Using header of image to determine supported format

src/image.c

@@ -37,21 +37,36 @@ typedef enum {
 static twin_image_format_t image_type_from_name(const char *path)
 {
     twin_image_format_t type = IMAGE_TYPE_unknown;
-    const char *extname = strrchr(path, '.');
-    if (!extname)
+    FILE *file = fopen(path, "rb");
+
+    if (!file) {
+        perror("File opening failed");
+        return IMAGE_TYPE_unknown;
+    }
+
+    unsigned char header[8];
+    size_t bytesRead = fread(header, 1, sizeof(header), file);
+    fclose(file);
+
+    if (bytesRead < 8) {
         return IMAGE_TYPE_unknown;
+    }
+
 #if LOADER_HAS(PNG)
-    else if (!strcasecmp(extname, ".png")) {
+    if (header[0] == 0x89 && header[1] == 0x50 && header[2] == 0x4E &&
+        header[3] == 0x47 && header[4] == 0x0D && header[5] == 0x0A &&
+        header[6] == 0x1A && header[7] == 0x0A) {
         type = IMAGE_TYPE_png;
     }
 #endif
+
 #if LOADER_HAS(JPEG)
-    else if (!strcasecmp(extname, ".jpg") || !strcasecmp(extname, ".jpeg")) {
+    else if (header[0] == 0xFF && header[1] == 0xD8 && header[2] == 0xFF) {
         type = IMAGE_TYPE_jpeg;
     }
 #endif
-    /* otherwise, unsupported format */
 
+    /* otherwise, unsupported format */
     return type;
 }