Implement async DNS resolution using c-ares

fix #2533

CMakeLists.txt

@@ -39,6 +39,12 @@ elseif(NOT WITHOUT_BOTAN)
   find_package(BOTAN)
 endif()
 
+if(WITH_CARES)
+  find_package(CARES REQUIRED)
+elseif(NOT WITHOUT_CARES)
+  find_package(CARES)
+endif()
+
 #
 ## Get the software version
 #
@@ -84,6 +90,10 @@ if(BOTAN_FOUND)
   include_directories(SYSTEM ${BOTAN_INCLUDE_DIRS})
 endif()
 
+if(CARES_FOUND)
+  include_directories(${CARES_INCLUDE_DIRS})
+endif()
+
 set(POLLER_DOCSTRING "Choose the poller between POLL and EPOLL (Linux-only)")
 if(${CMAKE_SYSTEM_NAME} MATCHES "Linux")
  set(POLLER "EPOLL" CACHE STRING ${POLLER_DOCSTRING})
@@ -145,6 +155,9 @@ target_link_libraries(network logger)
 if(BOTAN_FOUND)
   target_link_libraries(network ${BOTAN_LIBRARIES})
 endif()
+if(CARES_FOUND)
+  target_link_libraries(network ${CARES_LIBRARIES})
+endif()
 
 #
 ## irclib

src/config.h.cmake

@@ -4,4 +4,5 @@
 #cmakedefine SYSTEMD_FOUND
 #cmakedefine POLLER ${POLLER}
 #cmakedefine BOTAN_FOUND
+#cmakedefine CARES_FOUND
 #cmakedefine BIBOUMI_VERSION "${BIBOUMI_VERSION}"

src/main.cpp

@@ -1,4 +1,3 @@
-#include <network/tcp_socket_handler.hpp>
 #include <xmpp/xmpp_component.hpp>
 #include <utils/timed_events.hpp>
 #include <network/poller.hpp>
@@ -11,6 +10,10 @@
 
 #include <signal.h>
 
+#ifdef CARES_FOUND
+# include <network/dns_handler.hpp>
+#endif
+
 // A flag set by the SIGINT signal handler.
 static volatile std::atomic<bool> stop(false);
 // Flag set by the SIGUSR1/2 signal handler.
@@ -95,6 +98,10 @@ int main(int ac, char** av)
 
   xmpp_component->start();
 
+
+#ifdef CARES_FOUND
+  DNSHandler::instance.watch_dns_sockets(p);
+#endif
   auto timeout = TimedEventsManager::instance().get_timeout();
   while (p->poll(timeout) != -1)
   {
@@ -108,6 +115,9 @@ int main(int ac, char** av)
       exiting = true;
       stop.store(false);
       xmpp_component->shutdown();
+#ifdef CARES_FOUND
+      DNSHandler::instance.destroy();
+#endif
       // Cancel the timer for an potential reconnection
       TimedEventsManager::instance().cancel("XMPP reconnection");
     }
@@ -153,6 +163,10 @@ int main(int ac, char** av)
       xmpp_component->close();
     if (exiting && p->size() == 1 && xmpp_component->is_document_open())
       xmpp_component->close_document();
+#ifdef CARES_FOUND
+    if (!exiting)
+      DNSHandler::instance.watch_dns_sockets(p);
+#endif
     if (exiting) // If we are exiting, do not wait for any timed event
       timeout = utils::no_timeout;
     else

