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Supported Encodings for Backend Integration

Document updated on Jul 12, 2020

Setting the encoding is an important part of the backend definition, as it informs KrakenD how to parse the responses of your services.

Each backend can reply with a different encoding and KrakenD does not have any problem working with mixed encodings at the same time. You can use the following encoding in each backend section:

  • json
  • fast-json (Enterprise only)
  • safejson
  • xml
  • rss
  • string
  • no-op

Notice that all values are in lower case. Unknown values for encoding or no value at all, is treated as json.

Each backend declaration can set a different encoder to process the responses, and still, KrakenD can transparently work with the mixed content returning a unified encoding in the endpoint.

How to choose the backend encoding?

Follow this table to determine how to treat your backend content:

The backend returns…Then use encoding…
JSON inside an object ({})json or fast-json (EE only)
JSON inside an array/collection ([])json or fast-json with "is_collection": true
JSON with variable typessafejson
RSS Feed (types Atom, RSS or JSON )rss
Not an object, but a stringstring
Nevermind, just proxyno-op (read how)
Working with JSON arrays

If you want to return to the client a JSON array instead of an object, consider using the following combinations: output_encoding: json-collection in your endpoint, and is_collection: true in your backend. See response content types.

When hesitating whether to use safejson or json and the is_collection=true, the json encoder is faster and more performant but less resilient: it will fail when the content doesn’t have the expected type. If you are in control of the output of the service, choose json, if you are not, choose safejson.

Automatic content wrappers (collection and content)

When the content returned by your service is wrapped inside an array instead of an object, the gateway will wrap the response inside a collection object. This scenario is possible with is_collection=true , or when the safejson found an array in the response.

When the content returned by your service is a string, a float, integer, etc. but a type that is not an object or a collection, then the response is wrapped inside a content object. This scenario is possible with when the safejson finds a non-array or non-object type, or when you use a string encoding.

For instance, if your backend returns a simple Hello World!, the response of KrakenD (output_encoding=json) would be { "content": "Hello World!" }.

Similarly, if your backend returns [{"item": 1},{"item": 2}] then the response of KrakenD (output_encoding=json) would be { "collection": [{"item": 1},{"item": 2}] }.

Some ouput_encodings will revert this wrapping before returning the content to the user to match the exact value provided by the backend, but this gives you the oportunity to manipulate the content and work with it at the endpoint level. The output_encoding of string will remove the content wrapping, while the json-collection while remove the collection wrapping.

Example of mixed encodings

The following example demonstrates how an endpoint /abc is feeding on three different services and urls /a, /b, and /c and aggregates their responses. All the information is returned in JSON (output_encoding) despite it is consuming heterogeneous formats:

	"endpoints": [
      "endpoint": "/abc",
      "output_encoding": "json",
      "backend": [
          "url_pattern": "/a",
          "encoding": "json",
          "host": [
          "url_pattern": "/b",
          "encoding": "xml",
          "host": [
          "url_pattern": "/c",
          "encoding": "rss",
          "host": [

As you can see, having the encoding declaration inside every backend allows you to consume services with different content types. The endpoint /abc instead uses the encoding of your choice (e.g., JSON), but is feeding and merging from XML, RSS and JSON content simultaneously.


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