OpenSSL in C++ Socket Connection (HTTPS Client) - c++

Question

i wrote an script, who can create an connection to an HTTP Server and shows the content of the website in the console.
Very easy.
But i want to connect to an https server and do the same procedures.
I searched at google and didn't found what i searched.
Please help me and give me an tutorial who can i use the openssl library.
I tried myself on the openssl library, but the library is very complicated and difficult to understand.
Here is my code of the http client:
#include <iostream>
#include <ctype.h>
#include <cstring>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <netinet/in.h>
#include <unistd.h>
#include <sstream>
#include <fstream>
#include <string>
#include <arpa/inet.h>
#include <openssl/ssl.h>
using namespace std;
int sock;
struct sockaddr_in client;
int PORT = 80;
int main(int argc, char const *argv[])
{
bzero(&client, sizeof(client));
client.sin_family = AF_INET;
client.sin_port = htons( PORT );
client.sin_addr.s_addr = inet_addr("172.16.0.6");
sock = socket(AF_INET, SOCK_STREAM, 0);
if (sock < 0) {
cout << "Error creating socket." << endl;
exit(1);
}
if ( connect(sock, (struct sockaddr *)&client, sizeof(client)) < 0 ) {
close(sock);
cout << "Could not connect" << endl;
exit(1);
}
stringstream ss;
ss << "GET /" << "\r\n"
<< "Host: 172.16.1.4\r\n"
<< "Accept: application/json\r\n"
<< "Connection: close"
<< "\r\n\r\n";
string request = ss.str();
if (send(sock, request.c_str(), request.length(), 0) != (int)request.length()) {
cout << "Error sending request." << endl;
exit(1);
}
char cur;
while ( read(sock, &cur, 1) > 0 ) {
cout << cur;
}
return 0;
}

Answer 1

Here is a sample SSL client that connects to https://about.google/intl/en/ and prints downloaded a page : SSLClient.cpp
//============================================================================
// Name : SSLClient.cpp
// Compiling : g++ -c -o SSLClient.o SSLClient.cpp
// g++ -o SSLClient SSLClient.o -lssl -lcrypto
//============================================================================
#include <stdio.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <openssl/ssl.h>
#include <openssl/err.h>
#include <string.h>
using namespace std;
SSL *ssl;
int sock;
int RecvPacket()
{
int len=100;
char buf[1000000];
do {
len=SSL_read(ssl, buf, 100);
buf[len]=0;
printf("%s\n",buf);
// fprintf(fp, "%s",buf);
} while (len > 0);
if (len < 0) {
int err = SSL_get_error(ssl, len);
if (err == SSL_ERROR_WANT_READ)
return 0;
if (err == SSL_ERROR_WANT_WRITE)
return 0;
if (err == SSL_ERROR_ZERO_RETURN || err == SSL_ERROR_SYSCALL || err == SSL_ERROR_SSL)
return -1;
}
}
int SendPacket(const char *buf)
{
int len = SSL_write(ssl, buf, strlen(buf));
if (len < 0) {
int err = SSL_get_error(ssl, len);
switch (err) {
case SSL_ERROR_WANT_WRITE:
return 0;
case SSL_ERROR_WANT_READ:
return 0;
case SSL_ERROR_ZERO_RETURN:
case SSL_ERROR_SYSCALL:
case SSL_ERROR_SSL:
default:
return -1;
}
}
}
void log_ssl()
{
int err;
while (err = ERR_get_error()) {
char *str = ERR_error_string(err, 0);
if (!str)
return;
printf(str);
printf("\n");
fflush(stdout);
}
}
int main(int argc, char *argv[])
{
int s;
s = socket(AF_INET, SOCK_STREAM, 0);
if (s < 0) {
printf("Error creating socket.\n");
return -1;
}
struct sockaddr_in sa;
memset (&sa, 0, sizeof(sa));
sa.sin_family = AF_INET;
sa.sin_addr.s_addr = inet_addr("173.194.222.139"); // address of google.ru
sa.sin_port = htons (443);
socklen_t socklen = sizeof(sa);
if (connect(s, (struct sockaddr *)&sa, socklen)) {
printf("Error connecting to server.\n");
return -1;
}
SSL_library_init();
SSLeay_add_ssl_algorithms();
SSL_load_error_strings();
const SSL_METHOD *meth = TLSv1_2_client_method();
SSL_CTX *ctx = SSL_CTX_new (meth);
ssl = SSL_new (ctx);
if (!ssl) {
printf("Error creating SSL.\n");
log_ssl();
return -1;
}
sock = SSL_get_fd(ssl);
SSL_set_fd(ssl, s);
int err = SSL_connect(ssl);
if (err <= 0) {
printf("Error creating SSL connection. err=%x\n", err);
log_ssl();
fflush(stdout);
return -1;
}
printf ("SSL connection using %s\n", SSL_get_cipher (ssl));
char *request = "GET https://about.google/intl/en/ HTTP/1.1\r\n\r\n";
SendPacket(request);
RecvPacket();
return 0;
}
Note that if you want to exchange data between client and server with openssl, you might need to process error codes SSL_ERROR_WANT_READ and SSL_ERROR_WANT_WRITE as described in documentation. But it's not necessary here as HTTPS protocol is serial.