build.zig

const std = @import("std");
const builtin = @import("builtin");
const Builder = std.build.Builder;
const CrossTarget = std.zig.CrossTarget;
const BuildMode = std.builtin.Mode;
const Step = std.build.Step;
const LibExeObjStep = std.build.LibExeObjStep;
const OptionsStep = std.build.OptionsStep;

const chinadns_version = "2024.05.12";

var _b: *Builder = undefined;

// options
var _test: bool = undefined;
var _target: CrossTarget = undefined;
var _mode: BuildMode = undefined;
var _lto: bool = undefined;
var _strip: bool = undefined;
var _enable_wolfssl: bool = undefined;
var _wolfssl_noasm: bool = undefined;
var _enable_mimalloc: bool = undefined;
var _exe_name: []const u8 = undefined;

// conditional compilation for zig source files
var _build_opts: *OptionsStep = undefined;

const DependLib = struct {
    url: []const u8,
    version: []const u8,
    tarball: []const u8, // src tarball file path
    src_dir: []const u8,
    src_dir_always_clean: bool,
    base_dir: []const u8,
    include_dir: []const u8,
    lib_dir: []const u8,
};

var _dep_wolfssl: DependLib = b: {
    const version = "5.7.0";
    const src_dir = "dep/wolfssl-" ++ version;
    break :b .{
        .url = "https://github.com/wolfSSL/wolfssl/archive/refs/tags/v" ++ version ++ "-stable.tar.gz",
        .version = version,
        .tarball = src_dir ++ ".tar.gz",
        .src_dir = src_dir ++ "-stable",
        .src_dir_always_clean = false,
        .base_dir = undefined, // set by init()
        .include_dir = undefined, // set by init()
        .lib_dir = undefined, // set by init()
    };
};

const _dep_mimalloc: DependLib = b: {
    const version = "2.1.2";
    const src_dir = "dep/mimalloc-" ++ version;
    break :b .{
        .url = "https://github.com/microsoft/mimalloc/archive/refs/tags/v" ++ version ++ ".tar.gz",
        .version = version,
        .tarball = src_dir ++ ".tar.gz",
        .src_dir = src_dir,
        .src_dir_always_clean = true,
        .base_dir = src_dir, // same as src_dir, since mimalloc is linked to the exe as an object
        .include_dir = src_dir ++ "/include",
        .lib_dir = src_dir, // there is actually no lib_dir
    };
};

fn init(b: *Builder) void {
    _b = b;

    if (_b.verbose) {
        _b.verbose_cimport = true;
        _b.verbose_llvm_cpu_features = true;
        _b.prominent_compile_errors = true;
    }

    // keep everything in a local directory
    _b.global_cache_root = _b.cache_root;

    // -Dxxx options
    option_test();
    option_target();
    option_mode();
    option_lto();
    option_strip();
    option_wolfssl();
    option_wolfssl_noasm();
    option_mimalloc();
    option_name(); // must be at the end

    _dep_wolfssl.base_dir = with_target_desc(_dep_wolfssl.src_dir, .ReleaseFast); // dependency lib always ReleaseFast
    if (_wolfssl_noasm)
        _dep_wolfssl.base_dir = fmt("{s}+noasm", .{_dep_wolfssl.base_dir});
    _dep_wolfssl.include_dir = fmt("{s}/include", .{_dep_wolfssl.base_dir});
    _dep_wolfssl.lib_dir = fmt("{s}/lib", .{_dep_wolfssl.base_dir});

    // conditional compilation for zig source files
    _build_opts = _b.addOptions();
    _build_opts.addOption(bool, "is_test", _test);
    _build_opts.addOption(bool, "enable_wolfssl", _enable_wolfssl);
    _build_opts.addOption(bool, "enable_mimalloc", _enable_mimalloc);
    _build_opts.addOption([]const u8, "version", chinadns_version);
    _build_opts.addOption([]const u8, "commit_id", get_commit_id());
    _build_opts.addOption([]const u8, "wolfssl_version", _dep_wolfssl.version);
    _build_opts.addOption([]const u8, "mimalloc_version", _dep_mimalloc.version);
    _build_opts.addOption([]const u8, "target", desc_target());
    _build_opts.addOption([]const u8, "cpu", desc_cpu());
    _build_opts.addOption([]const u8, "mode", desc_mode(null));

