add netmgr functions to support outgoing DNS queries

- isc_nm_tcpdnsconnect() sets up up an outgoing TCP DNS connection.
- isc_nm_tcpconnect(), _udpconnect() and _tcpdnsconnect() now take a
  timeout argument to ensure connections time out and are correctly
  cleaned up on failure.
- isc_nm_read() now supports UDP; it reads a single datagram and then
  stops until the next time it's called.
- isc_nm_cancelread() now runs asynchronously to prevent assertion
  failure if reading is interrupted by a non-network thread (e.g.
  a timeout).
- isc_nm_cancelread() can now apply to UDP sockets.
- added shim code to support UDP connection in versions of libuv
  prior to 1.27, when uv_udp_connect() was added

all these functions will be used to support outgoing queries in dig,
xfrin, dispatch, etc.

lib/isc/netmgr/netmgr-int.h

@@ -135,8 +135,12 @@ struct isc_nmiface {
 };
 
 typedef enum isc__netievent_type {
+	netievent_udpconnect,
 	netievent_udpsend,
+	netievent_udpread,
 	netievent_udpstop,
+	netievent_udpcancel,
+	netievent_udpclose,
 
 	netievent_tcpconnect,
 	netievent_tcpsend,
@@ -145,9 +149,12 @@ typedef enum isc__netievent_type {
 	netievent_tcpchildaccept,
 	netievent_tcpaccept,
 	netievent_tcpstop,
+	netievent_tcpcancel,
 	netievent_tcpclose,
 
 	netievent_tcpdnssend,
+	netievent_tcpdnsread,
+	netievent_tcpdnscancel,
 	netievent_tcpdnsclose,
 	netievent_tcpdnsstop,
 
@@ -212,13 +219,16 @@ typedef struct isc__netievent__socket {
 } isc__netievent__socket_t;
 
 typedef isc__netievent__socket_t isc__netievent_udplisten_t;
+typedef isc__netievent__socket_t isc__netievent_udpread_t;
 typedef isc__netievent__socket_t isc__netievent_udpstop_t;
+typedef isc__netievent__socket_t isc__netievent_udpclose_t;
 typedef isc__netievent__socket_t isc__netievent_tcpstop_t;
 typedef isc__netievent__socket_t isc__netievent_tcpclose_t;
 typedef isc__netievent__socket_t isc__netievent_startread_t;
 typedef isc__netievent__socket_t isc__netievent_pauseread_t;
 typedef isc__netievent__socket_t isc__netievent_closecb_t;
 typedef isc__netievent__socket_t isc__netievent_tcpdnsclose_t;
+typedef isc__netievent__socket_t isc__netievent_tcpdnsread_t;
 typedef isc__netievent__socket_t isc__netievent_tcpdnsstop_t;
 
 typedef struct isc__netievent__socket_req {
@@ -227,6 +237,7 @@ typedef struct isc__netievent__socket_req {
 	isc__nm_uvreq_t *req;
 } isc__netievent__socket_req_t;
 
+typedef isc__netievent__socket_req_t isc__netievent_udpconnect_t;
 typedef isc__netievent__socket_req_t isc__netievent_tcpconnect_t;
 typedef isc__netievent__socket_req_t isc__netievent_tcplisten_t;
 typedef isc__netievent__socket_req_t isc__netievent_tcpsend_t;
@@ -248,6 +259,9 @@ typedef struct isc__netievent__socket_handle {
 	isc_nmhandle_t *handle;
 } isc__netievent__socket_handle_t;
 
+typedef isc__netievent__socket_handle_t isc__netievent_udpcancel_t;
+typedef isc__netievent__socket_handle_t isc__netievent_tcpcancel_t;
+typedef isc__netievent__socket_handle_t isc__netievent_tcpdnscancel_t;
 typedef isc__netievent__socket_handle_t isc__netievent_detach_t;
 
 typedef struct isc__netievent__socket_quota {
@@ -399,11 +413,14 @@ struct isc_nmsocket {
 	const isc_statscounter_t *statsindex;
 
 	/*%
-	 * TCP read timeout timer.
+	 * TCP read/connect timeout timers.
 	 */
 	uv_timer_t timer;
 	bool timer_initialized;
+	bool timer_running;
 	uint64_t read_timeout;
+	uint64_t connect_timeout;
+	bool timed_out;
 
