fix(ns-plug): inventory, better public IP retrieval (#1344)

The ifconfig.co site sometimes returns an HTML page and this info is wrongly sent to my.nethesis.it

New behavior:
- send an HTTP request to ifconfig.co and parse the response, if the remote server returns a valid IP address, return it
- otherwise, try to obtain the same info by executing a DNS query to OpenDNS
- return an empty string if none of the above responses are valid IP addresses

Author: gsanchietti

packages/ns-plug/files/inventory

@@ -8,6 +8,7 @@
 import re
 import json
 import subprocess
+import ipaddress
 from euci import EUci
 from struct import pack
 from nethsec import utils, inventory
@@ -71,6 +72,22 @@ def _get_gateway(interface):
     except:
         return ''
 
+def _get_public_ip():
+    # Try ifconfig.co: sometimes the site returns an HTML error page, ignore it
+    address = _run("curl --fail --max-time 5 --retry 2 https://ifconfig.co")
+    try:
+        ipaddress.ip_address(address)
+        return address
+    except:
+        # Fallback to DNS query
+        address = _run("dig +short myip.opendns.com @resolver1.opendns.com")
+
+    try:
+        ipaddress.ip_address(address)
+        return address
+    except:
+        return ''
+
 release = _run('grep VERSION= /etc/os-release | cut -d= -f 2 | tr -d \'"\'')
 cpu_info = _run_json('lscpu -J')['lscpu']
 binfo = _run_json("cat /etc/board.json")
@@ -152,7 +169,7 @@ data = {
         }
     },
     "rpms": { "nethserver-firewall-base-ui": _run("opkg status ns-ui | grep Version | awk '{print $2}'") },
-    "public_ip": _run("curl https://ifconfig.co"),
+    "public_ip": _get_public_ip(),
     "features": features
 }