/* Linux/glibc X11 capture adapter. Only preload into a leased Sunshine process.
 * Sunshine resolves XFixesGetCursorImage with dlsym(), so a plain symbol
 * interposer is insufficient. No system library or desktop theme is replaced.
 * ABI matches XFixesCursorImage from the Xorg Xfixes.h public header.
 */
#define _GNU_SOURCE
#include <stddef.h>
extern void *dlvsym(void *, const char *, const char *);
extern char *getenv(const char *);
extern int strcmp(const char *, const char *);
extern void abort(void);
extern int open(const char *, int, ...);
extern long write(int, const void *, unsigned long);
extern int close(int);
typedef struct {
    short x, y;
    unsigned short width, height, xhot, yhot;
    unsigned long serial;
    unsigned long *pixels;
    unsigned long atom;
    const char *name;
} CursorImage;
typedef void *(*Lookup)(void *, const char *);
typedef CursorImage *(*GetImage)(void *);
static GetImage real_image;

static CursorImage *capture_image(void *display) {
    GetImage fn = __atomic_load_n(&real_image, __ATOMIC_ACQUIRE);
    if (!fn) abort();
    CursorImage *image = fn(display);
    if (image && image->pixels) {
        unsigned long n = (unsigned long)image->width * image->height;
        if (n > 1048576) abort();
        for (unsigned long i = 0; i < n; ++i) image->pixels[i] = 0;
    }
    return image;
}

void *dlsym(void *handle, const char *name) {
    Lookup lookup = (Lookup)dlvsym((void *)-1L, "dlsym", "GLIBC_2.2.5");
    if (!lookup) abort();
    void *result = lookup(handle, name);
    if (result && getenv("VDI_CURSOR_LEASE") &&
            strcmp(name, "XFixesGetCursorImage") == 0) {
        __atomic_store_n(&real_image, (GetImage)result, __ATOMIC_RELEASE);
        const char *receipt = getenv("VDI_CURSOR_RECEIPT");
        if (receipt) {
            int fd = open(receipt, 0101 | 01000 | 02000000, 0600);
            if (fd >= 0) { write(fd, "xfixes-v1\n", 10); close(fd); }
        }
        return (void *)capture_image;
    }
    return result;
}