1 files changed, 119 insertions, 0 deletions
diff --git a/project2/proj2_s4498062/dns/cache.py b/project2/proj2_s4498062/dns/cache.py
new file mode 100644
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+++ b/project2/proj2_s4498062/dns/cache.py
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+"""A cache for resource records
+
+This module contains a class which implements a cache for DNS resource records,
+you still have to do most of the implementation. The module also provides a
+class and a function for converting ResourceRecords from and to JSON strings.
+It is highly recommended to use these.
+"""
+
+import json
+import time
+
+from dns.resource import ResourceRecord, RecordData
+from dns.types import Type
+from dns.classes import Class
+
+
+class ResourceEncoder(json.JSONEncoder):
+    """ Conver ResourceRecord to JSON
+
+    Usage:
+        string = json.dumps(records, cls=ResourceEncoder, indent=4)
+    """
+    def default(self, obj):
+        if isinstance(obj, ResourceRecord):
+            return {
+                "name":       obj.name,
+                "type":       Type.to_string(obj.type_),
+                "class":      Class.to_string(obj.class_),
+                "ttl":        obj.ttl,
+                "rdata":      obj.rdata.data,
+                "timestamp":  obj.timestamp
+            }
+        return json.JSONEncoder.default(self, obj)
+
+
+def resource_from_json(dct):
+    """ Convert JSON object to ResourceRecord
+
+    Usage:
+        records = json.loads(string, object_hook=resource_from_json)
+    """
+    name = dct["name"]
+    type_ = Type.from_string(dct["type"])
+    class_ = Class.from_string(dct["class"])
+    ttl = dct["ttl"]
+    rdata = RecordData.create(type_, dct["rdata"])
+    timestamp = dct["timestamp"]
+    return ResourceRecord(name, type_, class_, ttl, rdata, timestamp)
+
+
+class RecordCache(object):
+    """ Cache for ResourceRecords """
+
+    FILE = '.dns.cache'
+
+    def __init__(self, ttl):
+        """ Initialize the RecordCache
+
+        Args:
+            ttl (int): TTL of cached entries (if > 0)
+        """
+        self.records = []
+        self.read_cache_file()
+        self.ttl = ttl
+
+    def __del__(self):
+        self.write_cache_file()
+
+    def remove_old(self):
+        """Remove entries for which the TTL has expired"""
+        now = int(time.time())
+        for record in reversed(self.records):
+            if min(self.ttl, record.ttl) + record.timestamp < now:
+                self.records.remove(record)
+
+    def lookup(self, dname, type_, class_):
+        """ Lookup resource records in cache
+
+        Lookup for the resource records for a domain name with a specific type
+        and class.
+
+        Args:
+            dname (str): domain name
+            type_ (Type): type
+            class_ (Class): class
+        """
+        self.remove_old()
+        return [
+            r for r in self.records
+            if r.match(name=dname, type_=type_, class_=class_)]
+
+    def add_records_from(self, msg):
+        for record in msg.answers + msg.authorities + msg.additionals:
+            if record.type_ in [Type.A, Type.AAAA, Type.CNAME, Type.NS] and \
+                    record.class_ == Class.IN:
+                self.add_record(record)
+
+    def add_record(self, record):
+        """ Add a new Record to the cache
+
+        Args:
+            record (ResourceRecord): the record added to the cache
+        """
+        self.records.append(record)
+
+    def read_cache_file(self):
+        """ Read the cache file from disk """
+        try:
+            with open(self.FILE, 'r') as jsonfile:
+                self.records = json.load(
+                    jsonfile, object_hook=resource_from_json)
+        except IOError:
+            pass
+
+    def write_cache_file(self):
+        """ Write the cache file to disk """
+        self.remove_old()
+        with open(self.FILE, 'w') as jsonfile:
+            json.dump(self.records, jsonfile, cls=ResourceEncoder, indent=4)