4 files changed, 211 insertions, 0 deletions
diff --git a/Swiften/Base/LRUCache.h b/Swiften/Base/LRUCache.h
new file mode 100644
index 0000000..e4e652f
--- /dev/null
+++ b/Swiften/Base/LRUCache.h
@@ -0,0 +1,79 @@
+/*
+ * Copyright (c) 2017 Isode Limited.
+ * All rights reserved.
+ * See the COPYING file for more information.
+ */
+
+#pragma once
+
+#include <functional>
+#include <utility>
+
+#include <boost/multi_index_container.hpp>
+#include <boost/multi_index/member.hpp>
+#include <boost/multi_index/hashed_index.hpp>
+#include <boost/multi_index/sequenced_index.hpp>
+#include <boost/optional.hpp>
+
+namespace Swift {
+
+
+/**
+ * The \ref LRUCache templaged class implements a lookup cache which removes
+ * the least recently used cached item from the cache, if the cache size hits
+ * the \ref MAX_SIZE limit.
+ *
+ * An example use is a cache for entity capabilities hash to DiscoInfo.
+ */
+template <typename KEY_TYPE, typename VALUE_TYPE, size_t MAX_SIZE>
+class LRUCache {
+public:
+    using cacheMissFunction = std::function<boost::optional<VALUE_TYPE>(const KEY_TYPE& )>;
+
+public:
+    /**
+     * Inserts the key/value pair in the front of the cache. If the \ref key
+     * already exists in the cache, it is moved to the front instead. If
+     * afterwards, the cahe size exceeds the \ref MAX_SIZE limit, the least
+     * recently item is removed from the cache.
+     */
+    void insert(const KEY_TYPE& key, VALUE_TYPE value) {
+        auto pushResult = cache.push_front(entry_t(key, value));
+        if (!pushResult.second) {
+            cache.relocate(cache.begin(), pushResult.first);
+        }
+        else if (cache.size() > MAX_SIZE) {
+          cache.pop_back();
+        }
+    }
+
+    /**
+     * Looks up a cache entry based on the provided \ref key and moves it back
+     * to the front of the cache. If there is no cache entry for the provided
+     * \ref key, an uninitialized \ref boost::optional is returned.
+     * If the optional \ref missFunction is provided, it is called on a cache miss.
+     * If the \ref missFunction returns an initialized \ref boost::optional, the
+     * value is inserted in the cache.
+     */
+    boost::optional<VALUE_TYPE> get(const KEY_TYPE& key, cacheMissFunction missFunction = cacheMissFunction()) {
+        boost::optional<VALUE_TYPE> cachedValue;
+        auto cacheItemIterator = boost::multi_index::get<1>(cache).find(key);
+        if (cacheItemIterator != boost::multi_index::get<1>(cache).end()) {
+            cachedValue = cacheItemIterator->second;
+            cache.relocate(cache.begin(), cache.iterator_to(*cacheItemIterator));
+        }
+        else if (missFunction && (cachedValue = missFunction(key))) {
+            insert(key, cachedValue.get());
+        }
+        return cachedValue;
+    }
+
+private:
+    using entry_t =  std::pair<KEY_TYPE, VALUE_TYPE>;
+
+private:
+    boost::multi_index_container< entry_t, boost::multi_index::indexed_by< boost::multi_index::sequenced<>, boost::multi_index::hashed_unique<
+    BOOST_MULTI_INDEX_MEMBER(entry_t, KEY_TYPE, first)> > > cache;
+};
+
+}
diff --git a/Swiften/Base/LogSerializers.cpp b/Swiften/Base/LogSerializers.cpp
index ccc8437..5ac1e15 100644
--- a/Swiften/Base/LogSerializers.cpp
+++ b/Swiften/Base/LogSerializers.cpp
@@ -66,3 +66,13 @@ std::ostream& operator<<(std::ostream& stream, const Presence& presence) {
 }
 
