Separate the DNS resolution logic from the TCP communication logic

fix #3137

louloulibs/network/resolver.hpp

@@ -0,0 +1,129 @@
+#ifndef RESOLVER_HPP_INCLUDED
+#define RESOLVER_HPP_INCLUDED
+
+#include "louloulibs.h"
+
+#include <functional>
+#include <memory>
+#include <string>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <netdb.h>
+
+struct AddrinfoDeleter
+{
+  void operator()(struct addrinfo* addr)
+  {
+#ifdef CARES_FOUND
+    while (addr)
+      {
+        delete addr->ai_addr;
+        auto next = addr->ai_next;
+        delete addr;
+        addr = next;
+      }
+#else
+    freeaddrinfo(addr);
+#endif
+  }
+};
+
+class Resolver
+{
+public:
+  using ErrorCallbackType = std::function<void(const char*)>;
+  using SuccessCallbackType = std::function<void(const struct addrinfo*)>;
+
+  Resolver();
+  ~Resolver() = default;
+
+  bool is_resolving() const
+  {
+#ifdef CARES_FOUND
+    return this->resolving;
+#else
+    return false;
+#endif
+  }
+
+  bool is_resolved() const
+  {
+    return this->resolved;
+  }
+
+  const auto& get_result() const
+  {
+    return this->addr;
+  }
+  std::string get_error_message() const
+  {
+    return this->error_msg;
+  }
+
+  void clear()
+  {
+#ifdef CARES_FOUND
+    this->resolved6 = false;
+    this->resolved4 = false;
+#endif
+    this->resolved = false;
+    this->resolving = false;
+    this->addr.reset();
+    this->cares_addrinfo = nullptr;
+    this->port.clear();
+    this->error_msg.clear();
+  }
+
+  void resolve(const std::string& hostname, const std::string& port,
+               SuccessCallbackType success_cb, ErrorCallbackType error_cb);
+
+private:
+  void start_resolving(const std::string& hostname, const std::string& port);
+#ifdef CARES_FOUND
+  void on_hostname4_resolved(int status, struct hostent* hostent);
+  void on_hostname6_resolved(int status, struct hostent* hostent);
+
+  void fill_ares_addrinfo4(const struct hostent* hostent);
+  void fill_ares_addrinfo6(const struct hostent* hostent);
+
+  void on_resolved();
+
+  bool resolved4;
+  bool resolved6;
+
+  bool resolving;
+
+  /**
+   * When using c-ares to resolve the host asynchronously, we need the
+   * c-ares callbacks to fill a structure (a struct addrinfo, for
+   * compatibility with getaddrinfo and the rest of the code that works when
+   * c-ares is not used) with all returned values (for example an IPv6 and
+   * an IPv4). The pointer is given to the unique_ptr to manage its lifetime.
+   */
+  struct addrinfo* cares_addrinfo;
+  std::string port;
+
+#endif
+ /**
+  * Tells if we finished the resolution process. It doesn't indicate if it
+  * was successful (it is true even if the result is an error).
+  */
+  bool resolved;
+  std::string error_msg;
+
+
+  std::unique_ptr<struct addrinfo, AddrinfoDeleter> addr;
+
+  ErrorCallbackType error_cb;
+  SuccessCallbackType success_cb;
+
+  Resolver(const Resolver&) = delete;
+  Resolver(Resolver&&) = delete;
+  Resolver& operator=(const Resolver&) = delete;
+  Resolver& operator=(Resolver&&) = delete;
+};
+
+std::string addr_to_string(const struct addrinfo* rp);
+
+#endif /* RESOLVER_HPP_INCLUDED */