add paste functionality

Backend/paste/expiry.go

@@ -0,0 +1,42 @@
+package paste
+
+import (
+	"context"
+	"log/slog"
+	"time"
+)
+
+func StartExpiryWorker(ctx context.Context, s *Store, interval time.Duration) {
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+			deleteExpired(s)
+		}
+	}
+}
+
+func deleteExpired(s *Store) {
+	var expired []string
+	err := s.ForEach(func(p *Paste) error {
+		if p.ExpiresAt != nil && time.Now().After(*p.ExpiresAt) {
+			expired = append(expired, p.ID)
+		}
+		return nil
+	})
+	if err != nil {
+		slog.Error("expiry scan error", "err", err)
+		return
+	}
+	for _, id := range expired {
+		if err := s.Delete(id); err != nil {
+			slog.Error("expiry delete error", "id", id, "err", err)
+		}
+	}
+	if len(expired) > 0 {
+		slog.Info("deleted expired pastes", "count", len(expired))
+	}
+}

Backend/paste/handlers.go

@@ -0,0 +1,118 @@
+package paste
+
+import (
+	"encoding/json"
+	"errors"
+	"net/http"
+	"time"
+)
+
+type Handlers struct {
+	store *Store
+}
+
+func NewHandlers(store *Store) *Handlers {
+	return &Handlers{store: store}
+}
+
+type createRequest struct {
+	Title    string `json:"title"`
+	Content  string `json:"content"`
+	Language string `json:"language"`
+	Expiry   int    `json:"expiry"`
+}
+
+func writeJSON(w http.ResponseWriter, status int, v any) {
+	w.Header().Set("Content-Type", "application/json")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(v)
+}
+
+func writeError(w http.ResponseWriter, status int, msg string) {
+	writeJSON(w, status, map[string]string{"error": msg})
+}
+
+func (h *Handlers) Create(w http.ResponseWriter, r *http.Request) {
+	r.Body = http.MaxBytesReader(w, r.Body, 1_100_000)
+
+	var req createRequest
+	if err := json.NewDecoder(r.Body).Decode(&req); err != nil {
+		writeError(w, http.StatusBadRequest, "invalid request body")
+		return
+	}
+	if req.Content == "" {
+		writeError(w, http.StatusBadRequest, "content is required")
+		return
+	}
+	if len(req.Content) > 1_000_000 {
+		writeError(w, http.StatusRequestEntityTooLarge, "content exceeds 1,000,000 characters")
+		return
+	}
+	if len(req.Title) > 200 {
+		writeError(w, http.StatusBadRequest, "title exceeds 200 characters")
+		return
+	}
+
+	p := &Paste{
+		Title:    req.Title,
+		Content:  req.Content,
+		Language: req.Language,
+	}
+
+	if req.Expiry < 1 || req.Expiry > 10 {
+		writeError(w, http.StatusBadRequest, "expiry must be between 1 and 10 minutes")
+		return
+	}
+	t := time.Now().Add(time.Duration(req.Expiry) * time.Minute)
+	p.ExpiresAt = &t
+
+	if err := h.store.Create(p); err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to create paste")
+		return
+	}
+
+	writeJSON(w, http.StatusCreated, map[string]string{
+		"id":  p.ID,
+		"url": "/paste/" + p.ID,
+	})
+}
+
+func (h *Handlers) Get(w http.ResponseWriter, r *http.Request) {
+	id := r.PathValue("id")
+	p, err := h.store.Get(id)
+	if errors.Is(err, ErrNotFound) {
+		writeError(w, http.StatusNotFound, "paste not found")
+		return
+	}
+	if err != nil {
+		writeError(w, http.StatusInternalServerError, "failed to retrieve paste")
+		return
+	}
+	if p.ExpiresAt != nil && time.Now().After(*p.ExpiresAt) {
+		h.store.Delete(id)
+		writeError(w, http.StatusGone, "paste has expired")
+		return
+	}
+	writeJSON(w, http.StatusOK, p)
+}
+
+func (h *Handlers) GetRaw(w http.ResponseWriter, r *http.Request) {
+	id := r.PathValue("id")
+	p, err := h.store.Get(id)
+	if errors.Is(err, ErrNotFound) {
+		http.Error(w, "paste not found", http.StatusNotFound)
+		return
+	}
+	if err != nil {
+		http.Error(w, "failed to retrieve paste", http.StatusInternalServerError)
+		return
+	}
+	if p.ExpiresAt != nil && time.Now().After(*p.ExpiresAt) {
+		h.store.Delete(id)
+		http.Error(w, "paste has expired", http.StatusGone)
+		return
+	}
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	w.Write([]byte(p.Content))
+}