src/network/dns_handler.cpp

@@ -0,0 +1,112 @@
+#include <config.h>
+#ifdef CARES_FOUND
+
+#include <network/dns_socket_handler.hpp>
+#include <network/tcp_socket_handler.hpp>
+#include <network/dns_handler.hpp>
+#include <network/poller.hpp>
+
+#include <algorithm>
+#include <stdexcept>
+
+DNSHandler DNSHandler::instance;
+
+using namespace std::string_literals;
+
+void on_hostname4_resolved(void* arg, int status, int, struct hostent* hostent)
+{
+  TCPSocketHandler* socket_handler = static_cast<TCPSocketHandler*>(arg);
+  socket_handler->on_hostname4_resolved(status, hostent);
+}
+
+void on_hostname6_resolved(void* arg, int status, int, struct hostent* hostent)
+{
+  TCPSocketHandler* socket_handler = static_cast<TCPSocketHandler*>(arg);
+  socket_handler->on_hostname6_resolved(status, hostent);
+}
+
+DNSHandler::DNSHandler()
+{
+  int ares_error;
+  if ((ares_error = ::ares_library_init(ARES_LIB_INIT_ALL)) != 0)
+    throw std::runtime_error("Failed to initialize c-ares lib: "s + ares_strerror(ares_error));
+  if ((ares_error = ::ares_init(&this->channel)) != ARES_SUCCESS)
+    throw std::runtime_error("Failed to initialize c-ares channel: "s + ares_strerror(ares_error));
+}
+
+ares_channel& DNSHandler::get_channel()
+{
+  return this->channel;
+}
+
+void DNSHandler::destroy()
+{
+  this->socket_handlers.clear();
+  ::ares_destroy(this->channel);
+  ::ares_library_cleanup();
+}
+
+void DNSHandler::gethostbyname(const std::string& name,
+                               TCPSocketHandler* socket_handler, int family)
+{
+  socket_handler->free_cares_addrinfo();
+  if (family == AF_INET)
+    ::ares_gethostbyname(this->channel, name.data(), family,
+                         &::on_hostname4_resolved, socket_handler);
+  else
+    ::ares_gethostbyname(this->channel, name.data(), family,
+                         &::on_hostname6_resolved, socket_handler);
+}
+
+void DNSHandler::watch_dns_sockets(std::shared_ptr<Poller>& poller)
+{
+  fd_set readers;
+  fd_set writers;
+
+  FD_ZERO(&readers);
+  FD_ZERO(&writers);
+
+  int ndfs = ::ares_fds(this->channel, &readers, &writers);
+  // For each existing DNS socket, see if we are still supposed to watch it,
+  // if not then erase it
+  this->socket_handlers.erase(
+      std::remove_if(this->socket_handlers.begin(), this->socket_handlers.end(),
+                     [&readers](const auto& dns_socket)
+                     {
+                       return !FD_ISSET(dns_socket->get_socket(), &readers);
+                     }),
+      this->socket_handlers.end());
+
+  for (auto i = 0; i < ndfs; ++i)
+    {
+      bool read = FD_ISSET(i, &readers);
+      bool write = FD_ISSET(i, &writers);
+      // Look for the DNSSocketHandler with this fd
+      auto it = std::find_if(this->socket_handlers.begin(),
+                             this->socket_handlers.end(),
+                             [i](const auto& socket_handler)
+                             {
+        return i == socket_handler->get_socket();
+      });
+      if (!read && !write)      // No need to read or write to it
+        { // If found, erase it and stop watching it because it is not
+          // needed anymore
+          if (it != this->socket_handlers.end())
+            // The socket destructor removes it from the poller
+            this->socket_handlers.erase(it);
+        }
+      else            // We need to write and/or read to it
+        { // If not found, create it because we need to watch it
+          if (it == this->socket_handlers.end())
+            {
+              this->socket_handlers.emplace_front(std::make_unique<DNSSocketHandler>(poller, i));
+              it = this->socket_handlers.begin();
+            }
+          poller->add_socket_handler(it->get());
+          if (write)
+            poller->watch_send_events(it->get());
+        }
+    }
+}
+
+#endif /* CARES_FOUND */

