refactor: use unique_ptr for BPF resource pointers

Author: rhargreaves

src/bpf_program.cpp

@@ -13,8 +13,6 @@ static void configure_bpf_program(knock_bpf* skel, const knock_config& config)
 static void load_bpf_program(knock_bpf* skel)
 {
     if (knock_bpf__load(skel) != 0) {
-        knock_bpf__destroy(skel);
-        skel = nullptr;
         throw BpfError("Failed to load BPF program");
     }
 }
@@ -30,26 +28,16 @@ static void load_bpf_program(knock_bpf* skel)
 
 BpfProgram::BpfProgram(const knock_config& config)
 {
-    skel = open_bpf_program();
-    load_bpf_program(skel);
-    configure_bpf_program(skel, config);
+    skel.reset(open_bpf_program());
+    load_bpf_program(skel.get());
+    configure_bpf_program(skel.get(), config);
 }
 
-BpfProgram::~BpfProgram()
-{
-    if (link) {
-        bpf_link__destroy(link);
-        link = nullptr;
-    }
-    if (skel) {
-        knock_bpf__destroy(skel);
-        skel = nullptr;
-    }
-}
+BpfProgram::~BpfProgram() = default;
 
 void BpfProgram::attach_xdp(int ifindex, const std::string& interface)
 {
-    link = bpf_program__attach_xdp(skel->progs.knock, ifindex);
+    link.reset(bpf_program__attach_xdp(skel->progs.knock, ifindex));
     if (!link) {
         throw BpfError("Failed to attach XDP program to interface " + interface);
     }

src/bpf_program.hpp

@@ -2,11 +2,20 @@
 #include "knock.skel.h"
 #include "knock.h"
 #include <string>
+#include <memory>
+
+struct BpfLinkDeleter {
+    void operator()(bpf_link* link)
+    {
+        if (link)
+            bpf_link__destroy(link);
+    }
+};
 
 class BpfProgram {
 private:
-    knock_bpf* skel = nullptr;
-    bpf_link* link = nullptr;
+    std::unique_ptr<knock_bpf, void (*)(knock_bpf*)> skel { nullptr, knock_bpf__destroy };
+    std::unique_ptr<bpf_link, BpfLinkDeleter> link;
 
 public:
     explicit BpfProgram(const knock_config& config);