texture: Implement my own stupid header validation because libpngs dumb one doesnt work for some got dang reason

gosh

src/texture.cc

@@ -9,6 +9,11 @@
 #include <string>
 #include <unordered_map>
 
+#include <format>
+#include <numeric>
+
+#define PNG_HEADER_BYTES_TO_CHECK 8
+
 TextureLoader *TextureLoader::m_instance = NULL;
 
 TextureLoader *TextureLoader::get_instance() {
@@ -39,6 +44,24 @@ Texture *TextureLoader::load_texture(const std::string &path) {
   return m_texture_cache.at(path);
 }
 
+// FIXME: Figure out why png_sig_cmp never worked and replace this garbage
+static bool validate_png_sig(
+    const std::array<std::uint8_t, PNG_HEADER_BYTES_TO_CHECK> &bytes) {
+  std::array<std::uint8_t, 8> valid_header = {0x89, 0x50, 0x4e, 0x47,
+                                              0x0d, 0x0a, 0x1a, 0x0a};
+
+  for (size_t i = 0; i < PNG_HEADER_BYTES_TO_CHECK; i++) {
+    if (bytes[i] != valid_header[i]) {
+      spdlog::error(
+          "Byte header mismatch at position {} expected {:x} got {:x}", i,
+          valid_header[i], bytes[i]);
+      return false;
+    }
+  }
+
+  return true;
+}
+
 Texture::Texture(const std::string &path) {
   png_uint_32 width = 0, height = 0;
   int interlace_type = 0, bit_depth = 0, color_type = 0;
@@ -54,20 +77,37 @@ Texture::Texture(const std::string &path) {
     throw std::exception();
   }
 
-  png_byte header[4] = {0};
+  std::array<std::uint8_t, PNG_HEADER_BYTES_TO_CHECK> header;
 
-  fread(header, 1, 4, fp);
+  fread(header.data(), 1, PNG_HEADER_BYTES_TO_CHECK, fp);
 
   // I'm not sure why this cast has to be there but clangd doesn't like it not
   // being there...
   // FIXME: for some reason, this fails.
-  /*
-  if (!png_sig_cmp(header, 0, 4)) {
+  if (!validate_png_sig(header)) {
     spdlog::error("Texture file {} does not appear to be a png file.", path);
 
+    std::vector<unsigned char> v;
+
+    for (size_t i = 0; i < PNG_HEADER_BYTES_TO_CHECK; i++) {
+      v.emplace_back(header[i]);
+    }
+
+    auto begin = v.begin();
+    auto end = v.end();
+
+    std::string s = "";
+
+    s = std::accumulate(begin, end, s,
+                        [](std::string result, unsigned char value) {
+                          result += std::format("{:02x}", value);
+                          return result;
+                        });
+
+    spdlog::error("Bytes: {}", s);
+
     throw std::exception();
   }
-  */
 
   png_structp png_ptr =
       png_create_read_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
@@ -77,7 +117,7 @@ Texture::Texture(const std::string &path) {
   setjmp(png_jmpbuf(png_ptr));
 
   png_init_io(png_ptr, fp);
-  png_set_sig_bytes(png_ptr, 4);
+  png_set_sig_bytes(png_ptr, PNG_HEADER_BYTES_TO_CHECK);
 
   png_read_png(png_ptr, info_ptr,
                PNG_TRANSFORM_STRIP_16 | PNG_TRANSFORM_PACKING |