C-带有请求超时的Libevent HTTP客户端

Question

我正在使用libevent在特定时间间隔中获取网站的一些统计数据。我已经基于这个程序了。我唯一缺少的是在请求上的超时，最好是以秒准确性。

我已经尝试了几件事，但无法正常工作。我真的很感谢任何建议。

Answer 1

这是一个非常粗略的示例：我使用libevent计时器来实现超时。通过将计时器放入结构并将其取消在回调中，可以进一步改善这一点。

#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 %sn", req->response_code, req->response_code_line);
    } else {
        printf("success: %u %sn", 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 outn");
    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;
}