Implement async DNS resolution using c-ares

fix #2533

1 files changed, 112 insertions, 0 deletions

diff --git a/src/network/dns_handler.cpp b/src/network/dns_handler.cpp
new file mode 100644
index 0000000..45bf626
--- /dev/null
+++ b/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 */