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bind/doc/dev/unexpected
Ondřej Surý 58bd26b6cf Update the copyright information in all files in the repository
This commit converts the license handling to adhere to the REUSE
specification.  It specifically:

1. Adds used licnses to LICENSES/ directory

2. Add "isc" template for adding the copyright boilerplate

3. Changes all source files to include copyright and SPDX license
   header, this includes all the C sources, documentation, zone files,
   configuration files.  There are notes in the doc/dev/copyrights file
   on how to add correct headers to the new files.

4. Handle the rest that can't be modified via .reuse/dep5 file.  The
   binary (or otherwise unmodifiable) files could have license places
   next to them in <foo>.license file, but this would lead to cluttered
   repository and most of the files handled in the .reuse/dep5 file are
   system test files.
2022-01-11 09:05:02 +01:00

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Unexpected Errors
For portability, the ISC and DNS libraries define their own result codes
instead of using the operating system's. E.g. the ISC library uses
ISC_R_NOMEMORY instead of the UNIX-specific ENOMEM.
The ISC and DNS libraries have a common way of looking at errors and
other non-success results. An "expected" result is something that can
happen in the ordinary course of using a function, that is not very
improbable, and that the caller might care to know. For example, a
function which opens a file must have a way to say "file not found"
and "permission denied".
Other kinds of errors are "unexpected". For example, an I/O error
might occur. When an unexpected error occurs, we want to be able to
log the information, but we don't want to translate every
operating-system-specific error code into and ISC_R_ or DNS_R_ code
because the are too many of them, and they aren't meaningful to
clients anyway (they're unexpected errors). If we were using a
language where we could throw an exception, we'd do that. Since we're
not, we call UNEXPECTED_ERROR(). E.g.
#include <isc/error.h>
void foo() {
if (some_unix_thang() < 0) {
UNEXPECTED_ERROR(__FILE__, __LINE__,
"some_unix_thang() failed: %s",
strerror(errno));
return (ISC_R_UNEXPECTED);
}
}
The UNEXPECTED error routine may be specified by the calling application. It
will log the error somehow (e.g. via. syslog, or printing to stderr).
This method is a compromise. It makes useful error information available,
but avoids the complexity of a more sophisticated multi-library "error table"
scheme.
In the (rare) situation where a library routine encounters a fatal error and
has no way of reporting the error to the application, the library may call
FATAL_ERROR(). This will log the problem and then terminate the application.