    // generate a zig source file (@import all zig source files of this project)
    gen_modules_zig();
}

fn init_dep(step: *Step, dep: DependLib) void {
    if (dep.src_dir_always_clean and path_exists(dep.src_dir))
        return;

    if (!path_exists(dep.tarball))
        step.dependOn(add_download(dep.url, dep.tarball));

    step.dependOn(add_rm(dep.src_dir));

    step.dependOn(add_tar_extract(dep.tarball, "dep"));
}

// =========================================================================

fn option_test() void {
    _test = _b.option(bool, "test", "build artifacts for testing, default: false") orelse false;
}

fn option_target() void {
    _target = _b.standardTargetOptions(.{});
}

fn option_mode() void {
    const default = if (_test) ModeOpt.debug else ModeOpt.fast;
    const opt = _b.option(ModeOpt, "mode", "build mode, default: 'fast' (or 'debug' if testing)") orelse default;
    _mode = to_mode(opt);
}

fn option_lto() void {
    const default = switch (_mode) {
        .ReleaseFast, .ReleaseSmall, .ReleaseSafe => true,
        else => false,
    };
    _lto = _b.option(bool, "lto", "enable LTO, default to true if in fast/small/safe mode") orelse default;
}

fn option_strip() void {
    const default = switch (_mode) {
        .ReleaseFast, .ReleaseSmall => true,
        else => false,
    };
    _strip = _b.option(bool, "strip", "strip debug info, default to true if in fast/small mode") orelse default;
}

fn option_wolfssl() void {
    _enable_wolfssl = _b.option(bool, "wolfssl", "enable wolfssl to support DoT protocol, default: false") orelse false;
}

fn option_wolfssl_noasm() void {
    _wolfssl_noasm = _b.option(bool, "wolfssl-noasm", "disable the assembly acceleration option for wolfssl") orelse false;
}

fn option_mimalloc() void {
    _enable_mimalloc = _b.option(bool, "mimalloc", "using the mimalloc allocator (libc), default: false") orelse false;
}

fn option_name() void {
    var vec = std.ArrayList(u8).init(_b.allocator);
    defer vec.deinit();

    if (_test)
        vec.appendSlice("test") catch unreachable
    else
        vec.appendSlice("chinadns-ng") catch unreachable;

    if (_enable_wolfssl) {
        vec.appendSlice("+wolfssl") catch unreachable;

        if (_wolfssl_noasm)
            vec.appendSlice("_noasm") catch unreachable;
    }

    if (_enable_mimalloc)
        vec.appendSlice("+mimalloc") catch unreachable;

    const default = with_target_desc(vec.items, null);
    const desc = fmt("executable name, default: '{s}'", .{default});

    const name = _b.option([]const u8, "name", desc) orelse default;
    const trimmed = trim_whitespace(name);

    if (trimmed.len > 0 and std.mem.eql(u8, trimmed, name)) {
        _exe_name = name;
    } else {
        err_invalid("invalid executable name (-Dname): '{s}'", .{name});
        _exe_name = default;
    }
}

// =========================================================================

/// step: empty step to be used as a container
fn add_step(name: []const u8) *Step {
    const step = _b.allocator.create(Step) catch unreachable;
    step.* = Step.initNoOp(.custom, name, _b.allocator);
    return step;
}

/// step: log info
fn add_log(comptime format: []const u8, args: anytype) *Step {
    return &_b.addLog(format, args).step;
}

/// step: /bin/sh command
fn add_sh_cmd(sh_cmd: []const u8) *Step {
    const cmd = fmt("set -o nounset; set -o errexit; {s}", .{sh_cmd});
    const run_step = _b.addSystemCommand(&.{ "sh", "-c", cmd });
    run_step.print = false; // disable print (use `set -x` instead)
    return &run_step.step;
}

