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Re: issue #1796

From: Karl Fogel <kfogel_at_red-bean.com>
Date: Mon, 26 May 2008 17:34:56 -0400

Neels Janosch Hofmeyr <neels_at_elego.de> writes:
>> You're on the right track, but you don't have to make the function
>> public. Subversion has an intermediate level of inter-library privacy,
>> to allow a symbol to be shared among Subversion's modules without
>> publishing that symbol to the world. See here:
>> http://svn.collab.net/repos/svn/trunk/subversion/include/private
>> Does that help?
> Well, it would have, but there isn't any utf function published in
> include/private/ either.

It's okay to create a new private/svn_utf_private.h.

> I could go on to publish check_utf8 in include/private/. But all the
> other UTF-8 functions are declared in include/svn_utf.h. Wouldn't it be
> silly to publish check_utf8 in a completely different place from the
> rest of the UTF stuff? (I see check_utf8 in the category of "general
> purpose tools that are nice to have around".)

The groupings are about whether something is a published (supported) API
or a private API. After those groupings, we consider the question of
whether or not it's "UTF stuff" or not.

> If not, where in include/private/ would check_utf8 go? check_utf8 is
> defined in libsvn_subr/utf.c, but there is no include/private/svn_subr.h
> to add it to...

See above -- every file got created sometime :-).

> By the way, there is an alternative to check_utf8. Let's look at the
> implementation of check_utf8() in libsvn_subr/utf.c:
> /* Verify that the sequence DATA of length LEN is valid UTF-8 */
> static svn_error_t *
> check_utf8(const char *data, apr_size_t len, apr_pool_t *pool)
> {
> if (! svn_utf__is_valid(data, len))
> return invalid_utf8(data, len, pool);
> return SVN_NO_ERROR;
> }
> check_utf8 calls svn_utf__is_valid(), defined in libsvn_subr/utf_validate.c:
> svn_utf__is_valid(const char *data, apr_size_t len)
> {
> const char *end = data + len;
> int state = FSM_START;
> while (data < end)
> {
> unsigned char octet = *data++;
> int category = octet_category[octet];
> state = machine[state][category];
> }
> return state == FSM_START ? TRUE : FALSE;
> }
> The difference is that svn_utf__is_valid() returns a boolean, where
> check_utf8 returns a SVN_ERROR. Both of these functions are only
> accessible within libsvn_subr, and are neither in include/ nor in
> include/private.
> Any opinions on which one of these functions should be published (and
> where)?

It is precisely because the answer to questions like this are not always
clear that we share things privately unless they absolutely must be
public APIs, actually.

I would say create the new svn_utf_private.h and put the boolean
function in it to start. If you find that you also need the
error-returing function in more than one place, then that can also be
made privately shareable.

> Currently, a lot of functions that convert from/to UTF-8 are declared in
> include/svn_utf.h, but none that just verify. Should I rather attempt a
> conversion and discard the resulting copied data? No, right?



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Received on 2008-05-26 23:35:09 CEST

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