1 files changed, 120 insertions, 0 deletions
diff --git a/src/com/kenai/jbosh/RequestIDSequence.java b/src/com/kenai/jbosh/RequestIDSequence.java
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+++ b/src/com/kenai/jbosh/RequestIDSequence.java
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+/*
+ * Copyright 2009 Mike Cumings
+ *
+ * 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.
+ */
+
+package com.kenai.jbosh;
+
+import java.security.SecureRandom;
+import java.util.concurrent.atomic.AtomicLong;
+import java.util.concurrent.locks.Lock;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * Request ID sequence generator.  This generator generates a random first
+ * RID and then manages the sequence from there on out.
+ */
+final class RequestIDSequence {
+
+    /**
+     * Maximum number of bits available for representing request IDs, according
+     * to the XEP-0124 spec.s
+     */
+    private static final int MAX_BITS = 53;
+
+    /**
+     * Bits devoted to incremented values.
+     */
+    private static final int INCREMENT_BITS = 32;
+
+    /**
+     * Minimum number of times the initial RID can be incremented before
+     * exceeding the maximum.
+     */
+    private static final long MIN_INCREMENTS = 1L << INCREMENT_BITS;
+
+    /**
+     * Max initial value. 
+     */
+    private static final long MAX_INITIAL = (1L << MAX_BITS) - MIN_INCREMENTS;
+
+    /**
+     * Max bits mask.
+     */
+    private static final long MASK = ~(Long.MAX_VALUE << MAX_BITS);
+
+    /**
+     * Random number generator.
+     */
+    private static final SecureRandom RAND = new SecureRandom();
+
+    /**
+     * Internal lock.
+     */
+    private static final Lock LOCK = new ReentrantLock();
+
+    /**
+     * The last reqest ID used, or &lt;= 0 if a new request ID needs to be
+     * generated.
+     */
+    private AtomicLong nextRequestID = new AtomicLong();
+
+    ///////////////////////////////////////////////////////////////////////////
+    // Constructors:
+
+    /**
+     * Prevent direct construction.
+     */
+    RequestIDSequence() {
+        nextRequestID = new AtomicLong(generateInitialValue());
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+    // Public methods:
+
+    /**
+     * Calculates the next request ID value to use.  This number must be
+     * initialized such that it is unlikely to ever exceed 2 ^ 53, according
+     * to XEP-0124.
+     *
+     * @return next request ID value
+     */
+    public long getNextRID() {
+        return nextRequestID.getAndIncrement();
+    }
+
+    ///////////////////////////////////////////////////////////////////////////
+    // Private methods:
+
+    /**
+     * Generates an initial RID value by generating numbers until a number is
+     * found which is smaller than the maximum allowed value and greater
+     * than zero.
+     *
+     * @return random initial value
+     */
+    private long generateInitialValue() {
+        long result;
+        LOCK.lock();
+        try {
+            do {
+                result = RAND.nextLong() & MASK;
+            } while (result > MAX_INITIAL);
+        } finally {
+            LOCK.unlock();
+        }
+        return result;
+    }
+
+}