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diff --git a/src/shrpx_dns_resolver.h b/src/shrpx_dns_resolver.h
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+/*
+ * nghttp2 - HTTP/2 C Library
+ *
+ * Copyright (c) 2016 Tatsuhiro Tsujikawa
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files (the
+ * "Software"), to deal in the Software without restriction, including
+ * without limitation the rights to use, copy, modify, merge, publish,
+ * distribute, sublicense, and/or sell copies of the Software, and to
+ * permit persons to whom the Software is furnished to do so, subject to
+ * the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+ * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+ * LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+ * OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+#ifndef SHRPX_DNS_RESOLVER_H
+#define SHRPX_DNS_RESOLVER_H
+
+#include "shrpx.h"
+
+#include <sys/socket.h>
+#include <netinet/in.h>
+
+#include <vector>
+
+#include <ev.h>
+#include <ares.h>
+
+#include "template.h"
+#include "network.h"
+
+using namespace nghttp2;
+
+namespace shrpx {
+
+enum class DNSResolverStatus {
+  // Resolver is in initial status
+  IDLE,
+  // Resolver is currently resolving host name
+  RUNNING,
+  // Resolver successfully resolved host name
+  OK,
+  // Resolver failed to resolve host name
+  ERROR,
+};
+
+// Callback function called when host name lookup is finished.
+// |status| is either DNSResolverStatus::OK, or
+// DNSResolverStatus::ERROR.  If |status| is DNSResolverStatus::OK,
+// |result| points to the resolved address.  Note that port portion of
+// |result| is undefined, and must be initialized by application.
+// This callback function is not called if name lookup finishes in
+// DNSResolver::resolve() completely.  In this case, application
+// should call DNSResolver::get_status() to get current status and
+// result.  In other words, callback is called if get_status() returns
+// DNSResolverStatus::RUNNING.
+using CompleteCb =
+    std::function<void(DNSResolverStatus status, const Address *result)>;
+
+// DNSResolver is asynchronous name resolver, backed by c-ares
+// library.
+class DNSResolver {
+public:
+  DNSResolver(struct ev_loop *loop);
+  ~DNSResolver();
+
+  // Starts resolving hostname |name|.
+  int resolve(const StringRef &name, int family);
+  // Returns status.  If status_ is DNSResolverStatus::SUCCESS &&
+  // |result| is not nullptr, |*result| is filled.
+  DNSResolverStatus get_status(Address *result) const;
+  // Sets callback function when name lookup finishes.  The callback
+  // function is called in a way that it can destroy this DNSResolver.
+  void set_complete_cb(CompleteCb cb);
+  CompleteCb get_complete_cb() const;
+
+  // Calls these functions when read/write event occurred respectively.
+  int on_read(int fd);
+  int on_write(int fd);
+  int on_timeout();
+  // Calls this function when DNS query finished.
+  void on_result(int status, hostent *hostent);
+  void reset_timeout();
+
+  void start_rev(int fd);
+  void stop_rev(int fd);
+  void start_wev(int fd);
+  void stop_wev(int fd);
+
+private:
+  int handle_event(int rfd, int wfd);
+
+  std::vector<std::unique_ptr<ev_io>> revs_, wevs_;
+  Address result_;
+  CompleteCb completeCb_;
+  ev_timer timer_;
+  StringRef name_;
+  struct ev_loop *loop_;
+  // ares_channel is pointer type
+  ares_channel channel_;
+  // AF_INET or AF_INET6.  AF_INET for A record lookup, and AF_INET6
+  // for AAAA record lookup.
+  int family_;
+  DNSResolverStatus status_;
+};
+
+} // namespace shrpx
+
+#endif // SHRPX_DNS_RESOLVER_H