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Milestone 1: Build Baseline + Platform Layer

Goal: zig build test green natively; static musl executables for x86_64-linux and aarch64-linux linking pinned sqlite3 + mbedTLS; platform modules (address, tls_client, tls_server) implemented and tested; Gitea CI green. No DNS logic in this milestone.

Read first: AGENTS.md (values), specs/research/zig-0.16-api-notes.md (verified stdlib facts — pre-0.16 API knowledge is stale and MUST NOT be used). The Zig source of truth is /home/mokhtar/app/zig at tag 0.16.0.

Sessions

Five sessions. S1 runs first, alone. S2, S3, S4, S5 run in parallel after S1 is verified. The orchestrator (not any session) wires src/tests.zig imports and any build.zig additions afterward.

S1 ──> { S2, S3, S4, S5 } ──> orchestrator integration

Session S1: Build Baseline

S1.1 build.zig.zon

  • .name = .nxdns, .version = "0.1.0", .minimum_zig_version = "0.16.0", .paths = .{""}, .fingerprint (compiler suggests the value on first build — accept it).
  • Dependencies added with zig fetch --save=<name> <url> so the content hash is pinned:
    • sqlite: SQLite 3.53.4 amalgamation zip (https://sqlite.org/2026/sqlite-amalgamation-3530400.zip).
    • mbedtls: mbedTLS 3.6.7 LTS via the GitHub source tag tarball (refs/tags/mbedtls-3.6.7.tar.gz). The release asset is .tar.bz2, which zig fetch cannot decompress; the source tarball was diffed against it — identical library + 3rdparty content (3rdparty is in-tree in the 3.6 line).
  • As built: .gitignore also covers zig-pkg/ (0.16 unpacks deps there); build.zig adds -Dgit-commit (default "unknown") and a run step; mbedTLS compiles the 103 library/*.c files plus the five 3rdparty objects named by the everest/p256-m Makefile.inc fragments; installHeadersDirectory exposes mbedtls/psa headers to any module linking the lib (S4's shim needs no extra include wiring).

S1.2 build.zig

  • Comptime guard: @import("builtin").zig_version major==0 and minor==16, else @compileError.
  • Options: -Dintegration (bool, default false) exposed to tests via a build_options module (b.addOptions()); also embed version string + git commit (b.option([]const u8, "version-string", ...) defaulting to "0.1.0-dev") for src/version.zig.
  • C static libs, one per dependency, built with b.addLibrary(.{ .linkage = .static, ... }) (NOT addStaticLibrary — it does not exist in 0.16):
    • sqlite3: compile sqlite3.c from the sqlite dependency via lib.root_module.addCSourceFile; addIncludePath the dep root. Flags: -DSQLITE_ENABLE_FTS5, -DSQLITE_THREADSAFE=1, -DSQLITE_DEFAULT_WAL_SYNCHRONOUS=1, -DSQLITE_OMIT_LOAD_EXTENSION.
    • mbedtls: compile every library/*.c file via root_module.addCSourceFiles(.{ .root = dep.path("library"), .files = ... }) (paths must be relative — absolute paths panic) plus the 3rdparty/everest and 3rdparty/p256m sources; addIncludePath for include, library, and both 3rdparty include dirs. Default mbedtls_config.h, no custom config in this milestone.
  • Executable nxdns: root module src/main.zig, link_libc = true, links both libs. Native artifact + installed.
  • Test step test: b.addTest on a module rooted at src/tests.zig, importing build_options, linking both C libs.
  • Step cross: for x86_64-linux-musl and aarch64-linux-musl (via b.resolveTargetQuery), build the exe with exe.linkage = .static, install to zig-out/cross/<triple>/nxdns.
  • .gitignore: .zig-cache/, zig-out/.

S1.3 src/main.zig, src/version.zig, src/tests.zig

  • src/version.zig: pub const string / pub const zig_version_string pulled from build_options.
  • src/main.zig: parse first CLI arg. version → print version + zig version, exit 0. run, check, export, import → print not implemented, exit 2. No arg / unknown → usage on stderr, exit 64. Args come from std.process.Init (main(init: std.process.Init)) — std.process.args does not exist in 0.16; see the API notes.
  • src/tests.zig: comptime { _ = @import("main.zig"); _ = @import("version.zig"); } plus test block asserting the sqlite3 and mbedTLS C headers link: call sqlite3_libversion() and mbedtls_version_get_string_full() via @cImport-free extern declarations (declare the two extern fns manually) and check non-empty results.

