[scanner] implement the --list flag

cdist/argparse.py

@@ -486,6 +486,10 @@ def get_parsers():
         '-m', '--mode', help='Which modes should run',
         action='append', default=[],
         choices=['scan', 'trigger'])
+    parser['scan'].add_argument(
+        '--list',
+        action='store_true',
+        help='List the known hosts and exit')
     parser['scan'].add_argument(
         '--config',
         action='store_true',

cdist/scan/commandline.py

@@ -21,26 +21,11 @@
 
 import logging
 import sys
+from datetime import datetime
 
 log = logging.getLogger("scan")
 
-# CLI processing is defined outside of the main scan class to handle
-# non-available optional scapy dependency (instead of crashing mid-flight).
-def commandline(args):
-    log.debug(args)
-
-    # Check if we have the optional scapy dependency available.
-    try:
-        import cdist.scan.scan as scan
-    except ModuleNotFoundError:
-        log.error('cdist scan requires scapy to be installed. Exiting.')
-        sys.exit(1)
-
-    # Default operation mode.
-    if not args.mode:
-        # By default scan and trigger, but do not call any action.
-        args.mode = ['scan', 'trigger', ]
-
+def run(scan, args):
     # We run each component in a separate process since they
     # must not block on each other.
     processes = []
@@ -59,3 +44,47 @@ def commandline(args):
 
     for process in processes:
         process.join()
+
+def list(scan, args):
+    s = scan.Scanner(interfaces=args.interfaces, args=args)
+    hosts = s.list()
+
+    # A full IPv6 addresses id composed of 8 blocks of 4 hexa chars +
+    # 6 colons.
+    ipv6_max_size = 8 * 4 + 10
+    # We format dates as follow: YYYY-MM-DD HH:MM:SS
+    date_max_size =              8 + 2    + 6 + 2
+
+    print("{} | {}".format(
+        'link-local address'.ljust(ipv6_max_size),
+        'last seen'.ljust(date_max_size)))
+    print('=' * (ipv6_max_size + 3 + date_max_size))
+    for addr in hosts:
+        last_seen = datetime.strftime(
+                datetime.strptime(hosts[addr]['last_seen'].strip(), '%Y-%m-%d %H:%M:%S.%f'),
+                '%Y-%m-%d %H:%M:%S')
+        print("{} | {}".format(addr.ljust(ipv6_max_size),last_seen.ljust(date_max_size)))
+
+# CLI processing is defined outside of the main scan class to handle
+# non-available optional scapy dependency (instead of crashing mid-flight).
+def commandline(args):
+    log.debug(args)
+
+    # Check if we have the optional scapy dependency available.
+    try:
+        import cdist.scan.scan as scan
+    except ModuleNotFoundError:
+        log.error('cdist scan requires scapy to be installed. Exiting.')
+        sys.exit(1)
+
+    # Set default operation mode.
+    if not args.mode:
+        # By default scan and trigger, but do not call any action.
+        args.mode = ['scan', 'trigger', ]
+
+    # Print known hosts and exit is --list is specified - do not start
+    # the scanner.
+    if args.list:
+        list(scan, args)
+    else:
+        run(scan, args)

cdist/scan/scan.py

@@ -132,6 +132,23 @@ class Scanner(object):
             with open(fname, "w") as fd:
                 fd.write(f"{now}\n")
 
+    def list(self):
+        hosts = dict()
+        for linklocal_addr in os.listdir(self.outdir):
+            workdir = os.path.join(self.outdir, linklocal_addr)
+            # We ignore any (unexpected) file in this directory.
+            if os.path.isdir(workdir):
+                last_seen='-'
+                last_seen_file = os.path.join(workdir, 'last_seen')
+                if os.path.isfile(last_seen_file):
+                    with open(last_seen_file, "r") as fd:
+                        last_seen = fd.readline()
+
+                hosts[linklocal_addr] = {'last_seen': last_seen}
+
+        return hosts
+
+
     def config(self):
         """
         Configure a host