Implement class-based version of zkhander

daemon-common/zkhandler.py

@@ -21,164 +21,232 @@
 
 import time
 import uuid
+from kazoo.client import KazooClient
 
 
-# Exists function
+class ZKHandler(object):
-def exists(zk_conn, key):
+    def __init__(self, hosts):
-    stat = zk_conn.exists(key)
+        """
-    if stat:
+        Initialize an instance of the ZKHandler class with config
-        return True
-    else:
-        return False
 
+        A zk_conn object will be created but not started
+        """
+        self.encoding = 'utf8'
+        self.zk_conn = KazooClient(hosts=hosts)
 
-# Child list function
+    #
-def listchildren(zk_conn, key):
+    # State/connection management
-    children = zk_conn.get_children(key)
+    #
-    return children
+    def connect(self):
+        """
+        Start the zk_conn object and connect to the cluster
+        """
+        self.zk_conn.start()
 
+    def disconnect(self):
+        """
+        Stop and close the zk_conn object and disconnect from the cluster
 
-# Delete key function
+        The class instance may be reused later (avoids persistent connections)
-def deletekey(zk_conn, key, recursive=True):
+        """
-    zk_conn.delete(key, recursive=recursive)
+        self.zk_conn.stop()
+        self.zk_conn.close()
 
-
+    #
-# Rename key recursive function
+    # Key Actions
-def rename_key_element(zk_conn, zk_transaction, source_key, destination_key):
+    #
-    data_raw = zk_conn.get(source_key)
+    def exists(self, key):
-    data = data_raw[0]
+        """
-    zk_transaction.create(destination_key, data)
+        Check if a key exists
-
+        """
-    if zk_conn.get_children(source_key):
+        stat = self.zk_conn.exists(key)
-        for child_key in zk_conn.get_children(source_key):
+        if stat:
-            child_source_key = "{}/{}".format(source_key, child_key)
+            return True
-            child_destination_key = "{}/{}".format(destination_key, child_key)
-            rename_key_element(zk_conn, zk_transaction, child_source_key, child_destination_key)
-
-    zk_transaction.delete(source_key)
-
-
-# Rename key function
-def renamekey(zk_conn, kv):
-    # Start up a transaction
-    zk_transaction = zk_conn.transaction()
-
-    # Proceed one KV pair at a time
-    for source_key in sorted(kv):
-        destination_key = kv[source_key]
-
-        # Check if the source key exists or fail out
-        if not zk_conn.exists(source_key):
-            raise
-        # Check if the destination key exists and fail out
-        if zk_conn.exists(destination_key):
-            raise
-
-        rename_key_element(zk_conn, zk_transaction, source_key, destination_key)
-
-    # Commit the transaction
-    try:
-        zk_transaction.commit()
-        return True
-    except Exception:
-        return False
-
-
-# Data read function
-def readdata(zk_conn, key):
-    data_raw = zk_conn.get(key)
-    data = data_raw[0].decode('utf8')
-    return data
-
-
-# Data write function
-def writedata(zk_conn, kv):
-    # Start up a transaction
-    zk_transaction = zk_conn.transaction()
-
-    # Proceed one KV pair at a time
-    for key in sorted(kv):
-        data = kv[key]
-
-        # Check if this key already exists or not
-        if not zk_conn.exists(key):
-            # We're creating a new key
-            zk_transaction.create(key, str(data).encode('utf8'))
         else:
-            # We're updating a key with version validation
+            return False
-            orig_data = zk_conn.get(key)
-            version = orig_data[1].version
 
-            # Set what we expect the new version to be
+    def read(self, key):
-            new_version = version + 1
+        """
+        Read data from a key
+        """
+        return self.zk_conn.get(key)[0].decode(self.encoding)
 
-            # Update the data
+    def write(self, kvpairs):
-            zk_transaction.set_data(key, str(data).encode('utf8'))
+        """
+        Create or update one or more keys' data
+        """
+        if type(kvpairs) is not list:
+            print("ZKHandler error: Key-value sequence is not a list")
+            return False
 
-            # Set up the check
+        transaction = self.zk_conn.transaction()
-            try:
+
-                zk_transaction.check(key, new_version)
+        for kvpair in (kvpairs):
-            except TypeError:
+            if type(kvpair) is not tuple:
-                print('Zookeeper key "{}" does not match expected version'.format(key))
+                print("ZKHandler error: Key-value pair '{}' is not a tuple".format(kvpair))
                 return False
 
-    # Commit the transaction
+            key = kvpair[0]
-    try:
+            value = kvpair[1]
-        zk_transaction.commit()
-        return True
-    except Exception:
-        return False
 
+            if not self.exists(key):
+                # Creating a new key
+                transaction.create(key, str(value).encode(self.encoding))
 
-# Write lock function
-def writelock(zk_conn, key):
-    count = 1
-    while True:
-        try:
-            lock_id = str(uuid.uuid1())
-            lock = zk_conn.WriteLock('{}'.format(key), lock_id)
-            break
-        except Exception:
-            count += 1
-            if count > 5:
-                break
             else:
-                time.sleep(0.5)
+                # Updating an existing key
-                continue
+                data = self.zk_conn.get(key)
-    return lock
+                version = data[1].version
 
