pub const Ip4Address = extern struct {
    sa: posix.sockaddr.in,

    pub fn parse(buf: []const u8, port: u16) IPv4ParseError!Ip4Address {
        var result: Ip4Address = .{
            .sa = .{
                .port = mem.nativeToBig(u16, port),
                .addr = undefined,
            },
        };
        const out_ptr = mem.asBytes(&result.sa.addr);

        var x: u8 = 0;
        var index: u8 = 0;
        var saw_any_digits = false;
        var has_zero_prefix = false;
        for (buf) |c| {
            if (c == '.') {
                if (!saw_any_digits) {
                    return error.InvalidCharacter;
                }
                if (index == 3) {
                    return error.InvalidEnd;
                }
                out_ptr[index] = x;
                index += 1;
                x = 0;
                saw_any_digits = false;
                has_zero_prefix = false;
            } else if (c >= '0' and c <= '9') {
                if (c == '0' and !saw_any_digits) {
                    has_zero_prefix = true;
                } else if (has_zero_prefix) {
                    return error.NonCanonical;
                }
                saw_any_digits = true;
                x = try std.math.mul(u8, x, 10);
                x = try std.math.add(u8, x, c - '0');
            } else {
                return error.InvalidCharacter;
            }
        }
        if (index == 3 and saw_any_digits) {
            out_ptr[index] = x;
            return result;
        }

        return error.Incomplete;
    }

    pub fn resolveIp(name: []const u8, port: u16) !Ip4Address {
        if (parse(name, port)) |ip4| return ip4 else |err| switch (err) {
            error.Overflow,
            error.InvalidEnd,
            error.InvalidCharacter,
            error.Incomplete,
            error.NonCanonical,
            => {},
        }
        return error.InvalidIPAddressFormat;
    }

    pub fn init(addr: [4]u8, port: u16) Ip4Address {
        return Ip4Address{
            .sa = posix.sockaddr.in{
                .port = mem.nativeToBig(u16, port),
                .addr = @as(*align(1) const u32, @ptrCast(&addr)).*,
            },
        };
    }

    /// Returns the port in native endian.
    /// Asserts that the address is ip4 or ip6.
    pub fn getPort(self: Ip4Address) u16 {
        return mem.bigToNative(u16, self.sa.port);
    }

    /// `port` is native-endian.
    /// Asserts that the address is ip4 or ip6.
    pub fn setPort(self: *Ip4Address, port: u16) void {
        self.sa.port = mem.nativeToBig(u16, port);
    }

    pub fn format(
        self: Ip4Address,
        comptime fmt: []const u8,
        options: std.fmt.FormatOptions,
        out_stream: anytype,
    ) !void {
        if (fmt.len != 0) std.fmt.invalidFmtError(fmt, self);
        _ = options;
        const bytes = @as(*const [4]u8, @ptrCast(&self.sa.addr));
        try std.fmt.format(out_stream, "{}.{}.{}.{}:{}", .{
            bytes[0],
            bytes[1],
            bytes[2],
            bytes[3],
            self.getPort(),
        });
    }

    pub fn getOsSockLen(self: Ip4Address) posix.socklen_t {
        _ = self;
        return @sizeOf(posix.sockaddr.in);
    }
}