Dart Requires Chilkat v11.5.0+

curl with Variable Substitution in a JSON Request Body

See more CURL Examples

This example shows how to use variables inside a JSON request body using the {{variable_name}} syntax. When the HTTP request’s Content-Type indicates JSON, Chilkat automatically applies proper JSON escaping to each substituted value, ensuring the resulting JSON remains valid. Dart

import 'package:chilkat/chilkat.dart';

void main() {
  // Variable names are enclosed between {{ and }}
  // Important: The variable {{var_name}} should be placed inside the quotes.

  // This is correct:
  // curl -X POST https://api.example.com/messages \
  //   -H "Content-Type: application/json" \
  //   -d '{"text":"{{message}}"}'

  // This is incorrect:
  //   -d '{"text":{{message}}}'

  final sbCurl = CkStringBuilder();
  sbCurl.appendLn('curl -X POST https://api.example.com/messages \\');
  sbCurl.appendLn('  -H "Content-Type: application/json" \\');
  sbCurl.appendLn('  -d \'{"text":"{{message}}"}\'');

  final curl = CkHttpCurl();

  // In this example, the value we'll provide for the "message" variable
  // will contain chars that require JSON escaping.
  curl.setVar('message', 'He said "Hello, world!"');

  // To demonstrate how the variables are replaced, this example does not execute the curl command. 
  // Instead, it generates the raw HTTP request that would be sent if the curl command were run.
  final sbRawRequest = CkStringBuilder();
  try {
    curl.toRawRequest(sbCurl.getAsString(), sbRawRequest);
  } on ChilkatException catch (e) {
    print(e.lastErrorText);
    return;
  }

  print(sbRawRequest.getAsString());

  // The output is shown below.
  // Notice that the quote chars around "Hello World!" are properly JSON escaped.

  // POST /messages HTTP/1.1
  // Host: api.example.com
  // Content-Type: application/json
  // Content-Length: 36
  // 
  // {"text":"He said \"Hello, world!\""}
}