Don't die on libjpeg errors.

[nageru] / futatabi / jpeglib_error_wrapper.h

diff --git a/futatabi/jpeglib_error_wrapper.h b/futatabi/jpeglib_error_wrapper.h
new file mode 100644 (file)
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+++ b/futatabi/jpeglib_error_wrapper.h
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+#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