🔒 Fix asio::async_read_until lambda not called on \n-terminated string

[rain birch]

I'm working on a P2P Client with a particular protocol spec (https://p2pquake.github.io/epsp-specifications/epsp-specifications.html, might want to translate). It is very incomplete tho, but I'm currently on implementing the peer connection part.

I’m stuck because my async_read_until handler never runs even though the remote peer is sending \n‑terminated messages. The socket successfully connects to the peer, and writes just fine to the peer, but reading from the peer somehow breaks. I don't know whether its because of ncat or sth but it is not working. Using a debugger is fruitless.

Its expected to at least show a log saying "Received: <string> ..." or an error but nothing appears.

Here's the code

void ConnectionPeer::Peer::read() {
    auto self(shared_from_this());
    asio::async_read_until(
        self->socket, self->buffer, '\n',
        [self](asio::error_code ecode, std::size_t) -> void {
            if (ecode) {
                if (auto shared_parent = self->parent.lock()) {
                    shared_parent->peer_logger_->error(
                        "Read error: {}, from: {}", ecode.message(),
                        self->endpoint.address().to_string() + ":" +
                            std::to_string(self->endpoint.port()));
                }
                return;
            }

            std::istream input(&self->buffer);
            std::string line;
            std::getline(input, line);

            if (auto shared_parent = self->parent.lock()) {
                shared_parent->peer_logger_->info(
                    "Received: {}, from: {}", line,
                    self->endpoint.address().to_string() + ":" +
                        std::to_string(self->endpoint.port()));
            }

            if (line.size() < 5) {
                if (auto shared_parent = self->parent.lock()) {
                    shared_parent->peer_logger_->error(
                        "Invalid message: {}, from: {}", line,
                        self->endpoint.address().to_string() + ":" +
                            std::to_string(self->endpoint.port()));
                    shared_parent->stop(self->peer_id);
                }

                return;
            }

            self->handle_message(line);
            self->read();
        });
}

(Full repo: https://github.com/minhanhiscool/epsp-linux)

also any code review is appreciated 🙏 🙏🙏

[crude kernel]

Are you sending just \n or a full \r\n?

[rain birch]

a full \r\n

there is case handling for \n only though for debugging purpose

[crude kernel]

Is your lambda ever called at all?

[rain birch]

no

[carmine bridge]

@rain birch has reached level 1. GG!

[rain birch]

walked thru the debugger it just hung at a weird asio function

[crude kernel]

You init the server after you init the peer connection?

What does server mean in this context?

[rain birch]

alr init the server

[rain birch]

its just for the client to know what peers are availiable

after that the client must disconnect from the server

[crude kernel]

Shouldn't the server run before the client?

Also, don't you need two peers for this protocol?

[rain birch]

thats why there should be a dummy program

for me i use ncat since i dont want to code the server

peers too

[crude kernel]

Do you see your program's commands in ncat?

[rain birch]

yes

[crude kernel]

And your ::read() function is called right?

[rain birch]

it is called

[crude kernel]

Can you show the callstack for that call

[crude kernel]

I think my first step would be to simply every thing so that you basically just have a write followed by a read and get that working

[rain birch]

ok then ill try tmr

its getting late so im going to sleep

[crude kernel]

Is see you have another read that has to happen first, is that one working?

https://github.com/minhanhiscool/epsp-linux/blob/7bb284abd34ad689188d47f1642e4cad329326fe/src/comms/handshake.cpp#L45

[rain birch]

it does work normally

[carmine bridge]

@rain birch has reached level 2. GG!

[rain birch]

ok fixed bug. apparently had to add a work guard since the peer thread immediately exited after startup since no work is given to it. now the read() function works as expected

[wispy pagoda]

🔒 Fix asio::async_read_until lambda not called on \n-terminated string