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// Copyright 2026 Robby Zambito
//
// This file is part of zaprus.
//
// Zaprus is free software: you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the Free Software
// Foundation, either version 3 of the License, or (at your option) any later
// version.
//
// Zaprus is distributed in the hope that it will be useful, but WITHOUT ANY
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
// A PARTICULAR PURPOSE. See the GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License along with
// Zaprus. If not, see <https://www.gnu.org/licenses/>.
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;
return .{
.fd = socket,
.sockaddr_ll = sockaddr_ll,
.mac = mac,
};
}
pub fn setTimeout(self: *RawSocket, sec: isize, usec: i64) !void {
const timeout: std.os.linux.timeval = .{ .sec = sec, .usec = usec };
const timeout_ret = std.os.linux.setsockopt(self.fd, std.os.linux.SOL.SOCKET, std.os.linux.SO.RCVTIMEO, @ptrCast(&timeout), @sizeOf(@TypeOf(timeout)));
if (timeout_ret != 0) return error.SetTimeoutError;
}
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, incoming_src_port: ?u16, incoming_dest_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 = if (incoming_src_port) |inc_src| &[_]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 1 if true, skip 0 if false)
.{ .code = BPF.JMP | BPF.JEQ | BPF.K, .jt = 1, .jf = 0, .k = @as(u32, inc_src) },
// Return 0x0 (fail)
.{ .code = BPF.RET | BPF.K, .jt = 0, .jf = 0, .k = 0x0 },
// Load 2 bytes at offset 48 (absolute)
.{ .code = BPF.LD | BPF.H | BPF.ABS, .jt = 0, .jf = 0, .k = 48 },
// 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, incoming_dest_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 },
} else &[_]SockFilter{
// Load 2 bytes at offset 48 (absolute)
.{ .code = BPF.LD | BPF.H | BPF.ABS, .jt = 0, .jf = 0, .k = 48 },
// 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, incoming_dest_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 = @intCast(filter.len),
.filter = filter.ptr,
};
// 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");
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