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Issue #767: Buffer overflow printing a filename
The safe_fprintf function attempts to ensure clean output for an arbitrary sequence of bytes by doing a trial conversion of the multibyte characters to wide characters -- if the resulting wide character is printable then we pass through the corresponding bytes unaltered, otherwise, we convert them to C-style ASCII escapes. The stack trace in Issue #767 suggest that the 20-byte buffer was getting overflowed trying to format a non-printable multibyte character. This should only happen if there is a valid multibyte character of more than 5 bytes that was unprintable. (Each byte would get expanded to a four-charcter octal-style escape of the form "\123" resulting in >20 characters for the >5 byte multibyte character.) I've not been able to reproduce this, but have expanded the conversion buffer to 128 bytes on the belief that no multibyte character set has a single character of more than 32 bytes.
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