Request for Lower-Level net socket API for flexible port handling

[tttuuu888]

Hi @bakpakin and all,

I found that it seems impossible to implement a TFTP client using the basic Janet net APIs.

The net/connect function binds a port to the socket upon connection, which makes it difficult to implement the TFTP protocol's behavior where the server's response needs to be received on a different, temporary port.

Therefore, to implement a protocol that requires flexible port allocation, like TFTP, a lower-level API such as net/socket that creates an unbound socket seems necessary.

I have attached simplified C examples of a TFTP server/client.

example.zip

The core of these examples is as follows:

Server:

// Create socket and bind to port 8080
listen_sock = socket(AF_INET, SOCK_DGRAM, 0);
bind(listen_sock, ...);

// Receive message from client
recvfrom(listen_sock, buffer, BUF_SIZE, 0, ...);

// Create a new socket without bind() to send the response
new_sock = socket(AF_INET, SOCK_DGRAM, 0);
sendto(new_sock, "world", ..., client_addr, ...);

Client:

// Create a socket (without binding)
client_sock = socket(AF_INET, SOCK_DGRAM, 0);

// Send initial request to server on port 8080 (an ephemeral port is automatically assigned)
sendto(client_sock, "hello", ..., server_addr, ...);

// Receive the server's response from a new port
recvfrom(client_sock, buffer, BUF_SIZE, 0, ..., &from_addr, ...);
// from_addr.sin_port will contain the ephemeral port number

The log when the example runs successfully is shown below.

Server:

Server listening on 127.0.0.1:8080
Server received: hello from port 54379
Server sent: world from a new socket

Client:

Client socket created (unbound)
Client sent: hello
Client received: world from port 60914

As I understand it, this action seems difficult to implement with net/connect.
I would appreciate for any feedback.

Thank you.

[bakpakin]

I think this is addressed now, @tttuuu888 reopen this if anything else is needed.