src/network/dns_handler.hpp

@@ -0,0 +1,62 @@
+#ifndef DNS_HANDLER_HPP_INCLUDED
+#define DNS_HANDLER_HPP_INCLUDED
+
+#include <config.h>
+#ifdef CARES_FOUND
+
+class TCPSocketHandler;
+class Poller;
+class DNSSocketHandler;
+
+# include <ares.h>
+# include <memory>
+# include <string>
+# include <list>
+
+void on_hostname4_resolved(void* arg, int status, int, struct hostent* hostent);
+void on_hostname6_resolved(void* arg, int status, int, struct hostent* hostent);
+
+/**
+ * Class managing DNS resolution.  It should only be statically instanciated
+ * once in SocketHandler.  It manages ares channel and calls various
+ * functions of that library.
+ */
+
+class DNSHandler
+{
+public:
+  DNSHandler();
+  ~DNSHandler() = default;
+  void gethostbyname(const std::string& name, TCPSocketHandler* socket_handler,
+                     int family);
+  /**
+   * Call ares_fds to know what fd needs to be watched by the poller, create
+   * or destroy DNSSocketHandlers depending on the result.
+   */
+  void watch_dns_sockets(std::shared_ptr<Poller>& poller);
+  /**
+   * Destroy and stop watching all the DNS sockets. Then de-init the channel
+   * and library.
+   */
+  void destroy();
+  ares_channel& get_channel();
+
+  static DNSHandler instance;
+
+private:
+  /**
+   * The list of sockets that needs to be watched, according to the last
+   * call to ares_fds.  DNSSocketHandlers are added to it or removed from it
+   * in the watch_dns_sockets() method
+   */
+  std::list<std::unique_ptr<DNSSocketHandler>> socket_handlers;
+  ares_channel channel;
+
+  DNSHandler(const DNSHandler&) = delete;
+  DNSHandler(DNSHandler&&) = delete;
+  DNSHandler& operator=(const DNSHandler&) = delete;
+  DNSHandler& operator=(DNSHandler&&) = delete;
+};
+
+#endif /* CARES_FOUND */
+#endif /* DNS_HANDLER_HPP_INCLUDED */

src/network/dns_socket_handler.cpp

@@ -0,0 +1,45 @@
+#include <config.h>
+#ifdef CARES_FOUND
+
+#include <network/dns_socket_handler.hpp>
+#include <network/dns_handler.hpp>
+#include <network/poller.hpp>
+
+#include <ares.h>
+
+DNSSocketHandler::DNSSocketHandler(std::shared_ptr<Poller> poller,
+                                   const socket_t socket):
+  SocketHandler(poller, socket)
+{
+}
+
+DNSSocketHandler::~DNSSocketHandler()
+{
+}
+
+void DNSSocketHandler::connect()
+{
+}
+
+void DNSSocketHandler::on_recv()
+{
+  // always stop watching send and read events. We will re-watch them if the
+  // next call to ares_fds tell us to
+  this->poller->remove_socket_handler(this->socket);
+  ::ares_process_fd(DNSHandler::instance.get_channel(), this->socket, ARES_SOCKET_BAD);
+}
+
+void DNSSocketHandler::on_send()
+{
+  // always stop watching send and read events. We will re-watch them if the
+  // next call to ares_fds tell us to
+  this->poller->remove_socket_handler(this->socket);
+  ::ares_process_fd(DNSHandler::instance.get_channel(), ARES_SOCKET_BAD, this->socket);
+}
+
+bool DNSSocketHandler::is_connected() const
+{
+  return true;
+}
+
+#endif /* CARES_FOUND */

src/network/dns_socket_handler.hpp

@@ -0,0 +1,46 @@
+#ifndef DNS_SOCKET_HANDLER_HPP
+# define DNS_SOCKET_HANDLER_HPP
+
+#include <config.h>
+#ifdef CARES_FOUND
+
+#include <network/socket_handler.hpp>
+#include <ares.h>
+
+/**
+ * Manage a socket returned by ares_fds. We do not create, open or close the
+ * socket ourself: this is done by c-ares.  We just call ares_process_fd()
+ * with the correct parameters, depending on what can be done on that socket
+ * (Poller reported it to be writable or readeable)
+ */
+
+class DNSSocketHandler: public SocketHandler
+{
+public:
+  explicit DNSSocketHandler(std::shared_ptr<Poller> poller, const socket_t socket);
+  ~DNSSocketHandler();
+  /**
+   * Just call dns_process_fd, c-ares will do its work of send()ing or
+   * recv()ing the data it wants on that socket.
+   */
+  void on_recv() override final;
+  void on_send() override final;
+  /**
+   * Do nothing, because we are always considered to be connected, since the
+   * connection is done by c-ares and not by us.
+   */
+  void connect() override final;
+  /**
+   * Always true, see the comment for connect()
+   */
+  bool is_connected() const override final;
+
+private:
+  DNSSocketHandler(const DNSSocketHandler&) = delete;
+  DNSSocketHandler(DNSSocketHandler&&) = delete;
+  DNSSocketHandler& operator=(const DNSSocketHandler&) = delete;
+  DNSSocketHandler& operator=(DNSSocketHandler&&) = delete;
+};
+
+#endif // CARES_FOUND
+#endif // DNS_SOCKET_HANDLER_HPP