/// step: /bin/sh command (set -x)
fn add_sh_cmd_x(sh_cmd: []const u8) *Step {
    return add_sh_cmd(fmt("set -x; {s}", .{sh_cmd}));
}

/// step: remove dir or file
fn add_rm(path: []const u8) *Step {
    return &_b.addRemoveDirTree(path).step;
}

/// step: download file
fn add_download(url: []const u8, path: []const u8) *Step {
    const cmd_ =
        \\  url='{s}'; path='{s}'
        \\  mkdir -p "$(dirname "$path")"
        \\  echo "[INFO] downloading from $url"
        \\  if command -v wget >/dev/null; then
        \\      wget "$url" -O "$path"
        \\  elif command -v curl >/dev/null; then
        \\      curl -fL "$url" -o "$path"
        \\  else
        \\      echo "[ERROR] please install 'wget' or 'curl'" 1>&2
        \\      exit 1
        \\  fi
    ;
    const cmd = fmt(cmd_, .{ url, path });
    return add_sh_cmd(cmd);
}

/// step: tar -xf $tarball -C $dir
fn add_tar_extract(tarball_path: []const u8, to_dir: []const u8) *Step {
    const cmd = fmt("mkdir -p '{s}'; tar -xf '{s}' -C '{s}'", .{ to_dir, tarball_path, to_dir });
    return add_sh_cmd_x(cmd);
}

// =========================================================================

var _first_error: bool = true;

/// print to stderr, auto append '\n'
fn print(comptime format: []const u8, args: anytype) void {
    _ = std.io.getStdErr().write(fmt(format ++ "\n", args)) catch unreachable;
}

fn newline() void {
    return print("", .{});
}

/// print("> ERROR: msg")
fn print_err(comptime format: []const u8, args: anytype) void {
    if (_first_error) {
        _first_error = false;
        newline();
    }
    print("> ERROR: " ++ format, args);
}

/// print("> ERROR: msg") && mark user_input as invalid
fn err_invalid(comptime format: []const u8, args: anytype) void {
    print_err(format, args);
    _b.invalid_user_input = true;
}

/// print("> ERROR: msg") && std.os.exit(1)
fn err_exit(comptime format: []const u8, args: anytype) noreturn {
    print_err(format, args);
    newline();
    std.os.exit(1);
}

// =========================================================================

fn dupeZ(bytes: []const u8) [:0]u8 {
    return _b.allocator.dupeZ(u8, bytes) catch unreachable;
}

fn fmt(comptime format: []const u8, args: anytype) []const u8 {
    return _b.fmt(format, args);
}

fn path_exists(rel_path: []const u8) bool {
    return if (std.fs.cwd().access(rel_path, .{})) true else |_| false;
}

/// caller owns the returned memory `_b.allocator.free(mem)`
fn string_concat(str_list: []const []const u8, sep: []const u8) []const u8 {
    return std.mem.join(_b.allocator, sep, str_list) catch unreachable;
}

fn trim_whitespace(str: []const u8) []const u8 {
    return std.mem.trim(u8, str, " \t\r\n");
}

fn is_musl() bool {
    return _target.getAbi().isMusl();
}

/// return 0 if not x86_64 arch
fn get_x86_64_level() u8 {
    const name = _target.getCpuModel().name;
    if (!std.mem.startsWith(u8, name, "x86_64"))
        return 0;
    if (std.mem.eql(u8, name, "x86_64"))
        return 1;
    if (std.mem.eql(u8, name, "x86_64_v2"))
        return 2;
    if (std.mem.eql(u8, name, "x86_64_v3"))
        return 3;
    if (std.mem.eql(u8, name, "x86_64_v4"))
        return 4;
    unreachable;
}

