Question

我正在尝试恢复因互联网故障而失败的下载。我用来检查卷曲下载成功的函数是：
```
curl_multi_info_read
```
当互联网第一次丢失时，此函数会返回正确的错误代码（CURLE_COULDNT_CONNECT）。如果我再次尝试调用它，它将返回NULL指针，这意味着没有消息。实际上，我使用返回错误代码来检查是否存在互联网连接。这让我感到不安，因为如果没有互联网，它在第二次通话时不会返回任何错误代码。任何人都可以告诉我如何使用这个函数来检查返回代码，因为这个错误代码（CURLE_COULDNT_CONNECT）对我来说非常重要，因为我检查互联网的状态，并因此从我停止的地方恢复下载找回了连接....
为了恢复下载，我正在使用
```
curl_easy_setopt (curl, CURLOPT_RESUME_FROM, InternalOffset);
```
我每次收到丢失的互联网连接时都会调用此功能设置选项，以便在互联网连接恢复后可以恢复下载...

Daniel Stenberg的注释：

以下是有关platform和libcurl版本的一些细节：

curl version - libcurl 7.21.6
platform - Linux（Ubuntu）

评论：

是。你的观点是对的。我从堆栈中删除了easy handle，通过设置新选项（curl_easy_setopt(curl, CURLOPT_RESUME_FROM, InternalOffset)）再次添加到多个句柄，最后我做了多次执行。如果没有互联网连接，则返回正确的错误。我的问题是：每次我丢失互联网连接以获得正确的错误时，是否需要重复上述步骤？如果我不执行这些步骤， curl_multi_info_read 函数将始终返回NULL。
我做的另一个观察是下载开始恢复，当互联网连接恢复时。它从之前停止的位置开始下载。这对我来说是一个惊喜。 curl内部负责在重新上网时恢复下载。如果这是对的吗？我是否真的需要注意恢复下载或在正确处理时留下卷曲？

Answer 1

您可能需要提供更多信息。

例如：您没有明确说明您是使用multi interface还是easy interface ..＆amp;也许会提到你正在做什么平台＆amp;您正在使用的libcurl等等。

以下是针对easy的最小卷曲multi和libcurl/7.21.6次测试。
我很高兴地拉出网络电缆，停止了http服务器＆amp;所以〜似乎可以应付。

这些可能会对您有所帮助：

curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, dl_lowspeed_bytes); //bytes/sec
curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, dl_lowspeed_time); //seconds
curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

NB：当连接断开时，你必须非常努力地使 curl摔倒。这是设计的。但有些人会感到意外。

[编辑：]
我怀疑你是否想要使用CURLOPT_TIMEOUT。这会使转移超时。如果您的d / l很大，那么几乎可以肯定需要更长的时间才能确定您的网络连接是否存在问题〜＆gt;超时会被击中。相比之下，CURLOPT_LOW_SPEED_TIME超时可能永远不会被击中，即使在经过一段时间的传输时间之后也是如此。

curltest_easy.c：

/*----------------------------------------------------
curltest_easy.c 
WARNING: for test purposes only ~ 
*/
#include <stdio.h>
#include <unistd.h>
#include <curl/curl.h>
#include <curl/types.h>
#include <curl/easy.h>
#include <sys/stat.h>



static int dl_progress(void *clientp,double dltotal,double dlnow,double ultotal,double ulnow)
{
    if (dlnow && dltotal)
        printf("dl:%3.0f%%\r",100*dlnow/dltotal); //shenzi prog-mon 
    fflush(stdout);    
    return 0;
}

static size_t dl_write(void *buffer, size_t size, size_t nmemb, void *stream)
{    
    return fwrite(buffer, size, nmemb, (FILE*)stream); 
}


int do_dl(void) 
{
    CURL *curl;
    FILE *fp;
    CURLcode curl_retval;
    long http_response;
    double dl_size;
    int retval=0;
    long dl_lowspeed_bytes=1000; //1K
    long dl_lowspeed_time=10; //sec        
    /*put something biG here, preferably on a server that you can switch off at will ;) */
    char url[] = {"http://fc00.deviantart.net/fs26/f/2008/134/1/a/Dragon_VII_by_NegativeFeedback.swf"};
    char filename[]={"blah.dl"};

    struct stat st={0};    
    if (!stat(filename, &st));    
    printf("st.st_size:[%ld]\n", st.st_size);  


    if(!(fp=fopen(filename, "ab"))) /*append binary*/
      return 1; 


    curl_global_init(CURL_GLOBAL_DEFAULT);   
    curl = curl_easy_init();

    if (curl) 
    {   
        //http://linux.die.net/man/3/curl_easy_setopt
        curl_easy_setopt(curl, CURLOPT_URL, url);

