[SPARK-5154] [PySpark] [Streaming] Kafka streaming support in Python

This PR brings the Python API for Spark Streaming Kafka data source.

```
    class KafkaUtils(__builtin__.object)
     |  Static methods defined here:
     |
     |  createStream(ssc, zkQuorum, groupId, topics, storageLevel=StorageLevel(True, True, False, False,
2), keyDecoder=<function utf8_decoder>, valueDecoder=<function utf8_decoder>)
     |      Create an input stream that pulls messages from a Kafka Broker.
     |
     |      :param ssc:  StreamingContext object
     |      :param zkQuorum:  Zookeeper quorum (hostname:port,hostname:port,..).
     |      :param groupId:  The group id for this consumer.
     |      :param topics:  Dict of (topic_name -> numPartitions) to consume.
     |                      Each partition is consumed in its own thread.
     |      :param storageLevel:  RDD storage level.
     |      :param keyDecoder:  A function used to decode key
     |      :param valueDecoder:  A function used to decode value
     |      :return: A DStream object
```
run the example:

```
bin/spark-submit --driver-class-path external/kafka-assembly/target/scala-*/spark-streaming-kafka-assembly-*.jar examples/src/main/python/streaming/kafka_wordcount.py localhost:2181 test
```

Author: Davies Liu <davies@databricks.com>
Author: Tathagata Das <tdas@databricks.com>

Closes #3715 from davies/kafka and squashes the following commits:

d93bfe0 [Davies Liu] Update make-distribution.sh
4280d04 [Davies Liu] address comments
e6d0427 [Davies Liu] Merge branch 'master' of github.com:apache/spark into kafka
f257071 [Davies Liu] add tests for null in RDD
23b039a [Davies Liu] address comments
9af51c4 [Davies Liu] Merge branch 'kafka' of github.com:davies/spark into kafka
a74da87 [Davies Liu] address comments
dc1eed0 [Davies Liu] Update kafka_wordcount.py
31e2317 [Davies Liu] Update kafka_wordcount.py
370ba61 [Davies Liu] Update kafka.py
97386b3 [Davies Liu] address comment
2c567a5 [Davies Liu] update logging and comment
33730d1 [Davies Liu] Merge branch 'master' of github.com:apache/spark into kafka
adeeb38 [Davies Liu] Merge pull request #3 from tdas/kafka-python-api
aea8953 [Tathagata Das] Kafka-assembly for Python API
eea16a7 [Davies Liu] refactor
f6ce899 [Davies Liu] add example and fix bugs
98c8d17 [Davies Liu] fix python style
5697a01 [Davies Liu] bypass decoder in scala
048dbe6 [Davies Liu] fix python style
75d485e [Davies Liu] add mqtt
07923c4 [Davies Liu] support kafka in Python

1 files changed, 8 insertions, 1 deletions

diff --git a/python/pyspark/serializers.py b/python/pyspark/serializers.py
index b8bda83517..0ffb41d02f 100644
--- a/python/pyspark/serializers.py
+++ b/python/pyspark/serializers.py
@@ -70,6 +70,7 @@ class SpecialLengths(object):
     PYTHON_EXCEPTION_THROWN = -2
     TIMING_DATA = -3
     END_OF_STREAM = -4
+    NULL = -5
 
 
 class Serializer(object):
@@ -133,6 +134,8 @@ class FramedSerializer(Serializer):
 
     def _write_with_length(self, obj, stream):
         serialized = self.dumps(obj)
+        if serialized is None:
+            raise ValueError("serialized value should not be None")
         if len(serialized) > (1 << 31):
             raise ValueError("can not serialize object larger than 2G")
         write_int(len(serialized), stream)
@@ -145,8 +148,10 @@ class FramedSerializer(Serializer):
         length = read_int(stream)
         if length == SpecialLengths.END_OF_DATA_SECTION:
             raise EOFError
+        elif length == SpecialLengths.NULL:
+            return None
         obj = stream.read(length)
-        if obj == "":
+        if len(obj) < length:
             raise EOFError
         return self.loads(obj)
 
@@ -484,6 +489,8 @@ class UTF8Deserializer(Serializer):
         length = read_int(stream)
         if length == SpecialLengths.END_OF_DATA_SECTION:
             raise EOFError
+        elif length == SpecialLengths.NULL:
+            return None
         s = stream.read(length)
         return s.decode("utf-8") if self.use_unicode else s