local-etc-hosts-updater/src/util.zig

const std = @import("std");

const ArgError = error{
    NotEnoughArgs,
    BadDomain,
    InvalidAddressVer,
    InterfaceRequired,
    InvalidInterface,
};

pub const IP_VER_ENUM = enum(u3) {
    IPv4 = 4,
    IPv6 = 6,
};

pub const IP = std.net.Address;

pub const IPInfo = struct {
    version: IP_VER_ENUM,
    interface: ?[:0]const u8,
};

pub const Domain = struct {
    name: [:0]const u8,
    labels: [5][]const u8,
};

pub fn check_perms() !void {
    var f = try std.fs.openFileAbsolute("/etc/hosts", .{ .mode = .write_only });
    f.close();
}

pub fn get_input() !struct {
    Domain,
    IPInfo,
} {
    var args = std.process.args();
    _ = args.next(); // consume calling binary arg

    const domain_str = args.next() orelse return ArgError.NotEnoughArgs;
    const domain = try check_domain(domain_str);

    const ip_ver_str = args.next() orelse return ArgError.NotEnoughArgs;
    const ip_ver = std.meta.intToEnum(IP_VER_ENUM, std.fmt.parseInt(u3, ip_ver_str, 10) catch return ArgError.InvalidAddressVer) catch return ArgError.InvalidAddressVer;

    var iface: ?[:0]const u8 = null;
    if (ip_ver == IP_VER_ENUM.IPv6) {
        iface = args.next() orelse return ArgError.InterfaceRequired;
        if (std.c.if_nametoindex(iface.?) == 0) {
            return ArgError.InvalidInterface;
        }
    }

    return .{ domain, IPInfo{ .version = ip_ver, .interface = iface } };
}

fn check_domain(domain_str: [:0]const u8) !Domain {
    var domain = Domain{
        .name = domain_str,
        .labels = [_][]const u8{&[_]u8{}} ** 5,
    };
    var labels = std.mem.split(u8, domain_str, ".");
    var last: []const u8 = "";
    var i: usize = 0;
    while (labels.next()) |segment| {
        if (i >= 5) {
            return ArgError.BadDomain;
        }
        last = segment;
        domain.labels[i] = segment;
        i += 1;
    }
    if (domain.labels.len <= 1 or !std.mem.eql(u8, last, "local")) {
        return ArgError.BadDomain;
    }
    return domain;
}