        /*callbacks*/
        curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, dl_write);
        curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, dl_progress);
        curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);

        /*curl will keep running -so you have the freedom to recover 
        from network disconnects etc in your own way without
        distrubing the curl task in hand. ** this is by design :p ** */ 
        //curl_easy_setopt(curl, CURLOPT_TIMEOUT, 60);          
        //curl_easy_setopt(curl, CURLOPT_CONNECTTIMEOUT, 30);
        /*set up min download speed threshold & time endured before aborting*/
        curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, dl_lowspeed_bytes); //bytes/sec
        curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, dl_lowspeed_time); //seconds while below low spped limit before aborting


        curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);
        curl_easy_setopt(curl, CURLOPT_RESUME_FROM,st.st_size);

        /*uncomment this to get curl to tell you what its up to*/
        //curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);


        if(CURLE_OK != (curl_retval=curl_easy_perform(curl)))
        {                      
            printf("curl_retval:[%d]\n", curl_retval);
            switch(curl_retval) 
            {
                //Transferred a partial file
                case CURLE_WRITE_ERROR: //can be due to a dropped connection
                break;

                //all defined in curl/curl.h 

                default: //suggest quitting on unhandled error
                retval=0;
            };    


            curl_easy_getinfo(curl, CURLINFO_CONTENT_LENGTH_DOWNLOAD, &dl_size);
            printf("CURLINFO_CONTENT_LENGTH_DOWNLOAD:%f\n", dl_size);


            curl_retval=curl_easy_getinfo(curl, CURLINFO_RESPONSE_CODE, &http_response);

            //see: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
            printf("CURLINFO_RESPONSE_CODE:%ld\n", http_response);

            switch(http_response)
            {
            case 0: //eg connection down  from kick-off ~suggest retrying till some max limit
            break;

            case 200: //yay we at least got to our url
            break;

            case 206:
            case 416: //http://www.checkupdown.com/status/E416.html
            printf("ouch! you might want to handle this & others\n"); 

            default: //suggest quitting on an unhandled error
            retval=0;
            };            
        }
        else
        {
            printf("our work here is done ;)\n");
            retval=2;
        }


        if (fp)
            fclose(fp);

        if (curl)
            curl_easy_cleanup(curl);
    }

    printf("retval [%d]\n", retval);
    return retval;
}


int main(void) 
{
    while (!do_dl())
    {
        usleep(5000);
    }

    return 0;
}

/* notes ----

$sudo apt-get install libcurl4-gnutls-dev
$ curl-config --libs
-L/usr/lib/i386-linux-gnu -lcurl -Wl,-Bsymbolic-functions

#oook. lets do it:
$ gcc -o curltest_easy curltest_easy.c -L/usr/lib/i386-linux-gnu -lcurl -Wl,-Bsymbolic-functions
$ ./curltest
*/

curltest_multi.c：

/*----------------------------------------------------
curltest_mult1.c
WARNING: for test purposes only ~
*/
#include <stdio.h>
#include <unistd.h>
#include <curl/curl.h>
#include <curl/types.h>
#include <curl/easy.h>
#include <sys/stat.h>

typedef struct S_dl_byte_data
{
    double new_bytes_received;  //from the latest request
    double existing_filesize;
} dl_byte_data, *pdl_byte_data;

static int dl_progress(pdl_byte_data pdata,double dltotal,double dlnow,double ultotal,double ulnow)
{
    /*dltotal := hacky way of getting the Content-Length ~ less hacky would be to first
    do a HEAD request & then curl_easy_getinfo with CURLINFO_CONTENT_LENGTH_DOWNLOAD*/
    if (dltotal && dlnow)
    {
        pdata->new_bytes_received=dlnow;
        dltotal+=pdata->existing_filesize;
        dlnow+=pdata->existing_filesize;
        printf(" dl:%3.0f%% total:%.0f received:%.0f\r",100*dlnow/dltotal, dltotal, dlnow); //shenzi prog-mon
        fflush(stdout);
    }
    return 0;
}

static size_t dl_write(void *buffer, size_t size, size_t nmemb, void *stream)
{
    return fwrite(buffer, size, nmemb, (FILE*)stream);
}

////////////////////////
int do_dl(void)
{
    CURLM *multi_handle;
    CURL *curl;
    FILE *fp;
    CURLcode curl_retval;
    int retval=0;
    int handle_count=0;
    double dl_bytes_remaining, dl_bytes_received;
    dl_byte_data st_dldata={0};
    char curl_error_buf[CURL_ERROR_SIZE]={"meh"};
    long dl_lowspeed_bytes=1000, dl_lowspeed_time=10; /* 1KBs for 10 secs*/