/// get cli option value (string)
fn get_optval(name: []const u8) ?[]const u8 {
    const opt = _b.user_input_options.getPtr(name) orelse return null;
    return switch (opt.value) {
        .scalar => |v| v,
        else => null,
    };
}

fn get_optval_target() ?[]const u8 {
    return get_optval("target");
}

fn get_optval_cpu() ?[]const u8 {
    return get_optval("cpu");
}

/// caller owns the returned stdout `_b.allocator.free(mem)`
fn exec_command(argv: []const []const u8, exit_code: ?*u8) Builder.ExecError![]u8 {
    var code: u8 = undefined;
    const p_code = exit_code orelse &code;
    return _b.execAllowFail(argv, p_code, .Inherit) catch |err| {
        const cmd = string_concat(argv, " ");
        defer _b.allocator.free(cmd);
        print_err("failed to execute: {s} ({s} exit_code:{d})", .{ cmd, @errorName(err), p_code.* });
        return err;
    };
}

// =========================================================================

const ModeOpt = enum { fast, small, safe, debug };

fn to_mode(opt: ModeOpt) BuildMode {
    return switch (opt) {
        .fast => .ReleaseFast,
        .small => .ReleaseSmall,
        .safe => .ReleaseSafe,
        .debug => .Debug,
    };
}

fn to_mode_opt(mode: BuildMode) ModeOpt {
    return switch (mode) {
        .ReleaseFast => .fast,
        .ReleaseSmall => .small,
        .ReleaseSafe => .safe,
        .Debug => .debug,
    };
}

/// caller owns the returned stdout `_b.allocator.free(mem)`
fn show_builtin() []const u8 {
    var argv = std.ArrayList([]const u8).init(_b.allocator);
    defer argv.deinit();

    argv.appendSlice(&.{ _b.zig_exe, "build-exe" }) catch unreachable;

    if (get_optval_target()) |target|
        argv.appendSlice(&.{ "-target", target }) catch unreachable;

    if (get_optval_cpu()) |cpu|
        argv.append(fmt("-mcpu={s}", .{cpu})) catch unreachable;

    argv.append("--show-builtin") catch unreachable;

    return exec_command(argv.items, null) catch unreachable;
}

fn get_glibc_version() std.builtin.Version {
    const builtin_info = show_builtin();
    defer _b.allocator.free(builtin_info);

    var stream = std.io.fixedBufferStream(builtin_info);
    const reader = stream.reader();

    var buffer: [512]u8 = undefined;

    while (reader.readUntilDelimiterOrEof(&buffer, '\n') catch unreachable) |raw_line| {
        const line = trim_whitespace(raw_line);

        if (std.mem.eql(u8, line, ".glibc = .{")) {
            // .glibc = .{
            //     .major = 2,
            //     .minor = 38,
            //     .patch = 0,
            // },

            var major_buf: [100]u8 = undefined;
            var minor_buf: [100]u8 = undefined;
            var patch_buf: [100]u8 = undefined;

            const major_line = trim_whitespace((reader.readUntilDelimiterOrEof(&major_buf, '\n') catch unreachable).?);
            const minor_line = trim_whitespace((reader.readUntilDelimiterOrEof(&minor_buf, '\n') catch unreachable).?);
            const patch_line = trim_whitespace((reader.readUntilDelimiterOrEof(&patch_buf, '\n') catch unreachable).?);

            if (!std.mem.startsWith(u8, major_line, ".major = "))
                err_exit("failed to get glibc version for given target: invalid major line: {s}", .{major_line});

            if (!std.mem.startsWith(u8, minor_line, ".minor = "))
                err_exit("failed to get glibc version for given target: invalid minor line: {s}", .{minor_line});

            if (!std.mem.eql(u8, patch_line, ".patch = 0,"))
                err_exit("failed to get glibc version for given target: invalid patch line: {s}", .{patch_line});

            return .{
                .major = std.fmt.parseInt(u32, major_line[9 .. major_line.len - 1], 10) catch unreachable,
                .minor = std.fmt.parseInt(u32, minor_line[9 .. minor_line.len - 1], 10) catch unreachable,
            };
        }
    }

