(Node.js) 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.

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on Windows, Linux, MacOS

var os = require('os');
if (os.platform() == 'win32') {  
  var chilkat = require('@chilkat/ck-node23-win64'); 
} else if (os.platform() == 'linux') {
    if (os.arch() == 'arm') {
        var chilkat = require('@chilkat/ck-node23-linux-arm');
    } else if (os.arch() == 'arm64') {
        var chilkat = require('@chilkat/ck-node23-linux-arm64');
    } else {
        var chilkat = require('@chilkat/ck-node23-linux-x64');
    }
} else if (os.platform() == 'darwin') {
  var chilkat = require('@chilkat/ck-node23-mac-universal');
}

function chilkatExample() {

    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 chilkat.StringBuilder();
    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 chilkat.HttpCurl();

    // 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 chilkat.StringBuilder();
    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!\""}

}

chilkatExample();