Linux网络编程一步一步学-HTTPS客户端程序示例

源代码如下：

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <sys/types.h>

#include <sys/socket.h>

#include <errno.h>

#include <unistd.h>

#include <netinet/in.h>

#include <limits.h>

#include <netdb.h>

#include <arpa/inet.h>

#include <ctype.h>

#include <openssl/crypto.h>

#include <openssl/ssl.h>

#include <openssl/err.h>

#include <openssl/rand.h>

#define DEBUG 1

/********************************************

功能：搜索字符串右边起的第一个匹配字符

********************************************/

char *Rstrchr(char *s, char x)

{

int i = strlen(s);

if (!(*s))

return 0;

while (s[i - 1])

if (strchr(s + (i - 1), x))

return (s + (i - 1));

else

i--;

return 0;

}

/**************************************************************

功能：从字符串src中分析出网站地址和端口，并得到用户要下载的文件

***************************************************************/

void GetHost(char *src, char *web, char *file, int *port)

{

char *pA;

char *pB;

memset(web, 0, sizeof(web));

memset(file, 0, sizeof(file));

*port = 0;

if (!(*src))

return;

pA = src;

if (!strncmp(pA, "http://", strlen("http://")))

pA = src + strlen("http://");

else if (!strncmp(pA, "https://", strlen("https://")))

pA = src + strlen("https://");

pB = strchr(pA, '/');

if (pB) {

memcpy(web, pA, strlen(pA) - strlen(pB));

if (pB + 1) {

memcpy(file, pB + 1, strlen(pB) - 1);

file[strlen(pB) - 1] = 0;

}

} else

memcpy(web, pA, strlen(pA));

if (pB)

web[strlen(pA) - strlen(pB)] = 0;

else

web[strlen(pA)] = 0;

pA = strchr(web, ':');

if (pA)

*port = atoi(pA + 1);

else

*port = 443;

}

/************关于本文档********************************************

*filename: https-client.c

*purpose: 演示HTTPS客户端编程方法

*wrote by: zhoulifa(zhoulifa@163.com) 周立发(http://zhoulifa.bokee.com)

Linux爱好者 Linux知识传播者 SOHO族 开发者 最擅长C语言

*date time:2007-01-30 20:06

*Note: 任何人可以任意复制代码并运用这些文档，当然包括你的商业用途

* 但请遵循GPL

*Thanks to:Google

*Hope:希望越来越多的人贡献自己的力量，为科学技术发展出力

* 科技站在巨人的肩膀上进步更快！感谢有开源前辈的贡献！

*********************************************************************/

int main(int argc, char *argv[])

{

int sockfd, ret;

char buffer[1024];

struct sockaddr_in server_addr;

struct hostent *host;

int portnumber, nbytes;

char host_addr[256];

char host_file[1024];

char local_file[256];

FILE *fp;

char request[1024];

int send, totalsend;

int i;

char *pt;

SSL *ssl;

SSL_CTX *ctx;

if (argc != 2) {

if (DEBUG)

fprintf(stderr, "Usage:%s webpage-address/a/n", argv[0]);

exit(1);

}

if (DEBUG)

printf("parameter.1 is: %s/n", argv[1]);

GetHost(argv[1], host_addr, host_file, &portnumber); /*分析网址、端口、文件名等 */

if (DEBUG)

printf("webhost:%s/n", host_addr);

if (DEBUG)

printf("hostfile:%s/n", host_file);

if (DEBUG)

printf("portnumber:%d/n/n", portnumber);

if ((host = gethostbyname(host_addr)) == NULL) { /*取得主机IP地址 */

if (DEBUG)

fprintf(stderr, "Gethostname error, %s/n", strerror(errno));

exit(1);

}

/* 客户程序开始建立 sockfd描述符 */

if ((sockfd = socket(AF_INET, SOCK_STREAM, 0)) == -1) { /*建立SOCKET连接 */

if (DEBUG)

fprintf(stderr, "Socket Error:%s/a/n", strerror(errno));

exit(1);

