libvirt: Yaml validator

Test plan:
    PASS: No pylint errors
    PASS: No pep8 errors
    PASS: All data validation accurate
    PASS: Misc Fixes relating to efficiency

Story: 2010816
Task: 48424

Change-Id: I54b48ca0f05c48989c5ae8fb7d18c7ae12d2faad
Signed-off-by: Bailey Henry <Henry.Bailey@windriver.com>

libvirt/config.py

@@ -1,25 +1,137 @@
 #!/usr/bin/python3
 
+import ipaddress
 import sys
 import yaml
 
+# Interface names are limited to 15 characters. 5 are reserved for VLANS
+# ('.####'), it also add a single digit for the four enumerated bridges
+# of the virtual lab. Meaning that 9 characters are left for the end
+# user to choose.
 
+BRIDGE_LIMIT = 9
+
+# Fields that should be set in a Yaml configuration file
+
+GEN_FIELDS = ('bridge_interface', 'controller', 'worker',
+              'domain_dir', 'storage')
+
+IP_FIELDS = ('ext_network', 'ext_IP')
+
+NODES_NUM = ('worker_nodes_num', 'storage_nodes_num')
+
+FIELDS = GEN_FIELDS + IP_FIELDS + NODES_NUM
+
+
+# Allows the user to see how this script is used
 def print_help():
-    print("./config.py <config_file> <key>",
+    print("use: ./config.py <config_file> <key>"
+          " or use: ./config.py --validate <config_file>",
           file=sys.stderr)
 
 
-def readvalue(config_file, key):
+# Checks if there are any unexpected fields in the file
+def existence_check(data):
+    for key in data:
+        if key not in FIELDS:
+            print('unexpected field: %s' % key)
 
+
+# Opens the config file and returns its contents
+def reader(config_file):
     try:
         with open(config_file, 'r', encoding="utf-8") as f:
-            data = yaml.load(f, Loader=yaml.Loader)
+            content = yaml.load(f, Loader=yaml.Loader)
 
-        value = data[key]
-        print(value)
+        return content
 
     except yaml.YAMLError as e:
         print('YAMLError: %s' % e, file=sys.stderr)
+        sys.exit(1)
+    except OSError as e:
+        print('OSError: %s' % e, file=sys.stderr)
+        sys.exit(1)
+
+
+# Allows the user to check if their configuration values
+# exist and are valid
+def validator(config_file):
+
+    ERROR = 0
+
+    data = reader(config_file)
+
+    existence_check(data)
+
+    # For every field checks if they exist and has various checks to
+    # ensure all values are valid
+    for field in FIELDS:
+
+        try:
+            value = data[field]
+        except KeyError:
+            print(' %s does not exist' % field)
+            ERROR += 1
+            continue
+
+        # Checking that most fields are alphanumerical
+        if (field in GEN_FIELDS):
+
+            # Checks if bridge_interface is smaller that nine
+            # characters long
+
+            if (field == 'bridge_interface' and len(value) > BRIDGE_LIMIT):
+
+                print(field + ' variable too long')
+                ERROR += 1
+
+            if value.isalnum() is False:
+                print(field + ' is not alphanumerical')
+                ERROR += 1
+
+        # Checking that there are valid IPv4 addresses
+        elif (field in IP_FIELDS):
+            # Removing the /24 subnet mask
+            try:
+                IP, netmask = value.split('/')
+            except ValueError:
+                print(field + ' does not look like IP/mask', file=sys.stderr)
+                ERROR += 1
+                continue
+
+            try:
+                netmask = int(netmask)
+            except ValueError:
+                print(field + ': not a valid netmask')
+                ERROR += 1
+
+            try:
+                ipaddress.ip_address(IP)
+            except (ValueError):
+                print(field + ' is not a valid IP address', file=sys.stderr)
+                ERROR += 1
+
+        # Checking that node counts are numbers
+        elif (field in NODES_NUM):
+            try:
+                int(value)
+            except ValueError:
+                print(field + ' does not have an integer', file=sys.stderr)
+                ERROR += 1
+
+    if ERROR > 0:
+        print('total errors: %s ' % ERROR)
+        sys.exit(1)
+
+
+# Allows the user to read any value in their configuration file
+def readvalue(config_file, key):
+    data = reader(config_file)
+
+    try:
+        value = data[key]
+        print(value)
+
     except KeyError as e:
         print('KeyError: %s' % e, file=sys.stderr)
 
@@ -29,7 +141,18 @@ if __name__ == "__main__":
 
     if '--help' in args:
         print_help()
-        sys.exit(1)
+        sys.exit(0)
+
+    if '--validate' == args[0]:
+        if len(args) == 2:
+            validator(args[1])
+            sys.exit(0)
+
+        else:
+            print('Validate requires only one parameter: config_file',
+                  file=sys.stderr)
+            print_help()
+            sys.exit(1)
 
     if len(args) == 2:
         input_file = args[0]