具有请求超时的libevent http客户端

I am using libevent to get some stats of a web site in certain time intervals. I've based the program on this. The only thing I'm missing is a timeout on the request, preferably in subsecond accuracy.

我正在使用libevent在一定的时间间隔内获取网站的一些统计数据。我已经把程序建立在这个基础上了。我唯一缺少的是请求超时，最好是在次秒精度。

I've tried a few things, but couldn't get it to work. I'd really appreciate any pointers on this.

我试了几样东西，但都没能成功。我很感激你能给我指点。

1 个解决方案

#1

This is a very crude example: I've used libevent timers to implement the timeout. This could be further improved by putting the timer in the struct and cancelling it in the callback.

这是一个非常粗糙的例子:我使用libevent计时器来实现超时。通过将计时器放在结构体中并在回调中取消它，可以进一步改进这一点。

#include <stdio.h>
#include <event.h>
#include <evhttp.h>
#include <stdlib.h>
#include <unistd.h>


struct http_client {
    struct evhttp_connection *conn;
    struct evhttp_request *req;
    bool finished;
};

void _reqhandler(struct evhttp_request *req, void *state) {
    struct http_client *hc = (http_client*)state;
    hc->finished = true;

    if (req == NULL) {
        printf("timed out!\n");
    } else if (req->response_code == 0) {
        printf("connection refused!\n");
    } else if (req->response_code != 200) {
        printf("error: %u %s\n", req->response_code, req->response_code_line);
    } else {
        printf("success: %u %s\n", req->response_code, req->response_code_line);
    }
    event_loopexit(NULL);
}

void timeout_cb(int fd, short event, void *arg) {
    struct http_client *hc = (http_client*)arg;
    printf("Timed out\n");

    if (hc->finished == false){ // Can't cancel request if the callback has already executed
        evhttp_cancel_request(hc->req);
    }
}

int main(int argc, char *argv[]) {
    struct http_client *hc = (struct http_client *)malloc(sizeof(struct http_client));
    hc->finished = false;

    struct event ev;
    struct timeval tv;

    tv.tv_sec = 3; // Timeout is set to 3.005 seconds
    tv.tv_usec = 5000;


    const char *addr = "173.194.39.64"; //google.com
    unsigned int port = 80;

    event_init();

    hc->conn = evhttp_connection_new(addr, port);
    evhttp_connection_set_timeout(hc->conn, 5);

    hc->req = evhttp_request_new(_reqhandler, (void*)hc);
    evhttp_add_header(hc->req->output_headers, "Host", addr);
    evhttp_add_header(hc->req->output_headers, "Content-Length", "0");
    evhttp_make_request(hc->conn, hc->req, EVHTTP_REQ_GET, "/");

    evtimer_set(&ev, timeout_cb, (void*)hc); // Set a timer to cancel the request after certain time
    evtimer_add(&ev, &tv);

    printf("starting event loop..\n");
    printf("\n");
    event_dispatch();

    return 0;
}