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

const std = @import("std");

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

pub const IP_VER_ENUM = enum(u3) {
    Both = 0,
    IPv4 = 4,
    IPv6 = 6,
};

pub const IPs = struct {
    v4: [:0]const u8,
    v6: [:0]const u8,
};

pub const Domain = struct {
    name: [:0]const u8,
    labels: u4,
};

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

pub fn get_input() !struct {
    Domain,
    IP_VER_ENUM,
} {
    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, try std.fmt.parseInt(u3, ip_ver_str, 10)) catch return ArgError.InvalidAddressVer;

    return .{ domain, ip_ver };
}

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