问题1：当使用libcurl下载url时，如何保留下载文件的原始名称？LibCurl要求程序员生成文件名。当URL具有例如，在下面的url中，它很容易找到目标名称是vimqrc.pdf.
http://tnerual.eriogerg.free.fr/vimqrc.pdf)
但是当URL动态生成目标名称时，例如以下URL下载AdbeRdr1010_euES.exe.带有wget（除了URL之外没有参数）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如何计算的名称
//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: %sn",
curl_easy_strerror(res));
/* always cleanup */
curl_easy_cleanup(curl);
ret = 0;
fclose(fp);
bail:
return ret;
}
我在libcurl源代码中找到了答案。看起来"远程名称"是标头中"内容处置"标记的一部分。Libcurl正在解析标头，并在内容处置标记中查找"filename="。此解析是在通过CURLOPT_HEADERFUNCTION选项提供的回调中完成的。最后，在写入数据的回调（通过CURLOPT_WRITEFUNCTION提供）中，这个远程名称用于创建输出文件。
如果缺少文件名，只需从URL本身查找即可。这几乎是从lib-ccurl中复制的代码，我自己也做了一些修改，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 != ' ' && *val != ';') {
//printf (".... %cn", *val);
*oname++ = *val++;
}
*oname = ' ';
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 != ' ') {
//printf (".... %cn", *u);
*oname++ = *u++;
}
*oname = ' ';
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: %sn", hdr_str);
}
if (!strncasecmp(hdr_str, cdtag, strlen(cdtag))) {
printf ("Found c-d: %sn", 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 %sn", 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 %dn", "URL", cerr); goto bail;}
cerr = curl_easy_setopt(curl, CURLOPT_HEADERFUNCTION, dnld_header_parse);
if (cerr) { printf ("%s: failed with err %dn", "HEADER", cerr); goto bail;}
cerr = curl_easy_setopt(curl, CURLOPT_HEADERDATA, &dnld_params);
if (cerr) { printf ("%s: failed with err %dn", "HEADER DATA", cerr); goto bail;}
cerr = curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_cb);
if (cerr) { printf ("%s: failed with err %dn", "WR CB", cerr); goto bail;}
cerr = curl_easy_setopt(curl, CURLOPT_WRITEDATA, &dnld_params);
if (cerr) { printf ("%s: failed with err %dn", "WR Data", cerr); goto bail;}
cerr = curl_easy_perform(curl);
if(cerr != CURLE_OK) {
fprintf(stderr, "curl_easy_perform() failed: %sn", curl_easy_strerror(cerr));
}
printf ("Remote name: %sn", dnld_params.dnld_remote_fname);
fclose(dnld_params.dnld_stream);
/* always cleanup */
curl_easy_cleanup(curl);
ret = 0;
printf ("file size : %lun", dnld_params.dnld_file_sz);
bail:
return ret;
}
int main(int argc, char *argv[])
{
if (argc != 2) {
printf ("Bad argsn");
return -1;
}
return download_url(argv[1]);
}
决定文件名的是您的程序，而不是libcurl。在您的示例中，您可以简单地将char *location = "/tmp/test/out";更改为char *location = "/tmp/test/vimqrc.pdf";以获得所需的效果。
如果你想在给定url和父目录的情况下用程序推导下载文件路径，你可以做如下操作：
int url_to_location(char* location, unsigned int location_length, const char* url, const char* parent_directory)
{
//char location[MAX_PATH];
//const char *url = "http://tnerual.eriogerg.free.fr/vimqrc.pdf";
//const char *parent_directory = "/tmp/test/";
int last_slash_index = -1;
int current_index = (int)strlen(url);
while (current_index >= 0)
{
if (url[current_index] == '/')
{
last_slash_index = current_index;
break;
}
current_index--;
}
unsigned int parent_directory_length = strlen(parent_directory)
if (parent_directory_length <= location_length)
return -1;
strcpy(location, parent_directory);
if (last_slash_index == -1) //no slashes found, use relative url as filename
{
if (parent_directory_length + strlen(url) <= location_length)
return -1;
strcat(location, url);
}
else //use the characters of the url following the last slash as filename
{
if (parent_directory_length + strlen(url + last_slash_index + 1) <= location_length)
return -1;
strcat(location, url + last_slash_index + 1);
}
return strlen(location);
}