Telegram API -sendMessage and -sendDocument using URLSession (Swift)

telegram.swift

// URLSession wrapper to send messages and text files to Telegram chat.
final class TelegramAPI {
  
  /// -sendMessage endpoint
  private let sendMessageEndpoint: String
  
  /// -sendDocument endpoint
  private let sendDocumentEndpoint: String
  
  /// Unique identifier for the target chat or username of the target channel
  private let chatId: String
  
  // MARK: Init
  init(token: String /* = YOUR_BOT_TOKEN*/, chatId: String /* = YOUR_CHAT_ID*/) {
    self.sendMessageEndpoint = "https://api.telegram.org/bot\(token)/sendMessage"
    self.sendDocumentEndpoint = "https://api.telegram.org/bot\(token)/sendDocument"
    self.chatId = chatId
  }
  
  // MARK: API
  /// Send a message to a Telegram chat.
  public func send(message: String) {
    do {
      let session = URLSession.shared
      let request = NSMutableURLRequest(url: URL(string: sendMessageEndpoint)!)
      request.httpMethod = "POST"
      let encoder = JSONEncoder()
      let payload = TelegramParameters(chat_id: chatId, text: message)
      let encodedPayload = try encoder.encode(payload)
      guard let parameters = String(bytes: encodedPayload, encoding: .utf8) else { return }
      request.httpBody = parameters.data(using: .utf8)
      request.addValue("application/json", forHTTPHeaderField: "Content-Type")
      let task = session.dataTask(with: request as URLRequest) { (data: Data?, response: URLResponse?, error: Error?) in
        if let data = data, let responseData = String(data: data, encoding: .utf8) {
          print("TelegramAPI -send received data contents: ", responseData)
        }
        if let error = error {
          print("TelegramAPI -send failed with error: ", error)
        }
      }
      task.resume()
    } catch let e {
      print("TelegramAPI -send failed to make cURL request due to error: ", e)
    }
  }
  
  /// Send a text file to a Telegram chat.
  /// - Parameters:
  ///   - contents: Contents for text file.
  ///   - filename: Filename ending in ".txt"
  public func sendTextFile(contents: String, filename: String) {
    if let contentsData = contents.data(using: .utf8) {
      let session = URLSession.shared
      let parameters = ["chat_id": "\(chatId)"]
      let request = NSMutableURLRequest(url: URL(string: sendDocumentEndpoint)!)
      request.httpMethod = "POST"
      let boundary = "Boundary-\(NSUUID().uuidString)"
      request.httpBody = makeHTTPBody(withParameters: parameters, fileData: contentsData, boundary: boundary, filename: filename, mimeType: "text/plain")
      request.addValue("multipart/form-data; boundary=\(boundary)", forHTTPHeaderField: "Content-Type")
      let task = session.dataTask(with: request as URLRequest) { (data: Data?, response: URLResponse?, error: Error?) in
        if let data = data, let responseData = String(data: data, encoding: .utf8) {
          print("TelegramAPI -sendReport received data contents: ", responseData)
        }
        if let error = error {
          print("TelegramAPI -sendReport failed with error: ", error)
        }
      }
      task.resume()
    }
  }
  
  /// Create Data representation for message body of HTTP POST request to -sendDocument.
  /// - Parameters:
  ///   - params:
  ///   - fileData: Document data that is being sent to Telegram.
  ///   - boundary: A short string used to separate key/value parameters in body when using multipart/form-data content type.
  ///   - filename: Filename for the document uploaded to Telegram.
  ///   - mimeType: MIME type for file (e.g. plain/text for text file)
  /// - Returns: Data for HTTP message body.
  private func makeHTTPBody(withParameters params: [String: String]?, fileData: Data, boundary: String, filename: String, mimeType: String) -> Data {
    let lineBreak = "\r\n"
    var body = Data()
    if let parameters = params {
      for (key, value) in parameters {
        body.append("--\(boundary + lineBreak)")
        body.append("Content-Disposition: form-data; name=\"\(key)\"\(lineBreak + lineBreak)")
        body.append("\(value + lineBreak)")
      }
    }
    let fieldName = "document"
    body.append("--\(boundary + lineBreak)")
    body.append("Content-Disposition: form-data; name=\"\(fieldName)\"; filename=\"\(filename)\"\(lineBreak)")
    body.append("Content-Type: \(mimeType + lineBreak + lineBreak)")
    body.append(fileData)
    body.append(lineBreak)
    body.append("--\(boundary)--\(lineBreak)")
    return body
  }
}


fileprivate extension Data {
  mutating func append(_ string: String) {
    if let data = string.data(using: .utf8) {
      append(data)
    }
  }
}

fileprivate struct TelegramParameters: Codable {
  let chat_id: String
  let text: String
  // ... add additional parameters as required
}

Usage

// Initialize with token and chat id
let telegram = TelegramAPI(token: "YOUR_TOKEN", chatId: "CHAT_ID")

// Send message
telegram.send(message: "Hello")

// Send text file
telegram.sendTextFile(contents: "Hello, \n\n Goodbye.", filename: "file.txt")