Help designing a packet registry and abstraction

[sick nebula]

I've been working on a minecraft server implementation in zig for a bit and I wanted to make a better packet parsing and handling system. I understand that sounds high level and not really help appropriate but I need help with understanding how something like this can be laid out in zig:

interface Packet
impl HandshakePacket {
field1: []const u8
field2: i32
}

fn readPacket(reader: std.net.Stream.Reader) Packet {
    // return the interface but still retain ability to access the implementation and sort of "cast" it
    
}

I originally thought of using packed structs and using readStruct in std.net.Stream.Reader but because of how terrible the minecraft network protocol is ,they use different varints than the reader can read and I dont think its possible to implement it using a packed struct. Even if it was id still not know how to "cast" it and keep an abstracted type to return

[steep delta]

how does the packet look in memory?

[sick nebula]

base is

id: i32 <- minecrafts own varint
body: []u8 <- gets parsed depending on the id

you first read size, then id, then the rest is the payload (size bytes)

[steep delta]

I think it's probably easier to read the fields manually then using readStructEndian. you can read the id with readInt().

you can't really make a struct with the same in-memory representation as the one you receive because it's big-endian and you need little-endian (so you have to byteSwap) and it's variable length, but zig doesn't support variable-length structs

a packed struct is only for bitfields, generally you would want an extern struct for defined memory layouts and only use a packed struct for specific parts of it that need it

[sick nebula]

I thought of this but I do not see it being possible

atleast viable

[steep delta]

what do you mean?

what's difficult about it?

[sick nebula]

maybe because im just slow

i cant see how i would implement that

yet alone abstract it

[steep delta]

fn readPacket(reader: ..) Packet {
    const id = try reader.readInt(i32, .big);
    const body = allocator.alloc(u8, len);
    const read_len = try reader.readAll(body);
}

something like this

not sure what your goals are for abstraction

[sick nebula]

Yeah i did this exactly but I want to have Packet be like an interface, I have this as a FramedPacket, I want to convert it to any other struct that has ties to a "interface'" packet. So for example my method would be fn sendPacket(self: Player, packet: Packet) void {} where i could pass all the packet types

my bad for not being clear enough

I hope that makes sense

[steep delta]

you can make packet a union(enum) of all the different packet types

[sick nebula]

same with reading

[sick nebula]

How would this work

Especially because different connection states have packets with the same id as other states

[steep delta]

union(enum) {
    handshake: HandshakePacket,
    another: AnotherPacket,
    ...
}

[sick nebula]

I confused union(enum) with enum(union) which is not a real thing

whoops

I see, I guess that's a good idea yeah, and for writing and reading I could make a big switch statement ig idk

[steep delta]

yeah basically

[sick nebula]

That makes sense