+#ifndef _JPEGLIB_ERROR_WRAPPER
+#define _JPEGLIB_ERROR_WRAPPER 1
+
+/*
+ A wrapper class for libjpeg's very cumbersome error handling.
+ By default, any error will simply exit(); you can set your own
+ error handler, but it can't return. You can't throw exceptions
+ through C code legally, so the only real choice is setjmp/longjmp,
+ which is also what libjpeg recommends. However, longjmp has
+ undefined behavior if a similar try/catch pair would invoke
+ running any nontrivial destructors, so it's better to wrap it
+ into a common class where we know for sure there are no such
+ destructors; we choose to simply convert it into a normal
+ true/false idiom for success/failure.
+
+ Use as:
+
+ JPEGWrapErrorManager error_mgr(&cinfo);
+ if (!error_mgr.run([&cinfo]{ jpeg_read_header(&cinfo, true); })) {
+ // Something went wrong.
+ return nullptr;
+ }
+ if (!error_mgr.run([&cinfo]{ jpeg_start_decompress(&cinfo); })) {
+ // Something went wrong.
+ return nullptr;
+ }
+ // etc.
+
+ If you call libjpeg calls outside of run() and they fail, or if
+ you declare objects with nontrivial destructors in your lambda
+ (including in the capture), you end up in undefined behavior.
+ */
+
+#include <jpeglib.h>
+#include <setjmp.h>
+
+struct JPEGWrapErrorManager {
+ struct jpeg_error_mgr pub;
+ jmp_buf setjmp_buffer;
+
+ explicit JPEGWrapErrorManager(jpeg_compress_struct *cinfo) // Does not take ownership.
+ {
+ cinfo->err = jpeg_std_error(&pub);
+ pub.error_exit = error_exit_thunk;
+ }
+
+ explicit JPEGWrapErrorManager(jpeg_decompress_struct *dinfo) // Does not take ownership.
+ {
+ dinfo->err = jpeg_std_error(&pub);
+ pub.error_exit = error_exit_thunk;
+ }
+
+ static void error_exit_thunk(jpeg_common_struct *cinfo)
+ {
+ ((JPEGWrapErrorManager *)cinfo->err)->error_exit(cinfo);
+ }
+
+ void error_exit(jpeg_common_struct *cinfo)
+ {
+ (pub.output_message)(cinfo);
+ longjmp(setjmp_buffer, 1);
+ }
+
+ // Returns false if and only if the call failed.
+ template<class T>
+ inline bool run(T &&func)
+ {
+ if (setjmp(setjmp_buffer)) {
+ return false;
+ }
+ func();
+ return true;
+ }
+};
+
+#endif
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