MEDIUM: connection: add an ->init function to data layer

SSL need to initialize the data layer before proceeding with data. At
the moment, this data layer is automatically initialized from itself,
which will not be possible once we extract connection from sessions
since we'll only create the data layer once the handshake is finished.

So let's have the application layer initialize the data layer before
using it.

include/proto/connection.h

@@ -30,6 +30,16 @@
  */
 int conn_fd_handler(int fd);
 
+/* calls the init() function of the data layer if any. Returns <0 in case of
+ * error.
+ */
+static inline int conn_data_init(struct connection *conn)
+{
+	if (conn->data && conn->data->init)
+		return conn->data->init(conn);
+	return 0;
+}
+
 /* Calls the close() function of the data layer if any */
 static inline void conn_data_close(struct connection *conn)
 {

include/types/connection.h

@@ -143,6 +143,7 @@ struct data_ops {
 	void (*shutr)(struct connection *, int);    /* shutr function */
 	void (*shutw)(struct connection *, int);    /* shutw function */
 	void (*close)(struct connection *);         /* close the data channel on the connection */
+	int  (*init)(struct connection *conn);      /* initialize the data layer */
 };
 
 /* app_cb describes read and write callbacks which are called upon detected I/O

src/proto_tcp.c

@@ -458,6 +458,10 @@ int tcp_connect_server(struct connection *conn, int data)
 	fdtab[fd].iocb = conn_fd_handler;
 	fd_insert(fd);
 	conn_sock_want_send(conn);  /* for connect status */
+
+	if (conn_data_init(conn) < 0)
+		return SN_ERR_RESOURCE;
+
 	if (data)
 		conn_data_want_send(conn);  /* prepare to send data if any */
 

src/session.c

@@ -278,6 +278,8 @@ int session_accept(struct listener *l, int cfd, struct sockaddr_storage *addr)
 	fdtab[cfd].flags = 0;
 	fdtab[cfd].iocb = conn_fd_handler;
 	conn_data_want_recv(&s->si[0].conn);
+	if (conn_data_init(&s->si[0].conn) < 0)
+		goto out_free_rep;
 
 	if (p->accept && (ret = p->accept(s)) <= 0) {
 		/* Either we had an unrecoverable error (<0) or work is