Add LinuxAdmin::NetworkInterface.list

Previously there wasn't a method for listing interfaces on the system,
which was okay because we assumed an eth0 was available but as we move
away from that and use the standard predictable network interface names
it would be helpful to get a list.

lib/linux_admin/network_interface.rb

@@ -20,6 +20,21 @@ def self.dist_class(clear_cache = false)
       end
     end
 
+    def self.list
+      ip_link.pluck("ifname").map { |iface| new(iface) }
+    rescue AwesomeSpawn::CommandResultError => e
+      raise NetworkInterfaceError.new(e.message, e.result)
+    end
+
+    private_class_method def self.ip_link
+      require "json"
+
+      ip_link = Common.run!(Common.cmd("ip"), :params => ["--json", "link"])
+      JSON.parse(ip_link.output)
+    rescue AwesomeSpawn::CommandResultError, JSON::ParserError => e
+      raise NetworkInterfaceError.new(e.message, e.result)
+    end
+
     # Creates an instance of the correct NetworkInterface subclass for the local distro
     def self.new(*args)
       self == LinuxAdmin::NetworkInterface ? dist_class.new(*args) : super

spec/network_interface_spec.rb

@@ -55,11 +55,21 @@
   end
 
   context "on all systems" do
-    IP_SHOW_ARGS = [
+    IP_LINK_ARGS = [
+      LinuxAdmin::Common.cmd("ip"),
+      :params => %w(--json link)
+    ]
+
+    IP_SHOW_ARGS = IP_SHOW_ETH0_ARGS = [
       LinuxAdmin::Common.cmd("ip"),
       :params => %w(addr show eth0)
     ]
 
+    IP_SHOW_LO_ARGS = [
+      LinuxAdmin::Common.cmd("ip"),
+      :params => %w(addr show lo)
+    ]
+
     IP_ROUTE_ARGS = [
       LinuxAdmin::Common.cmd("ip"),
       :params => ['-4', 'route']
@@ -80,6 +90,19 @@
       :params => ["eth0"]
     ]
 
+    IP_LINK_OUT = <<~IP_OUT
+      [{"ifindex":1,"ifname":"lo","flags":["LOOPBACK","UP","LOWER_UP"],"mtu":65536,"qdisc":"noqueue","operstate":"UNKNOWN","linkmode":"DEFAULT","group":"default","txqlen":1000,"link_type":"loopback","address":"00:00:00:00:00:00","broadcast":"00:00:00:00:00:00"},{"ifindex":2,"ifname":"eth0","flags":["BROADCAST","MULTICAST","UP","LOWER_UP"],"mtu":1500,"qdisc":"fq_codel","operstate":"UP","linkmode":"DEFAULT","group":"default","txqlen":1000,"link_type":"ether","address":"52:54:00:e8:67:81","broadcast":"ff:ff:ff:ff:ff:ff","altnames":["enp0s2","ens2"]}]
+    IP_OUT
+
+    IP_ADDR_LO_OUT = <<~IP_OUT
+    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
+    IP_OUT
+
     IP_ADDR_OUT = <<-IP_OUT
 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP qlen 1000
     link/ether 00:0c:29:ed:0e:8b brd ff:ff:ff:ff:ff:ff
@@ -115,6 +138,18 @@
     link/ether 52:54:00:ce:b4:f4 brd ff:ff:ff:ff:ff:ff
 IP_OUT
 
+    subject(:subj_list) do
+      allow(LinuxAdmin::Distros).to receive(:local).and_return(LinuxAdmin::Distros.generic)
+      described_class.dist_class(true)
+
+      allow(AwesomeSpawn).to receive(:run!).with(*IP_LINK_ARGS).and_return(result(IP_LINK_OUT, 0))
+      allow(AwesomeSpawn).to receive(:run!).with(*IP_SHOW_LO_ARGS).and_return(result(IP_ADDR_LO_OUT, 0))
+      allow(AwesomeSpawn).to receive(:run!).with(*IP_SHOW_ETH0_ARGS).and_return(result(IP_ADDR_OUT, 0))
+      allow(AwesomeSpawn).to receive(:run!).with(*IP_ROUTE_ARGS).and_return(result(IP_ROUTE_OUT, 0))
+      allow(AwesomeSpawn).to receive(:run!).with(*IP6_ROUTE_ARGS).and_return(result(IP6_ROUTE_OUT, 0))
+      described_class.list
+    end
+
     subject(:subj) do
       allow(LinuxAdmin::Distros).to receive(:local).and_return(LinuxAdmin::Distros.generic)
       described_class.dist_class(true)
@@ -149,6 +184,14 @@ def result(output, exit_status)
       AwesomeSpawn::CommandResult.new("", output, "", nil, exit_status)
     end
 
+    describe ".list" do
+      it "returns a list of NetworkInterface objects" do
+        interfaces = subj_list
+        expect(interfaces.count).to eq(2)
+        expect(interfaces.map(&:interface)).to match_array(["eth0", "lo"])
+      end
+    end
+
     describe "#reload" do
       it "returns false when ip addr show fails" do
         subj