BindIPAddress when force address family to IPV6 and set outbound interface

[CyberKoo]

//
// Created by Kotarou on 2022/4/6.
//
#include <httplib.h>

std::unique_ptr<httplib::Client>
get_http_client(std::string_view url, int family = AF_UNSPEC, const char *nif_name = nullptr) {
    auto client = std::make_unique<httplib::Client>(url.data());

    // set outbound interface
    if (nif_name != nullptr) {
        client->set_interface(nif_name);
    }

    // set address family
    client->set_address_family(family);
    client->set_connection_timeout(5);
    client->set_read_timeout(5, 1000);
    client->set_follow_location(true);
    client->set_default_headers({{"User-Agent", "Mozilla"}});

    return client;
}

void print_response(const httplib::Result &result) {
    if (result) {
        std::cout << result->body << std::endl;
    } else {
        std::cerr << "Error: " << httplib::to_string(result.error()) << std::endl;
    }
}

int main(int argc, char *argv[]) {
    std::cout << "AF_UNSPEC, no nif" << std::endl;
    auto client = get_http_client("https://api.ip.sb:443");
    auto response = client->Get("/ip");
    print_response(response);

    std::cout << "AF_UNSPEC, en0" << std::endl;
    client = get_http_client("https://api.ip.sb:443", AF_UNSPEC, "en0");
    response = client->Get("/ip");
    print_response(response);

    std::cout << "AF_INET, no nif" << std::endl;
    client = get_http_client("https://api.ip.sb:443", AF_INET);
    response = client->Get("/ip");
    print_response(response);

    std::cout << "AF_INET, en0" << std::endl;
    client = get_http_client("https://api.ip.sb:443", AF_INET, "en0");
    response = client->Get("/ip");
    print_response(response);

    std::cout << "AF_INET6, no nif" << std::endl;
    client = get_http_client("https://api.ip.sb:443", AF_INET6);
    response = client->Get("/ip");
    print_response(response);

    std::cout << "AF_INET6, en0" << std::endl;
    client = get_http_client("https://api.ip.sb:443", AF_INET6, "en0");
    response = client->Get("/ip");
    print_response(response);
    
    return 0;
}

Output:

AF_UNSPEC, no nif
2405:aacf:acdc:6dc:33:cda2:153e:745

AF_UNSPEC, en0
38.13.192.76

AF_INET, no nif
38.13.192.76

AF_INET, en0
38.13.192.76

AF_INET6, no nif
2405:aacf:acdc:6dc:33:cda2:153e:745

AF_INET6, en0
Error: BindIPAddress

not sure what cause this, but when set address family to AF_INET6 and also force to use en0 as outbound interface, library returned a bind ip error.

[yhirose]

@CyberKoo, I feel that it's a general HTTP problem, not a cpp-httplib specific problem. Could you try with other HTTP libraries (or just use the system socket library) on your machine, so that we can check if it's a really cpp-httplib problem?
Thanks for your help!

[CyberKoo]

//
// Created by Kotarou on 2022/4/6.
//
#include <arpa/inet.h>
#include <netinet/in.h>
#include <cstdio>
#include <cstdlib>
#include <sys/socket.h>
#include <unistd.h>
#include <net/if.h>

#include <iostream>

int main(int argc, char *argv[]) {
    int fd;
    fd = socket(AF_INET6, SOCK_STREAM, IPPROTO_TCP);

    // nif (macos)
    uint32_t nif_index = if_nametoindex("en0");

    struct sockaddr_in6 server_addr{};
    inet_pton(AF_INET6, "2606:4700:20::ac43:4bac", &server_addr.sin6_addr);    // ipv6.ip.sb
    server_addr.sin6_family = AF_INET6;
    server_addr.sin6_port = htons(80);
    server_addr.sin6_scope_id = nif_index;

    connect(fd, (struct sockaddr *) &server_addr, sizeof(server_addr));

    const char request[] = "GET / HTTP/1.0\n"
                           "Host: ipv6.ip.sb\n"
                           "User-Agent: {}\n"
                           "Accept: */*\r\n\r\n";

    write(fd, &request, sizeof(request));

    char buffer[1024] = {};
    read(fd, &buffer, 1023);

    std::cout << buffer << std::endl;

    close(fd);

    return 0;
}

output

HTTP/1.1 301 Moved Permanently
Date: Wed, 06 Apr 2022 12:47:48 GMT
Content-Type: text/html
Connection: close
Location: https://ipv6.ip.sb/
CF-Cache-Status: DYNAMIC
Report-To: {"endpoints":[{"url":"https:\/\/a.nel.cloudflare.com\/report\/v3?s=jJxo4kyHV0UC8zH5jjnlVqwTsF35whVW3f8JkYdaAZ8%2BO%2BidWU%2FszhuLQpMW6n%2F7%2FZcYdaDJqOOI%2F4%2F63wDhr52KDXQZJQtw8 6fcd47e6a q7fU2fjyrtMzwGI%3D"}],"group":"cf-nel","max_age":604800}
NEL: {"success_fraction":0,"report_to":"cf-nel","max_age":604800}
Server: cloudflare
CF-RAY: 6f7aa25hU4p3H7q-LAX
alt-svc: h3=":443"; ma=86400, h3-29=":443"; ma=86400

<html>
<head><title>301 Moved Permanently</title></head>
<body>
<center><h1>301 Moved Permanently</h1></center>
<hr><center>nginx</center>
</body>
</html>

[CyberKoo]

I think this problem was cause by the if2ip function, which only return IPV4 address.

cpp-httplib/httplib.h

Line 2652 in 020b0db

inline std::string if2ip(const std::string &ifn) {

[yhirose]

Thanks for the report. Could you try again with #1236?

[CyberKoo]

Thanks for the fix, but here are some issues I've found.

1. this fix will return an ipv6 address even the address family is set to AF_INET, need to pass the address_family from create_client_socket to if2ip.

2. incorrect ipv6 address returned from if2ip, cast ifa->ifa_addr to sockaddr_in then use inet_ntop to extract IP address will result the address in backward.

for ipv6 address use struct sockaddr_in6 and &sa->sin6_addr

auto sa = reinterpret_cast<struct sockaddr_in6 *>(ifa->ifa_addr);
if (inet_ntop(af, &sa->sin6_addr, &buf[0], bufsiz)) {
  freeifaddrs(ifap);
  return buf;
}

3. function will return link-local address (fe80) instead of global unicast address.4.
   may be use if_nametoindex from <net/if.h> for POSIX systems? this will rule out need to dealing with ip address

[yhirose]

@CyberKoo, I updated #1236. Could you test again to see if it makes any progress?

[CyberKoo]

Now, I'm getting Connection error.

[yhirose]

@CyberKoo, since I can't run properly your example code on my machine, I am not able to reproduce and debug the problem... Could you debug my changes for me on your machine? (As you can see here, I actually made your 3 suggestions.) Thanks in advance!

[yhirose]

@CyberKoo, any response?

[CyberKoo]

Sorry for the delay, I've been busy lately.

Here is the full test project
https://github.com/CyberKoo/cpp-httplib_test

[CyberKoo]

here is the output of my example code.

if pass AF_UNSPEC to if2ip no ip address will be returned.

[yhirose]

@CyberKoo, thanks for the more information. I would not like to access api.ip.sb since I basically don't trust external sites that are not commonly known. :)

Is it another way to reproduce the problem with AF_INET6 and en0? If I can reproduce it on my machine, I'll start debugging it. Otherwise, could you debug it and send me a pull request? Thanks a lot!