(Swift) 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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func chilkatTest() {
    var success: Bool = 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}}}'

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

    let curl = CkoHttpCurl()!

    // In this example, the value we'll provide for the "message" variable
    // will contain chars that require JSON escaping.
    curl.setVar("message", varValue: "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.
    let sbRawRequest = CkoStringBuilder()!
    success = curl.toRawRequest(sbCurl.getAsString(), sb: sbRawRequest)
    if success == false {
        print("\(curl.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!\""}

}