Merge pull request scrapy#174 from scrapinghub/fix-import-crash

fixing crash on settings import when kafka-python isn't installed

Author: sibiryakov

docs/source/topics/frontera-settings.rst

@@ -158,8 +158,7 @@ KAFKA_CODEC_LEGACY
 
 Default: ``KAFKA_CODEC_LEGACY``
 
-Kafka-python 0.x version codec, could be one of ``CODEC_NONE``, ``CODEC_SNAPPY`` or ``CODEC_GZIP``,
-imported from ``kafka.protocol``.
+Kafka-python 0.x version compression codec to use, is a string and could be one of ``none``, ``snappy`` or ``gzip``.
 
 
 .. setting:: LOGGING_CONFIG

frontera/contrib/backends/remote/kafka.py

@@ -224,3 +224,7 @@ def __init__(self, manager):
 
     def get_next_requests(self, max_n_requests, **kwargs):
         return self._buffer.get_next_requests(max_n_requests, **kwargs)
+
+
+raise DeprecationWarning("KafkaBackend and KafkaOverusedBackend is deprecated, and will be removed soon please use "
+                         "MessageBusBackend instead")

frontera/contrib/messagebus/kafkabus.py

@@ -211,7 +211,20 @@ def __init__(self, settings):
         self.spider_partition_id = settings.get('SPIDER_PARTITION_ID')
         self.max_next_requests = settings.MAX_NEXT_REQUESTS
         self.hostname_partitioning = settings.get('QUEUE_HOSTNAME_PARTITIONING')
-        self.codec = settings.get('KAFKA_CODEC_LEGACY')
+
+        self.codec = None
+        codec = settings.get('KAFKA_CODEC_LEGACY')
+        if codec == 'none':
+            from kafka.protocol import CODEC_NONE
+            self.codec = CODEC_NONE
+        if codec == 'snappy':
+            from kafka.protocol import CODEC_SNAPPY
+            self.codec = CODEC_SNAPPY
+        if codec == 'gzip':
+            from kafka.protocol import CODEC_GZIP
+            self.codec = CODEC_GZIP
+        if not self.codec:
+            raise NameError("Non-existent Kafka compression codec.")
 
         self.conn = KafkaClient(server)
 

frontera/settings/default_settings.py

@@ -1,5 +1,4 @@
 from datetime import timedelta
-from kafka.protocol import CODEC_NONE
 
 
 AUTO_START = True
@@ -19,7 +18,7 @@
 HBASE_STATE_CACHE_SIZE_LIMIT = 3000000
 HBASE_QUEUE_TABLE = 'queue'
 KAFKA_GET_TIMEOUT = 5.0
-KAFKA_CODEC_LEGACY = CODEC_NONE
+KAFKA_CODEC_LEGACY = "none"
 MAX_NEXT_REQUESTS = 64
 MAX_REQUESTS = 0
 MESSAGE_BUS = 'frontera.contrib.messagebus.zeromq.MessageBus'