src/network/socket_handler.hpp

@@ -1,6 +1,7 @@
 #ifndef SOCKET_HANDLER_HPP
 # define SOCKET_HANDLER_HPP
 
+#include <config.h>
 #include <memory>
 
 class Poller;
@@ -19,6 +20,7 @@ public:
   virtual void on_send() = 0;
   virtual void connect() = 0;
   virtual bool is_connected() const = 0;
+
   socket_t get_socket() const
   { return this->socket; }
 

src/network/tcp_socket_handler.cpp

@@ -1,4 +1,5 @@
 #include <network/tcp_socket_handler.hpp>
+#include <network/dns_handler.hpp>
 
 #include <utils/timed_events.hpp>
 #include <utils/scopeguard.hpp>
@@ -42,8 +43,22 @@ TCPSocketHandler::TCPSocketHandler(std::shared_ptr<Poller> poller):
   use_tls(false),
   connected(false),
   connecting(false)
+#ifdef CARES_FOUND
+  ,resolved(false),
+  resolved4(false),
+  resolved6(false),
+  cares_addrinfo(nullptr),
+  cares_error()
+#endif
 {}
 
+TCPSocketHandler::~TCPSocketHandler()
+{
+#ifdef CARES_FOUND
+  this->free_cares_addrinfo();
+#endif
+}
+
 void TCPSocketHandler::init_socket(const struct addrinfo* rp)
 {
   if ((this->socket = ::socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol)) == -1)
@@ -71,10 +86,36 @@ void TCPSocketHandler::connect(const std::string& address, const std::string& po
   struct addrinfo* addr_res;
 
   if (!this->connecting)
+    {
+      // Get the addrinfo from getaddrinfo (or ares_gethostbyname), only if
+      // this is the first call of this function.
+#ifdef CARES_FOUND
+      if (!this->resolved)
         {
           log_info("Trying to connect to " << address << ":" << port);
-      // Get the addrinfo from getaddrinfo, only if this is the first call
-      // of this function.
+          // Start the asynchronous process of resolving the hostname. Once
+          // the addresses have been found and `resolved` has been set to true
+          // (but connecting will still be false), TCPSocketHandler::connect()
+          // needs to be called, again.
+          DNSHandler::instance.gethostbyname(address, this, AF_INET6);
+          DNSHandler::instance.gethostbyname(address, this, AF_INET);
+          return;
+        }
+      else
+        {
+          // The c-ares resolved the hostname and the available addresses
+          // where saved in the cares_addrinfo linked list. Now, just use
+          // this list to try to connect.
+          addr_res = this->cares_addrinfo;
+          if (!addr_res)
+            {
+              this->close();
+              this->on_connection_failed(this->cares_error);
+              return ;
+            }
+        }
+#else
+      log_info("Trying to connect to " << address << ":" << port);
       struct addrinfo hints;
       memset(&hints, 0, sizeof(struct addrinfo));
       hints.ai_flags = 0;
@@ -94,6 +135,7 @@ void TCPSocketHandler::connect(const std::string& address, const std::string& po
       // Make sure the alloced structure is always freed at the end of the
       // function
       sg.add_callback([&addr_res](){ freeaddrinfo(addr_res); });
+#endif
     }
   else
     { // This function is called again, use the saved addrinfo structure,
@@ -321,7 +363,11 @@ bool TCPSocketHandler::is_connected() const
 
