add node interface method for getting maximum mempool size

src/interfaces/node.h

@@ -162,6 +162,9 @@ public:
     //! Get mempool dynamic usage.
     virtual size_t getMempoolDynamicUsage() = 0;
 
+    //! Get mempool maximum memory usage.
+    virtual size_t getMempoolMaxUsage() = 0;
+
     //! Get header tip height and time.
     virtual bool getHeaderTip(int& height, int64_t& block_time) = 0;
 

src/node/interfaces.cpp

@@ -273,6 +273,7 @@ public:
     int64_t getTotalBytesSent() override { return m_context->connman ? m_context->connman->GetTotalBytesSent() : 0; }
     size_t getMempoolSize() override { return m_context->mempool ? m_context->mempool->size() : 0; }
     size_t getMempoolDynamicUsage() override { return m_context->mempool ? m_context->mempool->DynamicMemoryUsage() : 0; }
+    size_t getMempoolMaxUsage() override { return m_context->mempool ? m_context->mempool->m_opts.max_size_bytes : 0; }
     bool getHeaderTip(int& height, int64_t& block_time) override
     {
         LOCK(::cs_main);