input: survive controlling-terminal/pty hangup on stdin

Since the 0.16.13 callback/poll rework, an EPOLLERR on stdin (controlling
terminal or pty hangup) reaches Poll::process(), which aborts the whole
client with an internal_error because InputEvent never registered for error
events:

    Poll::process() received error event for event not in error: input-fd:0

Register stdin for error events (insert_error) and handle event_error() by
dropping stdin from the poll set with this_thread::poll()->remove_and_close().
rtorrent then keeps running without keyboard input instead of dying.

remove() guards on the fd state (is_open()), mirroring SCgiTask: event_error()
clears the fd after remove_and_close(), and the shutdown path (Control::cleanup)
still calls remove(); without the guard the second remove_and_close() throws
'event not found' via event_mask(). insert()/remove() take the thread poll
implicitly (this_thread::poll()) instead of a Poll* argument.

src/control.cc

@@ -76,7 +76,7 @@ Control::initialize() {
   m_ui->init(this);
 
   if(!display::Canvas::daemon())
-    m_inputStdin->insert(torrent::this_thread::poll());
+    m_inputStdin->insert();
 }
 
 void
@@ -86,7 +86,7 @@ Control::cleanup() {
   torrent::this_thread::scheduler()->erase(&m_task_shutdown);
 
   if(!display::Canvas::daemon())
-    m_inputStdin->remove(torrent::this_thread::poll());
+    m_inputStdin->remove();
 
   if (scgi_thread::thread()->is_active())
     scgi_thread::thread()->stop_thread_wait();

src/input/input_event.cc

@@ -2,20 +2,34 @@
 
 #include "input_event.h"
 
+#include <torrent/common.h>
+#include <torrent/system/poll.h>
+
 #include "display/attributes.h"
 
 namespace input {
 
 void
-InputEvent::insert(torrent::system::Poll* p) {
-  p->open(this);
-  p->insert_read(this);
+InputEvent::insert() {
+  torrent::this_thread::poll()->open(this);
+  torrent::this_thread::poll()->insert_read(this);
+  // EPOLLERR/EPOLLHUP is always delivered by epoll regardless of registration;
+  // register for it so a controlling-terminal/pty hangup on stdin is dispatched
+  // to event_error() instead of aborting the whole client (see event_error()).
+  torrent::this_thread::poll()->insert_error(this);
 }
 
 void
-InputEvent::remove(torrent::system::Poll* p) {
-  p->remove_read(this);
-  p->close(this);
+InputEvent::remove() {
+  // The file descriptor doubles as the open-state guard, mirroring SCgiTask.
+  // event_error() may already have dropped stdin from the poll set and cleared
+  // the fd; the shutdown path (Control::cleanup) still calls remove(), and a
+  // second remove_and_close() would throw "event not found" via event_mask().
+  if (!is_open())
+    return;
+
+  torrent::this_thread::poll()->remove_and_close(this);
+  set_file_descriptor(-1);
 }
 
 void
@@ -32,6 +46,14 @@ InputEvent::event_write() {
 
 void
 InputEvent::event_error() {
+  // The controlling terminal/pty hung up (EPOLLERR on stdin). Drop stdin from
+  // the poll set instead of letting Poll::process() throw an internal_error and
+  // kill the client -- a regression introduced with the 0.16.13 callback/poll
+  // rework. rtorrent keeps running with no keyboard input. Once removed the
+  // event is out of the poll table, so no further event_error() is dispatched
+  // to it; clearing the fd lets the shutdown remove() no-op.
+  torrent::this_thread::poll()->remove_and_close(this);
+  set_file_descriptor(-1);
 }
 
 }

src/input/input_event.h

@@ -4,7 +4,6 @@
 #include <functional>
 
 #include <torrent/event.h>
-#include <torrent/system/poll.h>
 
 namespace input {
 
@@ -16,8 +15,8 @@ public:
 
   const char*         type_name() const override { return "input"; }
 
-  void                insert(torrent::system::Poll* p);
-  void                remove(torrent::system::Poll* p);
+  void                insert();
+  void                remove();
 
   void                event_read() override;
   void                event_write() override;