通过Swift程序发送EHLO命令

Question

我想发送ehlo命令以从smtp服务器获取响应，而不使用任何第三方库。我正在使用TCP流与套接字连接。因此，我想知道如何将“ EHLO”命令发送到服务器并获得响应。

class Connection: NSObject {
static let shared = Connection()

private var inputStream: InputStream!
private var outputStream: OutputStream!

private let maxReadLength = 4096

func setupServerCommunication() {
    var readStream: Unmanaged<CFReadStream>?
    var writeStream: Unmanaged<CFWriteStream>?

    let host = "domain_name" as CFString

    CFStreamCreatePairWithSocketToHost(kCFAllocatorDefault, host, 25, &readStream, &writeStream)

    inputStream = readStream!.takeRetainedValue()
    outputStream = writeStream!.takeRetainedValue()

    inputStream.schedule(in: .current, forMode: .commonModes)
    outputStream.schedule(in: .current, forMode: .commonModes)

    inputStream.open()
    inputStream.delegate = self
    outputStream.open()
}

func quitSession() {
    inputStream.close()
    outputStream.close()

    inputStream.remove(from: .current, forMode: .commonModes)
    outputStream.remove(from: .current, forMode: .commonModes)

    inputStream = nil
    outputStream = nil
}
}