    err_exit("failed to get glibc version for given target: invalid format", .{});
}

fn desc_target() []const u8 {
    const cpu_arch = _target.getCpuArch();
    const os_tag = _target.getOsTag();
    const abi = _target.getAbi();

    if (_target.isGnuLibC()) {
        const glibc_version = _target.glibc_version orelse get_glibc_version();
        return fmt("{s}-{s}-{s}.{}", .{ @tagName(cpu_arch), @tagName(os_tag), @tagName(abi), glibc_version });
    } else {
        return fmt("{s}-{s}-{s}", .{ @tagName(cpu_arch), @tagName(os_tag), @tagName(abi) });
    }
}

fn desc_cpu() []const u8 {
    if (get_optval_cpu()) |cpu| return cpu;
    const cpu_model = _target.getCpuModel().name;
    return if (_target.isNativeCpu()) fmt("{s}+native", .{cpu_model}) else cpu_model;
}

/// @mode: default is `_mode`
/// {fast | small | safe | debug} [+lto]
fn desc_mode(mode: ?BuildMode) []const u8 {
    const res = @tagName(to_mode_opt(mode orelse _mode));
    return if (_lto) fmt("{s}+lto", .{res}) else res;
}

/// @in_mode: default is `_mode`
fn with_target_desc(name: []const u8, in_mode: ?BuildMode) []const u8 {
    const target = desc_target();
    const cpu = desc_cpu();
    const mode = desc_mode(in_mode orelse _mode);
    return fmt("{s}@{s}@{s}@{s}", .{ name, target, cpu, mode });
}

/// for zig cc (build wolfssl)
fn get_target_mcpu() []const u8 {
    const target = get_optval_target() orelse "native";
    return if (get_optval_cpu()) |cpu|
        fmt("-target {s} -mcpu={s}", .{ target, cpu })
    else
        fmt("-target {s}", .{target});
}

fn get_commit_id() []const u8 {
    const str = exec_command(&.{ "git", "rev-parse", "--short", "HEAD" }, null) catch "unknown";
    return trim_whitespace(str);
}

fn gen_modules_zig() void {
    var f = std.fs.cwd().createFile("src/modules.zig", .{}) catch unreachable;
    defer f.close();

    var dir = std.fs.cwd().openIterableDir("src", .{}) catch unreachable;
    defer dir.close();

    var list = std.ArrayList([]const u8).init(_b.allocator);
    defer list.deinit();

    var it = dir.iterate();
    while (it.next() catch unreachable) |file| {
        if (file.kind != .File)
            continue;
        if (!std.mem.endsWith(u8, file.name, ".zig"))
            continue;
        list.append(_b.dupe(file.name[0 .. file.name.len - 4])) catch unreachable;
    }

    std.sort.sort([]const u8, list.items, {}, struct {
        fn cmp(_: void, a: []const u8, b: []const u8) bool {
            return std.mem.order(u8, a, b).compare(.lt);
        }
    }.cmp);

    var text = std.ArrayList(u8).init(_b.allocator);
    defer text.deinit();

    text.appendSlice("pub const name_list = .{ ") catch unreachable;
    var i: usize = 0; // make zls 0.12 happy
    for (list.items) |name| {
        defer i += 1;
        if (i > 0)
            text.appendSlice(", ") catch unreachable;
        text.append('"') catch unreachable;
        text.appendSlice(name) catch unreachable;
        text.append('"') catch unreachable;
    }
    text.appendSlice(" };\n") catch unreachable;

    text.appendSlice("pub const module_list = .{ ") catch unreachable;
    i = 0;
    for (list.items) |name| {
        defer i += 1;
        if (i > 0)
            text.appendSlice(", ") catch unreachable;
        text.appendSlice(name) catch unreachable;
    }
    text.appendSlice(" };\n\n") catch unreachable;

    for (list.items) |name| {
        text.appendSlice("const ") catch unreachable;
        text.appendSlice(name) catch unreachable;
        text.appendSlice(" = @import(\"") catch unreachable;
        text.appendSlice(name) catch unreachable;
        text.appendSlice(".zig\");\n") catch unreachable;
    }

    f.writeAll(text.items) catch unreachable;
}

// =========================================================================

/// wolfssl dependency lib
fn build_wolfssl() *Step {
    const wolfssl = add_step("wolfssl");