}

/* 客户程序填充服务端的资料 */

bzero(&server_addr, sizeof(server_addr));

server_addr.sin_family = AF_INET;

server_addr.sin_port = htons(portnumber);

server_addr.sin_addr = *((struct in_addr *) host->h_addr);

/* 客户程序发起连接请求 */

if (connect(sockfd, (struct sockaddr *) (&server_addr), sizeof(struct sockaddr)) == -1) { /*连接网站 */

if (DEBUG)

fprintf(stderr, "Connect Error:%s/a/n", strerror(errno));

exit(1);

}

/* SSL初始化 */

SSL_library_init();

SSL_load_error_strings();

ctx = SSL_CTX_new(SSLv23_client_method());

if (ctx == NULL) {

ERR_print_errors_fp(stderr);

exit(1);

}

ssl = SSL_new(ctx);

if (ssl == NULL) {

ERR_print_errors_fp(stderr);

exit(1);

}

/* 把socket和SSL关联 */

ret = SSL_set_fd(ssl, sockfd);

if (ret == 0) {

ERR_print_errors_fp(stderr);

exit(1);

}

RAND_poll();

while (RAND_status() == 0) {

unsigned short rand_ret = rand() % 65536;

RAND_seed(&rand_ret, sizeof(rand_ret));

}

ret = SSL_connect(ssl);

if (ret != 1) {

ERR_print_errors_fp(stderr);

exit(1);

}

sprintf(request, "GET /%s HTTP/1.1/r/nAccept: */*/r/nAccept-Language: zh-cn/r/n/

User-Agent: Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)/r/n/

Host: %s:%d/r/nConnection: Close/r/n/r/n", host_file, host_addr,

portnumber);

if (DEBUG)

printf("%s", request); /*准备request，将要发送给主机 */

/*取得真实的文件名 */

if (host_file && *host_file)

pt = Rstrchr(host_file, '/');

else

pt = 0;

memset(local_file, 0, sizeof(local_file));

if (pt && *pt) {

if ((pt + 1) && *(pt + 1))

strcpy(local_file, pt + 1);

else

memcpy(local_file, host_file, strlen(host_file) - 1);

} else if (host_file && *host_file)

strcpy(local_file, host_file);

else

strcpy(local_file, "index.html");

if (DEBUG)

printf("local filename to write:%s/n/n", local_file);

/*发送https请求request */

send = 0;

totalsend = 0;

nbytes = strlen(request);

while (totalsend < nbytes) {

send = SSL_write(ssl, request + totalsend, nbytes - totalsend);

if (send == -1) {

if (DEBUG)

ERR_print_errors_fp(stderr);

exit(0);

}

totalsend += send;

if (DEBUG)

printf("%d bytes send OK!/n", totalsend);

}

fp = fopen(local_file, "a");

if (!fp) {

if (DEBUG)

printf("create file error! %s/n", strerror(errno));

return 0;

}

if (DEBUG)

printf("/nThe following is the response header:/n");

i = 0;

/* 连接成功了，接收https响应，response */

while ((nbytes = SSL_read(ssl, buffer, 1)) == 1) {

if (i < 4) {

if (buffer[0] == '/r' || buffer[0] == '/n')

i++;

else

i = 0;

if (DEBUG)

printf("%c", buffer[0]); /*把https头信息打印在屏幕上 */

} else {

fwrite(buffer, 1, 1, fp); /*将https主体信息写入文件 */

i++;

if (i % 1024 == 0)

fflush(fp); /*每1K时存盘一次 */

}

}

fclose(fp);

/* 结束通讯 */

ret = SSL_shutdown(ssl);

if (ret != 1) {

ERR_print_errors_fp(stderr);

exit(1);

}

close(sockfd);

SSL_free(ssl);

SSL_CTX_free(ctx);

ERR_free_strings();

exit(0);

}

编译此程序用下列命令：
gcc -Wall https-client.c -lssl -o httpsclient

运行此程序来取得HTTPS服务器上的页面，比如：
./httpsclient https://127.0.0.1/test.html
关键之处在于建立socket之后的SSL相关初始化以及中间的recv/send用SSL_read和SSL_write代替，最后记得释放SSL资源即可。
可以对比之前的文章来发现异同：

HTTP协议的C语言编程实现实例