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* [musl] Proposal to match behaviour of gethostbyname to glibc
@ 2020-03-13 21:46 Wolf
  2020-03-13 22:16 ` Rich Felker
  2020-03-14  8:24 ` Florian Weimer
  0 siblings, 2 replies; 6+ messages in thread
From: Wolf @ 2020-03-13 21:46 UTC (permalink / raw)
  To: musl

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Hello,

today I've noticed difference in behavior of gethostbyname in musl and
in glibc. Given /etc/hosts

	127.0.0.1   foo.bar foo
	127.0.0.1   bar.foo foo

and simple test program

	#include <netdb.h>
	#include <stdio.h>

	int main(int argc, char **argv) {
		struct hostent *he = gethostbyname(argv[1]);
		printf("Hostname: %s\n", he->h_name);
	}

, I've run it both under musl (alpine) and glibc (archlinux).

musl:

	/test # ./test foo
	Hostname: bar.foo

glibc:

	[root@foo test]# ./test foo
	Hostname: foo.bar

I don't think there is an actual reason to iterate through all of the
/etc/hosts and first match can be returned instead. Following patch
should in my opinion fix this.



diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
index c93263a9..da8db9d4 100644
--- a/src/network/lookup_name.c
+++ b/src/network/lookup_name.c
@@ -87,7 +87,10 @@ static int name_from_hosts(struct address buf[static MAXADDRS], char canon[stati
                for (; *p && isspace(*p); p++);
                for (z=p; *z && !isspace(*z); z++);
                *z = 0;
-               if (is_valid_hostname(p)) memcpy(canon, p, z-p+1);
+               if (is_valid_hostname(p)) {
+                       memcpy(canon, p, z-p+1);
+                       break;
+               }
        }
        __fclose_ca(f);
        return cnt ? cnt : badfam;



While this is admittedly edge case that most users will not run into, I
still think it would be nice to behave the same way as glibc does on
this one. And as a bonus, it will be *tiny* bit faster, since there
would not be any need to iterate rest of the /etc/hosts file.



Thank you for considering this,

W.

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] Proposal to match behaviour of gethostbyname to glibc
  2020-03-13 21:46 [musl] Proposal to match behaviour of gethostbyname to glibc Wolf
@ 2020-03-13 22:16 ` Rich Felker
  2020-03-13 23:43   ` Wolf
  2020-03-14  8:24 ` Florian Weimer
  1 sibling, 1 reply; 6+ messages in thread
From: Rich Felker @ 2020-03-13 22:16 UTC (permalink / raw)
  To: musl

On Fri, Mar 13, 2020 at 10:46:48PM +0100, Wolf wrote:
> Hello,
> 
> today I've noticed difference in behavior of gethostbyname in musl and
> in glibc. Given /etc/hosts
> 
> 	127.0.0.1   foo.bar foo
> 	127.0.0.1   bar.foo foo
> 
> and simple test program
> 
> 	#include <netdb.h>
> 	#include <stdio.h>
> 
> 	int main(int argc, char **argv) {
> 		struct hostent *he = gethostbyname(argv[1]);
> 		printf("Hostname: %s\n", he->h_name);
> 	}
> 
> , I've run it both under musl (alpine) and glibc (archlinux).
> 
> musl:
> 
> 	/test # ./test foo
> 	Hostname: bar.foo
> 
> glibc:
> 
> 	[root@foo test]# ./test foo
> 	Hostname: foo.bar
> 
> I don't think there is an actual reason to iterate through all of the
> /etc/hosts and first match can be returned instead. Following patch
> should in my opinion fix this.
> 
> 
> 
> diff --git a/src/network/lookup_name.c b/src/network/lookup_name.c
> index c93263a9..da8db9d4 100644
> --- a/src/network/lookup_name.c
> +++ b/src/network/lookup_name.c
> @@ -87,7 +87,10 @@ static int name_from_hosts(struct address buf[static MAXADDRS], char canon[stati
>                 for (; *p && isspace(*p); p++);
>                 for (z=p; *z && !isspace(*z); z++);
>                 *z = 0;
> -               if (is_valid_hostname(p)) memcpy(canon, p, z-p+1);
> +               if (is_valid_hostname(p)) {
> +                       memcpy(canon, p, z-p+1);
> +                       break;
> +               }
>         }
>         __fclose_ca(f);
>         return cnt ? cnt : badfam;
> 
> 
> 
> While this is admittedly edge case that most users will not run into, I
> still think it would be nice to behave the same way as glibc does on
> this one. And as a bonus, it will be *tiny* bit faster, since there
> would not be any need to iterate rest of the /etc/hosts file.
> 
> 
> 
> Thank you for considering this,

I don't really see any downsides to doing this, even if "matching
glibc" isn't a terribly useful goal. If nothing else it's faster. Do
you know if there's widespread match for this behavior across other
systems too?

