Table of Contents

• Month 4 — Runnable Examples
• How to run
• Index (Week 1 — net/http, routing, middleware, JSON, lifecycle)
• Index (Week 2 — databases, pooling, migrations, repositories, transactions)
• Index (Week 3 — validation, logging, config, rate limiting, auth)
• Index (Week 4 — capstone: layered architecture, integration tests, OpenAPI)

Month 4 — Runnable Examples

Single-concept, stdlib-only programs backing the Month 4 daily notes (web, REST APIs & databases). Each folder is its own package main.

How to run

go run ./examples/month-04/<topic>
# then in another terminal, curl the printed address

Index (Week 1 — net/http, routing, middleware, JSON, lifecycle)

Topic	Concept	Day
servemux/	http.Server + Go 1.22 method/pattern routing, {id}, {path...}, {$}, auto-405	085
middleware/	func(http.Handler) http.Handler, a Chain combinator, request-id / logger / recoverer	088
json-api/	writeJSON/decodeJSON helpers, DisallowUnknownFields, MaxBytesReader, struct tags	089
graceful/	server timeouts, signal.NotifyContext, Server.Shutdown, ErrServerClosed	090

chi routing (Day 087) needs github.com/go-chi/chi/v5, a third-party module outside the stdlib, so it lives as a snippet in the day note rather than as a runnable example here. The servemux/ example shows how far the standard library alone now gets you.

Tip: the JSON and routing handlers are unit-tested with net/http/httptest in exercises/month-04/week-1/ — no live server needed.

Index (Week 2 — databases, pooling, migrations, repositories, transactions)

Topic	Concept	Day
pool/	bounded connection pool from a buffered channel; Acquire(ctx) respects cancellation; defer Release	093
migrate/	forward-only, idempotent migration runner ordered by integer version; duplicate-version guard	095
repository/	repository pattern: consumer-side interface + in-memory adapter; domain ErrNotFound/ErrConflict via errors.Is	096
txn/	Begin → Commit/Rollback over an in-memory store; the deferred-Rollback WithTx helper; context-checked commit	097

database/sql (Day 092), pgx / pgxpool (Day 093) and sqlc (Day 094) all require a real driver or a third-party module (github.com/jackc/pgx/v5, the sqlc generator), so they live as snippets in the day notes. The examples above model the underlying concepts — pooling, migrations, repositories, transactions — with the standard library only, so they compile and run here.

Tip: the planner, repository and transaction logic are unit-tested in exercises/month-04/week-2/ — no live database needed.

Index (Week 3 — validation, logging, config, rate limiting, auth)

Topic	Concept	Day
validation/	decode-then-validate, FieldErrors collected, 400 vs 422, net/mail.ParseAddress	099
reqlog/	per-request log/slog line; ResponseWriter wrapper for status/bytes; request-id in context	100
ratelimit/	per-client token bucket (rate vs burst), lazy refill under a mutex, 429 + Retry-After, idle eviction	103
jwt/	stdlib HS256 sign/verify, alg-pinning, hmac.Equal, exp, RequireRole RBAC middleware (401 vs 403)	104

pagination (Day 101) and env config (Day 102) are pure logic, so they live as tested packages in exercises/month-04/week-3/ (paginate, envconfig) rather than as runnable servers. golang.org/x/time/rate (Day 103) and github.com/golang-jwt/jwt (Day 104) are third-party, so the ratelimit/ and jwt/ examples model the same algorithms with the standard library only — production should reach for those packages.

Index (Week 4 — capstone: layered architecture, integration tests, OpenAPI)

Topic	Concept	Day
layered/	full handler → service → repo wiring; domain errors mapped to HTTP status in one place; in-process httptest.Server demo	106
httptest/	integration testing with httptest.NewRecorder vs httptest.NewServer; MaxBytesReader + DisallowUnknownFields	109
openapi/	model an OpenAPI 3.0 document as structs, marshal to JSON, serve /openapi.json + a docs page	110

testcontainers (Day 109) (github.com/testcontainers/testcontainers-go), swaggo/swag (Day 110), the Dockerfile/CI tooling (Day 111), and the chi/pgx stack the real project uses are third-party or out-of-band, so they live as snippets in the day notes. The httptest/ example models the exact "boot the app, hit it like a client, assert" loop that a containerised test performs — only the database backing it differs.

Tip: the service, handler and OpenAPI builder are unit-tested in exercises/month-04/week-4/ — go test ./exercises/month-04/week-4/....