feat: add ability to limit message snapshot size (#6602)

Reviewed-by: pajlada <rasmus.karlsson@pajlada.com>

src/messages/LimitedQueue.hpp

@@ -324,6 +324,18 @@ public:
         return LimitedQueueSnapshot<T>(this->buffer_);
     }
 
+    [[nodiscard]] LimitedQueueSnapshot<T> lastN(size_t nItems) const
+    {
+        std::shared_lock lock(this->mutex_);
+        return LimitedQueueSnapshot<T>::lastN(this->buffer_, nItems);
+    }
+
+    [[nodiscard]] LimitedQueueSnapshot<T> firstN(size_t nItems) const
+    {
+        std::shared_lock lock(this->mutex_);
+        return LimitedQueueSnapshot<T>::firstN(this->buffer_, nItems);
+    }
+
     // Actions
 
     /**

src/messages/LimitedQueueSnapshot.hpp

@@ -22,6 +22,24 @@ private:
     {
     }
 
+    static LimitedQueueSnapshot lastN(const boost::circular_buffer<T> &buf,
+                                      size_t n)
+    {
+        return {buf.end() - std::min(n, buf.size()), buf.end()};
+    }
+
+    static LimitedQueueSnapshot firstN(const boost::circular_buffer<T> &buf,
+                                       size_t n)
+    {
+        return {buf.begin(), buf.begin() + std::min(n, buf.size())};
+    }
+
+    template <typename It>
+    LimitedQueueSnapshot(It begin, It end)
+        : buffer_(std::move(begin), std::move(end))
+    {
+    }
+
 public:
     LimitedQueueSnapshot() = default;