2N/ACopyright (C) 1999, 2000 Internet Software Consortium.

2N/ASee COPYRIGHT in the source root or http://www.isc.org/copyright for terms.

2N/A

2N/AUnexpected Errors

2N/A

2N/AFor portability, the ISC and DNS libraries define their own result codes

2N/Ainstead of using the operating system's. E.g. the ISC library uses

2N/AISC_R_NOMEMORY instead of the UNIX-specific ENOMEM.

2N/A

2N/AThe ISC and DNS libraries have a common way of looking at errors and

2N/Aother non-success results. An "expected" result is something that can

2N/Ahappen in the ordinary course of using a function, that is not very

2N/Aimprobable, and that the caller might care to know. For example, a

2N/Afunction which opens a file must have a way to say "file not found"

2N/Aand "permission denied".

2N/A

2N/AOther kinds of errors are "unexpected". For example, an I/O error

2N/Amight occur. When an unexpected error occurs, we want to be able to

2N/Alog the information, but we don't want to translate every

2N/Aoperating-system-specific error code into and ISC_R_ or DNS_R_ code

2N/Abecause the are too many of them, and they aren't meaningful to

2N/Aclients anyway (they're unexpected errors). If we were using a

2N/Alanguage where we could throw an exception, we'd do that. Since we're

2N/Anot, we call UNEXPECTED_ERROR(). E.g.

2N/A

2N/A#include <isc/error.h>

2N/A

2N/Avoid foo() {

2N/A if (some_unix_thang() < 0) {

2N/A UNEXPECTED_ERROR(__FILE__, __LINE__,

2N/A "some_unix_thang() failed: %s",

2N/A strerror(errno));

2N/A return (ISC_R_UNEXPECTED);

2N/A }

2N/A}

2N/A

2N/AThe UNEXPECTED error routine may be specified by the calling application. It

2N/Awill log the error somehow (e.g. via. syslog, or printing to stderr).

2N/A

2N/AThis method is a compromise. It makes useful error information available,

2N/Abut avoids the complexity of a more sophisticated multi-library "error table"

2N/Ascheme.

2N/A

2N/AIn the (rare) situation where a library routine encounters a fatal error and

2N/Ahas no way of reporting the error to the application, the library may call

2N/AFATAL_ERROR(). This will log the problem and then terminate the application.

2N/A