Fix bind signature in raw.lua pattern

[sneaky-potato]

We need separate call signatures for

• receiving socket (protocol is required, passed in the form of packed string)
• transmitting socket (only numeric interface index is passed to bind)

Related PR
#360

[sneaky-potato]

If we want to do this in a single new method, we can pass whatever arguments we get to the bind call
something like this

-- Arguments are forwarded verbatim to socket:bind().
--
-- Examples:
--   raw.new(string.pack(">H", ETH_P_ALL), ifindex) RX-style bind
--   raw.new(ifindex) TX-style bind
--   raw.new() unbound socket
--
function raw.new(...)
    local s = socket.new(af.PACKET, sock.RAW)

    local argc = select("#", ...)
    if argc > 0 then
        s:bind(...)
    end

    return s
end

return raw

[lneto]

Wouldn't this work for sending as well? Are you sure?

[sneaky-potato]

I tried to use this form to send frames over raw socket

local function worker()
	local tx <close> = socket.new(socket.af.PACKET, socket.sock.RAW, ETH_P_LLDP)
	tx:bind(string.pack(">H", ETH_P_LLDP), ifindex)

	while (not shouldstop()) do
		tx:send(lldp_frame)
		print(string.format("[lldpd] frame sent on ifindex=%d (%d bytes)", ifindex, #lldp_frame))
		linux.schedule(config.tx_interval_ms)
	end

	print("[lldpd] worker stopped")
end

return worker

got this error
[ 495.463722] luathread: [000000004887f053] ENXIO

The socket starts working when called with bind(ifindex)

[sneaky-potato]

I believe this branch executes when bind is called with string parameter.
So it blindly copies 2 bytes (ETH_P_LLDP) into sockaddr_storage.__data
Everything else is uninitialized garbage. (This explains ENXIO no such device error)

Summary

• bind(ifindex) binds on a specific interface (this cannot be used to capture traffic because protocol is never set in this case)
• bind(string.pack(">H", proto)) binds on all interfaces (0) (should be used when receiving frames)
• anything else does not make sense

[lneto]

We were using ">I2" instead ">H" on tap.. why did you change it?

[sneaky-potato]

I read this line in the documentation.

[lneto]

I don't think it's correct as short might vary depending on arch.. I would fix both the code and the doc

[lneto]

I would create a "new" function just to avoid repeat this line.. not fond of tx/Rx but couldn't figure better names.. it's up to you.. I can merge it

[sneaky-potato]

What about bind and connect as the names for the methods?

[lneto]

I think it's better from the API client's perspective.. though it sounds a bit misleading to bind() on connect(), I will leave this decision to you ;-)

[sneaky-potato]

I think a single bind call will suffice, we can call bind(ifindex) if ifindex is given else the usual listening socket bind(string.pack(">I2", proto))

[lneto]

Ah.. you need to add this to config.ld right?

[sneaky-potato]

@lneto from the luasocket_bind and more specifically luasocket_checkaddr, it seems that binding a listening AF_PACKET socket to a specific interface is not currently supported.

For AF_PACKET

• when the argument is a number, it is always interpreted as sll_ifindex, and no path sets sll_protocol.
• string-based path copies raw bytes into sockaddr_storage but does not populate struct sockaddr_ll fields in a structured way.

For a listening raw socket bound to an interface, we would need something equivalent to:

sll_protocol = htons(ETH_P_ALL);
sll_ifindex  = ifindex;

Currently there’s no way to express this combination from Lua. Is this by design? If not, would it make sense to open an issue to track proper AF_PACKET bind support for listening sockets?

[lneto]

it's looking good to me, just a small comment.. btw, can you take the opportunity and bump the copyright year of those files as well? thanks

[lneto]

Suggested change

	-- SPDX-FileCopyrightText: (c) 2026 Ashwani Kumar Kamal <[email protected]>
	-- SPDX-FileCopyrightText: (c) 2025-2026 Ashwani Kumar Kamal <[email protected]>

right?