1、ttcp作用：檢測TCP吞吐量

2、ttcp協議：

3、一次寫一定長度的資料

static int write_n(int sockfd, const void* buf, int length)
{
  int written = 0;
  while (written < length)
  {
    ssize_t nw = ::write(sockfd, static_cast<const char*>(buf) + written, length - written);
    if (nw > 0)
    {
      written += static_cast<int>(nw);
    }
    else if (nw == 0)
    {
      break;  // EOF
    }
    else if (errno != EINTR)
    {
      perror("write");
      break;
    }
  }
  return written;
}
 

4、一次讀一定長度的資料

static int read_n(int sockfd, void* buf, int length)
{
  int nread = 0;
  while (nread < length)
  {
    ssize_t nr = ::read(sockfd, static_cast<char*>(buf) + nread, length - nread);
    if (nr > 0)
    {
      nread += static_cast<int>(nr);
    }
    else if (nr == 0)
    {
      break;  // EOF
    }
    else if (errno != EINTR)
    {
      perror("read");
      break;
    }
  }
  return nread;
}
 

5、協議實現過程

//傳送端

//先發送SessionMessage，確定傳送資料的包數，以及每包大小

struct SessionMessage sessionMessage = { 0, 0 };
  sessionMessage.number = htonl(opt.number);
  sessionMessage.length = htonl(opt.length);
  if (write_n(sockfd, &sessionMessage, sizeof(sessionMessage)) != sizeof(sessionMessage))
  {
    perror("write SessionMessage");
    exit(1);
  }
//生成測試資料

const int total_len = static_cast<int>(sizeof(int32_t) + opt.length);
  PayloadMessage* payload = static_cast<PayloadMessage*>(::malloc(total_len));
  assert(payload);
  payload->length = htonl(opt.length);
  for (int i = 0; i < opt.length; ++i)
  {
    payload->data[i] = "0123456789ABCDEF"[i % 16];
  }
//傳送資料
 for (int i = 0; i < opt.number; ++i)
  {
    int nw = write_n(sockfd, payload, total_len);
    assert(nw == total_len);

    int ack = 0;
    int nr = read_n(sockfd, &ack, sizeof(ack));//資料傳送完，等待服務端回覆接收資料的長度
    assert(nr == sizeof(ack));
    ack = ntohl(ack);
    assert(ack == opt.length);//判斷資料長度是否滿足
  }
  double elapsed = timeDifference(muduo::Timestamp::now(), start);
  printf("%.3f seconds\n%.3f MiB/s\n", elapsed, total_mb / elapsed);
//最後記錄時間差，計算出吞吐量
//接收端---和客戶端一樣

//接收SessionMessage
struct SessionMessage sessionMessage = { 0, 0 };
  if (read_n(sockfd, &sessionMessage, sizeof(sessionMessage)) != sizeof(sessionMessage))
  {
    perror("read SessionMessage");
    exit(1);
  }
//接收每一包
for (int i = 0; i < sessionMessage.number; ++i)
  {
    payload->length = 0;
    if (read_n(sockfd, &payload->length, sizeof(payload->length)) != sizeof(payload->length))
    {
      perror("read length");
      exit(1);
    }
    payload->length = ntohl(payload->length);
    assert(payload->length == sessionMessage.length);
    if (read_n(sockfd, payload->data, payload->length) != payload->length)
    {
      perror("read payload data");
      exit(1);
    }
    int32_t ack = htonl(payload->length);//資料包長度
    if (write_n(sockfd, &ack, sizeof(ack)) != sizeof(ack))//應答回覆接收到的資料包長度
    {
      perror("write ack");
      exit(1);
    }
  }