Date: Wed, 9 Dec 2015 10:25:39 -0500 From: Ken Moore <ken@pcbsd.org> To: Hiroki Sato <hrs@FreeBSD.org> Cc: freebsd-net@freebsd.org Subject: Re: IPv6 Address as text (C) Message-ID: <566847F3.7060900@pcbsd.org> In-Reply-To: <20151209.233515.1592617248580059512.hrs@allbsd.org> References: <5668369F.9020309@pcbsd.org> <20151209.233515.1592617248580059512.hrs@allbsd.org>
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On 12/09/2015 09:35, Hiroki Sato wrote:
> Ken Moore <ken@pcbsd.org> wrote
> in <5668369F.9020309@pcbsd.org>:
>
> ke> Note: Please CC me on replies - I am not subscribed to this list.
> ke>
> ke> I am having a bit of trouble getting an accurate string representation
> ke> of the current IPv6 address for a given device using the C system
> ke> libraries and was wondering of somebody with more experience than me
> ke> might be able to spot the error...
> ke>
> ke> Background:
> ke> I have been working on a couple simple C/C++/Qt functions to return
> ke> printable forms of the current ipv4 and ipv6 addresses assigned to a
> ke> particular device, and while the ipv4 function works fine the ipv6
> ke> address is consistently wrong and almost always the same string -
> ke> making me think it is converting some internal error code to a string
> ke> ("::XXe2:ffff:ff7f:0" where the "X"s are the only two characters which
> ke> ever change).
> ke>
> ke> The two functions are nearly identical, and I think the error probably
> ke> comes from needing to use inet_ntop() for the ipv6 address because
> ke> there is no ipv6-compatible version of the inet_ntoa() function.
> ke> Do you have any thoughts or ideas about where the error might be
> ke> coming from or a better way to read off the ipv6 address as a string?
> ke>
> ke> Here are the two functions:
> ke> Note: "name" is the QString of the device name (wlan0, re0, other...),
> ke> and is an internal variable for the overall "NetDevice" class
> ke> [code]
> ke> //Fetch the IPv4 address and return it as a QString
> ke> QString NetDevice::ipAsString(){
> ke> struct ifreq ifr;
> ke> memset(&ifr, 0, sizeof(struct ifreq));
> ke>
> ke> strncpy(ifr.ifr_name, name.toLocal8Bit(), IFNAMSIZ);
> ke> int s = socket(PF_INET, SOCK_DGRAM, 0);
> ke>
> ke> ioctl(s, SIOCGIFADDR, &ifr);
> ke> struct in_addr in = ((sockaddr_in *) &ifr.ifr_addr)->sin_addr;
> ke>
> ke> return QString( inet_ntoa(in) );
> ke> }
> ke>
> ke> //Fetch the IPv6 address and return it as a QString
> ke> QString NetDevice::ipv6AsString(){
> ke> struct ifreq ifr;
> ke> memset(&ifr, 0, sizeof(struct ifreq));
> ke>
> ke> strncpy(ifr.ifr_name, name.toLocal8Bit(), IFNAMSIZ);
> ke> int s = socket(PF_INET6, SOCK_DGRAM, 0);
> ke>
> ke> ioctl(s, SIOCGIFADDR, &ifr);
>
> Should this be SIOCGIFADDR_IN6 here? You should check the error
> code.
There does not appear to be any *_IN6 definitions in any of the
/usr/include/[sys, net, netinet]/* include files (sys/sockio.h appears
to hold the defines needed - nothing ipv6 related though).
> Anyway, you should use getnameinfo() for IPv4 and IPv6 instead of
> inet_ntop() and inet_ntoa() for this purpose. It is an address
> family independent API which accepts struct sockaddr directly like
> this:
>
> ----
> struct sockaddr *sa; /* input */
> char hbuf[NI_MAXHOST];
> int error;
>
> error = getnameinfo(sa, sa->sa_len, hbuf, sizeof(hbuf), NULL,
> 0, NI_NUMERICHOST);
> if (error) {
> errx(1, "getnameinfo: %s", gai_strerror(error));
> /* NOTREACHED */
> }
> printf("host=%s\n", hbuf);
> ----
>
> See getnameinfo(3) for more details.
>
> -- Hiroki
So I adjusted the function to use getnameinfo() as you recommended: and
the reported error is "ai_family not supported".
[code]
QString NetDevice::ipv6AsString(){
struct ifreq ifr;
memset(&ifr, 0, sizeof(struct ifreq));
strncpy(ifr.ifr_name, name.toLocal8Bit(), IFNAMSIZ);
int s = socket(PF_INET6, SOCK_DGRAM, 0);
ioctl(s, SIOCGIFADDR, &ifr);
sockaddr *in = (&ifr.ifr_addr);
char straddr[INET6_ADDRSTRLEN];
int err = getnameinfo(in, in->sa_len, straddr,
sizeof(straddr),NULL, 0, NI_NUMERICHOST);
if(err){ return QString(gai_strerror(err)); }
else{ return QString(straddr); }
}
[/code]
--
~~ Ken Moore ~~
PC-BSD/iXsystems
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