diff --git a/services/mediametrics/ValidateId.cpp b/services/mediametrics/ValidateId.cpp
new file mode 100644
index 0000000..0cc8593
--- /dev/null
+++ b/services/mediametrics/ValidateId.cpp
@@ -0,0 +1,65 @@
+/*
+ * 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.
+ */
+
+//#define LOG_NDEBUG 0
+#define LOG_TAG "MediaMetricsService"  // not ValidateId
+#include <utils/Log.h>
+
+#include "ValidateId.h"
+
+namespace android::mediametrics {
+
+std::string ValidateId::dump() const
+{
+    std::stringstream ss;
+    ss << "Entries:" << mIdSet.size() << "  InvalidIds:" << mInvalidIds << "\n";
+    ss << mIdSet.dump(10);
+    return ss.str();
+}
+
+void ValidateId::registerId(const std::string& id)
+{
+    if (id.empty()) return;
+    if (!mediametrics::stringutils::isLogSessionId(id.c_str())) {
+        ALOGW("%s: rejecting malformed id %s", __func__, id.c_str());
+        return;
+    }
+    ALOGV("%s: registering %s", __func__, id.c_str());
+    mIdSet.add(id);
+}
+
+const std::string& ValidateId::validateId(const std::string& id)
+{
+    static const std::string empty{};
+    if (id.empty()) return empty;
+
+    // reject because the id is malformed
+    if (!mediametrics::stringutils::isLogSessionId(id.c_str())) {
+        ALOGW("%s: rejecting malformed id %s", __func__, id.c_str());
+        ++mInvalidIds;
+        return empty;
+    }
+
+    // reject because the id is unregistered
+    if (!mIdSet.check(id)) {
+        ALOGW("%s: rejecting unregistered id %s", __func__, id.c_str());
+        ++mInvalidIds;
+        return empty;
+    }
+    return id;
+}
+
+} // namespace android::mediametrics