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C program to resolve UTF-8 IDNs

Sean Conner sean at conman.org

Thu Mar 18 02:13:18 GMT 2021

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It was thus said that the Great Scot once stated:

Hi Sean,

Hi Scot!

I think you were wondering whether it's possible to resolve UTF-8

IDNs with a C or Lua program. This Linux C program [7] will do so

via glibc's getaddrinfo(). For platforms without glibc such as the

BSDs, ports of the libidn library [1] are available.

Microsoft provides IdnToAscii() [2] for use with Windows 7 and it

looks as if they support automatic conversion to punycode [3]

in their implemenation of getaddrinfo() as of Windows 8.

Slides 30 through 48 of this presentation [4] describe how Apple

approaches network name internationalization. iOS 10 and

macOS Sierra will try to query a given UTF-8 name via DNS. If

the server doesn't have an entry for the UTF-8 name, it

converts to punycode and tries again.

Android 2.3 has the java.net.IDN package [5] for converting

IDNs and Android 7.0 has android.icu.text.IDNA [6].

Thoughts?

Thank you *so* much for the sample code, and providing much neededbackground information about this. This will make the final decision on IRIsupport a bit easier to make. I was not aware of the GNU-specific AI_IDNflag to getaddrinfo() (and I wish it was standard actually), and yes, itdoes work on systems that have it (Linux).

Just one thing though---you might want to be careful when pasting codeinto email---the code below contained non-breaking spaces that my C compiler(gcc) did not like. It's an easy fix, so this is mostly an FYI gettingweird errors when compiling the code below.

Again, thank you for your message.

-spc

[1] https://www.gnu.org/software/libidn/

[2] https://docs.microsoft.com/en-us/windows/win32/api/winnls/nf-winnls-idntoascii

[3] https://docs.microsoft.com/en-us/windows/win32/api/ws2tcpip/nf-ws2tcpip-getaddrinfo

[4] https://devstreaming-cdn.apple.com/videos/wwdc/2016/714urluxe140lardrb7/714/714_networking_for_the_modern_internet.pdf?dl=1

[5] https://developer.android.com/reference/kotlin/java/net/IDN

[6] https://developer.android.com/reference/android/icu/text/IDNA

[7] Public domain example C program to resolve UTF-8 IDNs

P.S. Here's the code with the non-breaking spaces removed.

include <locale.h>#include <netdb.h>#include <stdio.h>#include <string.h>#include <arpa/inet.h>#include <netinet/in.h>#include <sys/socket.h>#include <sys/types.h>

define ADDR_LEN 1024

void show_ip(char *name) { struct addrinfo filter, *info; char address[ADDR_LEN]; void *addr; memset (&filter, 0, sizeof(filter)); filter.ai_family = PF_UNSPEC; filter.ai_socktype = SOCK_STREAM; filter.ai_flags = AI_IDN; if (getaddrinfo (name, NULL, &filter, &info) == 0) { printf ("\nHost: %s\n", name); while (info) { if (info-

ai_family == AF_INET) { addr = &((struct sockaddr_in *) info-

ai_addr)-

sin_addr; inet_ntop (AF_INET, addr, address, ADDR_LEN); printf (" IPv4 address: %s\n", address); } else if (info-

ai_family == AF_INET6) { addr = &((struct sockaddr_in6 *) info-

ai_addr)-

sin6_addr; inet_ntop (AF_INET6, addr, address, ADDR_LEN); printf (" IPv6 address: %s\n", address); } info = info-

ai_next; } } else perror ("getaddrinfo"); freeaddrinfo(info);}

int main() { setlocale(LC_ALL, ""); show_ip("蛸.jp"); show_ip("xn--td2a.jp"); show_ip("gémeaux.bortzmeyer.org"); show_ip("xn--gmeaux-bva.bortzmeyer.org"); show_ip("café.mozz.us"); show_ip("xn--caf-dma.mozz.us");}