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template Action

The <template> action is the primary tool for generating JSON data in FLAT's Template Language.

Syntax

  • in: Location of input data

    Either a file (e.g. in="conf.json") or a variable (in="$body"). The input sets the template's initial context ({{.}}). It may be a JSON or XML document.

    in="" signals that no input data is used.

    The context can be changed within the template with {{with …}}.

    Default: fit://request/content

  • out: Location of output data

    Where the generated JSON should be stored.

    This can be a variable. Variables will hold the typed result, such as a JSON object or e.g. a boolean value.

    <template out="$postBody">

    Default: fit://request/content

  • src: Location of the template file

    The template definition can be stored in a separate file. The file path is resolved relatively to the flow file.

    <template src="big.tmpl"/>

    There is no obligatory file extension. However, we recommend tmpl or tpl.

  • check: Check output

    The generated JSON will be parsed and checked. If the template has produced an invalid JSON string, an error will be logged.

    The generated text will still be written to the configured out location. In that case, if out is a variable, the output is not typed.

    Checking can be disabled with check="false".

    Default: true

Examples

Accessing JSON data received from client's

The pre-defined variable $body holds the HTTP body of incoming POST requests.

<flow>
  <template in="$body">
  {
    "inputData": {{.}}
  }
  </template>
</flow>

Request with curl:

$ curl -s -H 'content-type: application/json' --data '{"cool":true}' localhost:8080

Output:

{
  "inputData": {
    "cool": true
  }
}

Accessing JSON data loaded from upstream servers

In this example, we pass the client's POST body to httpbin.org to have it reflected back.

<flow>
  <request>
  {
    "url": "https://httpbin.org/anything",
    "method": "POST",
    "body": {
      "src": "$body"
    }
  }
  </request>

  <template>
  {
    "upstreamResponse": {{.}}
  }
  </template>
</flow>

Request with curl:

$ curl -s -H 'content-type: application/json' --data '{"cool":true}' localhost:8080

Output:

{
  "upstreamResponse": {
    "args": {},
    "data": "{\"cool\":true}",
    "files": {},
    "form": {},
    "headers": {
      "Accept": "*/*",
      "Accept-Encoding": "deflate, gzip",
      "Connection": "close",
      "Content-Length": "13",
      "Content-Type": "application/json",
      "Host": "httpbin.org",
      "User-Agent": "FLAT"
    },
    "json": {
      "cool": true
    },
    "method": "POST",
    "origin": "78.35.14.35",
    "url": "https://httpbin.org/anything"
  }
}

Using a template file

<flow>
  <request>{ "url": "https://httpbin.org/anything" }</request>
  <template src="modifyResponse.tmpl"/>
</flow>

The file path modifyResponse.tmpl is resolved relatively to the flow file.

modifyResponse.tmpl:

{
  "ip": {{ origin }},
  "word": {{ method }}
}