Rust 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. Rust

// 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 sb_curl = chilkat::StringBuilder::new();
let _ = sb_curl.append_ln("curl -X POST https://api.example.com/messages \\");
let _ = sb_curl.append_ln("  -H \"Content-Type: application/json\" \\");
let _ = sb_curl.append_ln("  -d '{\"text\":\"{{message}}\"}'");

let curl = chilkat::HttpCurl::new();

// In this example, the value we'll provide for the "message" variable
// will contain chars that require JSON escaping.
curl.set_var("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.
let sb_raw_request = chilkat::StringBuilder::new();
if curl.to_raw_request(&sb_curl.get_as_string().unwrap_or_default(), &sb_raw_request).is_err() {
    println!("{}", curl.last_error_text());
    return;
}

println!("{}", sb_raw_request.get_as_string().unwrap_or_default());

// 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!\""}