如何解决libcurl外部套接字示例，如何从套接字读取？
我发现了关于如何使用自定义套接字的简单libcurl example。
/***************************************************************************
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* / __| | | | |_) | |
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*
* Copyright (C) 1998 - 2019,Daniel Stenberg,<daniel@haxx.se>,et al.
*
* This software is licensed as described in the file COPYING,which
* you should have received as part of this distribution. The terms
* are also available at https://curl.haxx.se/docs/copyright.html.
*
* You may opt to use,copy,modify,merge,publish,distribute and/or sell
* copies of the Software,and permit persons to whom the Software is
* furnished to do so,under the terms of the COPYING file.
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* This software is distributed on an "AS IS" basis,WITHOUT WARRANTY OF ANY
* KIND,either express or implied.
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***************************************************************************/
/* <DESC>
* An example demonstrating how an application can pass in a custom
* socket to libcurl to use. This example also handles the connect itself.
* </DESC>
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <curl/curl.h>
#ifdef WIN32
#include <windows.h>
#include <winsock2.h>
#include <ws2tcpip.h>
#define close closesocket
#else
#include <sys/types.h> /* socket types */
#include <sys/socket.h> /* socket definitions */
#include <netinet/in.h>
#include <arpa/inet.h> /* inet (3) functions */
#include <unistd.h> /* misc. Unix functions */
#endif
#include <errno.h>
/* The IP address and port number to connect to */
#define IPADDR "127.0.0.1"
#define PORTNUM 80
#ifndef INADDR_NONE
#define INADDR_NONE 0xffffffff
#endif
static size_t write_data(void *ptr,size_t size,size_t nmemb,void *stream)
{
size_t written = fwrite(ptr,size,nmemb,(FILE *)stream);
return written;
}
static int closecb(void *clientp,curl_socket_t item)
{
(void)clientp;
printf("libcurl wants to close %d now\n",(int)item);
return 0;
}
static curl_socket_t opensocket(void *clientp,curlsocktype purpose,struct curl_sockaddr *address)
{
curl_socket_t sockfd;
(void)purpose;
(void)address;
sockfd = *(curl_socket_t *)clientp;
/* the actual externally set socket is passed in via the OPENSOCKETDATA
option */
return sockfd;
}
static int sockopt_callback(void *clientp,curl_socket_t curlfd,curlsocktype purpose)
{
(void)clientp;
(void)curlfd;
(void)purpose;
/* This return code was added in libcurl 7.21.5 */
return CURL_SOCKOPT_ALREADY_CONNECTED;
}
int main(void)
{
CURL *curl;
CURLcode res;
struct sockaddr_in servaddr; /* socket address structure */
curl_socket_t sockfd;
#ifdef WIN32
WSADATA wsaData;
int initwsa = WSAStartup(MAKEWORD(2,0),&wsaData);
if(initwsa != 0) {
printf("WSAStartup failed: %d\n",initwsa);
return 1;
}
#endif
curl = curl_easy_init();
if(curl) {
/*
* Note that libcurl will internally think that you connect to the host
* and port that you specify in the URL option.
*/
curl_easy_setopt(curl,CURLOPT_URL,"http://99.99.99.99:9999");
/* Create the socket "manually" */
sockfd = socket(AF_INET,SOCK_STREAM,0);
if(sockfd == CURL_SOCKET_BAD) {
printf("Error creating listening socket.\n");
return 3;
}
memset(&servaddr,sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(PORTNUM);
servaddr.sin_addr.s_addr = inet_addr(IPADDR);
if(INADDR_NONE == servaddr.sin_addr.s_addr) {
close(sockfd);
return 2;
}
if(connect(sockfd,(struct sockaddr *) &servaddr,sizeof(servaddr)) ==
-1) {
close(sockfd);
printf("client error: connect: %s\n",strerror(errno));
return 1;
}
/* no progress meter please */
curl_easy_setopt(curl,CURLOPT_NOPROGRESS,1L);
/* send all data to this function */
curl_easy_setopt(curl,CURLOPT_WRITEFUNCTION,write_data);
/* call this function to get a socket */
curl_easy_setopt(curl,CURLOPT_OPENSOCKETFUNCTION,opensocket);
curl_easy_setopt(curl,CURLOPT_OPENSOCKETDATA,&sockfd);
/* call this function to close sockets */
curl_easy_setopt(curl,CURLOPT_CLOSESOCKETFUNCTION,closecb);
curl_easy_setopt(curl,CURLOPT_CLOSESOCKETDATA,&sockfd);
/* call this function to set options for the socket */
curl_easy_setopt(curl,CURLOPT_SOCKOPTFUNCTION,sockopt_callback);
curl_easy_setopt(curl,CURLOPT_VERBOSE,1);
res = curl_easy_perform(curl);
curl_easy_cleanup(curl);
close(sockfd);
if(res) {
printf("libcurl error: %d\n",res);
return 4;
}
}
#ifdef WIN32
WSACleanup();
#endif
return 0;
}
我知道现在如何创建自己的套接字，但是不清楚libcurl从何处读取。我只能看到写入打开的套接字的写函数。如果我想从插座中读取该怎么办？ libcurl如何才能仅将自定义套接字用于写入？
解决方法
您检查了文档吗？
https://curl.haxx.se/libcurl/c/CURLOPT_WRITEFUNCTION.html说：
使用CURLOPT_WRITEDATA选项设置userdata [在您的情况下为流]参数。
然后再来
：将此选项设置为NULL，以获取内部默认函数而不是回调函数。内部默认函数会将数据写入CURLOPT_WRITEDATA给出的FILE *。
示例似乎有些不完整，您可能只需将CURLOPT_WRITEDATA设置为FILE *。
再次阅读问题，可能是我误解了你的意思。
...目前还不清楚libcurl从何处读取。
它从连接到（http://99.99.99.99:9999）的http服务器读取。
还是您有关读取本地文件和上传数据的问题？在这种情况下，您应该看看https://curl.haxx.se/libcurl/c/CURLOPT_READFUNCTION.html
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