zaprus/src/RawSocket.zig

const RawSocket = @This();

const is_debug = builtin.mode == .Debug;

fd: i32,
sockaddr_ll: std.posix.sockaddr.ll,
mac: [6]u8,

pub const max_payload_len = 1000;

const Ifconf = extern struct {
    ifc_len: i32,
    ifc_ifcu: extern union {
        ifcu_buf: ?[*]u8,
        ifcu_req: ?[*]std.os.linux.ifreq,
    },
};

pub fn init() !RawSocket {
    const socket: i32 = std.math.cast(i32, std.os.linux.socket(std.os.linux.AF.PACKET, std.os.linux.SOCK.RAW, 0)) orelse return error.SocketError;
    if (socket < 0) return error.SocketError;

    var ifreq_storage: [16]std.os.linux.ifreq = undefined;
    var ifc = Ifconf{
        .ifc_len = @sizeOf(@TypeOf(ifreq_storage)),
        .ifc_ifcu = .{ .ifcu_req = &ifreq_storage },
    };

    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFCONF, @intFromPtr(&ifc)) != 0) {
        return error.NicError;
    }

    const count = @divExact(ifc.ifc_len, @sizeOf(std.os.linux.ifreq));

    // Get the first non loopback interface
    var ifr = for (ifreq_storage[0..@intCast(count)]) |*ifr| {
        if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(ifr)) == 0) {
            if (ifr.ifru.flags.LOOPBACK) continue;
            break ifr;
        }
    } else return error.NoInterfaceFound;

    // 2. Get Interface Index
    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFINDEX, @intFromPtr(ifr)) != 0) {
        return error.NicError;
    }
    const ifindex: i32 = ifr.ifru.ivalue;

    // 3. Get Real MAC Address
    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFHWADDR, @intFromPtr(ifr)) != 0) {
        return error.NicError;
    }
    var mac: [6]u8 = ifr.ifru.hwaddr.data[0..6].*;
    if (builtin.cpu.arch.endian() == .little) std.mem.reverse(u8, &mac);

    // 4. Set Flags (Promiscuous/Broadcast)
    if (std.os.linux.ioctl(socket, std.os.linux.SIOCGIFFLAGS, @intFromPtr(ifr)) != 0) {
        return error.NicError;
    }
    ifr.ifru.flags.BROADCAST = true;
    ifr.ifru.flags.PROMISC = true;
    if (std.os.linux.ioctl(socket, std.os.linux.SIOCSIFFLAGS, @intFromPtr(ifr)) != 0) {
        return error.NicError;
    }

    const sockaddr_ll = std.mem.zeroInit(std.posix.sockaddr.ll, .{
        .family = std.posix.AF.PACKET,
        .ifindex = ifindex,
        .protocol = std.mem.nativeToBig(u16, @as(u16, std.os.linux.ETH.P.IP)),
    });

    const bind_ret = std.os.linux.bind(socket, @ptrCast(&sockaddr_ll), @sizeOf(@TypeOf(sockaddr_ll)));
    if (bind_ret != 0) return error.BindError;

    const timeout: std.os.linux.timeval = .{ .sec = 60 * if (is_debug) 1 else 10, .usec = 0 };
    const timeout_ret = std.os.linux.setsockopt(socket, std.os.linux.SOL.SOCKET, std.os.linux.SO.RCVTIMEO, @ptrCast(&timeout), @sizeOf(@TypeOf(timeout)));
    if (timeout_ret != 0) return error.SetTimeoutError;

    return .{
        .fd = socket,
        .sockaddr_ll = sockaddr_ll,
        .mac = mac,
    };
}

pub fn deinit(self: *RawSocket) void {
    _ = std.os.linux.close(self.fd);
    self.* = undefined;
}

pub fn send(self: RawSocket, payload: []const u8) !void {
    const sent_bytes = std.os.linux.sendto(
        self.fd,
        payload.ptr,
        payload.len,
        0,
        @ptrCast(&self.sockaddr_ll),
        @sizeOf(@TypeOf(self.sockaddr_ll)),
    );
    _ = sent_bytes;
}

pub fn receive(self: RawSocket, buf: []u8) ![]u8 {
    const len = std.os.linux.recvfrom(
        self.fd,
        buf.ptr,
        buf.len,
        0,
        null,
        null,
    );
    if (std.os.linux.errno(len) != .SUCCESS) {
        return error.Timeout; // TODO: get the real error, assume timeout for now.
    }
    return buf[0..len];
}

pub fn attachSaprusPortFilter(self: RawSocket, port: u16) !void {
    const BPF = std.os.linux.BPF;
    // BPF instruction structure for classic BPF
    const SockFilter = extern struct {
        code: u16,
        jt: u8,
        jf: u8,
        k: u32,
    };

    const SockFprog = extern struct {
        len: u16,
        filter: [*]const SockFilter,
    };

    // Build the filter program
    const filter = [_]SockFilter{
        // Load 2 bytes at offset 46 (absolute)
        .{ .code = BPF.LD | BPF.H | BPF.ABS, .jt = 0, .jf = 0, .k = 46 },
        // Jump if equal to port (skip 0 if true, skip 1 if false)
        .{ .code = BPF.JMP | BPF.JEQ | BPF.K, .jt = 0, .jf = 1, .k = @as(u32, port) },
        // Return 0xffff (pass)
        .{ .code = BPF.RET | BPF.K, .jt = 0, .jf = 0, .k = 0xffff },
        // Return 0x0 (fail)
        .{ .code = BPF.RET | BPF.K, .jt = 0, .jf = 0, .k = 0x0 },
    };

    const fprog = SockFprog{
        .len = filter.len,
        .filter = &filter,
    };

    // Attach filter to socket using setsockopt
    const rc = std.os.linux.setsockopt(
        self.fd,
        std.os.linux.SOL.SOCKET,
        std.os.linux.SO.ATTACH_FILTER,
        @ptrCast(&fprog),
        @sizeOf(SockFprog),
    );

    if (rc != 0) {
        return error.BpfAttachFailed;
    }
}

const std = @import("std");
const builtin = @import("builtin");