test/system: Add tests for pasta(1) connectivity

These tests should cover all the basic networking functionality with
pasta(1). Namely, they check:

- IPv4 and IPv6 addressing and routing settings

- TCP and UDP port forwarding over IPv4 and IPv6

- data transfers and ICMP/ICMPv6 echo requests

- the (exceedingly simple) lifecycle handling

These tests need some new helpers, to obtain IPv4 and IPv4 addresses
and routes, as well as MTU and interface names. Those use jq(1) for
parsing.

Some availability checks are implemented as well, to skip tests if
pasta(1) is not available, or if IPv4 and IPv6 are not usable.

To get consistent outcomes across distributions, and to enable
uncomplicated termination for UDP tests based on zero-sized packets,
use socat(1), which, unlike netcat, doesn't suffer from option
inconsistencies depending on flavours (traditional, BSD, NMAP) and
versions.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

test/system/helpers.network.bash

@@ -1,6 +1,51 @@
 # -*- bash -*-
 
 
+### Feature Checks #############################################################
+
+# has_ipv4() - Check if one default route is available for IPv4
+function has_ipv4() {
+    [ -n "$(ip -j -4 route show | jq -rM '.[] | select(.dst == "default")')" ]
+}
+
+# has_ipv6() - Check if one default route is available for IPv6
+function has_ipv6() {
+    [ -n "$(ip -j -6 route show | jq -rM '.[] | select(.dst == "default")')" ]
+}
+
+# skip_if_no_ipv4() - Skip current test if IPv4 traffic can't be routed
+# $1:	Optional message to display
+function skip_if_no_ipv4() {
+    if ! has_ipv4; then
+        local msg=$(_add_label_if_missing "$1" "IPv4")
+        skip "${msg:-not applicable with no routable IPv4}"
+    fi
+}
+
+# skip_if_no_ipv6() - Skip current test if IPv6 traffic can't be routed
+# $1:	Optional message to display
+function skip_if_no_ipv6() {
+    if ! has_ipv6; then
+        local msg=$(_add_label_if_missing "$1" "IPv6")
+        skip "${msg:-not applicable with no routable IPv6}"
+    fi
+}
+
+# has_pasta() - Check if the pasta(1) command is available
+function has_pasta() {
+    command -v pasta >/dev/null
+}
+
+# skip_if_no_pasta() - Skip current test if pasta(1) is not available
+# $1:	Optional message to display
+function skip_if_no_pasta() {
+    if ! has_pasta; then
+        local msg=$(_add_label_if_missing "$1" "pasta")
+        skip "${msg:-not applicable with no pasta binary}"
+    fi
+}
+
+
 ### procfs access ##############################################################
 
 # ipv6_to_procfs() - RFC 5952 IPv6 address text representation to procfs format
@@ -52,7 +97,21 @@ function ipv4_to_procfs() {
 }
 
 
-### Addresses ##################################################################
+### Addresses, Routes, Links ###################################################
+
+# ipv4_get_addr_global() - Print first global IPv4 address reported by netlink
+# $1:	Optional output of 'ip -j -4 address show' from a different context
+function ipv4_get_addr_global() {
+    local expr='[.[].addr_info[] | select(.scope=="global")] | .[0].local'
+    echo "${1:-$(ip -j -4 address show)}" | jq -rM "${expr}"
+}
+
+# ipv6_get_addr_global() - Print first global IPv6 address reported by netlink
+# $1:	Optional output of 'ip -j -6 address show' from a different context
+function ipv6_get_addr_global() {
+    local expr='[.[].addr_info[] | select(.scope=="global")] | .[0].local'
+    echo "${1:-$(ip -j -6 address show)}" | jq -rM "${expr}"
+}
 
 # random_rfc1918_subnet() - Pseudorandom unused subnet in 172.16/12 prefix
 #
@@ -80,6 +139,34 @@ function random_rfc1918_subnet() {
     die "Could not find a random not-in-use rfc1918 subnet"
 }
 
+# ipv4_get_route_default() - Print first default IPv4 route reported by netlink
+# $1:	Optional output of 'ip -j -4 route show' from a different context
+function ipv4_get_route_default() {
+    local jq_expr='[.[] | select(.dst == "default").gateway] | .[0]'
+    echo "${1:-$(ip -j -4 route show)}" | jq -rM "${jq_expr}"
+}
+
+# ipv6_get_route_default() - Print first default IPv6 route reported by netlink
+# $1:	Optional output of 'ip -j -6 route show' from a different context
+function ipv6_get_route_default() {
+    local jq_expr='[.[] | select(.dst == "default").gateway] | .[0]'
+    echo "${1:-$(ip -j -6 route show)}" | jq -rM "${jq_expr}"
+}
+
+# ether_get_mtu() - Get MTU of first Ethernet-like link
+# $1:	Optional output of 'ip -j link show' from a different context
+function ether_get_mtu() {
+    local jq_expr='[.[] | select(.link_type == "ether").mtu] | .[0]'
+    echo "${1:-$(ip -j link show)}" | jq -rM "${jq_expr}"
+}
+
+# ether_get_name() - Get name of first Ethernet-like interface
+# $1:	Optional output of 'ip -j link show' from a different context
+function ether_get_name() {
+    local jq_expr='[.[] | select(.link_type == "ether").ifname] | .[0]'
+    echo "${1:-$(ip -j link show)}" | jq -rM "${jq_expr}"
+}
+
 
 ### Ports and Ranges ###########################################################