    // already installed ?
    if (path_exists(_dep_wolfssl.base_dir))
        return wolfssl;

    init_dep(wolfssl, _dep_wolfssl);

    const cmd_ =
        \\  install_dir='{s}'
        \\  src_dir='{s}'
        \\  zig_exe='{s}'
        \\  target_mcpu='{s}'
        \\  target_triple='{s}'
        \\  zig_cache_dir='{s}'
        \\  is_musl='{s}'
        \\  lto='{s}'
        \\  aesni='{s}'
        \\  intelasm='{s}'
        \\  armasm='{s}'
        \\  aarch64='{s}'
        \\  cwd="$PWD"
        \\
        \\  cd "$src_dir"
        \\
        \\  export ZIG_LOCAL_CACHE_DIR="$zig_cache_dir"
        \\  export ZIG_GLOBAL_CACHE_DIR="$zig_cache_dir"
        \\
        \\  [ "$is_musl" = 1 ] && pic_flags='-fno-pic -fno-PIC' || pic_flags=''
        \\  export CC="$zig_exe cc $target_mcpu -g0 -O3 -Xclang -O3 $lto -fno-pie -fno-PIE $pic_flags -ffunction-sections -fdata-sections"
        \\  export AR="$zig_exe ar"
        \\  export RANLIB="$zig_exe ranlib"
        \\
        \\  [ "$target_triple" ] && host="--host=$target_triple" || host=""
        \\  [ "$aarch64" = 1 ] && opt_sha512="--enable-sha512" || opt_sha512="--disable-sha512"
        \\
        \\  ./autogen.sh
        \\  ./configure \
        \\      $host \
        \\      $aesni \
        \\      $intelasm \
        \\      $armasm \
        \\      --prefix="$install_dir" \
        \\      --enable-static \
        \\      --disable-shared \
        \\      --enable-asm \
        \\      --disable-harden \
        \\      --disable-ocsp \
        \\      --disable-oldnames \
        \\      --enable-sys-ca-certs \
        \\      --disable-memory \
        \\      --disable-staticmemory \
        \\      --enable-singlethreaded \
        \\      --disable-threadlocal \
        \\      --disable-asyncthreads \
        \\      --disable-errorqueue \
        \\      --disable-error-queue-per-thread \
        \\      --disable-openssl-compatible-defaults \
        \\      --disable-opensslextra \
        \\      --disable-opensslall \
        \\      --disable-dtls \
        \\      --disable-oldtls \
        \\      --enable-tls13 \
        \\      --enable-chacha \
        \\      --enable-poly1305 \
        \\      --enable-aesgcm \
        \\      --disable-aescbc \
        \\      --enable-sni \
        \\      --enable-session-ticket \
        \\      --disable-md5 \
        \\      --disable-sha \
        \\      --disable-sha3 \
        \\      --disable-sha224 \
        \\      $opt_sha512 \
        \\      --disable-pkcs7 \
        \\      --disable-pkcs8 \
        \\      --disable-pkcs11 \
        \\      --disable-pkcs12 \
        \\      --disable-dh \
        \\      --enable-ecc \
        \\      --enable-rsa \
        \\      --disable-oaep \
        \\      --enable-coding \
        \\      --disable-base64encode \
        \\      --disable-asn-print \
        \\      --disable-pwdbased \
        \\      --disable-secure-renegotiation-info \
        \\      --disable-crypttests \
        \\      --disable-benchmark \
        \\      --disable-examples \
        \\      EXTRA_CFLAGS="-include $cwd/src/wolfssl_opt.h"
        \\  make install
    ;

