image.c: Parse header of image to determine supported format.

src/image.c

@@ -40,28 +40,35 @@ static twin_image_format_t image_type_from_name(const char *path)
     FILE *file = fopen(path, "rb");
 
     if (!file) {
-        perror("File opening failed");
+        perror("Failed to open %s");
         return IMAGE_TYPE_unknown;
     }
 
-    unsigned char header[8];
-    size_t bytesRead = fread(header, 1, sizeof(header), file);
+    uint8_t header[8];
+    size_t bytes_read = fread(header, 1, sizeof(header), file);
     fclose(file);
 
-    if (bytesRead < 8) {
+    if (bytes_read < 8) {
         return IMAGE_TYPE_unknown;
     }
 
 #if LOADER_HAS(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) {
+#if __BYTE_ORDER == __BIG_ENDIAN
+    uint8_t png_header[8] = {0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A};
+    if (memcmp(header, png_header, sizeof(png_header)) == 0) {
         type = IMAGE_TYPE_png;
     }
+#else
+    uint8_t png_header[8] = {0x0A, 0x1A, 0x0A, 0x0D, 0x47, 0x4E, 0x50, 0x89};
+    if (memcmp(header, png_header, sizeof(png_header)) == 0) {
+        type = IMAGE_TYPE_png;
+    }
+#endif
 #endif
 
 #if LOADER_HAS(JPEG)
-    else if (header[0] == 0xFF && header[1] == 0xD8 && header[2] == 0xFF) {
+    uint8_t jpg_header[3] = {0xFF, 0xD8, 0xFF};
+    if (memcmp(header, jpg_header, sizeof(jpg_header)) == 0) {
         type = IMAGE_TYPE_jpeg;
     }
 #endif