Move the basic socket implementation into the SocketHandler class

(that is, the read/write/connect/etc)
Because this code is actually common for both the IrcClient and
XmppComponent class. These two classes have to implement some higher level
callbacks (parsing the data provided in the buffers, doing stuff when the
connection is done) instead of doing the read/write/connect low level
things.

src/network/socket_handler.cpp

@@ -0,0 +1,113 @@
+#include <network/socket_handler.hpp>
+
+#include <utils/scopeguard.hpp>
+#include <network/poller.hpp>
+
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <cstring>
+#include <netdb.h>
+#include <unistd.h>
+
+#include <iostream>
+
+SocketHandler::SocketHandler():
+  poller(nullptr)
+{
+  if ((this->socket = ::socket(AF_INET, SOCK_STREAM, 0)) == -1)
+    throw std::runtime_error("Could not create socket");
+}
+
+void SocketHandler::connect(const std::string& address, const std::string& port)
+{
+  std::cout << "Trying to connect to " << address << ":" << port << std::endl;
+  struct addrinfo hints;
+  memset(&hints, 0, sizeof(struct addrinfo));
+  hints.ai_flags = 0;
+  hints.ai_family = AF_INET;
+  hints.ai_socktype = SOCK_STREAM;
+  hints.ai_protocol = 0;
+
+  struct addrinfo* addr_res;
+  const int res = ::getaddrinfo(address.c_str(), port.c_str(), &hints, &addr_res);
+  // Make sure the alloced structure is always freed at the end of the
+  // function
+  utils::ScopeGuard sg([&addr_res](){ freeaddrinfo(addr_res); });
+
+  if (res != 0)
+    {
+      perror("getaddrinfo");
+      throw std::runtime_error("getaddrinfo failed");
+    }
+  for (struct addrinfo* rp = addr_res; rp; rp = rp->ai_next)
+    {
+      std::cout << "One result" << std::endl;
+      if (::connect(this->socket, rp->ai_addr, rp->ai_addrlen) == 0)
+        {
+          std::cout << "Connection success." << std::endl;
+          this->on_connected();
+          return ;
+        }
+      std::cout << "Connection failed:" << std::endl;
+      perror("connect");
+    }
+  std::cout << "All connection attempts failed." << std::endl;
+  this->close();
+}
+
+void SocketHandler::set_poller(Poller* poller)
+{
+  this->poller = poller;
+}
+
+void SocketHandler::on_recv()
+{
+  char buf[4096];
+
+  ssize_t size = ::recv(this->socket, buf, 4096, 0);
+  if (0 == size)
+    this->on_connection_close();
+  else if (-1 == static_cast<ssize_t>(size))
+    throw std::runtime_error("Error reading from socket");
+  else
+    {
+      this->in_buf += std::string(buf, size);
+      this->parse_in_buffer();
+    }
+}
+
+void SocketHandler::on_send()
+{
+  const ssize_t res = ::send(this->socket, this->out_buf.data(), this->out_buf.size(), 0);
+  if (res == -1)
+    {
+      perror("send");
+      this->close();
+    }
+  else
+    {
+      this->out_buf = this->out_buf.substr(res, std::string::npos);
+      if (this->out_buf.empty())
+        this->poller->stop_watching_send_events(this);
+    }
+}
+
+void SocketHandler::close()
+{
+  this->poller->remove_socket_handler(this->get_socket());
+  ::close(this->socket);
+}
+
+socket_t SocketHandler::get_socket() const
+{
+  return this->socket;
+}
+
+void SocketHandler::send_data(std::string&& data)
+{
+  this->out_buf += std::move(data);
+  if (!this->out_buf.empty())
+    {
+      this->poller->watch_send_events(this);
+    }
+}

src/network/socket_handler.hpp

@@ -1,6 +1,8 @@
 #ifndef SOCKET_HANDLER_INCLUDED
 # define SOCKET_HANDLER_INCLUDED
 
+#include <string>
+
 typedef int socket_t;
 
 class Poller;
@@ -14,34 +16,65 @@ class Poller;
 class SocketHandler
 {
 public:
-  explicit SocketHandler():
-    poller(nullptr)
-  {}
+  explicit SocketHandler();
+  virtual ~SocketHandler() {}
+  /**
+   * Connect to the remote server, and call on_connected() if this succeeds
+   */
+  void connect(const std::string& address, const std::string& port);
   /**
    * Set the pointer to the given Poller, to communicate with it.
    */
-  void set_poller(Poller* poller)
-  {
-    this->poller = poller;
-  };
+  void set_poller(Poller* poller);
   /**
-   * Happens when the socket is ready to be received from.
+   * Reads data in our in_buf and the call parse_in_buf, for the implementor
+   * to handle the data received so far.
    */
-  virtual void on_recv() = 0;
+  void on_recv();
   /**
-   * Happens when the socket is ready to be written to.
+   * Write as much data from out_buf as possible, in the socket.
    */
-  virtual void on_send() = 0;
+  void on_send();
+  /**
+   * Add the given data to out_buf and tell our poller that we want to be
+   * notified when a send event is ready.
+   */
+  void send_data(std::string&& data);
   /**
    * Returns the socket that should be handled by the poller.
    */
-  virtual socket_t get_socket() const = 0;
+  socket_t get_socket() const;
   /**
-   * Close the connection.
+   * Close the connection, remove us from the poller
    */
-  virtual void close() = 0;
+  void close();
+  /**
+   * Called when the connection is successful.
+   */
+  virtual void on_connected() = 0;
+  /**
+   * Called when we detect a disconnection from the remote host.
+   */
+  virtual void on_connection_close() = 0;
+  /**
+   * Handle/consume (some of) the data received so far. If some data is used, the in_buf
+   * should be truncated, only the unused data should be left untouched.
+   */
+  virtual void parse_in_buffer() = 0;
 
 protected:
+  socket_t socket;
+  /**
+   * Where data read from the socket is added, until we can parse a whole
+   * IRC message, the used data is then removed from that buffer.
+   *
+   * TODO: something more efficient than a string.
+   */
+  std::string in_buf;
+  /**
+   * Where data is added, when we want to send something to the client.
+   */
+  std::string out_buf;
   /**
    * A pointer to the poller that manages us, because we need to communicate
    * with it, sometimes (for example to tell it that he now needs to watch