X-Git-Url: https://git.sesse.net/?a=blobdiff_plain;f=futatabi%2Fjpeglib_error_wrapper.h;fp=futatabi%2Fjpeglib_error_wrapper.h;h=3818f53b4db47782918d6fed67c50301a1563255;hb=996c5ad2c506048694b32988f7e376a97924c3e9;hp=0000000000000000000000000000000000000000;hpb=18a66015dbeac5447b62f4ef869a252f9e7000e6;p=nageru

diff --git a/futatabi/jpeglib_error_wrapper.h b/futatabi/jpeglib_error_wrapper.h
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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