I am trying to get the window owner names via CGWindowListCopyWindowInfo in Rust. So far I have managed to get the CFDictionaryRef but I am unable to use the right pointers for CFDictionaryGetValueIfPresent.
This is the method signature: https://docs.rs/CoreFoundation-sys/0.1.4/CoreFoundation_sys/dictionary/fn.CFDictionaryGetValueIfPresent.html
const options: CGWindowListOption = kCGWindowListOptionOnScreenOnly + kCGWindowListExcludeDesktopElements;
const ptr_window_list_info: CFArrayRef = unsafe { CGWindowListCopyWindowInfo(options, kCGNullWindowID) as CFArrayRef };
const count = unsafe { CFArrayGetCount(ptr_window_list_info) };
for i in 0..count-1 {
let dic_ref = CFArrayGetValueAtIndex(ptr_window_list_info, i) as CFDictionaryRef;
//let key = CFString::new("kCGWindowOwnerName");
let b = CFDictionaryGetValueIfPresent(dic_ref, ?, ?);
println!("window owner name: {}", value);
}
I am new to Rust and would appreciate any help.
CFDictionaryGetValueIfPresent
looks like this:
Boolean CFDictionaryGetValueIfPresent(CFDictionaryRef theDict, const void *key, const void **value);
In core_foundation, it looks like this:
pub unsafe extern "C" fn CFDictionaryGetValueIfPresent(
theDict: CFDictionaryRef,
key: *const c_void,
value: *mut *const c_void
) -> Boolean
I believe the key wants to be CFStringRef
; in C there is a macro to make that easier (CFSTR("cstring")
), here we must use a slightly longer form:
let c_key = CString::new("kCGWindowOwnerName").unwrap();
let cf_key = unsafe {
CFStringCreateWithCString(std::ptr::null(), c_key.as_ptr(), kCFStringEncodingUTF8)
};
That gives us CFStringRef
, in core_foundation it's defined like this:
pub type CFStringRef = *const __CFString;
It's already a *const
pointer, just not the type we need. You can transmute to c_void
instead:
let key_ptr: *const c_void = unsafe { std::mem::transmute(cf_key) };
The value argument just wants a raw double pointer to store the result. Create a null pointer:
let mut value: *const c_void = std::ptr::null();
And pass a mutable reference to it (&mut value
) to get *mut *const c_void
.
There are a few mistakes and oddities in your rust code. Here is a commented, working example:
use core_graphics::display::*;
use core_foundation::string::*;
use std::ffi::{ CStr, CString, c_void };
fn main() {
// CGWindowListOption is a bitmask, combine the flags with bitwise OR
const OPTIONS: CGWindowListOption = kCGWindowListOptionOnScreenOnly | kCGWindowListExcludeDesktopElements;
// No need to specify the type or use 'as'; CFArrayRef is the return type from CGWindowListCopyWindowInfo
let window_list_info = unsafe { CGWindowListCopyWindowInfo(OPTIONS, kCGNullWindowID) };
// Don't use const here, CFArrayGetCount returns CFIndex (long)
let count: i64 = unsafe { CFArrayGetCount(window_list_info) };
for i in 0..count-1 {
// Here we need the 'as', CFArrayGetValueAtIndex just returns void*
let dic_ref = unsafe { CFArrayGetValueAtIndex(window_list_info, i) as CFDictionaryRef };
// Create a CString from the key name we are interested in
let c_key = CString::new("kCGWindowOwnerName").unwrap();
// Create a CFString, needs to be released with `CFRelease`. I leave that as an exercise for the reader.
let cf_key = unsafe { CFStringCreateWithCString(std::ptr::null(), c_key.as_ptr(), kCFStringEncodingUTF8) };
// cf_key is a CFStringRef, which is a type alias to *const __CFString
// We transmute it into *const c_void since that is what CFDictionaryGetValueIfPresent wants
let key_ptr: *const c_void = unsafe { std::mem::transmute(cf_key) };
// A raw void* to hold the result
let mut value: *const c_void = std::ptr::null();
if unsafe { CFDictionaryGetValueIfPresent(dic_ref, key_ptr, &mut value) != 0 } {
// CFDictionaryGetValueIfPresent returned true; that means value must point to a CFStringRef
let cf_ref = value as core_foundation::string::CFStringRef;
// Get a pointer to a C-string buffer with the characters from the CFString
let c_ptr = unsafe { CFStringGetCStringPtr(cf_ref, kCFStringEncodingUTF8) };
// The value may be null; don't pass it to CStr::from_ptr
if c_ptr.is_null() { continue; }
// Wrap the pointer in a rust CStr so we can convert a str
let c_value = unsafe { CStr::from_ptr(c_ptr) };
println!("{}", c_value.to_str().unwrap());
}
}
}
For reference, here is the same example in C:
#import <Foundation/Foundation.h>
#import <CoreGraphics/CoreGraphics.h>
int main(int argc, const char * argv[]) {
@autoreleasepool {
CGWindowListOption options = kCGWindowListOptionOnScreenOnly | kCGWindowListExcludeDesktopElements;
CFArrayRef windows = CGWindowListCopyWindowInfo(options, kCGNullWindowID);
CFIndex count = CFArrayGetCount(windows);
for (int i = 0; i < count; i++)
{
CFDictionaryRef windowDict = CFArrayGetValueAtIndex(windows, i);
CFStringRef key = CFStringCreateWithCString(NULL, "kCGWindowOwnerName", kCFStringEncodingUTF8);
const void* value = nil;
if (CFDictionaryGetValueIfPresent(windowDict, key, &value) == YES)
{
const char* c_value = CFStringGetCStringPtr(value, kCFStringEncodingUTF8);
NSLog(@"window: %s", c_value);
}
CFRelease(key);
}
}
return 0;
}
Disclaimer I am also relatively new to rust and this may not be the idiomatic solution