zaprus/src/RawSocketWriter.zig

const std = @import("std");
const gcat = @import("gatorcat");
const RawSocketWriter = @This();
const Writer = std.Io.Writer;
const assert = std.debug.assert;

interface: Writer,
socket: gcat.nic.RawSocket,

fn drain(io_w: *std.Io.Writer, data: []const []const u8, splat: usize) Writer.Error!usize {
    const w: *RawSocketWriter = @alignCast(@fieldParentPtr("interface", io_w));
    const rem_buf = io_w.unusedCapacitySlice();
    var rem_w = Writer.fixed(rem_buf);
    const res = rem_w.writeSplat(data, splat) catch rem_buf.len;
    io_w.advance(res);
    const buffered = io_w.buffered();
    w.socket.linkLayer().send(buffered) catch return error.WriteFailed;
    _ = io_w.consumeAll();

    return res;
}

pub fn init(interface_name: [:0]const u8, buffer: []u8) !RawSocketWriter {
    std.debug.assert(buffer.len > 0);
    return .{
        .interface = .{
            .vtable = &.{ .drain = drain },
            .buffer = buffer,
        },
        .socket = try .init(interface_name),
    };
}