AvroConsumer for handling schema registry (#80)

* AvroProducer for handling  schema registry

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* Consumer client for handling  avro schemas

Author: roopahc

README.md

@@ -60,6 +60,33 @@ avroProducer = AvroProducer({'bootstrap.servers': 'mybroker,mybroker2', 'schema.
 avroProducer.produce(topic='my_topic', value=value, key=key)
 ```
 
+**AvroConsumer**
+```
+import sys
+import traceback
+from confluent_kafka import KafkaError
+from confluent_kafka.avro import AvroConsumer
+from confluent_kafka.avro.serializer import SerializerError
+
+c = AvroConsumer({'bootstrap.servers': 'mybroker,mybroker2', 'group.id': 'groupid', 'schema.registry.url': 'http://127.0.0.1:8081'})
+c.subscribe(['my_topic'])
+running = True
+while running:
+    try:
+        msg = c.poll(10)
+        if msg:
+            if not msg.error():
+                print(msg.value())
+            elif msg.error().code() != KafkaError._PARTITION_EOF:
+                print(msg.error())
+                running = False
+    except SerializerError as e:
+        print("Message deserialization failed for %s: %s" % (msg, e))
+        running = False
+        
+c.close()
+```
+
 See [examples](examples) for more examples.
 
 
@@ -100,15 +127,15 @@ Install
 
     $ pip install confluent-kafka
 
-    # for AvroProducer
+    # for AvroProducer or AvroConsumer
     $ pip install confluent-kafka[avro]
 
 
 **Install from source / tarball:**
 
     $ pip install .
 
-    # for AvroProducer
+    # for AvroProducer or AvroConsumer
     $ pip install .[avro]
 
 

confluent_kafka/avro/__init__.py

@@ -4,7 +4,7 @@
 """
 import sys
 
-from confluent_kafka import Producer
+from confluent_kafka import Producer, Consumer
 
 VALID_LEVELS = ['NONE', 'FULL', 'FORWARD', 'BACKWARD']
 
@@ -112,3 +112,43 @@ def produce(self, **kwargs):
                 raise SerializerError("Avro schema required for key")
 
         super(AvroProducer, self).produce(topic, value, key, **kwargs)
+
+
+class AvroConsumer(Consumer):
+    """
+    Kafka Consumer client which does avro schema decoding of messages.
+    Handles message deserialization.
+
+    Constructor takes below parameters
+
+    @:param: config: dict object with config parameters containing url for schema registry (schema.registry.url).
+    """
+    def __init__(self, config):
+
+        if ('schema.registry.url' not in config.keys()):
+            raise ValueError("Missing parameter: schema.registry.url")
+        schem_registry_url = config["schema.registry.url"]
+        del config["schema.registry.url"]
+
+        super(AvroConsumer, self).__init__(config)
+        self._serializer = MessageSerializer(CachedSchemaRegistryClient(url=schem_registry_url))
+
+    def poll(self, timeout):
+        """
+        This is an overriden method from confluent_kafka.Consumer class. This handles message
+        deserialization using avro schema
+
+        @:param timeout
+        @:return message object with deserialized key and value as dict objects
+        """
+        message = super(AvroConsumer, self).poll(timeout)
+        if not message:
+            return message
+        if not message.error():
+            if message.value() is not None:
+                decoded_value = self._serializer.decode_message(message.value())
+                message.set_value(decoded_value)
+            if message.key() is not None:
+                decoded_key = self._serializer.decode_message(message.key())
+                message.set_key(decoded_key)
+        return message

confluent_kafka/avro/cached_schema_registry_client.py

@@ -26,6 +26,7 @@
 import requests
 
 from . import ClientError, VALID_LEVELS
+from . import loads
 
 # Common accept header sent
 ACCEPT_HDR = "application/vnd.schemaregistry.v1+json, application/vnd.schemaregistry+json, application/json"
@@ -161,7 +162,7 @@ def get_by_id(self, schema_id):
             # need to parse the schema
             schema_str = result.get("schema")
             try:
-                result = avro.loads(schema_str)
+                result = loads(schema_str)
                 # cache it
                 self._cache_schema(result, schema_id)
                 return result
@@ -200,7 +201,7 @@ def get_latest_schema(self, subject):
             schema = self.id_to_schema[schema_id]
         else:
             try:
-                schema = avro.loads(result['schema'])
+                schema = loads(result['schema'])
             except:
                 # bad schema - should not happen
                 raise ClientError("Received bad schema from registry.")

confluent_kafka/src/confluent_kafka.c

@@ -332,6 +332,23 @@ static PyObject *Message_timestamp (Message *self, PyObject *ignore) {
 			     self->timestamp);
 }
 
+static PyObject *Message_set_value (Message *self, PyObject *new_val) {
+   if (self->value)
+        Py_DECREF(self->value);
+   self->value = new_val;
+   Py_INCREF(self->value);
+
+   Py_RETURN_NONE;
+}
+
+static PyObject *Message_set_key (Message *self, PyObject *new_key) {
+   if (self->key)
+        Py_DECREF(self->key);
+   self->key = new_key;
+   Py_INCREF(self->key);
+
+   Py_RETURN_NONE;
+}
 
 static PyMethodDef Message_methods[] = {
 	{ "error", (PyCFunction)Message_error, METH_NOARGS,
@@ -391,6 +408,20 @@ static PyMethodDef Message_methods[] = {
 	  "  :rtype: (int, int)\n"
 	  "\n"
 	},
+	{ "set_value", (PyCFunction)Message_set_value, METH_O,
+	  "  Set the field 'Message.value' with new value.\n"
+	  "  :param: object value: Message.value.\n"
+	  "  :returns: None.\n"
+	  "  :rtype: None\n"
+	  "\n"
+	},
+	{ "set_key", (PyCFunction)Message_set_key, METH_O,
+	  "  Set the field 'Message.key' with new value.\n"
+	  "  :param: object value: Message.key.\n"
+	  "  :returns: None.\n"
+	  "  :rtype: None\n"
+	  "\n"
+	},
 	{ NULL }
 };
 
@@ -1219,7 +1250,7 @@ rd_kafka_conf_t *common_conf_setup (rd_kafka_type_t ktype,
 				Py_DECREF(ks);
 				return NULL;
                         }
-			
+
 			if (h->stats_cb) {
 				Py_DECREF(h->stats_cb);
 				h->stats_cb = NULL;