Pondering strings in Apache 3.x

["William A. Rowe, Jr." <wr...@rowe-clan.net>]

Greg and a few others voiced interest in moving from null-term
strings to counted strings for a future version of Apache.  
This was too broad a scope change to make it into 2.0, of course,
and was dropped on the floor for the time being.

I'm wondering today; what metadata interests us in an ap_string_t
prefix header?  I have a hunch that a short, 65536, is enough
to map most data we want to handle in one chunk; brigades are
better for handling large sets of data.  Of course we could push
that to an int, or size_t, but there would be a small memory
penalty.  It might be overcome by cpu-specific optimized int
or size_t handling behavior, since the assembly code wouldn't
need to truncate short values.

Perhaps, both bytes allocated/used, in order to play optimized
games with string allocation.  Perhaps, a refcount?  (This
doesn't play well with pool allocations, obviously.)

But the byte count clearly isn't enough.  I'm thinking of;

  encoding;  is this data URI escaped or un-escaped?

  tainted;   is it raw?  or has it been untainted with 
             context-specific validity checks?

  charset;   is this native?  (e.g. EBCDIC).  utf-8?
             opaque or otherwise a specific set?

What else interests us within an 'ap_string_t' header, that
would help eliminate bugs within httpd?  A random trailing
short following the string, in a 'string debug' mode, to 
detect buffer overflows?  Something similar to detect 
underflows?

Open to all ideas.

Bill

Re: Pondering strings in Apache 3.x

[André Malo <nd...@perlig.de>]

* Brian Pane wrote:

> And although I like the performance benefits of the pool memory
> allocators, I remember how tricky it was to debug some of the
> pool and bucket lifetime problems that we encountered during
> the development of 2.0 (especially in filters).  All things considered,
> I don't think I'd mind the overhead of a garbage collection thread.

The pool problems should be solved now... (mostly)

> Thus I can't help but wonder: Would 3.0 be a good time to consider
> trying a Java-based httpd?

If you ask me: Nope. Try Tomcat instead ;)

What we need for 3.0 is just a clean design and definitions of what is core 
(not much, imo) and what is not core. This was started for 2.0 but never 
finished. Further a standardized exception handling would be nice (like 
svn's). 
The "core" could provide several convenience data types like ap_string_t.

I would, btw, just store the length of the string in such a type. Other 
properties (url-encoding state, ...) imo belong to a different layer. Like 
a bucket or just a wrapper type.

nd
-- 
"Das Verhalten von Gates hatte mir bewiesen, dass ich auf ihn und seine
beiden Gefährten nicht zu zählen brauchte" -- Karl May, "Winnetou III"

Im Westen was neues: <http://pub.perlig.de/books.html#apache2>

Re: Pondering strings in Apache 3.x

[Brian Pane <br...@apache.org>]

On Jul 19, 2005, at 12:55 PM, William A. Rowe, Jr. wrote:

> Greg and a few others voiced interest in moving from null-term
> strings to counted strings for a future version of Apache.
> This was too broad a scope change to make it into 2.0, of course,
> and was dropped on the floor for the time being.
>
> I'm wondering today; what metadata interests us in an ap_string_t
> prefix header?  I have a hunch that a short, 65536, is enough
> to map most data we want to handle in one chunk; brigades are
> better for handling large sets of data.  Of course we could push
> that to an int, or size_t, but there would be a small memory
> penalty.  It might be overcome by cpu-specific optimized int
> or size_t handling behavior, since the assembly code wouldn't
> need to truncate short values.
>
> Perhaps, both bytes allocated/used, in order to play optimized
> games with string allocation.  Perhaps, a refcount?  (This
> doesn't play well with pool allocations, obviously.)
>
> But the byte count clearly isn't enough.  I'm thinking of;
>
>   encoding;  is this data URI escaped or un-escaped?
>
>   tainted;   is it raw?  or has it been untainted with
>              context-specific validity checks?
>
>   charset;   is this native?  (e.g. EBCDIC).  utf-8?
>              opaque or otherwise a specific set?
>
> What else interests us within an 'ap_string_t' header, that
> would help eliminate bugs within httpd?  A random trailing
> short following the string, in a 'string debug' mode, to
> detect buffer overflows?  Something similar to detect
> underflows?
>
> Open to all ideas.

This may be a bit more radical than you were hoping for, but...

I like the idea of using a reference-counted, non-null-terminated
string type for 3.x.

More generally, it would be great to have overflow detection
on all arrays.

And although I like the performance benefits of the pool memory
allocators, I remember how tricky it was to debug some of the
pool and bucket lifetime problems that we encountered during
the development of 2.0 (especially in filters).  All things considered,
I don't think I'd mind the overhead of a garbage collection thread.

Thus I can't help but wonder: Would 3.0 be a good time to consider
trying a Java-based httpd?

Brian

Re: Pondering strings in Apache 3.x

[Jeff White <jl...@earthlink.net>]

From: "William A. Rowe, Jr." 

> 
> What else interests us within an 
> 'ap_string_t' header, that would help 
> eliminate bugs within httpd?  A random 
> trailing short following the string, in a 
> 'string debug' mode, to detect buffer 
> overflows?  Something similar to detect 
> underflows?
> 
> Open to all ideas.
> 

What are the newer C / C++ compiler
standard Safer C Library Functions?

Jeff