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The /__echo/ endpoint

Document updated on Mar 21, 2023

The /__echo/ endpoint is a developer tool to help you debug configurations. It works similarly to the /__debug/ endpoint, but instead of printing the requests in the log and returning a {"message": "pong"}, they are printed in the response. It replies with an object containing all the request details, and you can use it as an endpoint or backend. As KrakenD has a zero-trust approach, you will find out the exact information that passes through in this endpoint.

Ends in slash!
Notice that the /__echo/ endpoint has two slashes in its definition.

Configuration

To enable the /__echo/ endpoint, you should add in the configuration (service level) the flag echo_endpoint, and then use it directly by calling http://krakend:8080/__echo/ or by adding it as a backend in any endpoint.

Fields of "false"
* required fields
echo_endpoint

boolean
Enables the /__echo/ endpoint for this configuration, that returns information about the incoming request. When using /__echo as a backend you can check the actual headers and content a backend receives after all the zero-trust filtering.
Defaults to false

When used as a backend, you have a fake backend that is very useful for seeing the interaction between the gateway and the backends and testing all sorts of KrakenD components.

Response fields

Given a request following the format [scheme:][//[userinfo@]host][/]path[?query][#fragment], the /__echo/ endpoint will answer with the following structure:

{
  "req_uri": "/__echo/foo/bar/vaz?q=foo#fragment",
  "req_uri_details": {
    "user": "userinfo",
    "host": "krakend:8080",
    "path": "/__echo/foo/bar/vaz",
    "query": "?q=foo",
    "fragment": "fragment"
  },
  "req_method": "POST",
  "req_querystring": {
     "q": ["foo"]
  },
  "req_body": {
     "@comment": "The correct parsing of the body is not guaranteed as its content is unknown (and even binary)"
  },
  "req_headers": {
     "Content-Type": ["application/json"]
  }
}

Echo endpoint example

The most beneficial case is when you add KrakenD itself as another backend using the /__echo/ endpoint. Then, you can see exactly what headers and query string parameters your backends receive in the responses.

To test it, save the content of this file in a krakend.json and start the server:

{
  "version": 3,
  "port": 8080,
  "echo_endpoint": true,
  "endpoints": [
    {
      "endpoint": "/test/{var}",
      "backend": [
        {
          "host": ["http://127.0.0.1:8080"],
          "url_pattern": "/__echo/{var}"
        }
      ]
    }
  ]
}

Default behavior:

Ignore query strings by default 
$curl -i -H'Test: foo' 'http://localhost:8080/test/one?a=1&b=2&c=3'

In the response, you will see that a, b, and c do not appear, neither the sent headers. The curl command automatically sends the Accept and User-Agent headers, but they are not in the backend call either. Instead, you see the KrakenD User-Agent as set by the gateway.

Play now with the parameter forwarding, such as the input_headers and input_query_strings, and repeat the test.

Scarf

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