c - libcurl:如何使用原始文件名下载 url？ (相当于 "-O/--remote-name")

Question

问题一:使用libcurl下载url时，如何保留下载文件的原名？ LibCurl 要求程序员生成文件名。当 URL 有例如在下面的 url 中，很容易找出目标名称是 vimqrc.pdf。

 http://tnerual.eriogerg.free.fr/vimqrc.pdf)  

但是当 URL 动态生成目标名称时，例如下面的 URL 下载 AdbeRdr1010_eu_ES.exe。 使用 wget(除 URL 外没有参数)和 curl(参数 -O)

http://get.adobe.com/reader/download/?installer=Reader_10.1_Basque_for_Windows&standalone=1%22

curl (-O) 或 wget 如何计算出

//invoked as ./a.out <URL>

#include <stdio.h>
#include <curl/curl.h>

char *location = "/tmp/test/out";

size_t write_data(void *ptr, size_t size, size_t nmemb, FILE *stream) {
    size_t written = fwrite(ptr, size, nmemb, stream);
    return written;
}

int main(int argc, char *argv[])
{
    CURL        *curl;
    CURLcode    res;
    int         ret = -1;


    if (argc!= 2) {
        //invoked as ./a.out <URL>
        return -1;
    } 

    curl = curl_easy_init();
    if (!curl) {
        goto bail;
    }

    FILE *fp = fopen(location, "wb");
    curl_easy_setopt(curl, CURLOPT_URL, argv[1]); //invoked as ./a.out <URL>
    /* example.com is redirected, so we tell libcurl to follow redirection */
    curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data);
    curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp);

    /* Perform the request, res will get the return code */
    res = curl_easy_perform(curl);
    /* Check for errors */
    if(res != CURLE_OK)
        fprintf(stderr, "curl_easy_perform() failed: %s\n",
                curl_easy_strerror(res));

    /* always cleanup */
    curl_easy_cleanup(curl);
    ret = 0;
    fclose(fp);

bail:
    return ret;
}

Answer 1

我在 libcurl 源代码中找到了答案。看起来“远程名称”是 header 中“内容配置”标签的一部分。 Libcurl 正在解析 header 并在 content-disposition 标记中查找“filename=”。此解析在通过 CURLOPT_HEADERFUNCTION 选项提供的回调中完成。最后，在写入数据的回调中(通过 CURLOPT_WRITEFUNCTION 提供)，此远程名称用于创建输出文件。

如果缺少文件名，只需从 URL 本身中找出即可。这几乎是从 lib curl 复制的代码和我自己的少量修改以使其更简单并符合我的要求。

#define _GNU_SOURCE 
#include <stdio.h>
#include <curl/curl.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <stdlib.h>

typedef unsigned long uint64_t;
typedef struct {
    char        dnld_remote_fname[4096];
    char        dnld_url[4096]; 
    FILE        *dnld_stream;
    FILE        *dbg_stream;
    uint64_t    dnld_file_sz;
} dnld_params_t;

static int get_oname_from_cd(char const*const cd, char *oname)
{
    char    const*const cdtag   = "Content-disposition:";
    char    const*const key     = "filename=";
    int     ret                 = 0;
    char    *val                = NULL;

    /* Example Content-Disposition: filename=name1367; charset=funny; option=strange */

    /* If filename is present */
    val = strcasestr(cd, key);
    if (!val) {
        printf("No key-value for \"%s\" in \"%s\"", key, cdtag);
        goto bail;
    }

    /* Move to value */
    val += strlen(key);

    /* Copy value as oname */
    while (*val != '\0' && *val != ';') {
        //printf (".... %c\n", *val);
        *oname++ = *val++;
    }
    *oname = '\0';

bail:
    return ret;
}

static int get_oname_from_url(char const* url, char *oname)
{
    int         ret = 0;
    char const  *u  = url;

    /* Remove "http(s)://" */
    u = strstr(u, "://");
    if (u) {
        u += strlen("://");
    }

    u = strrchr(u, '/');

    /* Remove last '/' */
    u++;