 };
+
+::std::ostream& operator<<(::std::ostream& os, const boost::optional<std::string>& optStr) {
+    if (optStr.is_initialized()) {
+        return os << "boost::optional<std::string>(\"" << optStr.get() << "\")";
+    }
+    else {
+        return os << "boost::optional<std::string>()";
+    }
+}
+
diff --git a/Swiften/Base/LogSerializers.h b/Swiften/Base/LogSerializers.h
index 3d60426..be992bb 100644
--- a/Swiften/Base/LogSerializers.h
+++ b/Swiften/Base/LogSerializers.h
@@ -11,6 +11,8 @@
 #include <string>
 #include <vector>
 
+#include <boost/optional.hpp>
+
 namespace Swift {
 
 class Presence;
@@ -45,3 +47,6 @@ std::ostream& operator<<(std::ostream& stream, const std::vector<T>& vec) {
 std::ostream& operator<<(std::ostream& stream, const Presence& presence);
 
 };
+
+::std::ostream& operator<<(::std::ostream& os, const boost::optional<std::string>& optStr);
+
diff --git a/Swiften/Base/UnitTest/LRUCacheTest.cpp b/Swiften/Base/UnitTest/LRUCacheTest.cpp
new file mode 100644
index 0000000..7d54c5c
--- /dev/null
+++ b/Swiften/Base/UnitTest/LRUCacheTest.cpp
@@ -0,0 +1,117 @@
+/*
+ * Copyright (c) 2017 Isode Limited.
+ * All rights reserved.
+ * See the COPYING file for more information.
+ */
+
+#include <string>
+
+#include <boost/optional.hpp>
+
+#include <Swiften/Base/LogSerializers.h>
+#include <Swiften/Base/LRUCache.h>
+
+#include <gtest/gtest.h> // This has to go after Swiften/Base/LogSerializers.h.
+
+using namespace Swift;
+namespace b = boost;
+
+TEST(LRUCacheTest, testCacheLimit) {
+    LRUCache<std::string, std::string, 3> testling;
+
+    testling.insert("A", "AA");
+    testling.insert("B", "BB");
+    testling.insert("C", "CC");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>(), testling.get("D"));
+
+    testling.insert("D", "DD");
+
+    ASSERT_EQ(b::optional<std::string>(), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>("DD"), testling.get("D"));
+}
+
+TEST(LRUCacheTest, testMoveRecentToFrontOnGet) {
+    LRUCache<std::string, std::string, 3> testling;
+
+    testling.insert("A", "AA");
+    testling.insert("B", "BB");
+    testling.insert("C", "CC");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>(), testling.get("D"));
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+
+    testling.insert("D", "DD");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>(), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>("DD"), testling.get("D"));
+}
+
+TEST(LRUCacheTest, testMoveRecentToFrontOnReinsert) {
+    LRUCache<std::string, std::string, 3> testling;
+
+    testling.insert("A", "AA");
+    testling.insert("B", "BB");
+    testling.insert("C", "CC");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>(), testling.get("D"));
+
+    testling.insert("B", "BB");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>(), testling.get("D"));
+
+    testling.insert("D", "DD");
+
+    ASSERT_EQ(b::optional<std::string>(), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+    ASSERT_EQ(b::optional<std::string>("DD"), testling.get("D"));
+}
+
+TEST(LRUCacheTest, testCacheReturnsValuesPreviouslyInserted) {
+    LRUCache<std::string, std::string, 3> testling;
+
+    testling.insert("A", "AA");
+    testling.insert("B", "BB");
+    testling.insert("C", "CC");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+}
+
+TEST(LRUCacheTest, testCacheMissFunctionIsUsedOnCacheMiss) {
+    LRUCache<std::string, std::string, 3> testling;
+
+    testling.insert("A", "AA");
+    testling.insert("B", "BB");
+
+    ASSERT_EQ(b::optional<std::string>("AA"), testling.get("A"));
+    ASSERT_EQ(b::optional<std::string>("BB"), testling.get("B"));
+
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C", [](const std::string&) {
+        return boost::optional<std::string>(std::string("CC"));
+    }));
+    ASSERT_EQ(b::optional<std::string>("CC"), testling.get("C"));
+
+    ASSERT_EQ(b::optional<std::string>(), testling.get("D", [](const std::string&) {
+        return boost::optional<std::string>();
+    }));
+    ASSERT_EQ(b::optional<std::string>(), testling.get("D"));
+}