每種協議通過實現Curl_handler這個結構體裡面的部分函式,再把它放入到這個結構體數組裡面,這種協議就可以使用了.

static const struct Curl_handler * const protocols[] = {
#ifndef CURL_DISABLE_HTTP
    &Curl_handler_http,
#endif

#ifndef CURL_DISABLE_FTP
    &Curl_handler_ftp,
#endif

#if defined(USE_SSL) && !defined(CURL_DISABLE_FTP)
    &Curl_handler_ftps,
#endif

#ifndef CURL_DISABLE_TELNET
    &Curl_handler_telnet,
#endif

#ifndef CURL_DISABLE_FILE
    &Curl_handler_file,
#endif

#ifndef CURL_DISABLE_TFTP
    &Curl_handler_tftp,
#endif

    (struct Curl_handler *) NULL
};
 

例如在webkit中curl的使用,下面是我在閱讀webkit程式碼時的一點記錄:

writeCallback/headerCallback是怎麼完成的：
Webkit使用lite註冊了一個定時器，在使用main_loop的時候會執行這個定時器的回撥函式.最後會調到curl_multi_perform，看下這次請求是否有資料需要讀寫。如果有的話由curl來控制不斷傳回資料直到結束。也就是說整個過程都是同步的,在這裡會阻塞。當然阻塞是在curl裡面的。
在ResourceHandleManager::downloadTimerCallback(）中呼叫的curl_multi_perform:
while (curl_multi_perform(m_curlMultiHandle, &runningHandles) == CURLM_CALL_MULTI_PERFORM) { }
而這句話是錯誤的，我的意思是根本沒有必要這麼寫。寫成curl_multi_perform(m_curlMultiHandle, &runningHandles);就夠了，沒有必要要while因為這裡的返回值絕對不會是CURLM_CALL_MULTI_PERFORM, 不相信我就看下這個函式的原始碼。

CURLMcode curl_multi_perform(CURLM *multi_handle, int *running_handles)
{
    struct Curl_multi *multi=(struct Curl_multi *)multi_handle;
    struct Curl_one_easy *easy;
    CURLMcode returncode=CURLM_OK;
    struct Curl_tree *t;

    if(!GOOD_MULTI_HANDLE(multi))
        return CURLM_BAD_HANDLE;

    easy=multi->easy.next;
    while(easy != &multi->easy) {
        CURLMcode result;
        struct WildcardData *wc = &easy->easy_handle->wildcard;

        if(easy->easy_handle->set.wildcardmatch) {
            if(!wc->filelist) {
                CURLcode ret = Curl_wildcard_init(wc); /* init wildcard structures */
                if(ret)
                    return CURLM_OUT_OF_MEMORY;
            }
        }

        do
            result = multi_runsingle(multi, easy);
        while (CURLM_CALL_MULTI_PERFORM == result);//它會在這裡形成迴圈判斷,所以不可能出現這個值,我的理解對嗎?

        if(easy->easy_handle->set.wildcardmatch) {
            if(wc->state == CURLWC_DONE || result)
                Curl_wildcard_dtor(wc);
        }

        if(result)
            returncode = result;

        easy = easy->next; /* operate on next handle */
    }
    do {
        struct timeval now = Curl_tvnow();

        multi->timetree = Curl_splaygetbest(now, multi->timetree, &t);
        if(t) {
            struct SessionHandle *d = t->payload;
            struct timeval* tv = &d->state.expiretime;

            tv->tv_sec = 0;
            tv->tv_usec = 0;
        }

    } while(t);

    *running_handles = multi->num_alive;

    if( CURLM_OK >= returncode )
        update_timer(multi);

    return returncode;
}