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Re: Status of IDN support?

From: Tim Ruehsen <tim.ruehsen_at_gmx.de>
Date: Wed, 11 Jan 2017 12:49:00 +0100

On Wednesday, January 11, 2017 12:23:34 PM CET Tim Ruehsen wrote:
> On Tuesday, January 10, 2017 11:40:49 PM CET Daniel Stenberg wrote:
> > On Tue, 10 Jan 2017, Alessandro Ghedini wrote:
> > >> TESTFAIL: These test cases failed: 165 1034 1035 2046 2047
> > >
> > > Note that this is with curl 7.52.1 and libidn2 0.14 from Debian
> > > unstable.
> >
> > I suspect this has something to do with libidn2's limitations, but we
> > haven't changed any IDN code in curl since 7.52.1 that I can recall and I
> > use 0.14 too.
>
> Sorry for dropping in late... I made the recent changes to libidn2 which is
> basically TR46 support.
>
> Now the bad news: I introduced a bug (regression) regarding NFC conversion
> in libidn 0.14. A fix is already in upstream repo but not released yet.
> This might introduce the test failures you experience... on some systems
> UTF-8/Unicode might be decomposed and on some it is composed. Using
> decomposed codepoints with IDN2_NFC_INPUT fails with libidn 0.14.
>
> But if you enable the new TR46 feature, the input is NFCed (and lowercased)
> automatically:
>
> Example:
> $ printf "\x62\x6c\x61\xcc\x8a\x62\xc3\xa6\x72\x67\x72\xc3\xb8\x64\x2e\x6e
> \x6f"|idn2
> idn2: lookup: string is not in Unicode NFC format
>
> $ printf "\x62\x6c\x61\xcc\x8a\x62\xc3\xa6\x72\x67\x72\xc3\xb8\x64\x2e\x6e
> \x6f"|idn2 -T
>
> You can check for TR46 availability:
>
> #if IDN2_VERSION_NUMBER >= 0x00140000
> if ((rc = idn2_lookup_u8((uint8_t *)utf8, (uint8_t **)ascii,
> IDN2_TRANSITIONAL)) == IDN2_OK)
> ...
> #else
> ...
> #endif
>
> The IDN2_TRANSITIONAL enables TR46 'transitional' conversion (tries to be
> compatible to IDNA2008 and IDNA2003 as much as possible),
> IDN2_NONTRANSITIONAL enables TR46 'non-transitional (IDNA2008, the way that
> every app should go... may arise some incompatibilties with IDNA2003 which
> is still under heavy use).

I just looked at lib/url.c... how do you NFC'ed the input to idn2_lookup_ul(),
couldn't find any conversion using a quick grep ?

My suggestion would be:

diff --git a/lib/url.c b/lib/url.c
index 7944d7b0c..81cd490e0 100644
--- a/lib/url.c
+++ b/lib/url.c
@@ -4010,7 +4010,12 @@ static void fix_hostname(struct connectdata *conn,
struct hostname *host)
 #ifdef USE_LIBIDN2
     if(idn2_check_version(IDN2_VERSION)) {
       char *ace_hostname = NULL;
- int rc = idn2_lookup_ul((const char *)host->name, &ace_hostname, 0);
+#ifdef IDN2_TRANSITIONAL
+ int flags = IDN2_TRANSITIONAL;
+#else
+ int flags = IDN2_INPUT_NFC;
+#endif
+ int rc = idn2_lookup_ul((const char *)host->name, &ace_hostname, flags);
       if(rc == IDN2_OK) {
         host->encalloc = (char *)ace_hostname;
         /* change the name pointer to point to the encoded hostname */

That way there is a chance that the tests work more stable between different
systems.

Regards, Tim

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Received on 2017-01-11