Improve XLib-XInput error handling

xdg/xinput_devnodes/Makefile

@@ -1,5 +0,0 @@
-main: main.c
-	$(CC) -O2 --std=gnu99 -pedantic -Wall main.c xslaves.c devnodes.c -o devnodes -lX11 -lXi
-clean:
-	rm -f devnodes
-

xdg/xinput_devnodes/devnodes.c

@@ -1,13 +1,11 @@
 /*
- * Loosely based on a mix of:
+* Loosely based on a mix of:
- *   - xorg-xinput
+*   - xorg-xinput
- *     https://github.com/freedesktop/xorg-xinput/blob/master/src/property.c::print_property_xi2
+*     https://github.com/freedesktop/xorg-xinput/blob/master/src/property.c::print_property_xi2
- *   - xkbcat
+*   - xkbcat
- *     https://github.com/anko/xkbcat
+*     https://github.com/anko/xkbcat
 */
 
-#define _GNU_SOURCE
-
 #include "devnodes.h"
 
 #include <stdlib.h>
@@ -18,6 +16,7 @@
 
 #include <X11/extensions/XInput2.h>
 #include <X11/Xatom.h>
+#include <X11/Xlib.h>
 
 
 char* get_property_xi2(Display* dpy, int deviceid, Atom property, const char* property_name)
@@ -93,8 +92,8 @@ XSlaves* build_slave_info(Display* disp)
             char* devnode = get_property_xi2(disp, current_slave->deviceid, props[nprops], "Device Node");
             if (current_slave->name != NULL && devnode != NULL)
             {
-                int success = add_slaveinfo(slaves, current_slave->name, devnode);
+                int err = add_slaveinfo(slaves, current_slave->name, devnode);
-                if (success != 0)
+                if (err)
                     fail = true;
             }
             free(devnode);
@@ -103,6 +102,7 @@ XSlaves* build_slave_info(Display* disp)
         if (fail)
         {
             free_xslaves(slaves);
+            slaves = NULL;
             break;
         }
 
@@ -116,73 +116,48 @@ int is_xinput2_available(Display* disp)
     int xiOpcode;
     int queryEvent, queryError;
     if (! XQueryExtension(disp, "XInputExtension", &xiOpcode, &queryEvent, &queryError))
-    {
+        return XINPUTEXTUNAVAIL;
-        fprintf(stderr, "XInput extension not available\n");
-        return -1;
-    }
 
     int major = 2, minor = 0;
     int queryResult = XIQueryVersion(disp, &major, &minor);
     if (queryResult == BadRequest)
-    {
+        return XINPUT20UNAVAIL;
-        fprintf(stderr, "XInput 2.0 support required (got %d.%d)\n", major, minor);
-        return -2;
-    }
     else if (queryResult != Success)
-    {
+        return XINPUTQUERYVERSIONFAILED;
-        fprintf(stderr, "XIQueryVersion failed\n");
-        return -3;
-    }
 
     return 0;
 }
 
-Display* connect_to_x(const char* xDisplayName)
+Display* connect_to_x(const char* xDisplayName, int* error)
 {
     Display* disp = XOpenDisplay(xDisplayName);
-    if (NULL == disp)
+    if (disp == NULL)
     {
-        fprintf(stderr, "Cannot open X display '%s'\n", xDisplayName);
+        *error = BADDISPLAY;
         return NULL;
     }
 
-    if (is_xinput2_available(disp) != 0)
+    int err = is_xinput2_available(disp);
+    if (err)
     {
         XCloseDisplay(disp);
+        *error = err;
         return NULL;
     }
 
     return disp;
 }
 
-XSlaves* get_slave_info()
+XSlaves* get_slave_info(const char* xDisplayName, int* error)
 {
-    char* xDisplayName = getenv("DISPLAY");
+    Display* disp = connect_to_x(xDisplayName, error);
-    if (xDisplayName == NULL)
+    if (*error)
-    {
+        return NULL;
-        fprintf(stderr, "DISPLAY environment variable not found\n");
-        exit(1);
-    }
-
-    Display* disp = connect_to_x(xDisplayName);
-    if (disp == NULL)
-        exit(1);
 
