基于openssl的https client例子

因为微信公众获取access_token需要用到https，开始用http请求的时候发现不行查了之后，
发现它是需要https方式访问的.因为这方面的资料感觉有点少这里就再写一下，我也是参照大神的：
只是想多一个链接让多 一点人知道而已：

#include <sys/socket.h>#include <sys/types.h>#include <netinet/in.h>#include <netdb.h>#include <stdio.h>#include <string.h>#include <stdlib.h>#include <unistd.h>#include <errno.h>#include <openssl/rand.h>#include <openssl/ssl.h>#include <openssl/err.h>// Simple structure to keep track of the handle, and// of what needs to be freed later.typedef struct{    int socket;    SSL *sslHandle;    SSL_CTX *sslContext;} connection;// For this example, we'll be testing on openssl.org#define SERVER  "183.57.48.62" // api.weixin.qq.com 服务器地址#define PORT 443// Establish a regular tcp connectionint tcpConnect (){    int error, handle;    struct hostent *host;    struct sockaddr_in server;    host = gethostbyname (SERVER);    handle = socket (AF_INET, SOCK_STREAM, 0);    if (handle == -1)    {        perror ("Socket");        handle = 0;    }    else    {        server.sin_family = AF_INET;        server.sin_port = htons (PORT);        server.sin_addr = *((struct in_addr *) host->h_addr);        bzero (&(server.sin_zero), 8);        error = connect (handle, (struct sockaddr *) &server,                         sizeof (struct sockaddr));        if (error == -1)        {            perror ("Connect");            handle = 0;        }    }    return handle;}// Establish a connection using an SSL layerconnection *sslConnect (void){    connection *c;    c = malloc (sizeof (connection));    c->sslHandle = NULL;    c->sslContext = NULL;    c->socket = tcpConnect ();    if (c->socket)    {        // Register the error strings for libcrypto & libssl        SSL_load_error_strings ();        // Register the available ciphers and digests        SSL_library_init ();        OpenSSL_add_all_algorithms();        // New context saying we are a client, and using SSL 2 or 3        c->sslContext = SSL_CTX_new (SSLv23_client_method ());        if (c->sslContext == NULL)            ERR_print_errors_fp (stderr);        // Create an SSL struct for the connection        c->sslHandle = SSL_new (c->sslContext);        if (c->sslHandle == NULL)            ERR_print_errors_fp (stderr);        // Connect the SSL struct to our connection        if (!SSL_set_fd (c->sslHandle, c->socket))            ERR_print_errors_fp (stderr);        // Initiate SSL handshake        if (SSL_connect (c->sslHandle) != 1)            ERR_print_errors_fp (stderr);    }    else    {        perror ("Connect failed");    }    return c;}// Disconnect & free connection structvoid sslDisconnect (connection *c){    if (c->socket)        close (c->socket);    if (c->sslHandle)    {        SSL_shutdown (c->sslHandle);        SSL_free (c->sslHandle);    }    if (c->sslContext)        SSL_CTX_free (c->sslContext);    free (c);}// Read all available text from the connectionchar *sslRead (connection *c){    const int readSize = 1024;    char *rc = NULL;    int received, count = 0;    char buffer[1024];    if (c)    {        while (1)        {            if (!rc)                rc = malloc (readSize * sizeof (char) + 1);            else                rc = realloc (rc, (count + 1) *                              readSize * sizeof (char) + 1);            memset(rc,0,readSize + 1);            received = SSL_read (c->sslHandle, buffer, readSize);            buffer[received] = '\0';            if (received > 0)                strcat (rc, buffer);            if (received < readSize)                break;            count++;        }    }    return rc;}// Write text to the connectionvoid sslWrite (connection *c, char *text){    if (c)        SSL_write (c->sslHandle, text, strlen (text));}// Very basic main: we send GET / and print the response.int main (int argc, char **argv){    connection *c;    char *response;    c = sslConnect ();    //sslWrite (c, "GET / HTTP/1.1\r\nHost: localhost\r\nconnection: close\r\n\r\n");    // 这里记得写上自己的申请的appid 和 secret就可以了    sslWrite (c, "GET /cgi-bin/token?grant_type=client_credential&appid=your_appid&"    "secret=your_secret HTTP/1.1\r\nHost: localhost\r\nconnection: close\r\n\r\n");    response = sslRead (c);    printf ("%s\n", response);    sslDisconnect (c);    free (response);    return 0;}

参考：
[1]两个基于openssl的https client例子[EB/OL].https://my.oschina.net/vincentwy/blog/620282?p=1