    /*put something biG here, preferably on a server that you can switch off at will ;) */
    char url[] = {"http://fc00.deviantart.net/fs26/f/2008/134/1/a/Dragon_VII_by_NegativeFeedback.swf"};

    char outfilename[]={"blah.swf"}, filename[]={"blah.dl"};
    struct stat st={0};


    if (!(fp=fopen(filename, "ab")) || -1==fstat(fileno(fp), &st)) //append binary
      return -1;

    if (curl_global_init(CURL_GLOBAL_DEFAULT))
      return -2;

    if (!(multi_handle = curl_multi_init()))
      return -3;

    if (!(curl = curl_easy_init()))
      return -4;


    st_dldata.new_bytes_received=st_dldata.existing_filesize=st.st_size;

    //http://curl.haxx.se/libcurl/c/curl_easy_setopt.html
    curl_easy_setopt(curl, CURLOPT_URL, url);

    /*callbacks*/
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, dl_write);
    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, dl_progress);
    curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, &st_dldata);
    curl_easy_setopt(curl, CURLOPT_NOPROGRESS, 0);

    /*curl will keep running -so you have the freedom to recover from network disconnects etc
    in your own way without distrubing the curl task in hand. ** this is by design :p **
    The follwoing sets up min download speed threshold & time endured before aborting*/
    curl_easy_setopt(curl, CURLOPT_LOW_SPEED_LIMIT, dl_lowspeed_bytes); //bytes/sec
    curl_easy_setopt(curl, CURLOPT_LOW_SPEED_TIME, dl_lowspeed_time); //seconds while below low spped limit before aborting
    //alternatively these are available in libcurl 7.25
    //curl_easy_setopt(curl, CURLOPT_TCP_KEEPALIVE,1L);
    //curl_easy_setopt(curl, CURLOPT_TCP_KEEPIDLE,10);
    //curl_easy_setopt(curl, CURLOPT_TCP_KEEPINTVL,10);

    curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);

    /*uncomment this to get curl to tell you what its up to*/
    //curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

    curl_easy_setopt(curl, CURLOPT_ERRORBUFFER, curl_error_buf);


    do
    {
        if (st_dldata.new_bytes_received) //set the new range for the partial transfer if we have previously received some bytes 
        {
            printf("resuming d/l..\n");
            fflush(fp);
            //get the new filesize & sanity check for file; on error quit outer do-loop & return to main
            if (-1==(retval=fstat(fileno(fp), &st)) || !(st_dldata.existing_filesize=st.st_size)) break; 
            //see also: CURLOPT_RANGE for passing a string with our own X-Y range
            curl_easy_setopt(curl, CURLOPT_RESUME_FROM, st.st_size);
            st_dldata.new_bytes_received=0;
        }
        printf("\n\nbytes already received:[%.0f]\n", st_dldata.existing_filesize);

        //re-use the curl handle again & again & again & again... lol
        curl_multi_add_handle(multi_handle, curl);

        do //curl_multi_perform event-loop
        {
            CURLMsg *pMsg;
            int msgs_in_queue;

            while (CURLM_CALL_MULTI_PERFORM == curl_multi_perform(multi_handle, &handle_count));

            //check for any mesages regardless of handle count
            while(pMsg=curl_multi_info_read(multi_handle, &msgs_in_queue))
            {
                long http_response;

                printf("\nmsgs_in_queue:[%d]\n",msgs_in_queue);
                if (CURLMSG_DONE != pMsg->msg)
                {
                    fprintf(stderr,"CURLMSG_DONE != pMsg->msg:[%d]\n", pMsg->msg);
                }
                else
                {
                    printf("pMsg->data.result:[%d] meaning:[%s]\n",pMsg->data.result,curl_easy_strerror(pMsg->data.result));
                    if (CURLE_OK != pMsg->data.result) printf("curl_error_buf:[%s]\n", curl_error_buf);
                    switch(pMsg->data.result)
                    {
                    case CURLE_OK: ///////////////////////////////////////////////////////////////////////////////////////
                    printf("CURLE_OK: ");
                    curl_easy_getinfo(pMsg->easy_handle, CURLINFO_CONTENT_LENGTH_DOWNLOAD, &dl_bytes_remaining);
                    curl_easy_getinfo(pMsg->easy_handle, CURLINFO_SIZE_DOWNLOAD, &dl_bytes_received);
                    if (dl_bytes_remaining == dl_bytes_received)
                    {
                        printf("our work here is done ;)\n");
                        rename(filename, outfilename);
                        retval=1;
                    }
                    else
                    {
                        printf("ouch! st_dldata.new_bytes_received[%f]\n",st_dldata.new_bytes_received);
                        printf("ouch! dl_bytes_received[%f] dl_bytes_remaining[%f]\n",dl_bytes_received,dl_bytes_remaining);
                        retval=dl_bytes_received < dl_bytes_remaining ? 0 : -5;
                    }
                    break; /////////////////////////////////////////////////////////////////////////////////////////////////

