libev + 非阻塞socket 持续调用回调

Question

我正在使用 libev + 非阻塞套接字向服务器发送请求。我正在使用 Keep Alive，因为我需要通过同一连接向目的地发送未来的请求。

行为运行程序，它获取 URL 并按预期记录到控制台。完成后，等待，不要按 ctrl+c 退出程序。

预计应用程序应保持打开状态，因为事件循环正在等待未来的响应，但不应在初始响应后控制台记录任何内容。

实际离开应用运行。 30 多秒后，它将开始一遍又一遍地向控制台记录相同的响应，没有结束。

问题为什么 libev 在没有发送新请求并且没有收到新响应数据时重复调用我的回调 (example_cb)？我该如何解决这个问题？

#include <ev.h>
#include <stdio.h>
#include <iostream>
#include <ctype.h>
#include <cstring>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <netdb.h>
#include <netinet/in.h>
#include <unistd.h>
#include <sstream>
#include <fstream>
#include <string>

using namespace std;

void sendRequest(int sockfd)
{
  puts("------");
  puts("sendRequest() was called");
  stringstream ss;
  ss << "GET /posts/11 HTTP/1.1\r\n"
      << "Host: jsonplaceholder.typicode.com\r\n"
      << "Accept: application/json\r\n"
      << "\r\n";
  string request = ss.str();

  if (send(sockfd, request.c_str(), request.length(), 0) != (int)request.length()) {
    cout << "Error sending request." << endl;
    exit(1);
  }
  cout << "Request sent. No err occured." << endl;
}

static void delay_cb(EV_P_ ev_timer *w, int revents)
{
  puts("------");
  puts("delay_cb() was called");
  sendRequest(3);
}


static void example_cb(EV_P_ ev_io *w, int revents)
{
  puts("------");
  puts("example_cb() was called");
  int sockfd = 3;

  size_t len = 80*1024, nparsed; // response must be <= 80 Kb
  char buf[len];
  ssize_t recved;

  recved = recv(sockfd, &buf, len, 0);

  if (recved < 0) {
    perror("recved was <1");
  }

  // don't process keep alives
  if (buf[0] != '[=10=]') {
    std::cout << buf << std::endl;
  }

  // clear buf
  buf[0] = '[=10=]';
  std::cout << "buf after clear attempt: " << buf << std::endl;
}

int example_request()
{
  std::string hostname = "jsonplaceholder.typicode.com";
  int PORT = 80;

  struct sockaddr_in client;
  struct hostent * host = gethostbyname(hostname.c_str());
  if (host == NULL || host->h_addr == NULL) {
    cout << "Error retrieving DNS information." << endl;
    exit(1);
  }

  bzero(&client, sizeof(client));
  client.sin_family = AF_INET;
  client.sin_port = htons( PORT );
  memcpy(&client.sin_addr, host->h_addr, host->h_length);

  // create a socket
  int sockfd = socket(PF_INET, SOCK_STREAM, 0);
  if (sockfd < 0) {
    cout << "Error creating socket." << endl;
    exit(1);
  }
  cout << "Socket created" << endl;

  // enable keep alive
  int val = 1;
  setsockopt(sockfd, SOL_SOCKET, SO_KEEPALIVE, &val, sizeof val);

  if (connect(sockfd, (struct sockaddr *)&client, sizeof(client)) < 0) {
    close(sockfd);
    cout << "Could not connect" << endl;
    exit(1);
  }
  cout << "Socket connected" << endl;

  // make non-blocking
  int status = fcntl(sockfd, F_SETFL, fcntl(sockfd, F_GETFL, 0) | O_NONBLOCK);
  if (status == -1) {
    perror("ERROR making socket non-blocking");
  }
  std::cout << "Socket set to non-blocking" << std::endl;

  std::cout << "Sockfd is: " << sockfd << std::endl;
  return sockfd;
}

int main(void)
{
  // establish socket connection
  int sockfd = example_request();

  struct ev_loop *loop = EV_DEFAULT;

  ev_io example_watcher;
  ev_io_init(&example_watcher, example_cb, sockfd, EV_READ);
  ev_io_start(loop, &example_watcher);

  // used to send the request 2 sec later
  ev_timer delay_watcher;
  ev_timer_init(&delay_watcher, delay_cb, 2, 0.0);
  ev_timer_start(loop, &delay_watcher);

  ev_run(loop, 0);

  return 0;
}

编辑：根据评论中的建议更新了代码

Answer 1

问题的根源在于您没有检查 recved == 0 与对方关闭连接相对应的条件。当发生这种情况时，OS 将套接字设置为 "closed mode"，其中（至少在 linux 下）总是准备好读取，随后对 recv 的调用将总是 return 0.

所以您需要做的是检查该条件，在文件描述符上调用 close(fd);（可能之前使用 shutdown）并在关联的观察者上调用 ev_io_stop。如果你想在那一点继续，那么你必须打开一个新的套接字和 eo_io_start 新的观察者。

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