Backend/paste/ratelimit.go

@@ -0,0 +1,82 @@
+package paste
+
+import (
+	"log/slog"
+	"net"
+	"net/http"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/time/rate"
+)
+
+type ipLimiter struct {
+	limiter  *rate.Limiter
+	lastSeen time.Time
+}
+
+type RateLimiter struct {
+	mu       sync.Mutex
+	limiters map[string]*ipLimiter
+	rate     rate.Limit
+	burst    int
+}
+
+func NewRateLimiter(r rate.Limit, burst int) *RateLimiter {
+	rl := &RateLimiter{
+		limiters: make(map[string]*ipLimiter),
+		rate:     r,
+		burst:    burst,
+	}
+	go rl.cleanup()
+	return rl
+}
+
+func (rl *RateLimiter) get(ip string) *rate.Limiter {
+	rl.mu.Lock()
+	defer rl.mu.Unlock()
+	entry, ok := rl.limiters[ip]
+	if !ok {
+		entry = &ipLimiter{limiter: rate.NewLimiter(rl.rate, rl.burst)}
+		rl.limiters[ip] = entry
+	}
+	entry.lastSeen = time.Now()
+	return entry.limiter
+}
+
+func (rl *RateLimiter) cleanup() {
+	for range time.Tick(5 * time.Minute) {
+		rl.mu.Lock()
+		for ip, entry := range rl.limiters {
+			if time.Since(entry.lastSeen) > 10*time.Minute {
+				delete(rl.limiters, ip)
+			}
+		}
+		rl.mu.Unlock()
+	}
+}
+
+func (rl *RateLimiter) Middleware(next http.HandlerFunc) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		ip := extractIP(r)
+		if !rl.get(ip).Allow() {
+			slog.Warn("rate limit exceeded", "ip", ip)
+			writeError(w, http.StatusTooManyRequests, "rate limit exceeded")
+			return
+		}
+		next(w, r)
+	}
+}
+
+func extractIP(r *http.Request) string {
+	if fwd := r.Header.Get("X-Forwarded-For"); fwd != "" {
+		parts := strings.SplitN(fwd, ",", 2)
+		return strings.TrimSpace(parts[0])
+	}
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return host
+}

Backend/paste/store.go

@@ -0,0 +1,95 @@
+package paste
+
+import (
+	"crypto/rand"
+	"errors"
+	"sync"
+	"time"
+)
+
+var ErrNotFound = errors.New("paste not found")
+
+type Paste struct {
+	ID        string     `json:"id"`
+	Title     string     `json:"title"`
+	Content   string     `json:"content"`
+	Language  string     `json:"language"`
+	CreatedAt time.Time  `json:"created_at"`
+	ExpiresAt *time.Time `json:"expires_at"`
+}
+
+type Store struct {
+	mu     sync.RWMutex
+	pastes map[string]*Paste
+}
+
+func NewStore() *Store {
+	return &Store{pastes: make(map[string]*Paste)}
+}
+
+func (s *Store) Create(p *Paste) error {
+	id, err := generateID()
+	if err != nil {
+		return err
+	}
+	p.ID = id
+	p.CreatedAt = time.Now().UTC()
+
+	s.mu.Lock()
+	s.pastes[id] = p
+	s.mu.Unlock()
+	return nil
+}
+
+func (s *Store) Get(id string) (*Paste, error) {
+	s.mu.RLock()
+	p, ok := s.pastes[id]
+	s.mu.RUnlock()
+	if !ok {
+		return nil, ErrNotFound
+	}
+	return p, nil
+}
+
+func (s *Store) Delete(id string) error {
+	s.mu.Lock()
+	delete(s.pastes, id)
+	s.mu.Unlock()
+	return nil
+}
+
+func (s *Store) ForEach(fn func(p *Paste) error) error {
+	s.mu.RLock()
+	ids := make([]string, 0, len(s.pastes))
+	for id := range s.pastes {
+		ids = append(ids, id)
+	}
+	s.mu.RUnlock()
+
+	for _, id := range ids {
+		s.mu.RLock()
+		p, ok := s.pastes[id]
+		s.mu.RUnlock()
+		if !ok {
+			continue
+		}
+		if err := fn(p); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+const base62Chars = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
+
+func generateID() (string, error) {
+	b := make([]byte, 8)
+	if _, err := rand.Read(b); err != nil {
+		return "", err
+	}
+	result := make([]byte, 8)
+	for i, v := range b {
+		result[i] = base62Chars[int(v)%62]
+	}
+	return string(result), nil
+}