MaraDNS' coding style
MaraDNS is a divergent body of code that has been developed, in
some form or other, for over seven years. While some changes
have been made to that code during this time period, notably the
tab and bracing style, some other things about the code have
stayed the same. These coding style guidelines have always been
in mind as I was writing MaraDNS code. Now that MaraDNS is
becoming popular enough that other people are starting to
contribute to it, I am documenting these guidelines so that
people can make patches that I will accept.
So, without further ado:
All indexed writes must be protected against overflows
In other words, all code that writes to arrays must be checked,
before a write is made, to verify that the write in question is
within the bounds of the array. For example, this code violates
MaraDNS coding styles:
c = &some_array;
while(*c != 0) {
if(*c > 'A' && *c < 'Z')
*c += 32;
c++;
}
In order for this kind of code to be accepted in to MaraDNS
code, it must be revised to look like this:
c = &some_array;
limit = size_of_array;
while(*c != 0 && limit > 0) {
if(*c > 'A' && *c < 'Z')
*c += 32;
c++;
limit--;
}
All arrays must be at least one byte bigger than they should be
All arrays must be at least one byte bigger than they should be,
and should ideally be about three bytes bigger than they should
be. In other words, let us suppose we have a character array
that is MAX_BYTES long, where the bounds checking makes sure we
don't write past MAX_BYTES. Then we declare the array in this
form:
char s[MAX_BYTES + 3];
The reason for this 3-byte cushion is to prevent off-by-one
errors. An off-by-one error can be very dangerous. This kind of
error is why OpenBSD had a remote code execution exploit with
its FTP daemon. In MaraDNS' code, there was once a potential
buffer overflow that was only stopped because I always have
these cushions at the end of arrays.
No old MaraDNS configuration file should be broken
Unless there is a compelling reason to do so, no changes that
break or change how an old mararc file or zone file is parsed
should be done. For example, there is a mararc variable entitled
default_rrany_set that does nothing in MaraDNS 1.2; we still
support this variable (and have it do nothing) since people
using MaraDNS since 1.0 might have this variable set.
As another example, when I changed the zone file format in
MaraDNS 1.3, I went to a good deal of effort to make sure over
99% of MaraDNS 1.2 zone files work completely unchanged in
MaraDNS 1.3, and that a MaraDNS user can set a single mararc
variable, csv2_tilde_handling in order to make MaraDNS 1.4 100%
compatible with MaraDNS 1.2 zone files.
Indeed, MaraDNS 1.4 still supports MaraDNS 1.0 zone files, even
though I am encouraging people to upgrade to the newer zone file
format, and even though I have a Perl script that converts a
MaraDNS 1.0 zone file in to a MaraDNS 1.2+ zone file.
I have sometimes sometimes made old configuration files not
compatible with newer versions of MaraDNS. These changes are
only done when:
* There is a compelling reason to make the change in question
* The change in question impacts the minimum number of MaraDNS
users
* The change in question is fully documented in MaraDNS'
upgrade document.
For example, MaraDNS 1.0 had a bug where it would silently
ignore a misspelled mararc parameter. In MaraDNS 1.2, I changed
this behavior to one where MaraDNS will exit with a fatal error
should there be a misspelled mararc variable. I made this change
to make life easier for system administrators who are wondering
why a change isn't working in MaraDNS because they made a typo
in their mararc. This change, of course, is fully documented in
the MaraDNS update document.
The reason for this is because MaraDNS users have better things
to do in their life than to follow every single change made to
MaraDNS; it's difficult enough for people to adjust to MaraDNS.
There is no good reason why we should force users to adjust to
each new version just because we have some silly idea about what
makes MaraDNS' configuration files neater. This is a problem
Linux and X11 developers have; I have had to change my custom
keyboard mapping file that allows me to type Spanish letters and
accents on a US keyboard no less than twice in the last few
years.
There's also the issue, with French users of MaraDNS, of the
French documentation not being updated since the 1.0 days of
MaraDNS.
Note that MaraDNS 2.0 will break many configurations, since the
same IP will be unable to be both a recursive and authoritative
DNS server. This is why I will continue to support MaraDNS 1.4
after when and if MaraDNS 2.0 comes out.
Brace and tab style
MaraDNS' tabbing and brace style has changed over the years. The
current style is to not have tabs in the code at all; a script
converts all tabs in to spaces every time MaraDNS is updated.
When contributing new code to MaraDNS, keep this in mind:
* When making a change to already existing code, try to
maintain the bracing and spacing style of that code.
* For new code, there is a somewhat informal bracing style.
Here is the bracing and tab style for new code in MaraDNS:
int main() {
int a;
for(a = 0; a < 100; a++ ) {
printf("a is %c\n",a);
}
}
Licensing and copyright issues
Contributions made to MaraDNS can not be accepted unless you are
willing to license your contributions under the conditions of
MaraDNS' license, which is a BSD license as follows:
Copyright (c) 2002-2009 Sam Trenholme and others
TERMS
Redistribution and use in source and binary forms, with or
without modification, are permitted provided that the
following conditions are met:
1. Redistributions of source code must retain the above
copyright notice, this list of conditions and the
following disclaimer.
2. Redistributions in binary form must reproduce the above
copyright notice, this list of conditions and the
following disclaimer in the documentation and/or other
materials provided with the distribution.
This software is provided 'as is' with no guarantees of
correctness or fitness for purpose.
Contributed code must not break anything in MaraDNS
Any contributed code, before it is accepted, must not break
anything in MaraDNS. This means the following:
* The patched code must compile with no warnings nor errors
when compiling MaraDNS with -Wall set (the default when
compiling MaraDNS).
* The patched code must pass all tests in the sqa/regressions
directory. To perform this test, first compile the patched
MaraDNS. Next, enter the sqa/regressions directory. Next,
become root. Finally sh ./do.tests
Finally, thank you for your interest in MaraDNS
Finally, I would like to thank you for your interest in MaraDNS,
and really appreciate the time you take to make patches for it.
I hope these coding style guidelines are not too bothersome;
they make MaraDNS' code a more secure, reliable DNS server.
