Add IPv6 availability check to skip tests when unavailable (#2674)

Skip IPv6 tests automatically when IPv6 is not available.

This fixes the problem that tests fail when IPv6 is not available on the
system, which can worry users when they run `make test`.

IPv6 availibility is detected by opening a dummy server socket and
trying to connect to it using a client socket over IPv6.

Fixes #2643

---------

Signed-off-by: diego-ciciani01 <[email protected]>
Signed-off-by: Viktor Söderqvist <[email protected]>
Co-authored-by: Viktor Söderqvist <[email protected]>

Author: diego-ciciani01

tests/support/server.tcl

@@ -268,6 +268,11 @@ proc tags_acceptable {tags err_return} {
         return 0
     }
 
+    if {[lsearch $tags "ipv6"] >= 0 && ![is_ipv6_available]} {
+        set err "IPv6 not available on this system"
+        return 0
+    }
+
     return 1
 }
 

tests/test_helper.tcl

@@ -1002,6 +1002,21 @@ proc close_replication_stream {s} {
     return
 }
 
+# IPv6 detection utilities
+# for this detection: the socket connection on ::1 address
+proc is_ipv6_available {} {
+    if {[catch {
+        set server [socket -server dummy -myaddr ::1 0]
+        set port [lindex [chan configure $server -sockname] 2]
+        set client [socket ::1 $port]
+        close $server
+        close $client
+    }] == 0} {
+        return 1
+    }
+    return 0
+}
+
 # With the parallel test running multiple server instances at the same time
 # we need a fast enough computer, otherwise a lot of tests may generate
 # false positives.

tests/unit/introspection.tcl

@@ -265,7 +265,7 @@ start_server {tags {"introspection"}} {
     } {}
 
     start_server {tags {"ipv6"} overrides {bind {127.0.0.1 ::1}}} {
-        test {CLIENT LIST with IPv6 filter} {
+        test {CLIENT KILL with IPv6 filter} {
             set c [valkey ::1 [srv 0 port] 0 $::tls]
             $c client setname "client-ipv6"