S1.4 Acceptance Criteria

  • zig build test exits 0 natively; the C-link test prints/asserts both library version strings.
  • zig build cross exits 0; file zig-out/cross/x86_64-linux-musl/nxdns and the aarch64 one both report "statically linked".
  • ./zig-out/bin/nxdns version prints the version and Zig 0.16.0, exit 0.
  • ./zig-out/bin/nxdns (no args) exits 64 with usage on stderr.
  • git status clean of build artifacts (gitignore works).

Session S2: platform/address.zig

Pure module. No std.Io operations — only type conversions to/from std.Io.net.IpAddress values. Unit tests in-file.

S2.1 Types + API

pub const NetAddress = union(enum) {
    ip4: [4]u8,
    ip6: [16]u8,

    pub const Key = [17]u8; // tag byte (4 or 6) + address bytes, zero-padded for ip4

    pub fn parse(text: []const u8) error{InvalidAddress}!NetAddress; // "1.2.3.4", "fd00::1"; no port, no brackets
    pub fn format(self: NetAddress, w: *std.Io.Writer) std.Io.Writer.Error!void; // v4 dotted; v6 RFC 5952 lowercase, :: compression
    pub fn key(self: NetAddress) Key;
    pub fn fromIp(addr: std.Io.net.IpAddress) NetAddress; // drops port; IPv4-mapped IPv6 (::ffff:a.b.c.d) normalizes to .ip4
    pub fn toIp(self: NetAddress, port: u16) std.Io.net.IpAddress;
    pub fn eql(a: NetAddress, b: NetAddress) bool;
};

pub const Prefix = struct {
    addr: NetAddress, // host bits zeroed on parse
    bits: u8,         // <= 32 for ip4, <= 128 for ip6

    pub fn parse(text: []const u8) error{InvalidPrefix}!Prefix; // "192.168.1.0/24", "fd00:abcd::/48"
    pub fn contains(self: Prefix, addr: NetAddress) bool;       // family mismatch => false
    pub fn format(self: Prefix, w: *std.Io.Writer) std.Io.Writer.Error!void;
};

/// Longest-prefix winner; ties broken by lower `priority` value. Returns null when nothing matches.
pub fn matchLongest(comptime T: type, entries: []const T, addr: NetAddress) ?*const T;
// T must have fields: prefix: Prefix, priority: i64

Implement parse/format by hand or delegate to std.Io.net.Ip4Address/Ip6Address parsing where it fits — but the RFC 5952 output rules (lowercase hex, longest zero-run compressed, no compression of a single group) must hold and be tested either way.

S2.2 Acceptance Criteria

  • Round-trip tests: parse→format is identity for canonical inputs ("192.168.1.1", "fd00::1", "::", "2001:db8::8:800:200c:417a").
  • RFC 5952 tests: "2001:0DB8:0:0:1::1" formats as "2001:db8::1:0:0:0:1"-style rules — specifically: longest run compressed, single zero group NOT compressed, lowercase.
  • fromIp on an IPv4-mapped IPv6 address yields .ip4.
  • Prefix.contains: 192.168.1.0/24 contains .1.5, not .2.5; /0 contains everything of its family; family mismatch false.
  • matchLongest: /24 beats /16; equal bits → lower priority value wins.
  • All tests pass via zig test src/platform/address.zig (orchestrator wires them into zig build test later).

Session S3: platform/tls_client.zig

Wrapper over std.crypto.tls.Client for upstream DoT (and reused by anything needing client TLS over a std.Io.net.Stream). See the API notes §std.crypto.tls.Client for exact init requirements.

