Re: IPv6 support

On Thu, 3 Mar 2005, [ISO-8859-1] Xuân Baldauf wrote:

> The "#if ENABLE_IPV6" conditions are to provide a more smooth transition to
> enabled IPv6 support. The idea is: When "ENABLE_IPV6==0", then everything is
> as before. But when ENABLE_IPV6==1, every variable and every struct which
> refers IPv4 adresses (the old way) just do not exist.

I know, and this is what I dislike.

By using the ifdefs, the IPv6 code can not be introduced into HEAD in a
meaningful manner as it is bound to bitrot pretty quickly unless all
developers switches to build their Squids IPv6 enabled, as even trivial
errors won't be detected compile time. Also it considerably obfuscates the
code and makes maintenance a burden.

Yes, doing it proper from start may requires a little bigger initial
effort, but only marginally so I think (not counting the effort you have
already put into doing it..). In both cases a new type for ipv6 needs to
be introduced, and in both cases the compiler will tell you which lines is
affected due to the type change.

> This approach (of breaking compileability with intent) has the side effect
> that, until IPv6 support has been provided nearly completely, the modified
> code would not compile. Thus, the modification is encapsulated by "#if
> ENABLE_IPV6" to protect uninterested developers to be forced to fix IPv6
> generated compiler error messages.

The same can be acheived by providing a typecast operator to the old
address types only when IPv6 is not enabled and use this in the glue
between converted and not yet converted code.

In addition, this part of the discussion is only interesting when it comes
to merging the IPv6 support into HEAD, not the initial efforts.

> lacking, just subclassing an "Address" class to an "IPv6Address" class is not
> possible (the "Address" class is missing... ;-)).

Only because something is missing does not say it should stay that way. It
should not stay that way.

> HEAD tree would be able to create a failed sync between "HEAD" and
> "squid-ipv6" branches, because a separate "squid-ipv6" branch would not
> exist, the "#if ENABLE_IPV6" sections are the branch.)

The current #if ENABLE_IPV6 won't make it into HEAD for the reasons
outlined above. This style of programming is bound to stay in a separate
branch until done proper.

> Having "#if ENABLE_IPV6" statements should be only temporary. When there are
> no IPv6 support compile error messages anymore, ENABLE_IPV6==1 should become
> the default. After some more testing, all
>
> #if ENABLE_IPV6
> /* new code */
> #else
> /* old code */
> #endif
>
> sections in the sourcecode shall be replaced by
>
> /* new code */
>
> so the "#if ENABLE_IPV6" statements will then be removed, too.
>
> This will be possible, because "ENABLE_IPV6" does not really mean that we are
> going away from IPv4, but just that the software will be IP version neutral,
> explicitly supporting both IPv4 and IPv6.

Not all OS:es where Squid builds is IPv6 enabled which complicates matters
somewhat. By introducing a new proper address class this dependency gets
isolated down to the address class, keeping the bulk of the code clean.

Regards
Henrik
Received on Wed Mar 02 2005 - 18:48:55 MST