diff --git a/services/mediametrics/ValidateId.h b/services/mediametrics/ValidateId.h
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+/*
+ * 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.
+ */
+
+#pragma once
+
+#include "LruSet.h"
+#include "StringUtils.h"
+#include "Wrap.h"
+
+namespace android::mediametrics {
+
+/*
+ * ValidateId is used to check whether the log session id is properly formed
+ * and has been registered (i.e. from the Java MediaMetricsManagerService).
+ *
+ * The default memory window to track registered ids is set to SINGLETON_LRU_SET_SIZE.
+ *
+ * This class is not thread-safe, but the singleton returned by get() uses LockWrap<>
+ * to ensure thread-safety.
+ */
+class ValidateId {
+    mediametrics::LruSet<std::string> mIdSet;
+    size_t mInvalidIds = 0;  // count invalid ids encountered.
+public:
+    /** Creates a ValidateId object with size memory window. */
+    explicit ValidateId(size_t size) : mIdSet{size} {}
+
+    /** Returns a string dump of recent contents and stats. */
+    std::string dump() const;
+
+    /**
+     * Registers the id string.
+     *
+     * If id string is malformed (not 16 Base64Url chars), it is ignored.
+     * Once registered, calling validateId() will return id (instead of the empty string).
+     * ValidateId may "forget" the id after not encountering it within the past N ids,
+     * where N is the size set in the constructor.
+     *
+     * param id string (from MediaMetricsManagerService).
+     */
+    void registerId(const std::string& id);
+
+    /**
+     * Returns the empty string if id string is malformed (not 16 Base64Url chars)
+     * or if id string has not been seen (in the recent size ids);
+     * otherwise it returns the same id parameter.
+     *
+     * \param id string (to be sent to statsd).
+     */
+    const std::string& validateId(const std::string& id);
+
+    /** Singleton set size */
+    static inline constexpr size_t SINGLETON_LRU_SET_SIZE = 2000;
+
+    using LockedValidateId = mediametrics::LockWrap<ValidateId>;
+    /**
+     * Returns a singleton locked ValidateId object that is thread-safe using LockWrap<>.
+     *
+     * The Singleton ValidateId object is created with size LRU_SET_SIZE (during first call).
+     */
+    static inline LockedValidateId& get() {
+        static LockedValidateId privateSet{SINGLETON_LRU_SET_SIZE};
+        return privateSet;
+    }
+};
+
+} // namespace android::mediametrics