S3.1 API

pub const ErrorClass = enum { handshake, certificate, io, protocol };

pub fn classify(err: anyerror) ErrorClass;

pub const TlsStream = struct {
    // all fields private in practice; struct is pinned: MUST NOT move after init
    // (tls.Client holds its reader/writer by value)

    pub const Options = struct {
        host: []const u8,                       // SNI + verification name (always sent as SNI)
        // insecure_skip_verify skips CA/expiry verification but keeps SNI and leaf
        // hostname matching (stdlib couples SNI to .host = .explicit)
        ca: enum { system, insecure_skip_verify },
        // buffers supplied by caller; read_buffer.len >= std.crypto.tls.Client.min_buffer_len
        read_buffer: []u8,
        write_buffer: []u8,
        stream_read_buffer: []u8,
        stream_write_buffer: []u8,
    };

    /// In-place init (pinned struct). `bundle` is scanned lazily for .system via
    /// std.crypto.Certificate.Bundle.rescan when empty; caller owns bundle + lock lifetime.
    pub fn init(
        self: *TlsStream,
        io: std.Io,
        stream: *std.Io.net.Stream,
        bundle: *std.crypto.Certificate.Bundle,
        bundle_lock: *std.Io.RwLock,
        gpa: std.mem.Allocator,
        options: Options,
    ) InitError!void;

    pub fn reader(self: *TlsStream) *std.Io.Reader;   // plaintext
    pub fn writer(self: *TlsStream) *std.Io.Writer;   // plaintext
    pub fn close(self: *TlsStream) void;              // close_notify via Client.end, errors swallowed to log-level
};
  • Entropy: 240 bytes via io.random; realtime_now via the Io clock (io.now(.real) — check the exact 0.16 name in /home/mokhtar/app/zig/lib/std/Io.zig before use).
  • classify maps the stdlib error sets: cert/trust errors → .certificate; handshake alerts/negotiation → .handshake; ReadFailed/WriteFailed/connection errors → .io; everything else → .protocol. Write the mapping exhaustively over std.crypto.tls.Client.InitError — a switch with explicit arms, no else => .protocol catch-all for that set.

S3.2 Tests

  • Unit: classify mapping table (pick 6+ representative errors across the four classes).
  • Integration: lives in src/platform/tls_client_integration_test.zig (separate file — conditional imports are impossible in 0.16; see API notes). Runtime guard if (!build_options.integration) return error.SkipZigTest; — the body stays type-checked in every build, runs only under -Dintegration. Connects to 1.1.1.1:853 (IPv4 literal — this host's IPv6 egress is dead and the anycast address is documented) with .host = "cloudflare-dns.com" so SNI + hostname verification run against the real name; .ca = .system; clean close. NOT part of default zig build test, NOT part of blocking CI.
  • As built: InitError = tls.Client.InitError || error{CertificateBundleLoadFailure} (bundle rescan folded in, std.http.Client style). classify reaches exhaustiveness via inline for over @typeInfo(tls.Client.InitError).error_set.? — one mapping site, new stdlib errors break the build there.

S3.3 Acceptance Criteria

  • zig test src/platform/tls_client.zig passes (unit tests only).
  • classify covers InitError exhaustively (compiles with explicit arms — adding a new stdlib error breaks the build here, by design).
  • Integration test compiles under -Dintegration (orchestrator runs it after wiring; a live-network failure is an environment finding, not a session failure).

Session S4: platform/tls_server.zig

mbedTLS-backed server-side TLS termination exposing std.Io.Reader/std.Io.Writer, so std.http.Server and the DoT server can sit on top of any accepted TCP stream.

S4.1 mbedTLS extern layer

Declare the needed mbedTLS API as extern fns/opaque types in this file (no @cImport — keep translate-c out of the build). Needed surface: mbedtls_ssl_context, mbedtls_ssl_config, mbedtls_x509_crt, mbedtls_pk_context, mbedtls_entropy_context, mbedtls_ctr_drbg_context + their init/free/setup/parse functions, mbedtls_ssl_handshake, mbedtls_ssl_read, mbedtls_ssl_write, mbedtls_ssl_close_notify, mbedtls_ssl_set_bio, mbedtls_strerror. Sizes: allocate contexts with the C sizes via opaque + extern allocation pattern — simplest correct approach: define extern struct mirrors is NOT acceptable (fragile); instead heap-allocate via wrapper C-callable malloc(sizeof) is also not available — so: declare the context structs as opaque and allocate them with gpa.alignedAlloc(u8, .of(usize), mbedtls_ssl_context_size) where the sizes come from a tiny C shim file src/platform/mbedtls_shim.c exporting size_t nx_sizeof_ssl_context(void) etc. The shim is owned by this session and added to build by the orchestrator (S4 must NOT edit build.zig — note the shim path in the completion report).

