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50 lines
2.0 KiB
Plaintext
50 lines
2.0 KiB
Plaintext
Copyright (C) Internet Systems Consortium, Inc. ("ISC")
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See COPYRIGHT in the source root or http://isc.org/copyright.html for terms.
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$Id: unexpected,v 1.6 2004/03/05 05:04:50 marka Exp $
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Unexpected Errors
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For portability, the ISC and DNS libraries define their own result codes
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instead of using the operating system's. E.g. the ISC library uses
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ISC_R_NOMEMORY instead of the UNIX-specific ENOMEM.
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The ISC and DNS libraries have a common way of looking at errors and
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other non-success results. An "expected" result is something that can
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happen in the ordinary course of using a function, that is not very
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improbable, and that the caller might care to know. For example, a
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function which opens a file must have a way to say "file not found"
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and "permission denied".
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Other kinds of errors are "unexpected". For example, an I/O error
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might occur. When an unexpected error occurs, we want to be able to
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log the information, but we don't want to translate every
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operating-system-specific error code into and ISC_R_ or DNS_R_ code
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because the are too many of them, and they aren't meaningful to
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clients anyway (they're unexpected errors). If we were using a
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language where we could throw an exception, we'd do that. Since we're
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not, we call UNEXPECTED_ERROR(). E.g.
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#include <isc/error.h>
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void foo() {
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if (some_unix_thang() < 0) {
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UNEXPECTED_ERROR(__FILE__, __LINE__,
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"some_unix_thang() failed: %s",
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strerror(errno));
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return (ISC_R_UNEXPECTED);
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}
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}
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The UNEXPECTED error routine may be specified by the calling application. It
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will log the error somehow (e.g. via. syslog, or printing to stderr).
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This method is a compromise. It makes useful error information available,
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but avoids the complexity of a more sophisticated multi-library "error table"
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scheme.
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In the (rare) situation where a library routine encounters a fatal error and
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has no way of reporting the error to the application, the library may call
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FATAL_ERROR(). This will log the problem and then terminate the application.
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