 bool TCPSocketHandler::is_connecting() const
 {
+#ifdef CARES_FOUND
+  return this->connecting || !this->resolved;
+#else
   return this->connecting;
+#endif
 }
 
 void* TCPSocketHandler::get_receive_buffer(const size_t) const
@@ -413,4 +459,114 @@ void TCPSocketHandler::on_tls_activated()
 {
   this->send_data("");
 }
+
 #endif // BOTAN_FOUND
+
+#ifdef CARES_FOUND
+
+void TCPSocketHandler::on_hostname4_resolved(int status, struct hostent* hostent)
+{
+  this->resolved4 = true;
+  if (status == ARES_SUCCESS)
+    this->fill_ares_addrinfo4(hostent);
+  else
+    this->cares_error = ::ares_strerror(status);
+
+  if (this->resolved4 && this->resolved6)
+    {
+      this->resolved = true;
+      this->connect();
+    }
+}
+
+void TCPSocketHandler::on_hostname6_resolved(int status, struct hostent* hostent)
+{
+  this->resolved6 = true;
+  if (status == ARES_SUCCESS)
+    this->fill_ares_addrinfo6(hostent);
+  else
+    this->cares_error = ::ares_strerror(status);
+
+  if (this->resolved4 && this->resolved6)
+    {
+      this->resolved = true;
+      this->connect();
+    }
+}
+
+void TCPSocketHandler::fill_ares_addrinfo4(const struct hostent* hostent)
+{
+  struct addrinfo* prev = this->cares_addrinfo;
+  struct in_addr** address = reinterpret_cast<struct in_addr**>(hostent->h_addr_list);
+
+  while (*address)
+    {
+       // Create a new addrinfo list element, and fill it
+      struct addrinfo* current = new struct addrinfo;
+      current->ai_flags = 0;
+      current->ai_family = hostent->h_addrtype;
+      current->ai_socktype = SOCK_STREAM;
+      current->ai_protocol = 0;
+      current->ai_addrlen = sizeof(struct sockaddr_in);
+
+      struct sockaddr_in* addr = new struct sockaddr_in;
+      addr->sin_family = hostent->h_addrtype;
+      addr->sin_port = htons(strtoul(this->port.data(), nullptr, 10));
+      addr->sin_addr.s_addr = (*address)->s_addr;
+
+      current->ai_addr = reinterpret_cast<struct sockaddr*>(addr);
+      current->ai_next = nullptr;
+      current->ai_canonname = nullptr;
+
+      current->ai_next = prev;
+      this->cares_addrinfo = current;
+      prev = current;
+      ++address;
+    }
+}
+
+void TCPSocketHandler::fill_ares_addrinfo6(const struct hostent* hostent)
+{
+  struct addrinfo* prev = this->cares_addrinfo;
+  struct in6_addr** address = reinterpret_cast<struct in6_addr**>(hostent->h_addr_list);
+
+  while (*address)
+    {
+       // Create a new addrinfo list element, and fill it
+      struct addrinfo* current = new struct addrinfo;
+      current->ai_flags = 0;
+      current->ai_family = hostent->h_addrtype;
+      current->ai_socktype = SOCK_STREAM;
+      current->ai_protocol = 0;
+      current->ai_addrlen = sizeof(struct sockaddr_in6);
+
+      struct sockaddr_in6* addr = new struct sockaddr_in6;
+      addr->sin6_family = hostent->h_addrtype;
+      addr->sin6_port = htons(strtoul(this->port.data(), nullptr, 10));
+      ::memcpy(addr->sin6_addr.s6_addr, (*address)->s6_addr, 16);
+      addr->sin6_flowinfo = 0;
+      addr->sin6_scope_id = 0;
+
+      current->ai_addr = reinterpret_cast<struct sockaddr*>(addr);
+      current->ai_next = nullptr;
+      current->ai_canonname = nullptr;
+
+      current->ai_next = prev;
+      this->cares_addrinfo = current;
+      prev = current;
+      ++address;
+    }
+}
+
+void TCPSocketHandler::free_cares_addrinfo()
+{
+  while (this->cares_addrinfo)
+    {
+      delete this->cares_addrinfo->ai_addr;
+      auto next = this->cares_addrinfo->ai_next;
+      delete this->cares_addrinfo;
+      this->cares_addrinfo = next;
+    }
+}
+
+#endif  // CARES_FOUND

src/network/tcp_socket_handler.hpp

@@ -17,6 +17,10 @@
 
 #include "config.h"
 