 	/*% outer socket is for 'wrapped' sockets - e.g. tcpdns in tcp */
 	isc_nmsocket_t *outer;
@@ -452,6 +469,7 @@ struct isc_nmsocket {
 	atomic_bool closed;
 	atomic_bool listening;
 	atomic_bool listen_error;
+	atomic_bool connecting;
 	atomic_bool connected;
 	atomic_bool connect_error;
 	isc_refcount_t references;
@@ -506,9 +524,9 @@ struct isc_nmsocket {
 	isc_condition_t cond;
 
 	/*%
-	 * Used to pass a result back from TCP listening events.
+	 * Used to pass a result back from listen or connect events.
 	 */
-	isc_result_t result;
+	atomic_int_fast32_t result;
 
 	/*%
 	 * List of active handles.
@@ -551,6 +569,9 @@ struct isc_nmsocket {
 	isc_nm_recv_cb_t recv_cb;
 	void *recv_cbarg;
 
+	isc_nm_cb_t connect_cb;
+	void *connect_cbarg;
+
 	isc_nm_accept_cb_t accept_cb;
 	void *accept_cbarg;
 #ifdef NETMGR_TRACE
@@ -698,16 +719,41 @@ isc__nm_udp_send(isc_nmhandle_t *handle, isc_region_t *region, isc_nm_cb_t cb,
  * Back-end implementation of isc_nm_send() for UDP handles.
  */
 
+isc_result_t
+isc__nm_udp_read(isc_nmhandle_t *handle, isc_nm_recv_cb_t cb, void *cbarg);
+/*
+ * Back-end implementation of isc_nm_read() for UDP handles.
+ */
+
+void
+isc__nm_udp_close(isc_nmsocket_t *sock);
+/*%<
+ * Close a UDP socket.
+ */
+
+void
+isc__nm_udp_cancelread(isc_nmhandle_t *handle);
+/*%<
+ * Stop reading on a connected UDP handle.
+ */
+
 void
 isc__nm_udp_stoplistening(isc_nmsocket_t *sock);
 
 void
 isc__nm_async_udplisten(isc__networker_t *worker, isc__netievent_t *ev0);
-
+void
+isc__nm_async_udpconnect(isc__networker_t *worker, isc__netievent_t *ev0);
 void
 isc__nm_async_udpstop(isc__networker_t *worker, isc__netievent_t *ev0);
 void
 isc__nm_async_udpsend(isc__networker_t *worker, isc__netievent_t *ev0);
+void
+isc__nm_async_udpread(isc__networker_t *worker, isc__netievent_t *ev0);
+void
+isc__nm_async_udpcancel(isc__networker_t *worker, isc__netievent_t *ev0);
+void
+isc__nm_async_udpclose(isc__networker_t *worker, isc__netievent_t *ev0);
 /*%<
  * Callback handlers for asynchronous UDP events (listen, stoplisten, send).
  */
@@ -780,6 +826,8 @@ isc__nm_async_tcp_startread(isc__networker_t *worker, isc__netievent_t *ev0);
 void
 isc__nm_async_tcp_pauseread(isc__networker_t *worker, isc__netievent_t *ev0);
 void
+isc__nm_async_tcpcancel(isc__networker_t *worker, isc__netievent_t *ev0);
+void
 isc__nm_async_tcpclose(isc__networker_t *worker, isc__netievent_t *ev0);
 /*%<
  * Callback handlers for asynchronous TCP events (connect, listen,
@@ -802,6 +850,8 @@ isc__nm_tcpdns_close(isc_nmsocket_t *sock);
 void
 isc__nm_tcpdns_stoplistening(isc_nmsocket_t *sock);
 
+void
+isc__nm_async_tcpdnscancel(isc__networker_t *worker, isc__netievent_t *ev0);
 void
 isc__nm_async_tcpdnsclose(isc__networker_t *worker, isc__netievent_t *ev0);
 void
@@ -809,6 +859,18 @@ isc__nm_async_tcpdnssend(isc__networker_t *worker, isc__netievent_t *ev0);
 void
 isc__nm_async_tcpdnsstop(isc__networker_t *worker, isc__netievent_t *ev0);
 
+void
+isc__nm_async_tcpdnsread(isc__networker_t *worker, isc__netievent_t *ev0);
+
+isc_result_t
+isc__nm_tcpdns_read(isc_nmhandle_t *handle, isc_nm_recv_cb_t cb, void *cbarg);
+
+void
+isc__nm_tcpdns_cancelread(isc_nmhandle_t *handle);
+/*%<
+ * Stop reading on a connected TCPDNS handle.
+ */
+
 #define isc__nm_uverr2result(x) \
 	isc___nm_uverr2result(x, true, __FILE__, __LINE__)
 isc_result_t