                    case CURLE_COULDNT_CONNECT:      //no network connectivity ?
                    case CURLE_OPERATION_TIMEDOUT:   //cos of CURLOPT_LOW_SPEED_TIME
                    case CURLE_COULDNT_RESOLVE_HOST: //host/DNS down ?
                    printf("CURMESSAGE switch handle_count:[%d]\n",handle_count);
                    break; //we'll keep trying

                    default://see: http://curl.haxx.se/libcurl/c/libcurl-errors.html
                    handle_count=0;
                    retval=-5;
                    };


                    //see: http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
                    curl_retval=curl_easy_getinfo(pMsg->easy_handle, CURLINFO_RESPONSE_CODE, &http_response);
                    printf("CURLINFO_RESPONSE_CODE HTTP:[%ld]\n", http_response);
                    switch(http_response)
                    {
                    case 0:   //eg connection down  from kick-off ~suggest retrying till some max limit
                    case 200: //yay we at least got to our url
                    case 206: //Partial Content
                    break;

                    case 416:
                    //cannot d/l range ~ either cos no server support
                    //or cos we're asking for an invalid range ~ie: we already d/ld the file
                    printf("HTTP416: either the d/l is already complete or the http server cannot d/l a range\n");
                    retval=2;

                    default: //suggest quitting on an unhandled error
                    handle_count=0;
                    retval=-6;
                    };
                }
            }

            if (handle_count) //select on any active handles
            {
                fd_set fd_read={0}, fd_write={0}, fd_excep={0};
                struct timeval timeout={5,0};
                int select_retval;
                int fd_max;

                curl_multi_fdset(multi_handle, &fd_read, &fd_write, &fd_excep, &fd_max);
                if (-1 == (select_retval=select(fd_max+1, &fd_read, &fd_write, &fd_excep, &timeout)))
                {
                    //errno shall be set to indicate the error
                    fprintf(stderr, "yikes! select error :(\n");
                    handle_count=0;
                    retval=-7;
                    break;
                }
                else{/*check whatever*/}
            }

        } while (handle_count);

        curl_multi_remove_handle(multi_handle,curl);
        printf("continue from here?");
        getchar();        
    }
    while(retval==0);

    curl_multi_cleanup(multi_handle);
    curl_easy_cleanup(curl);
    curl_global_cleanup();
    if (fp) fclose(fp);

    return retval;
}

////////////////////////
int main(void)
{
    int retval;
    printf("\n\ncurl_multi d/l test ~curl version:[%s]\n", curl_version());
    while (1!=(retval=do_dl()))
    {
        printf("retval [%d] continue?\n\n", retval);
        printf("continue?");
        getchar();
    }
    printf("\nend of test!\n\n", retval);
    return retval;
}

/* notes ----

$sudo apt-get install libcurl4-gnutls-dev
$curl-config --libs
-L/usr/lib/i386-linux-gnu -lcurl -Wl,-Bsymbolic-functions

#oook. lets do it:
$gcc -o curltest_multi curltest_multi.c -L/usr/lib/i386-linux-gnu -lcurl -Wl,-Bsymbolic-functions
$./curltest_multi

*/

嗯，您可能想要记住在开始全新测试之前删除blah.dl文件。故意没有，因此您可以事先截断现有文件进行测试;）

NB：对于这样的事情，您可能应该*不仅仅依赖于CURLE_COULDNT_CONNECT〜您的代码应该主要是错误处理lol（;如果您的编程仅供个人使用，可能会更少;）

[编辑：] 我更新了curtest_multi.c以演示easy_handle重用。

并执行注意来自the documentaion的以下引用：

单次传输完成后，仍然可以轻松处理添加到多堆栈。您需要先移除简易手柄用curl_multi_remove_handle（3）然后用它关闭它 curl_easy_cleanup（3），或者可能为它设置新选项并添加它再次使用curl_multi_add_handle（3）开始另一次传输。

希望这会有所帮助;）

下载未使用Curl C API恢复

1 个答案: