte, big-endian)
+    uint32_t size = htobe32(static_cast<uint32_t>(content.size()));
+    out.write(reinterpret_cast<const char*>(&size), sizeof(size));
+
+    // write content
+    out << content;
+
+    return {};
+}
+
+} // namespace microdroid
+} // namespace android
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