(JavaScript) curl with Variable Substitution in a JSON Request Body

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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.

Note: This example requires Chilkat v11.5.0 or greater.

Note

This example is intended for running within a Chilkat.Js embedded JavaScript engine. All Chilkat JavaScript examples require Chilkat v11.4.0 or greater.

var success = false;

// 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}}}'

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

var curl = new 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.
var sbRawRequest = new CkStringBuilder();
success = curl.ToRawRequest(sbCurl.GetAsString(),sbRawRequest);
if (success == false) {
    console.log(curl.LastErrorText);
    return;
}

console.log(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!\""}