{"record":{"id":"6862a3d147e073e2","repo":"Yalantis/uCrop","slug":"load-png-encountered-unknown-fatal-error-in-lib","errorCode":null,"errorMessage":"load_png(): Encountered unknown fatal error in libpng for file '%s'.","messagePattern":"load_png\\(\\): Encountered unknown fatal error in libpng for file '(.+?)'\\.","errorType":"exception","errorClass":"CImgIOException","httpStatus":null,"severity":"error","filePath":"ucrop/src/main/jni/CImg.h","lineNumber":57426,"sourceCode":"                              \"load_png(): Failed to initialize 'info_ptr' structure for file '%s'.\",\n                              cimg_instance,\n                              nfilename?nfilename:\"(FILE*)\");\n      }\n      png_infop end_info = png_create_info_struct(png_ptr);\n      if (!end_info) {\n        if (!file) cimg::fclose(nfile);\n        png_destroy_read_struct(&png_ptr,&info_ptr,(png_infopp)0);\n        throw CImgIOException(_cimg_instance\n                              \"load_png(): Failed to initialize 'end_info' structure for file '%s'.\",\n                              cimg_instance,\n                              nfilename?nfilename:\"(FILE*)\");\n      }\n\n      // Error handling callback for png file reading.\n      if (setjmp(png_jmpbuf(png_ptr))) {\n        if (!file) cimg::fclose((std::FILE*)nfile);\n        png_destroy_read_struct(&png_ptr, &end_info, (png_infopp)0);\n        throw CImgIOException(_cimg_instance\n                              \"load_png(): Encountered unknown fatal error in libpng for file '%s'.\",\n                              cimg_instance,\n                              nfilename?nfilename:\"(FILE*)\");\n      }\n      png_init_io(png_ptr, nfile);\n      png_set_sig_bytes(png_ptr, 8);\n\n      // Get PNG Header Info up to data block.\n      png_read_info(png_ptr,info_ptr);\n      png_uint_32 W, H;\n      int bit_depth, color_type, interlace_type;\n      bool is_gray = false;\n      png_get_IHDR(png_ptr,info_ptr,&W,&H,&bit_depth,&color_type,&interlace_type,(int*)0,(int*)0);\n      png_set_interlace_handling(png_ptr);\n      if (bits_per_value) *bits_per_value = (unsigned int)bit_depth;\n\n      // Transforms to unify image data.\n      if (color_type==PNG_COLOR_TYPE_PALETTE) {","sourceCodeStart":57408,"sourceCodeEnd":57444,"githubUrl":"https://github.com/Yalantis/uCrop/blob/f788b534b48c144edf786c8cddbf0e029e637804/ucrop/src/main/jni/CImg.h#L57408-L57444","documentation":"libpng uses setjmp/longjmp error handling: any fatal libpng error during decoding (corrupt data, bad chunk, I/O failure) jumps back to this jmpbuf, and CImg throws CImgIOException reporting an 'unknown fatal error'. The underlying detail is only available via libpng's error callback, which CImg sets to none here.","triggerScenarios":"Any libpng error after the jmpbuf is set: corrupt/truncated PNG data, invalid chunk or CRC mismatch, unexpected end of file, or a read failure on the underlying FILE* during load_png().","commonSituations":"Partially downloaded/truncated PNG files, bit-corrupted images on disk, PNGs with malformed chunks, storage/SD-card read errors, or files produced by broken encoders.","solutions":["Validate the image with another tool (magick identify, a browser) to confirm corruption.","Re-obtain the file from its source; a truncated/corrupt file cannot be repaired by CImg.","Configure a libpng custom error function to get the real error message (or temporarily enable libpng's default stderr handler).","If the source is network storage, verify integrity (checksum) and re-download."],"exampleFix":"// before\nimg.load_png(path); // opaque 'unknown fatal error' on corrupt file\n// after\nstd::FILE *f = std::fopen(path, \"rb\");\nif (f) { std::fseek(f,0,SEEK_END); long n = std::ftell(f); std::fclose(f);\n         if (n < 33) throw std::runtime_error(\"PNG truncated\"); }\nimg.load_png(path);","handlingStrategy":"try-catch","validationCode":"bool plausiblePng(const char *p) {\n  unsigned char s[8] = {}; std::FILE *f = std::fopen(p,\"rb\");\n  if (!f) return false;\n  size_t n = std::fread(s,1,8,f); std::fclose(f);\n  return n==8 && std::memcmp(s,\"\\x89PNG\\r\\n\\x1a\\n\",8)==0;\n}","typeGuard":null,"tryCatchPattern":"try { img.load_png(path); }\ncatch (CImgIOException &e) {\n  std::fprintf(stderr, \"PNG decode failed for %s; verify/re-download file\\n\", path);\n  img.assign(); // leave image in empty, safe state\n}","preventionTips":["Checksum or size-verify files after transfer before decoding","Sniff the PNG signature before format-specific loads","Keep backups of original images; corrupted files are unrecoverable via this API"],"tags":["cimg","libpng","corrupt-file","decoding"],"backgroundTag":"file-read-failed","analyzedSha":"f788b534b48c144edf786c8cddbf0e029e637804","analyzedAt":"2026-09-08T08:36:04.887Z","contentChangedAt":"2026-09-08T08:36:04.887Z","schemaVersion":2},"datasetVersion":"2026-09-17T15:17:12.973Z"}