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[bug-gawk] getaddrinfo() in socketopen() (io.c) fails for AF_INET[46] --

From: Houder
Subject: [bug-gawk] getaddrinfo() in socketopen() (io.c) fails for AF_INET[46] -- unnecessarily
Date: Thu, 08 Feb 2018 18:59:04 +0100
User-agent: XS4ALL Webmail 
L.S.,

(Using Fedora 24)

gawkinet.pdf ("TCP/IP (Inter)Networking with gawk") outlines a simple
"Panic" webserver in section 3.1 (page 35).

The script is as follows:

BEGIN {
    RS = ORS = "\r\n"
    if (MyPort == 0) MyPort = 8080
    HttpService = "/inet/tcp/" MyPort "/0/0"
    #HttpService = "/inet4/tcp/" MyPort "/0/0"
    #HttpService = "/inet6/tcp/" MyPort "/0/0"
    Hello = "<HTML><HEAD><TITLE>Out Of Service</TITLE>" \
        "</HEAD><BODY><H1>" \
        "This site is temporarily out of service." \
        "</H1></BODY></HTML>"
    Len = length(Hello) + length(ORS)
    print "Ha!"
    HttpService
    #while ("awk" != "complex") {
    while (" ") {
        print "HTTP/1.0 200 OK" |& HttpService
        print "Content-Length: " Len ORS |& HttpService
        print Hello |& HttpService
        while ((HttpService |& getline) > 0)
            continue;
        close(HttpService)
    }
}

If "/inet" in the definition of HttpService (see above) is replaced
by either "/inet4" or "/inet6",

    the script fails in case the loopback interface is the only one
    that is up (i.e. all other network interfaces are down)

@@ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp3s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000 
    link/ether 74:d0:2b:a0:4b:40 brd ff:ff:ff:ff:ff:ff

Using gawk-4.2.0, the script fails with: (if using /inet4 i.s.o. /inet)

warning: local port 8080 invalid in `/inet': Name or service not known
fatal: can't open two way pipe `/inet4/tcp/8080/0/0' for input/output (No such file or directory) 

The script fails because getaddrinfo() in socketopen() (gawk-4.2.0/io.c)
fails ... but unnecessarily (I believe).
Modifying gawk-4.2.0/io.c as follows, prevents getaddrinfo() from failing: 

static int
socketopen(int family, int type, const char *localpname,
const char *remotepname, const char *remotehostname, bool *hard_error) 
{
[snip]

        memset(& lhints, '\0', sizeof (lhints));
/* if only the loopback interface is up and hints.ai_flags has AI_ADDRCONFIG, getaddrinfo() will return the addresses of the loopback interface, but only 
           if hints.ai_family == AF_UNSPEC
        */

        lhints.ai_flags = AI_PASSIVE | AI_ADDRCONFIG;

        lhints.ai_socktype = type;
        lhints.ai_family = family;
// do return the loopback address in case the loopback interface is the only one that 
// is up (and hints.ai_family == AF_INET[46])
if ( (lhints.ai_family == AF_INET) || (lhints.ai_family == AF_INET6) )
   lhints.ai_flags = AI_PASSIVE;


        lerror = getaddrinfo(NULL, localpname, & lhints, & lres);
...

Henri
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