+#ifdef CARES_FOUND
+# include <ares.h>
+#endif
+
 #ifdef BOTAN_FOUND
 # include <botan/botan.h>
 # include <botan/tls_client.h>
@@ -44,7 +48,7 @@ public:
 class TCPSocketHandler: public SocketHandler
 {
 protected:
-  ~TCPSocketHandler() {}
+  ~TCPSocketHandler();
 
 public:
   explicit TCPSocketHandler(std::shared_ptr<Poller> poller);
@@ -54,16 +58,16 @@ public:
    * start_tls() when the connection succeeds.
    */
   void connect(const std::string& address, const std::string& port, const bool tls);
-  void connect();
+  void connect() override final;
   /**
    * Reads raw data from the socket. And pass it to parse_in_buffer()
    * If we are using TLS on this connection, we call tls_recv()
    */
-  void on_recv();
+  void on_recv() override final;
   /**
    * Write as much data from out_buf as possible, in the socket.
    */
-  void on_send();
+  void on_send() override final;
   /**
    * Add the given data to out_buf and tell our poller that we want to be
    * notified when a send event is ready.
@@ -107,9 +111,19 @@ public:
    * The size argument is the size of the last chunk of data that was added to the buffer.
    */
   virtual void parse_in_buffer(const size_t size) = 0;
-  bool is_connected() const;
+  bool is_connected() const override final;
   bool is_connecting() const;
 
+#ifdef CARES_FOUND
+  void on_hostname4_resolved(int status, struct hostent* hostent);
+  void on_hostname6_resolved(int status, struct hostent* hostent);
+
+  void free_cares_addrinfo();
+
+  void fill_ares_addrinfo4(const struct hostent* hostent);
+  void fill_ares_addrinfo6(const struct hostent* hostent);
+#endif
+
 private:
   /**
    * Initialize the socket with the parameters contained in the given
@@ -185,7 +199,7 @@ private:
    */
   std::list<std::string> out_buf;
   /**
-   * Keep the details of the addrinfo the triggered a EINPROGRESS error when
+   * Keep the details of the addrinfo that triggered a EINPROGRESS error when
    * connect()ing to it, to reuse it directly when connect() is called
    * again.
    */
@@ -225,6 +239,27 @@ protected:
   bool connected;
   bool connecting;
 
+#ifdef CARES_FOUND
+  /**
+   * Whether or not the DNS resolution was successfully done
+   */
+  bool resolved;
+  bool resolved4;
+  bool resolved6;
+  /**
+   * When using c-ares to resolve the host asynchronously, we need the
+   * c-ares callback 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 next call of connect() will then try all these values
+   * (exactly like we do with the result of getaddrinfo) and save the one
+   * that worked (or returned EINPROGRESS) in the other struct addrinfo (see
+   * the members addrinfo, ai_addrlen, and ai_addr).
+   */
+  struct addrinfo* cares_addrinfo;
+  std::string cares_error;
+#endif  // CARES_FOUND
+
 private:
   TCPSocketHandler(const TCPSocketHandler&) = delete;
   TCPSocketHandler(TCPSocketHandler&&) = delete;

src/xmpp/xmpp_component.cpp

@@ -70,7 +70,7 @@ XmppComponent::~XmppComponent()
 
 void XmppComponent::start()
 {
-  this->connect("127.0.0.1", Config::get("port", "5347"), false);
+  this->connect("localhost", Config::get("port", "5347"), false);
 }
 
 bool XmppComponent::is_document_open() const