+                # Validate the expected version after the execution
+                new_version = version + 1
+
+                # Update the data
+                transaction.set_data(key, str(value).encode(self.encoding))
+
+                # Check the data
+                try:
+                    transaction.check(key, new_version)
+                except TypeError:
+                    print("ZKHandler error: Key '{}' does not match expected version".format(key))
+                    return False
 
-# Read lock function
-def readlock(zk_conn, key):
-    count = 1
-    while True:
         try:
-            lock_id = str(uuid.uuid1())
+            transaction.commit()
-            lock = zk_conn.ReadLock('{}'.format(key), lock_id)
+            return True
-            break
+        except Exception as e:
-        except Exception:
+            print("ZKHandler error: Failed to commit transaction: {}".format(e))
-            count += 1
+            return False
-            if count > 5:
-                break
-            else:
-                time.sleep(0.5)
-                continue
-    return lock
 
+    def delete(self, key, recursive=True):
+        """
+        Delete a key (defaults to recursive)
+        """
+        if self.zk_conn.delete(key, recursive=recursive):
+            return True
+        else:
+            return False
+
+    def children(self, key):
+        """
+        Lists all children of a key
+        """
+        return self.zk_conn.get_children(key)
+
+    def rename(self, kkpairs):
+        """
+        Rename one or more keys to a new value
+        """
+        if type(kkpairs) is not list:
+            print("ZKHandler error: Key-key sequence is not a list")
+            return False
+
+        transaction = self.zk_conn.transaction()
+
+        def rename_element(transaction, source_key, destnation_key):
+            data = self.zk_conn.get(source_key)[0]
+            transaction.create(destination_key, data)
+
+            if self.children(source_key):
+                for child_key in self.children(source_key):
+                    child_source_key = "{}/{}".format(source_key, child_key)
+                    child_destination_key = "{}/{}".format(destination_key, child_key)
+                    rename_element(transaction, child_source_key, child_destination_key)
+
+            transaction.delete(source_key, recursive=True)
+
+        for kkpair in (kkpairs):
+            if type(kkpair) is not tuple:
+                print("ZKHandler error: Key-key pair '{}' is not a tuple".format(kkpair))
+                return False
+
+            source_key = kkpair[0]
+            destination_key = kkpair[1]
+
+            if not self.exists(source_key):
+                print("ZKHander error: Source key '{}' does not exist".format(source_key))
+                return False
+            if self.exists(destination_key):
+                print("ZKHander error: Destination key '{}' already exists".format(destination_key))
+                return False
+
+            rename_element(transaction, source_key, destination_key)
 
-# Exclusive lock function
-def exclusivelock(zk_conn, key):
-    count = 1
-    while True:
         try:
-            lock_id = str(uuid.uuid1())
+            transaction.commit()
-            lock = zk_conn.Lock('{}'.format(key), lock_id)
+            return True
-            break
+        except Exception as e:
-        except Exception:
+            print("ZKHandler error: Failed to commit transaction: {}".format(e))
-            count += 1
+            return False
-            if count > 5:
+
+    #
+    # Lock actions
+    #
+    def readlock(self, key):
+        """
+        Acquires a read lock on a key
+        """
+        count = 1
+        lock = None
+
+        while True:
+            try:
+                lock_id = str(uuid.uuid1())
+                lock = self.zk_conn.ReadLock(key, lock_id)
                 break
-            else:
+            except Exception as e:
-                time.sleep(0.5)
+                if count > 5:
-                continue
+                    print("ZKHandler warning: Failed to acquire read lock after 5 tries: {}".format(e))
-    return lock
+                    break
+                else:
+                    time.sleep(0.5)
+                    count += 1
+                    continue
+
+        return lock
+
+    def writelock(self, key):
+        """
+        Acquires a write lock on a key
+        """
+        count = 1
+        lock = None
+
+        while True:
+            try:
+                lock_id = str(uuid.uuid1())
+                lock = self.zk_conn.WriteLock(key, lock_id)
+                break
+            except Exception as e:
+                if count > 5:
+                    print("ZKHandler warning: Failed to acquire write lock after 5 tries: {}".format(e))
+                    break
+                else:
+                    time.sleep(0.5)
+                    count += 1
+                    continue
+
+        return lock
+
+    def exclusivelock(self, key):
+        """
+        Acquires an exclusive lock on a key
+        """
+        count = 1
+        lock = None
+
+        while True:
+            try:
+                lock_id = str(uuid.uuid1())
+                lock = self.zk_conn.Lock(key, lock_id)
+                break
+            except Exception as e:
+                if count > 5:
+                    print("ZKHandler warning: Failed to acquire exclusive lock after 5 tries: {}".format(e))
+                    break
+                else:
+                    time.sleep(0.5)
+                    count += 1
+                    continue
+
+        return lock