go-codex

go-codex

A self-documenting codec library for Go inspired by Haskell's autodocodec. A single Codec[T] value simultaneously describes how to encode, decode, validate, and document a type. Write the codec once — derive JSON, YAML, OpenAPI, AsyncAPI, and more from the same definition.

No struct tags. No reflection. No code generation.

📚 Documentation

⭐ Flagship example: examples/sensor-service — everything go-codex is trying to achieve, in one runnable service: declare codecs, ports, and routes once, and get validation, typed pipelines, and OpenAPI/AsyncAPI specs from the same declarations. MQTT ingest → SQL persist → env-configured alerting → REST time series → auth-guarded file export, every IO hop a protocol-agnostic port, structured as a real project (domain / pipeline / ioports / adapters / observability). go run ./examples/sensor-service

The three layers

go-codex grows with your system. Use only what you need:

All three follow the same pattern: declare → register → handle.

// Layer 1 — define a codec once; constraints run on both encode and decode
var userCodec = codex.Struct[User](
    codex.RequiredField("name", codex.String().Refine(validate.NonEmptyString),
        func(u User) string { return u.Name },
        func(u *User, v string) { u.Name = v },
    ),
)

// Layer 2 — declare a typed route; same spec drives runtime + OpenAPI
var createUser = rest.NewRoute[CreateUserReq, User]("POST", "/users",
    reqCodec, userCodec,
    rest.RouteMeta{OperationID: "createUser"},
)
handle, _ := createUser.Register(builder)
req, _    := handle.Decode(body)           // validates automatically

// Layer 2 (client) — reuse the same route spec on the client side
user, _ := nethttp.Call(ctx, http.DefaultClient, serverURL, handle, req, nil, opts)

// Layer 3 — governed computation with automatic input/output validation
fn := forge.NewFunction[OEEInput, OEEResult]("oee", "1.0.0",
    inputCodec, outputCodec,
    func(in OEEInput) (OEEResult, error) { ... },
    forge.FunctionMeta{Author: "engineering@example.com"},
)
result, _ := fn.Apply(input)

Quick Start

go get github.com/DaniDeer/go-codex@latest

package main

import (
    "fmt"
    "github.com/DaniDeer/go-codex/codex"
    "github.com/DaniDeer/go-codex/format"
    "github.com/DaniDeer/go-codex/validate"
)

type User struct{ Name, Email string }

var UserCodec = codex.Struct[User](
    codex.RequiredField("name",
        codex.String().Refine(validate.NonEmptyString).WithDescription("Display name."),
        func(u User) string { return u.Name },
        func(u *User, v string) { u.Name = v },
    ),
    codex.RequiredField("email",
        codex.String().Refine(validate.Email).WithDescription("Email address."),
        func(u User) string { return u.Email },
        func(u *User, v string) { u.Email = v },
    ),
)

func main() {
    json := format.JSON(UserCodec)

    // Encode
    data, _ := json.Marshal(User{Name: "Alice", Email: "alice@example.com"})
    fmt.Println(string(data))
    // {"email":"alice@example.com","name":"Alice"}

    // Decode + validate
    _, err := json.Unmarshal([]byte(`{"name":"","email":"not-an-email"}`))
    fmt.Println(err)
    // validation errors: [name: expected non-empty string] [email: invalid email]
}

→ See docs/get-started.md for the next steps.

What you get

• One codec — four concerns — encode, decode, validate, and schema from a single Codec[T] value; no struct tags, no reflection, no code generation
• Multi-format — the same codec reads and writes JSON, YAML, TOML, Gob, and Binary (raw bytes) unchanged
• Structured errors — all failures are concrete types (ValidationErrors, ConstraintError, TypeMismatchError, …); use errors.As or pass directly to log/slog
• Builtin constraints — email, uuid, url, date, date-time, container-image, ranges, lengths, binary file formats (png, jpeg, pdf, zip, …) — validated and reflected into OpenAPI/AsyncAPI schema automatically
• OpenAPI 3.1 + AsyncAPI 3.0 — complete specs derived from the same codec; no manual YAML, no drift
• REST + HTTP client — typed Decode/Encode per route; nethttp.Call for typed client calls; both share the same Route definition
• MQTT events — typed subscribe/publish with topic validation, wildcard support, and AsyncAPI spec
• ZeroMQ — typed REQ/REP and PUB/SUB via the same codec declarations as REST and MQTT; AsyncAPI 3.0 with request-reply (api/zeromq); DEALER/ROUTER for concurrent patterns; transport-agnostic FramedSocket interface (no CGO in the adapter)
• MCP server — Tools, Resources, and Prompts follow the same declare → register → handle pattern; codec drives the inputSchema automatically
• SSE + templ SSR — codec-validated event streams; same route serves HTML and JSON via content negotiation
• Forge pipelines — named, versioned, governed KPI computation with SHA-256 contract hash and pipeline YAML spec

Import paths

go get github.com/DaniDeer/go-codex@latest

Go library as contract

Codecs are plain Go values — put them in a shared package. The Go compiler enforces the contract: a field rename breaks both the server and the client at compile time.

examples/adapters-nethttp-client/contract/  ← shared Route specs, codecs, types
examples/adapters-mqtt-contract/contract/   ← shared Channel specs, codecs, types
examples/gob-contract/contract/             ← shared Gob format contract

→ docs/concepts/codec-as-contract.md

Project Structure

→ Full annotated directory tree in the docs, or browse docs/reference/project-structure.md in the repo.

Key top-level directories:

codex/       — ⭐ PUBLIC API: Codec[T], primitives, struct, union, slice, constraints
format/      — format bridges: JSON, YAML, TOML, Gob, Binary, File I/O, embedded formats
api/         — transport-agnostic API builders (rest/, events/, mcp/, reqreply/)
adapters/    — transport adapters (nethttp, chi, mqtt, mqtt5, zeromq, sql, mcpgo, templ)
forge/       — governed KPI computation pipelines (synchronous, batch, signed, spec-generating)
stream/      — reactive stream pipelines: From, Apply, Filter, Tap, Buffer, Merge, Drain over chan T
render/      — spec renderers (openapi/, asyncapi/v2, asyncapi/v3, jsonschema/, pipeline/)
validate/    — reusable constraints (Email, UUID, URL, ranges, MQTT topics, …)
stats/       — observer interfaces (ValidationObserver → SQLObserver, LoggingObserver, NewFanout)
schema/      — schema model (pure data, zero dependencies)
route/       — HTTP route descriptors
examples/    — 40+ runnable demos (not importable by library packages)