Zig 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. Zig

const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // 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}}}'

    const sb_curl = try chilkat.StringBuilder.init();
    defer sb_curl.deinit();
    sb_curl.appendLn("curl -X POST https://api.example.com/messages \\") catch {};
    sb_curl.appendLn("  -H \"Content-Type: application/json\" \\") catch {};
    sb_curl.appendLn("  -d '{\"text\":\"{{message}}\"}'") catch {};

    const curl = try chilkat.HttpCurl.init();
    defer curl.deinit();

    // 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.
    const sb_raw_request = try chilkat.StringBuilder.init();
    defer sb_raw_request.deinit();
    curl.toRawRequest(try sb_curl.getAsString(alloc), sb_raw_request) catch {
        std.debug.print("{s}\n", .{try curl.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("{s}\n", .{try sb_raw_request.getAsString(alloc)});

    // 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!\""}
}