S4.2 API

pub const ServerContext = struct {
    // holds parsed cert chain + key + ssl_config + drbg; one per listener, reused across connections
    pub fn init(gpa: std.mem.Allocator, cert_pem: [:0]const u8, key_pem: [:0]const u8) InitError!ServerContext;
    pub fn deinit(self: *ServerContext, gpa: std.mem.Allocator) void;
};

pub const ServerStream = struct {
    // pinned after accept(); owns the ssl_context for one connection

    /// Performs the TLS handshake over an accepted TCP stream.
    /// BIO callbacks bridge mbedtls_ssl_read/write to stream.reader/writer interfaces.
    pub fn accept(
        self: *ServerStream,
        gpa: std.mem.Allocator,
        ctx: *ServerContext,
        io: std.Io,
        stream: *std.Io.net.Stream,
        read_buffer: []u8,
        write_buffer: []u8,
    ) AcceptError!void;

    pub fn reader(self: *ServerStream) *std.Io.Reader;   // plaintext, implemented via Io.Reader vtable over mbedtls_ssl_read
    pub fn writer(self: *ServerStream) *std.Io.Writer;   // plaintext, via mbedtls_ssl_write
    pub fn close(self: *ServerStream, gpa: std.mem.Allocator) void; // close_notify + free ssl_context
};
  • Error mapping: negative mbedTLS return codes → Zig error set with named errors for the common cases (CertParse, KeyParse, KeyMismatch, HandshakeFailed); include the raw code in a log via mbedtls_strerror.
  • MBEDTLS_ERR_SSL_WANT_READ/WANT_WRITE loop inside read/write — never surfaces to callers. ONLY those two codes retry; the *_IN_PROGRESS codes are misconfiguration (no async crypto configured) and surface as errors.
  • As built (review round 1): only an authenticated close_notify reads as clean error.EndOfStream; transport EOF without close_notify → error.ReadFailed with read_err = .TlsConnectionTruncated (no opt-out). ServerContext.init calls mbedtls_pk_check_pair (via the nx_x509_crt_pk shim accessor) → error.KeyMismatch on a mismatched pair, covered by the tests/fixtures/mismatched_key.pem fixture. mbedTLS compiles with MBEDTLS_THREADING_C + MBEDTLS_THREADING_PTHREAD (build.zig addMbedtlsThreadingMacros, applied to every module that sees mbedTLS headers — context sizes change with threading).

S4.3 Test fixture + loopback test

  • Generate once and commit: tests/fixtures/self_signed_cert.pem + self_signed_key.pem (openssl, EC P-256, CN=localhost, SAN DNS:localhost + IP:127.0.0.1, 100-year validity — a fixture, not a secret; note "test fixture, private key intentionally committed" in a tests/fixtures/README.md).
  • Loopback test (compiled only under build_options.integration): thread A: IpAddress.listen on 127.0.0.1:0 → accept → ServerStream.accept with the fixture → echo one message read back to the writer. Thread B (client): std.crypto.tls.Client with .host = .no_verification, .ca = .no_verification → write message → read echo → assert equality → clean close both sides. Drive both with io.concurrent on one Threaded instance.

S4.4 Acceptance Criteria

  • ServerContext.init with the fixture cert+key succeeds; with truncated PEM returns error.CertParse/error.KeyParse (unit tests, no network).
  • Loopback echo test passes under -Dintegration (orchestrator wires + runs).
  • No @cImport anywhere; extern decls + C shim only.
  • close sends close_notify (verified in the loopback test by the client reading EOF without error after end).

