Re: [libmicrohttpd] MHD_CONNECTION_INFO_CLIENT_ADDRESS results don't include port

[Evgeny Grin]

Hi Bruce,

First of all, you should not read 'struct sockaddr' directly except 
'sa_family' member. The idea of 'struct sockaddr' is to be abstract 
structure "large enough" to hold any specific protocol information.
Once you find that 'sa_family' is 'AF_INET' you should cast your 
'so_client' pointer to 'struct sockaddr_in*' and then read the data.
'sa_data' form 'struct sockaddr' is opaque data, not designed to be read 
directly.
You can easily find more information in sockets API documentation.

When you connect the client to the server, you have two sides: the 
server side and the client side. If both client and server are located 
on the same machine, you may have the same IP address for both of them, 
but ports will be different.
Unless you 'bind()' your client socket to some specific port, the client 
port will be chosen automatically from freely available ports.
The 'MHD_CONNECTION_INFO_CLIENT_ADDRESS' gives you an information about 
the *client* side. If the client is remote, you will see remote address 
here.
The 'MHD_CONNECTION_INFO_CONNECTION_FD' gives you local socket. If you 
use 'getsockname()' on it, you will get your local IP address (and port).
If you would use 'getpeername()' on the same socket, you will get IP 
address (and port) of the client.

--
Evgeny


On 11.12.2021 3:38, Bruce Eng wrote:
> Not sure emailing here is the right way to get help/info...
>
> If it is, I am using libmicrohttpd 0.9.73 built with MinGW-w64 i686 and 
> I am a bit lost on what results MHD_CONNECTION_INFO_CLIENT_ADDRESS is 
> returning. Here is my testing so far:
>
> const MHD_ConnectionInfo* info = MHD_get_connection_info(connection, 
> MHD_CONNECTION_INFO_CLIENT_ADDRESS);
>    const sockaddr* so_client = (info ? info->client_addr : NULL);
>
>    //something is wrong with the port...
>    //search for "s = accept (fd,". This is where the address structure 
> is first set.
>    if (so_client->sa_family == AF_INET) {
>      std::cout << "IP: " << (int)((unsigned char)so_client->sa_data[0]) 
> << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[1]) << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[2]) << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[3]) << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[4]) << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[5]) << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[6]) << ",";
>      std::cout << (int)((unsigned char)so_client->sa_data[7]) << "\n";
>    }
>
> As expected, elements 2,3,4,5 = "127,0,0,1" when connecting from 
> localhost, but elements 0 and 1 appear sort of random. They are the same 
> for each connection, but when I restart my program and reconnect, they 
> are different. Also if I connect with different hostnames like 
> "localhost" vs "127.0.0.1" they change. All the documentation I found 
> seemed to suggest that if the sa_family was AF_INET that these would 
> give the port.
>
> Additionally, if I do this:
>
> const MHD_ConnectionInfo* info2 = MHD_get_connection_info (connection, 
> MHD_CONNECTION_INFO_CONNECTION_FD);
>    struct sockaddr_in sin;
>    int addrlen = sizeof(sin);
>    if(getsockname(info2->connect_fd, (struct sockaddr *)&sin, &addrlen) 
> == 0 &&
>      sin.sin_family == AF_INET &&
>      addrlen == sizeof(sin))
>    {
>        int local_port = ntohs(sin.sin_port);
>        std::cout << "Port: " << local_port << "|" << (void*)sin.sin_port 
> << "\n";
>    }
>
> I am able to retrieve the correct port so getsockname seems to correctly 
> fill out the port portion of a sockaddr structure.
>
> So my question is: what is sa_data[0] and sa_data[1] when 
> using MHD_CONNECTION_INFO_CLIENT_ADDRESS?
>
> Thanks,
>
> Bruce

OpenPGP_signature
Description: OpenPGP digital signature