    const opt_musl: [:0]const u8 = if (is_musl()) "1" else "0";
    const opt_lto: [:0]const u8 = if (_lto) "-flto" else "";
    const opt_aesni: [:0]const u8 = if (_target.getCpuArch() == .x86_64) "--enable-aesni" else "";
    const opt_intelasm: [:0]const u8 = if (!_wolfssl_noasm and get_x86_64_level() >= 3) "--enable-intelasm" else "";
    const opt_armasm: [:0]const u8 = if (!_wolfssl_noasm and _target.getCpuArch() == .aarch64) "--enable-armasm" else "";
    const opt_aarch64: [:0]const u8 = if (_target.getCpuArch() == .aarch64) "1" else "0";

    const cmd = fmt(cmd_, .{
        _b.pathFromRoot(_dep_wolfssl.base_dir),
        _dep_wolfssl.src_dir,
        _b.zig_exe,
        get_target_mcpu(),
        get_optval_target() orelse "",
        _b.pathFromRoot(_b.cache_root),
        opt_musl,
        opt_lto,
        opt_aesni,
        opt_intelasm,
        opt_armasm,
        opt_aarch64,
    });

    wolfssl.dependOn(add_sh_cmd_x(cmd));

    return wolfssl;
}

fn setup_libexeobj_step(step: *LibExeObjStep) void {
    step.setTarget(_target);
    step.setBuildMode(_mode);

    step.want_lto = _lto;
    step.strip = _strip;

    // compile
    if (step.kind == .obj)
        step.use_stage1 = true; // required by async/await (.zig)

    step.single_threaded = true;

    step.link_function_sections = true;
    // step.link_data_sections = true; // not supported in 0.10.1

    // link
    if (step.kind == .exe or step.isDynamicLibrary())
        step.link_gc_sections = true;

    step.pie = false;

    if (is_musl())
        step.force_pic = false;

    // this is needed even for the compile step, as zig needs to do some preparation for linking libc
    step.linkLibC();
}

/// zig build-obj -cflags <CFLAGS...>
fn get_cflags(ex_cflags: []const []const u8) []const []const u8 {
    var cflags = std.ArrayList([]const u8).init(_b.allocator);
    defer cflags.deinit();

    cflags.appendSlice(&.{
        "-Werror", // https://github.com/ziglang/zig/issues/10800
        "-fno-pic",
        "-fno-PIC",
        "-fno-pie",
        "-fno-PIE",
        "-ffunction-sections",
        "-fdata-sections",
        "-fcolor-diagnostics",
        "-fcaret-diagnostics",
    }) catch unreachable;

    if (_mode == .ReleaseFast)
        cflags.append("-O3") catch unreachable; // default is -O2

    // append ex cflags
    cflags.appendSlice(ex_cflags) catch unreachable;

    return cflags.toOwnedSlice();
}

fn link_obj_mimalloc(exe: *LibExeObjStep) void {
    const obj = _b.addObject("mimalloc.c", null);
    setup_libexeobj_step(obj);

    init_dep(&exe.step, _dep_mimalloc);

    obj.addIncludePath(_dep_mimalloc.include_dir);

    obj.defineCMacro("NDEBUG", null);
    obj.defineCMacro("MI_MALLOC_OVERRIDE", null);

    const src_file = fmt("{s}/src/static.c", .{_dep_mimalloc.src_dir});

    const cflags = get_cflags(&.{
        "-std=gnu11",
        "-Wall",
        "-Wextra",
        "-Wpedantic",
        "-Wstrict-prototypes",
        "-Wno-unknown-pragmas",
        "-Wno-static-in-inline",
        "-fvisibility=hidden",
        "-fno-builtin-malloc",
        "-ftls-model=initial-exec",
    });

    obj.addCSourceFile(src_file, cflags);

