为什么libcurl有时会抱怨"无法解析主机名"？

Question

我编写了一个使用libcurl的多线程程序,但有时curl会抱怨它在exec curl_easy_perform之后无法解析主机名,有时候不会.

size_t Http::WriteMemoryCallback(void *contents, size_t size, size_t nmemb, void *userp)
{
    size_t realsize = size * nmemb;
    MemoryStruct *mem = (MemoryStruct *)userp;

    mem->memory = (char *)realloc(mem->memory, mem->size + realsize + 1);
    assert(NULL != mem->memory);
    memcpy(&(mem->memory[mem->size]), contents, realsize);
    mem->size += realsize;
    mem->memory[mem->size] = 0;

    return realsize;
}

void Http::run(const URL &url, Http::FinishedCallback cbk)
{
    CURL *handle = curl_easy_init();
    if (handle) 
    {

        MemoryStruct *chunk = new MemoryStruct;
        chunk->memory = (char *)malloc(1);  /* will be grown as needed by the realloc above */
        chunk->size = 0;    /* no data at this point */


        CURLcode res; 
        curl_easy_setopt(handle, CURLOPT_URL, url.getUrl().c_str());
        curl_easy_setopt(handle, CURLOPT_WRITEDATA, (void *)chunk);
        curl_easy_setopt(handle, CURLOPT_WRITEFUNCTION, WriteMemoryCallback);
        curl_easy_setopt(handle, CURLOPT_USERAGENT, "libcurl-agent/1.0");
        curl_easy_setopt(handle, CURLOPT_TIMEOUT, 10L);
        curl_easy_setopt(handle, CURLOPT_CONNECTTIMEOUT, 10L);
        res = curl_easy_perform(handle);

        /* check for errors */
        if (CURLE_OK != res) 
        {
            chunk->status = false;
            std::string errCode = std::to_string(res);
            chunk->memory = (char *)realloc(chunk->memory, chunk->size + errCode.size() + 1);
            memcpy(&(chunk->memory[chunk->size]), errCode.c_str(), errCode.size());
            chunk->size += errCode.size();
            chunk->memory[chunk->size] = 0;
        }
        else 
        {
            chunk->status = true;
        }

#ifdef _DEBUG
        chunk->url = url;
#endif
        cbk(chunk);
        free(chunk);
        curl_easy_cleanup(handle);
    }
}


void Http::get(URL url, FinishedCallback cbk)
{
    std::thread http(&Http::run, Http(), url, cbk);
    http.detach();
}

Http::~Http()
{
    curl_global_cleanup();
}

这是invocer.

int index = 0;
bool finish = false;
void func(Http::MemoryStruct *memo)
{
    if (!memo->status)
    {
#ifdef _DEBUG
        LOG(INFO) << "Failure:\t" << curl_easy_strerror((CURLcode)atoi(memo->memory)) << "\n";

#endif
    }
    else
    {
        //LOG(INFO) << memo->memory << '\n';
    }
    finish = memo->status;
    ++index;
}

int main(void)
{
    curl_global_init(CURL_GLOBAL_ALL);
    URL::AttribMap attribMap{ { "class", "System" }, { "token", "KY0SQ3FX996PU1ZO" }, { "type", "GetConfig" } };
    URL url("open.55.la", "/index.php", attribMap);
    Http http;
    while(index++ <=10)
    {
            try
            {
                http.get(url, func);
            }
            catch (std::_System_error &err)
            {
                LOG(INFO) << err.what();
            }
    }
    while (true)
    {
        ;
    }
    el::Loggers::flushAll();
    return EXIT_SUCCESS;
}

它可能是由数据崩溃引起的吗？

Answer 1

这是libcurl为CURLE_COULDNT_RESOLVE_HOST错误代码(6)返回的错误消息.

我将引用卷曲书中的退出状态部分

无法解析主机.给定的远程主机地址未解析.无法解析给定服务器的地址.给定的主机名是错误的,或者DNS服务器行为不端,并且在它应该或者甚至您运行的系统卷曲时配置错误时都不知道该名称,因此它找不到/使用正确的DNS服务器.

如果间歇性地返回有时有效但有时无效的主机名,则表明您的系统已经损坏,DNS服务器无法正常响应或者某种DOS预防错误调整.