X11: Check if XRRGetOutputInfo returned NULL (#709)

* X11: Check if XRRGetOutputInfo returned NULL

Fixes #693

* Change X11 error logging to actually use log

CHANGELOG.md

@@ -5,6 +5,7 @@
 - On Windows, catch panics in event loop child thread and forward them to the parent thread. This prevents an invocation of undefined behavior due to unwinding into foreign code.
 - On Windows, fix issue where resizing or moving window combined with grabbing the cursor would freeze program.
 - On Windows, fix issue where resizing or moving window would eat `Awakened` events.
+- On X11, fixed a segfault when using virtual monitors with XRandR.
 
 # Version 0.18.0 (2018-11-07)
 

src/platform/linux/mod.rs

@@ -382,7 +382,7 @@ unsafe extern "C" fn x_error_callback(
             minor_code: (*event).minor_code,
         };
 
-        eprintln!("[winit X11 error] {:#?}", error);
+        error!("X11 error: {:#?}", error);
 
         *xconn.latest_error.lock() = Some(error);
     }

src/platform/linux/x11/monitor.rs

@@ -65,11 +65,11 @@ impl MonitorId {
         id: u32,
         repr: util::MonitorRepr,
         primary: bool,
-    ) -> Self {
+    ) -> Option<Self> {
-        let (name, hidpi_factor) = unsafe { xconn.get_output_info(resources, &repr) };
+        let (name, hidpi_factor) = unsafe { xconn.get_output_info(resources, &repr)? };
         let (dimensions, position) = unsafe { (repr.get_dimensions(), repr.get_position()) };
         let rect = util::AaRect::new(position, dimensions);
-        MonitorId {
+        Some(MonitorId {
             id,
             name,
             hidpi_factor,
@@ -77,7 +77,7 @@ impl MonitorId {
             position,
             primary,
             rect,
-        }
+        })
     }
 
     pub fn get_name(&self) -> Option<String> {
@@ -153,13 +153,13 @@ impl XConnection {
                     let monitor = monitors.offset(monitor_index as isize);
                     let is_primary = (*monitor).primary != 0;
                     has_primary |= is_primary;
-                    available.push(MonitorId::from_repr(
+                    MonitorId::from_repr(
                         self,
                         resources,
                         monitor_index as u32,
                         monitor.into(),
                         is_primary,
-                    ));
+                    ).map(|monitor_id| available.push(monitor_id));
                 }
                 (xrandr_1_5.XRRFreeMonitors)(monitors);
             } else {
@@ -176,13 +176,13 @@ impl XConnection {
                         let crtc = util::MonitorRepr::from(crtc);
                         let is_primary = crtc.get_output() == primary;
                         has_primary |= is_primary;
-                        available.push(MonitorId::from_repr(
+                        MonitorId::from_repr(
                             self,
                             resources,
                             crtc_id as u32,
                             crtc,
                             is_primary,
-                        ));
+                        ).map(|monitor_id| available.push(monitor_id));
                     }
                     (self.xrandr.XRRFreeCrtcInfo)(crtc);
                 }

src/platform/linux/x11/util/randr.rs

@@ -79,12 +79,23 @@ impl From<*mut ffi::XRRCrtcInfo> for MonitorRepr {
 }
 
 impl XConnection {
-    pub unsafe fn get_output_info(&self, resources: *mut ffi::XRRScreenResources, repr: &MonitorRepr) -> (String, f64) {
+    pub unsafe fn get_output_info(
+        &self,
+        resources: *mut ffi::XRRScreenResources,
+        repr: &MonitorRepr,
+    ) -> Option<(String, f64)> {
         let output_info = (self.xrandr.XRRGetOutputInfo)(
             self.display,
             resources,
             repr.get_output(),
         );
+        if output_info.is_null() {
+            // When calling `XRRGetOutputInfo` on a virtual monitor (versus a physical display)
+            // it's possible for it to return null.
+            // https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=816596
+            let _ = self.check_errors(); // discard `BadRROutput` error
+            return None;
+        }
         let name_slice = slice::from_raw_parts(
             (*output_info).name as *mut u8,
             (*output_info).nameLen as usize,
@@ -95,6 +106,6 @@ impl XConnection {
             ((*output_info).mm_width as u64, (*output_info).mm_height as u64),
         );
         (self.xrandr.XRRFreeOutputInfo)(output_info);
-        (name, hidpi_factor)
+        Some((name, hidpi_factor))
     }
 }