Added rate limiting

.dockerignore

@@ -0,0 +1,5 @@
+.env
+cache.gob
+prayercal
+prayercal.ics
+.git

.gitignore

@@ -1,4 +1,5 @@
+.env
 cache.gob
 prayercal
-.env
 prayercal.ics
+data/

Dockerfile

@@ -0,0 +1,14 @@
+FROM --platform=$BUILDPLATFORM golang:1.27 AS build
+ARG TARGETOS TARGETARCH TARGETVARIANT
+WORKDIR /src
+COPY go.mod go.sum ./
+RUN go mod download
+COPY . .
+RUN CGO_ENABLED=0 GOOS=$TARGETOS GOARCH=$TARGETARCH \
+    GOARM=${TARGETVARIANT#v} \
+    go build -o /prayercal .
+
+FROM gcr.io/distroless/static
+COPY --from=build /prayercal /prayercal
+EXPOSE 5543
+ENTRYPOINT ["/prayercal"]

go.mod

@@ -5,4 +5,5 @@ go 1.27.0
 require (
 	github.com/arran4/golang-ical v0.3.7
 	github.com/joho/godotenv v1.5.1
+	golang.org/x/time v0.16.0
 )

go.sum

@@ -10,5 +10,7 @@ github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZb
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+golang.org/x/time v0.16.0 h1:vMb6ptszcQMkcwiRTAuNNU50gom6++Q/6gY2hDM6VDE=
+golang.org/x/time v0.16.0/go.mod h1:rVKOqvZeKvrDKTQiAHJ7wmwP0RzleSphoEA9RcdLA0s=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
 gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

main.go

@@ -17,6 +17,11 @@ import (
 	_ "time/tzdata"
 
 	ics "github.com/arran4/golang-ical"
+
+	"net"
+	"strconv"
+	"strings"
+	"golang.org/x/time/rate"
 )
 
 type prayerTimes struct {
@@ -39,12 +44,19 @@ func main() {
 	// example {1791571473 map[Asr:15:43 Dhuhr:12:53 Fajr:05:41 Isha:19:45 Maghrib:18:24 Sunrise:07:11]}
 
 	loc, err := time.LoadLocation("Europe/London")
-	time.Local = loc
 	if err != nil {
 		log.Fatal(err)
 	}
+	time.Local = loc
 
-	http.HandleFunc("/prayercal.ics", func(w http.ResponseWriter, r *http.Request) {
+	lim := newLimiter(
+		envFloat("RATE_LIMIT_RPS", 1),
+		envInt("RATE_LIMIT_BURST", 5),
+	)
+	trustProxy := envBool("TRUST_PROXY", false)
+
+	mux := http.NewServeMux()
+	mux.HandleFunc("/prayercal.ics", func(w http.ResponseWriter, r *http.Request) {
 		mu.Lock()
 		times, err := getTimes(url, "/data/cache.gob")
 		mu.Unlock()
@@ -64,7 +76,13 @@ func main() {
 		w.Header().Set("Content-Type", "text/calendar; charset=utf-8")
 		io.WriteString(w, out)
 	})
-	log.Fatal(http.ListenAndServe(":5543", nil))
+
+	srv := &http.Server{
+		Addr:              ":" + getenv("PORT", "5543"),
+		Handler:           lim.middleware(trustProxy, mux),
+		ReadHeaderTimeout: 5 * time.Second,
+	}
+	log.Fatal(srv.ListenAndServe())
 }
 
 func buildCal(times prayerTimes, loc *time.Location) (string, error) {
@@ -189,4 +207,98 @@ func getTimes(url, cache string) (prayerTimes, error) {
 	}
 
 	return form, nil
+}
+
+func envFloat(key string, def float64) float64 {
+	if v := os.Getenv(key); v != "" {
+		if f, err := strconv.ParseFloat(v, 64); err == nil {
+			return f
+		}
+		log.Printf("bad %s=%q, using %v", key, v, def)
+	}
+	return def
+}
+
+func envInt(key string, def int) int {
+	return int(envFloat(key, float64(def)))
+}
+
+func envBool(key string, def bool) bool {
+	if v := os.Getenv(key); v != "" {
+		if b, err := strconv.ParseBool(v); err == nil {
+			return b
+		}
+	}
+	return def
+}
+
+type client struct {
+	lim  *rate.Limiter
+	seen time.Time
+}
+
+type limiter struct {
+	mu      sync.Mutex
+	clients map[string]*client
+	rps     rate.Limit
+	burst   int
+}
+
+func newLimiter(rps float64, burst int) *limiter {
+	l := &limiter{clients: map[string]*client{}, rps: rate.Limit(rps), burst: burst}
+	go func() {
+		for range time.Tick(time.Minute) {
+			l.mu.Lock()
+			for ip, c := range l.clients {
+				if time.Since(c.seen) > 10*time.Minute {
+					delete(l.clients, ip)
+				}
+			}
+			l.mu.Unlock()
+		}
+	}()
+	return l
+}
+
+func (l *limiter) allow(ip string) bool {
+	l.mu.Lock()
+	defer l.mu.Unlock()
+	c, ok := l.clients[ip]
+	if !ok {
+		c = &client{lim: rate.NewLimiter(l.rps, l.burst)}
+		l.clients[ip] = c
+	}
+	c.seen = time.Now()
+	return c.lim.Allow()
+}
+
+func clientIP(r *http.Request, trustProxy bool) string {
+	if trustProxy {
+		if xff := r.Header.Get("X-Forwarded-For"); xff != "" {
+			return strings.TrimSpace(strings.Split(xff, ",")[0])
+		}
+	}
+	host, _, err := net.SplitHostPort(r.RemoteAddr)
+	if err != nil {
+		return r.RemoteAddr
+	}
+	return host
+}
+
+func (l *limiter) middleware(trustProxy bool, next http.Handler) http.Handler {
+	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if !l.allow(clientIP(r, trustProxy)) {
+			w.Header().Set("Retry-After", "1")
+			http.Error(w, "too many requests", http.StatusTooManyRequests)
+			return
+		}
+		next.ServeHTTP(w, r)
+	})
+}
+
+func getenv(key, def string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return def
 }

readme.md

@@ -0,0 +1,2 @@
+# Prayercal
+