Session S5: Gitea CI

S5.1 .gitea/workflows/ci.yml

House style: runs-on: ubuntu-24.04, actions/checkout@v4, top-level env: for versions (model: ~/app/phoenix_inertia_react_starter/.gitea/workflows/ci.yml). Runner: x86_64, dind, full egress, uses: resolves against github.com. Cache is ephemeral (runner restarts daily) — actions/cache@v4 allowed as best-effort, never load-bearing.

Jobs:

  1. test: checkout → mlugg/setup-zig@v2 with version: 0.16.0 → zig build test → zig build test -Dintegration is NOT run here (loopback integration runs are wired by the orchestrator in a later pass once tests.zig includes them; leave a commented job stub with a TODO referencing milestone-1 integration wiring).
  2. cross: checkout → setup-zig → zig build cross → assert both output binaries exist and file reports statically linked.

S5.2 .gitea/workflows/live-tls.yml

workflow_dispatch only. Runs zig build test -Dintegration (which includes the live DoT handshake test once wired). Non-blocking by construction.

S5.3 Acceptance Criteria

  • yamllint-clean (or at minimum python3 -c "import yaml,sys; yaml.safe_load(open('.gitea/workflows/ci.yml'))" passes for both files).
  • Workflow YAML uses only actions available from github.com (actions/checkout@v4, mlugg/setup-zig@v2, actions/cache@v4).
  • No job depends on cache hits for correctness.

Module Layout

AGENTS.md                     values + aim (exists)
PLAN.md                       source of truth (exists)
specs/milestone-1.md          this file
specs/research/zig-0.16-api-notes.md   stdlib ground truth (exists)
build.zig                     S1
build.zig.zon                 S1
.gitignore                    S1
src/main.zig                  S1  CLI dispatch stub
src/version.zig               S1  build_options plumbing
src/tests.zig                 S1  test aggregator (orchestrator extends)
src/platform/address.zig      S2  NetAddress/Prefix/matchLongest
src/platform/tls_client.zig   S3  stdlib TLS client wrapper
src/platform/tls_server.zig   S4  mbedTLS server wrapper
src/platform/mbedtls_shim.c   S4  sizeof shims
tests/fixtures/self_signed_cert.pem  S4
tests/fixtures/self_signed_key.pem   S4
tests/fixtures/mismatched_key.pem    S4  (review round 1: KeyMismatch fixture)
tests/fixtures/fixtures.zig          S4  (@embedFile module root for fixtures)
tests/fixtures/README.md      S4
.gitea/workflows/ci.yml       S5
.gitea/workflows/live-tls.yml S5

File Ownership

Files Owner Notes
build.zig, build.zig.zon, .gitignore, src/main.zig, src/version.zig, src/tests.zig S1 frozen after S1; orchestrator edits afterward
src/platform/address.zig S2
src/platform/tls_client.zig S3
src/platform/tls_server.zig, src/platform/mbedtls_shim.c, tests/fixtures/* S4 shim build-wiring done by orchestrator
.gitea/workflows/* S5

S2–S5 MUST NOT edit build.zig, build.zig.zon, or src/tests.zig. If a session needs a build change, it reports the exact needed change in its completion report; the orchestrator applies it.

Acceptance Criteria (Milestone 1 Complete)

  • zig build test exits 0 (aggregator includes address, tls_client unit, tls_server unit tests).
  • zig build test -Dintegration exits 0 locally (hermetic loopback TLS echo; deterministic, PR-blocking in CI).
  • zig build test -Dintegration -Dlive exits 0 locally (adds the live DoT handshake; manual workflow only — a live-network failure is an environment finding, not a gate).
  • zig build cross produces two statically linked executables that print nxdns version output under qemu-user or on-target (checked manually for aarch64 if qemu absent).
  • CI workflows valid YAML; test + cross jobs green on the Gitea runner.
  • All files committed with GPG-signed, lowercase-message commits.

Anti-Requirements

  • No DNS packet code, no sockets beyond the tests, no SQLite usage beyond the link check — that is milestone 2+.
  • No custom mbedtls_config.h, no cipher tuning, no session tickets.
  • No @cImport/translate-c anywhere.
  • No extra CLI behavior beyond the specified stubs.
  • No Docker/systemd packaging yet.
  • No third-party Zig packages.
  • Do not "fix" or extend files another session owns — report, don't touch.
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