[Swan-dev] printing IP addresses; reentrancy

[D. Hugh Redelmeier]

I just spent a bunch of time to simplify how IP addresses get
formatted in libreswan.

Why?

- addrtot, while complete and powerful, is tedious to invoke.

- ip_str was easy to invoke in common cases but had problems

  - it used a static buffer so

    -it wasn't safe to use in more than one thread.

    - It also wasn't safe to use more than once in the parameter list
      of a call to a function, something easy to do accidentally.

  - it was declared and defined several odd places.
    Defined in:
	lib/libswan/id.c (as pluto_ip_str)
	testing/lib/libpluto/spdbph1.c,
	testing/lib/libpluto/spdbv2.c,
	testing/lib/libpluto/spdbv2c.c
	programs/pluto/log.h (as a macro expanding to pluto_ip_str)
    Declared in:
  	include/id.h (as pluto_ip_str)

The replacement is ipstr().

It is defined in linux/net/ipsec/addrtot.c.  It is tiny and needs
addrtot() to function, so this seemed natural.  It adds no
dependencies to addrtot.c.

It is declared in linux/include/libreswan.h, just like addrtot().

One slightly novel thing is the way memory for the resulting formatted
string is handled.  The caller of ipstr has to provide an object of
type ipstr_buf that lasts as long as the string needs to be valid.
This type is not a string, but is considered opaque to the caller.  It
happens to have enough space for the longest possible string.

Typically, the string needs to live as long as the call to a function.
So a local variable of type ipstr_buf does the job.  One for each
ipstr result string live during a call.


We should try to avoid non-reentrant formatting routines, even though
they are convenient.  It is sometimes hard to notice when they cause
problems.

enum_showb (the reentrant version of enum_show) is a little more
intricate to use than ipstr because the buffer needed doesn't have a
simple known compile-time bound.  That applies to bitnamesofb too.
Using malloc to solve the problem seems expensive, awkward, and
leak-prone.


Please use the reentrant versions of these routines when it isn't too
difficult or awkward.