gistfile1.txt

private func makeIdempotencyKey(enabled: Bool) -> String? {
    guard enabled else { return nil }
    let key = UUID().uuidString
    return key
}

private func makePostRequest(text: String, idempotencyKey: String?) throws -> URLRequest {
    var request = makeRequest(path: "level2/tweets", method: "POST")
    request.setValue("application/json", forHTTPHeaderField: "Content-Type")
    if let idempotencyKey {
        request.setValue(idempotencyKey, forHTTPHeaderField: "Idempotency-Key")
    }
    request.httpBody = try encoder.encode(Level2PostBody(text: text))
    return request
}