Serialization

Serializers

By default every message is encoded using JSON, so sending Python data structures like dictionaries and lists works. YAML, msgpack and Python’s built-in pickle module is also supported, and if needed you can register any custom serialization scheme you want to use.

Each option has its advantages and disadvantages.

json – JSON is supported in many programming languages, is now

a standard part of Python (since 2.6), and is fairly fast to decode using the modern Python libraries such as cjson or simplejson.

The primary disadvantage to JSON is that it limits you to the following data types: strings, Unicode, floats, boolean, dictionaries, and lists. Decimals and dates are notably missing.

Also, binary data will be transferred using Base64 encoding, which will cause the transferred data to be around 34% larger than an encoding which supports native binary types.

However, if your data fits inside the above constraints and you need cross-language support, the default setting of JSON is probably your best choice.

pickle – If you have no desire to support any language other than

Python, then using the pickle encoding will gain you the support of all built-in Python data types (except class instances), smaller messages when sending binary files, and a slight speedup over JSON processing.

yaml – YAML has many of the same characteristics as json,

except that it natively supports more data types (including dates, recursive references, etc.)

However, the Python libraries for YAML are a good bit slower than the libraries for JSON.

If you need a more expressive set of data types and need to maintain cross-language compatibility, then YAML may be a better fit than the above.

To instruct Kombu to use an alternate serialization method, use one of the following options.

1. Set the serialization option on a per-producer basis:

   >>> producer = Producer(channel,
   ...                     exchange=exchange,
   ...                     serializer="yaml")
   

2. Set the serialization option per message:

   >>> producer.publish(message, routing_key=rkey,
   ...                  serializer="pickle")
   

Note that a Consumer do not need the serialization method specified. They can auto-detect the serialization method as the content-type is sent as a message header.

Sending raw data without Serialization

In some cases, you don’t need your message data to be serialized. If you pass in a plain string or Unicode object as your message, then Kombu will not waste cycles serializing/deserializing the data.

You can optionally specify a content_type and content_encoding for the raw data:

>>> with open("~/my_picture.jpg", "rb") as fh:
...     producer.publish(fh.read(),
                         content_type="image/jpeg",
                         content_encoding="binary",
                         routing_key=rkey)

The Message object returned by the Consumer class will have a content_type and content_encoding attribute.