HTTPS requests in socketwith proxy (https,socks4,socks5) in C - c

Question

i develop a program where i make i HTTPS requests in multithreading.
All work fine, however i need toimpleent use of proxy.
At the moment, i have this function for HTTPS Request :
struct string_builder* webrequest(const char* DEST_IP, const int DEST_PORT, const char* REQUEST) {
// Initialize ssl libraries and error messages
SSL_CTX *ssl_ctx = SSL_CTX_new (SSLv23_client_method());
// create a socket
int sockfd = socket(PF_INET, SOCK_STREAM, 0);
if (sockfd == -1) {
perror("Unable to create socket");
return NULL;
}
// destination info
struct sockaddr_in dest_addr;
dest_addr.sin_family = AF_INET; // host byte order
dest_addr.sin_port = htons(DEST_PORT); // short, network port
dest_addr.sin_addr.s_addr = inet_addr(DEST_IP); // destination address
memset(&(dest_addr.sin_zero), '\0', 8); // zero out the rest of the struct
// connect to the server
int status = connect(sockfd, (struct sockaddr*) &dest_addr, sizeof(struct sockaddr_in));
if (status == -1) {
perror("Unable to connect to the server");
close(sockfd);
return NULL;
}
// create SSL connection and attach it to the socket
SSL *conn = SSL_new(ssl_ctx);
SSL_set_fd(conn, sockfd);
SSL_connect(conn);
// send an encrypted message
ssize_t sendsize = SSL_write(conn, REQUEST, strlen(REQUEST));
if (sendsize == -1) {
perror("Unable to send to the server");
{
char *buf = malloc(sizeof(char) * 256);;
u_long err;
while ((err = ERR_get_error()) != 0) {
ERR_error_string_n(err, buf, sizeof(buf));
printf("*** %s\n", buf);
}
free(buf);
}
SSL_shutdown(conn);
ERR_free_strings();
ERR_remove_state(0);
SSL_CTX_free(ssl_ctx);
close(sockfd);
return NULL;
}
size_t i = 1;
struct string_builder *result = NULL;
result = string_builder_init();
while (i) {
// receive the response
const int RESPONSE_SIZE = 512;
char *response = malloc(sizeof(char)*512);
ssize_t recsize = SSL_read(conn, response, RESPONSE_SIZE-1);
if (recsize == -1) {
perror("Unable to send to the server");
SSL_shutdown(conn);
ERR_free_strings();
ERR_remove_state(0);
SSL_CTX_free(ssl_ctx);
close(sockfd);
return NULL;
}
response[recsize] = '\0';
if (recsize <= 0)
{
free(response);
break;
}
else if (i > 2 && recsize > 6)
{
string_builder_pushs(result, response);
}
free(response);
++i;
}
// close ssl connection
SSL_shutdown(conn);
ERR_free_strings();
ERR_remove_state(0);
SSL_free(conn);
SSL_CTX_free(ssl_ctx);
close(sockfd);
return result;
}
I use socket/send/recv function for socket, openssl library for HTTPS requests.
All work fine, no leak without proxy, but when i try to use a "CONNECT command" to connect to google (and socket connexion to proxy host), i have an error when i want to send.
Thanks in advance.