     XSlaves* s = build_slave_info(disp);
+    if (s == NULL)
+        *error = XSLAVEINFOQUERYFAILED;
+
     XCloseDisplay(disp);
     return s;
 }
-
-
-// int main(int argc, char * argv[])
-// {
-//     XSlaves* s = get_slave_info();
-//     for (int i = 0; i < s->length; i++)
-//     {
-//         XSlaveInfo si = s->slaves[i];
-//         printf("Name: %s\n", si.name);
-//         printf("Node: %s\n", si.dev_node);
-//         printf("\n");
-//     }
-//     free_xslaves(s);
-// }

xdg/xinput_devnodes/devnodes.h

@@ -3,4 +3,11 @@
 #include "xslaves.h"
 
 
-XSlaves* get_slave_info();
+#define BADDISPLAY -3
+#define XINPUTEXTUNAVAIL -4
+#define XINPUT20UNAVAIL -5
+#define XINPUTQUERYVERSIONFAILED -6
+#define XSLAVEINFOQUERYFAILED -7
+
+
+XSlaves* get_slave_info(const char* xDisplayName, int* error);

xdg/xinput_devnodes/main.c

@@ -1,16 +0,0 @@
-#include "devnodes.h"
-#include "xslaves.h"
-
-#include <stdio.h>
-
-
-int main(int argc, char** argv) {
-    XSlaves* xs = get_slave_info();
-    for (int i=0; i < xs->length; i++)
-    {
-        XSlaveInfo si = xs->slaves[i];
-        printf("%s = %s\n", si.name, si.dev_node);
-    }
-
-    free_xslaves(xs);
-}

xdg/xinput_devnodes/xinput_devnodes.go

@@ -10,6 +10,8 @@ import (
 	"fmt"
 	"unsafe"
 	"regexp"
+	"errors"
+	"os"
 )
 
 
@@ -39,7 +41,15 @@ func Print() {
 
 
 func GetXSlaveInfo() ([]C.XSlaveInfo, func()) {
-	xslaves := C.get_slave_info()
+	xDisplayName := C.CString(tryGetXDisplay())
+	defer C.free(unsafe.Pointer(xDisplayName))
+
+	var error C.int
+	xslaves := C.get_slave_info(xDisplayName, &error)
+	if (error != C.int(0)) {
+		panic(convertErrorIntToGoError(error))
+	}
+
 	arr := (*[1 << 30]C.XSlaveInfo)(unsafe.Pointer(xslaves.slaves))
 	slice := arr[:xslaves.length:xslaves.length]
 	freeMethod := func() {
@@ -49,3 +59,33 @@ func GetXSlaveInfo() ([]C.XSlaveInfo, func()) {
 	return slice, freeMethod
 }
 
+func tryGetXDisplay() string {
+	display := os.Getenv("DISPLAY")
+	if display == "" {
+		panic(errors.New("DISPLAY envvar not set"))
+	}
+	return display
+}
+
+func convertErrorIntToGoError(err C.int) error {
+	errorMsg := ""
+	switch err {
+	case C.MALLOCFAIL:
+		errorMsg = "Memory allocation failed"
+	case C.XSLAVESFULL:
+		errorMsg = "XSlaves full"
+	case C.BADDISPLAY:
+		errorMsg = "Failed to open X display"
+	case C.XINPUTEXTUNAVAIL:
+		errorMsg = "XInput extension unavailable"
+	case C.XINPUT20UNAVAIL:
+		errorMsg = "XInput extension is not 2.0"
+	case C.XINPUTQUERYVERSIONFAILED:
+		errorMsg = "Failed to query XInput extension version"
+	case C.XSLAVEINFOQUERYFAILED:
+		errorMsg = "Failed to query XInput slaves"
+	default:
+		errorMsg = fmt.Sprintf("Unknown error from devnodes.h: %v", err)
+	}
+	return errors.New(errorMsg)
+}

xdg/xinput_devnodes/xslaves.c

@@ -45,11 +45,18 @@ int add_slaveinfo(XSlaves* slaves, char* name, char* dev_node)
     XSlaveInfo si = new_slave_info();
     si.name = strdup(name);
     si.dev_node = strdup(dev_node);
+    if (si.name == NULL || si.dev_node == NULL)
+    {
+        free(si.name);
+        free(si.dev_node);
+        return MALLOCFAIL;
+    }
+
     if (slaves->length < slaves->capacity)
     {
         slaves->slaves[slaves->length] = si;
         slaves->length++;
         return 0;
     }
-    return -1;
+    return XSLAVESFULL;
 }

xdg/xinput_devnodes/xslaves.h

@@ -3,6 +3,10 @@
 #include <stddef.h>
 
 
+#define MALLOCFAIL -1
+#define XSLAVESFULL -2
+
+
 typedef struct XSlaveInfo
 {
     char* name;