feat: add Hetzner-hosted todo application stack

Implement the server-rendered Go todo application with PostgreSQL persistence, Tailwind styling, health checks, and test coverage.

Provision production and staging infrastructure with OpenTofu, including private networking, static IPs, Object Storage backups, and load balancing.

Configure Rocky Linux hosts with Ansible, rootless Podman, PostgreSQL, WAL-G backup automation, staging restores, and generated inventory.

app/internal/handler/handler.go

@@ -0,0 +1,167 @@
+package handler
+
+import (
+	"context"
+	"errors"
+	"html/template"
+	"io"
+	"log/slog"
+	"net/http"
+	"net/url"
+	"strconv"
+	"strings"
+
+	"todo-hetzner/app/internal/model"
+	"todo-hetzner/app/web"
+)
+
+const maxFormBytes = 4096
+
+type TodoStore interface {
+	List(context.Context) ([]model.Todo, error)
+	Create(context.Context, string) error
+	Toggle(context.Context, int64) (bool, error)
+	Delete(context.Context, int64) (bool, error)
+	Ping(context.Context) error
+}
+
+type Handler struct {
+	store     TodoStore
+	logger    *slog.Logger
+	templates *template.Template
+}
+
+func New(store TodoStore, logger *slog.Logger) (*Handler, error) {
+	tmpl, err := template.ParseFS(web.Assets, "templates/layouts/*.html", "templates/pages/*.html")
+	if err != nil {
+		return nil, err
+	}
+	return &Handler{store: store, logger: logger, templates: tmpl}, nil
+}
+
+func (h *Handler) Routes() http.Handler {
+	mux := http.NewServeMux()
+	mux.HandleFunc("GET /", h.list)
+	mux.HandleFunc("POST /todos", h.create)
+	mux.HandleFunc("POST /todos/{id}/toggle", h.toggle)
+	mux.HandleFunc("POST /todos/{id}/delete", h.delete)
+	mux.HandleFunc("GET /healthz", h.health)
+	mux.Handle("GET /static/", http.FileServerFS(web.Assets))
+	return h.security(h.accessLog(mux))
+}
+
+func (h *Handler) list(w http.ResponseWriter, r *http.Request) {
+	todos, err := h.store.List(r.Context())
+	if err != nil {
+		h.serverError(w, r, err)
+		return
+	}
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	if err := h.templates.ExecuteTemplate(w, "layout", struct{ Todos []model.Todo }{todos}); err != nil {
+		h.logger.Error("render response", "error", err, "request_id", requestID(r))
+	}
+}
+
+func (h *Handler) create(w http.ResponseWriter, r *http.Request) {
+	if !sameOrigin(r) {
+		http.Error(w, "invalid origin", http.StatusForbidden)
+		return
+	}
+	if err := parseForm(w, r); err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	title := strings.TrimSpace(r.FormValue("title"))
+	if title == "" || len([]rune(title)) > 200 {
+		http.Error(w, "title must contain 1 to 200 characters", http.StatusUnprocessableEntity)
+		return
+	}
+	if err := h.store.Create(r.Context(), title); err != nil {
+		h.serverError(w, r, err)
+		return
+	}
+	http.Redirect(w, r, "/", http.StatusSeeOther)
+}
+
+func (h *Handler) toggle(w http.ResponseWriter, r *http.Request) {
+	h.mutateByID(w, r, h.store.Toggle)
+}
+
+func (h *Handler) delete(w http.ResponseWriter, r *http.Request) {
+	h.mutateByID(w, r, h.store.Delete)
+}
+
+func (h *Handler) mutateByID(w http.ResponseWriter, r *http.Request, mutate func(context.Context, int64) (bool, error)) {
+	if !sameOrigin(r) {
+		http.Error(w, "invalid origin", http.StatusForbidden)
+		return
+	}
+	id, err := strconv.ParseInt(r.PathValue("id"), 10, 64)
+	if err != nil || id < 1 {
+		http.Error(w, "invalid todo ID", http.StatusBadRequest)
+		return
+	}
+	found, err := mutate(r.Context(), id)
+	if err != nil {
+		h.serverError(w, r, err)
+		return
+	}
+	if !found {
+		http.NotFound(w, r)
+		return
+	}
+	http.Redirect(w, r, "/", http.StatusSeeOther)
+}
+
+func (h *Handler) health(w http.ResponseWriter, r *http.Request) {
+	if err := h.store.Ping(r.Context()); err != nil {
+		http.Error(w, "unhealthy", http.StatusServiceUnavailable)
+		return
+	}
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	w.WriteHeader(http.StatusOK)
+	_, _ = io.WriteString(w, "ok\n")
+}
+
+func (h *Handler) serverError(w http.ResponseWriter, r *http.Request, err error) {
+	h.logger.Error("request failed", "error", err, "request_id", requestID(r))
+	http.Error(w, "internal server error", http.StatusInternalServerError)
+}
+
+func (h *Handler) security(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Content-Security-Policy", "default-src 'self'; style-src 'self'; form-action 'self'; frame-ancestors 'none'; base-uri 'self'")
+		w.Header().Set("Referrer-Policy", "no-referrer")
+		w.Header().Set("X-Content-Type-Options", "nosniff")
+		w.Header().Set("X-Frame-Options", "DENY")
+		next.ServeHTTP(w, r)
+	})
+}
+
+func (h *Handler) accessLog(next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		h.logger.Info("request", "method", r.Method, "path", r.URL.Path, "remote_addr", r.RemoteAddr, "request_id", requestID(r))
+		next.ServeHTTP(w, r)
+	})
+}
+
+func parseForm(w http.ResponseWriter, r *http.Request) error {
+	r.Body = http.MaxBytesReader(w, r.Body, maxFormBytes)
+	if err := r.ParseForm(); err != nil {
+		return errors.New("invalid form data")
+	}
+	return nil
+}
+
+func sameOrigin(r *http.Request) bool {
+	origin := r.Header.Get("Origin")
+	if origin == "" {
+		return true
+	}
+	u, err := url.Parse(origin)
+	return err == nil && strings.EqualFold(u.Host, r.Host)
+}
+
+func requestID(r *http.Request) string {
+	return r.Header.Get("X-Request-ID")
+}