Rich

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] Proposal to match behaviour of gethostbyname to glibc
  2020-03-13 22:16 ` Rich Felker
@ 2020-03-13 23:43   ` Wolf
  0 siblings, 0 replies; 6+ messages in thread
From: Wolf @ 2020-03-13 23:43 UTC (permalink / raw)
  To: musl

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On 2020-03-13 18:16:49 -0400, Rich Felker wrote:
 
> Do you know if there's widespread match for this behavior across other
> systems too?

Windows use the glibc behaviour, other than that I do not have systems
to test this on.

W.

-- 
There are only two hard things in Computer Science:
cache invalidation, naming things and off-by-one errors.

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^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] Proposal to match behaviour of gethostbyname to glibc
  2020-03-13 21:46 [musl] Proposal to match behaviour of gethostbyname to glibc Wolf
  2020-03-13 22:16 ` Rich Felker
@ 2020-03-14  8:24 ` Florian Weimer
  2020-03-14 14:54   ` Rich Felker
  1 sibling, 1 reply; 6+ messages in thread
From: Florian Weimer @ 2020-03-14  8:24 UTC (permalink / raw)
  To: Wolf; +Cc: musl

* Wolf:

> While this is admittedly edge case that most users will not run into, I
> still think it would be nice to behave the same way as glibc does on
> this one. And as a bonus, it will be *tiny* bit faster, since there
> would not be any need to iterate rest of the /etc/hosts file.

But something has to scan the entire file in “multi on” mode at least,
to find all relevant addresses.

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] Proposal to match behaviour of gethostbyname to glibc
  2020-03-14  8:24 ` Florian Weimer
@ 2020-03-14 14:54   ` Rich Felker
  2020-03-14 16:31     ` Jeffrey Walton
  0 siblings, 1 reply; 6+ messages in thread
From: Rich Felker @ 2020-03-14 14:54 UTC (permalink / raw)
  To: musl

On Sat, Mar 14, 2020 at 09:24:08AM +0100, Florian Weimer wrote:
> * Wolf:
> 
> > While this is admittedly edge case that most users will not run into, I
> > still think it would be nice to behave the same way as glibc does on
> > this one. And as a bonus, it will be *tiny* bit faster, since there
> > would not be any need to iterate rest of the /etc/hosts file.
> 
> But something has to scan the entire file in “multi on” mode at least,
> to find all relevant addresses.

musl doesn't use/support host.conf, so "multi on" isn't an issue for
us at present.

BTW it's not clear to me how the canonical name would/should be
determined in this example if you allow multiple hits.

Rich

^ permalink raw reply	[flat|nested] 6+ messages in thread

* Re: [musl] Proposal to match behaviour of gethostbyname to glibc
  2020-03-14 14:54   ` Rich Felker
@ 2020-03-14 16:31     ` Jeffrey Walton
  0 siblings, 0 replies; 6+ messages in thread
From: Jeffrey Walton @ 2020-03-14 16:31 UTC (permalink / raw)
  To: musl

On Sat, Mar 14, 2020 at 10:54 AM Rich Felker <dalias@libc.org> wrote:
>
> On Sat, Mar 14, 2020 at 09:24:08AM +0100, Florian Weimer wrote:
> > * Wolf:
> > ...
> > But something has to scan the entire file in “multi on” mode at least,
> > to find all relevant addresses.
>
> musl doesn't use/support host.conf, so "multi on" isn't an issue for
> us at present.
>
> BTW it's not clear to me how the canonical name would/should be
> determined in this example if you allow multiple hits.

Perhaps DHCP domain-search option?

Jeff

^ permalink raw reply	[flat|nested] 6+ messages in thread

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Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-13 21:46 [musl] Proposal to match behaviour of gethostbyname to glibc Wolf
2020-03-13 22:16 ` Rich Felker
2020-03-13 23:43   ` Wolf
2020-03-14  8:24 ` Florian Weimer
2020-03-14 14:54   ` Rich Felker
2020-03-14 16:31     ` Jeffrey Walton

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