    /* Copy value as oname */
    while (*u != '\0') {
        //printf (".... %c\n", *u);
        *oname++ = *u++;
    }
    *oname = '\0';

    return ret;
}

size_t dnld_header_parse(void *hdr, size_t size, size_t nmemb, void *userdata)
{
    const   size_t  cb      = size * nmemb;
    const   char    *hdr_str= hdr;
    dnld_params_t *dnld_params = (dnld_params_t*)userdata;
    char const*const cdtag = "Content-disposition:";

    /* Example: 
     * ...
     * Content-Type: text/html
     * Content-Disposition: filename=name1367; charset=funny; option=strange
     */
    if (strstr(hdr_str, "Content-disposition:")) {
        printf ("has c-d: %s\n", hdr_str);
    }

    if (!strncasecmp(hdr_str, cdtag, strlen(cdtag))) {
        printf ("Found c-d: %s\n", hdr_str);
        int ret = get_oname_from_cd(hdr_str+strlen(cdtag), dnld_params->dnld_remote_fname);
        if (ret) {
            printf("ERR: bad remote name");
        }
    }

    return cb;
}

FILE* get_dnld_stream(char const*const fname)
{
    char const*const pre = "/tmp/";
    char out[4096];

    snprintf(out, sizeof(out), "%s/%s", pre, fname);

    FILE *fp = fopen(out, "wb");
    if (!fp) {
        printf ("Could not create file %s\n", out);
    }

    return fp;
}

size_t write_cb(void *buffer, size_t sz, size_t nmemb, void *userdata)
{
    int ret = 0;
    dnld_params_t *dnld_params = (dnld_params_t*)userdata;

    if (!dnld_params->dnld_remote_fname[0]) {
        ret = get_oname_from_url(dnld_params->dnld_url, dnld_params->dnld_remote_fname);
    }

    if (!dnld_params->dnld_stream) {
        dnld_params->dnld_stream = get_dnld_stream(dnld_params->dnld_remote_fname);
    }

    ret = fwrite(buffer, sz, nmemb, dnld_params->dnld_stream);
    if (ret == (sz*nmemb)) {
       dnld_params->dnld_file_sz += ret;
    }
    return ret;
}


int download_url(char const*const url)
{
    CURL        *curl;
    int         ret = -1;
    CURLcode    cerr = CURLE_OK;
    dnld_params_t dnld_params;

    memset(&dnld_params, 0, sizeof(dnld_params));
    strncpy(dnld_params.dnld_url, url, strlen(url));

    curl = curl_easy_init();
    if (!curl) {
        goto bail;
    }

    cerr = curl_easy_setopt(curl, CURLOPT_URL, url);
    if (cerr) { printf ("%s: failed with err %d\n", "URL", cerr); goto bail;}

    cerr = curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, dnld_header_parse);
    if (cerr) { printf ("%s: failed with err %d\n", "HEADER", cerr); goto bail;}

    cerr = curl_easy_setopt(curl, CURLOPT_HEADERDATA, &dnld_params);
    if (cerr) { printf ("%s: failed with err %d\n", "HEADER DATA", cerr); goto bail;}

    cerr = curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_cb);
    if (cerr) { printf ("%s: failed with err %d\n", "WR CB", cerr); goto bail;}

    cerr = curl_easy_setopt(curl, CURLOPT_WRITEDATA, &dnld_params);
    if (cerr) { printf ("%s: failed with err %d\n", "WR Data", cerr); goto bail;}


    cerr = curl_easy_perform(curl);
    if(cerr != CURLE_OK) {
        fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(cerr));
    }

    printf ("Remote name: %s\n", dnld_params.dnld_remote_fname);
    fclose(dnld_params.dnld_stream);

    /* always cleanup */
    curl_easy_cleanup(curl);
    ret = 0;
    printf ("file size : %lu\n", dnld_params.dnld_file_sz);

bail:
    return ret;
}

int main(int argc, char *argv[])
{
    if (argc != 2) {
        printf ("Bad args\n");
        return -1;
    }
    return download_url(argv[1]);
}