    // link to exe
    exe.addObject(obj);
}

fn link_obj_chinadns(exe: *LibExeObjStep) void {
    // generic cflags
    const cflags = get_cflags(&.{
        "-std=c99",
        "-Wall",
        "-Wextra",
        "-Wvla",
    });

    var dir = std.fs.cwd().openIterableDir("src", .{}) catch unreachable;
    defer dir.close();

    var it = dir.iterate();

    while (it.next() catch unreachable) |file| {
        if (file.kind != .File)
            continue;

        const is_c_file = std.mem.endsWith(u8, file.name, ".c");
        const is_root_zig = std.mem.eql(u8, file.name, "main.zig");

        if (!is_c_file and !is_root_zig)
            continue;

        const filepath = fmt("src/{s}", .{file.name});

        const obj = _b.addObject(file.name, if (is_root_zig) filepath else null);
        setup_libexeobj_step(obj);

        // for .zig file
        if (is_root_zig) {
            obj.addIncludePath("."); // used to @cInclude("src/*.h")
            obj.addOptions("build_opts", _build_opts); // for conditional compilation
        }

        if (_test)
            obj.defineCMacroRaw("TEST");

        if (is_musl())
            obj.defineCMacroRaw("MUSL");

        // wolfssl lib
        if (_enable_wolfssl) {
            obj.defineCMacroRaw("ENABLE_WOLFSSL");
            obj.addIncludePath(_dep_wolfssl.include_dir);
        }

        // for log.h
        obj.defineCMacroRaw(fmt("LOG_FILENAME=\"{s}\"", .{file.name}));

        if (is_c_file)
            obj.addCSourceFile(filepath, cflags);

        // link to exe
        exe.addObject(obj);
    }
}

fn configure() void {
    // exe: chinadns-ng (or test)
    const exe = _b.addExecutable(_exe_name, null);
    setup_libexeobj_step(exe);

    // build the dependency library first
    if (_enable_wolfssl)
        exe.step.dependOn(build_wolfssl());

    // to ensure that the standard malloc interface resolves to the mimalloc library, link it as the first object file
    if (_enable_mimalloc)
        link_obj_mimalloc(exe);

    link_obj_chinadns(exe);

    // link wolfssl library
    if (_enable_wolfssl) {
        exe.addLibraryPath(_dep_wolfssl.lib_dir);
        exe.linkSystemLibrary("wolfssl");
    }

    // install to dest dir
    exe.install();

    const run_exe = exe.run();
    if (_b.args) |args|
        run_exe.addArgs(args);

    // zig build run [-- ARGS...]
    const run = _b.step("run", "run the executable: [-- ARGS...]");
    run.dependOn(_b.getInstallStep());
    run.dependOn(&run_exe.step);

    const rm_cache = add_rm(_b.cache_root);
    const rm_wolfssl = add_rm(_dep_wolfssl.base_dir); // current target
    const rm_wolfssl_all = add_sh_cmd(fmt("rm -fr {s}@*", .{_dep_wolfssl.src_dir})); // all targets

    // zig build clean-cache
    const clean_cache = _b.step("clean-cache", fmt("clean zig build cache: '{s}'", .{_b.cache_root}));
    clean_cache.dependOn(rm_cache);

    // zig build clean-wolfssl
    const clean_wolfssl = _b.step("clean-wolfssl", fmt("clean wolfssl build cache: '{s}'", .{_dep_wolfssl.base_dir}));
    clean_wolfssl.dependOn(rm_wolfssl);

    // zig build clean-wolfssl-all
    const clean_wolfssl_all = _b.step("clean-wolfssl-all", fmt("clean wolfssl build caches: '{s}@*'", .{_dep_wolfssl.src_dir}));
    clean_wolfssl_all.dependOn(rm_wolfssl_all);

    // zig build clean
    const clean = _b.step("clean", fmt("clean all build caches", .{}));
    clean.dependOn(clean_cache);
    clean.dependOn(clean_wolfssl);

    // zig build clean-all
    const clean_all = _b.step("clean-all", fmt("clean all build caches (*)", .{}));
    clean_all.dependOn(clean_cache);
    clean_all.dependOn(clean_wolfssl_all);
}

/// build.zig just generates the build steps (and the dependency graph), the real running is done by build_runner.zig
pub fn build(b: *Builder) void {
    init(b);

    configure();

    if (_b.invalid_user_input)
        newline();
}