feat: add rate limiter proxy

rate/README.md

@@ -0,0 +1,7 @@
+# Rate limiting proxy
+
+This is a service that's meant to sit between nginx (or another reverse proxy) and Foxnouns.Backend.
+To configure, copy `proxy-config.example.json` to your working directory, rename it to `proxy-config.json`,
+and change any keys you need to.
+
+Build with `go build -v .` and run with `./rate`

rate/handler.go

@@ -0,0 +1,192 @@
+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"strconv"
+	"strings"
+	"time"
+)
+
+const notFoundError = `{"status":404,"code":"NOT_FOUND","message":"Not found"}`
+const internalServerErrorTemplate = `{"status":500,"code":"INTERNAL_SERVER_ERROR","error_id":"%v","message":"Internal server error"}`
+const rateLimitedErrorTemplate = `{"status":429,"code":"RATE_LIMITED","reset":%v,"message":"You are being rate limited"}`
+
+// error ID chosen by fair duckduckgo search, guaranteed to be random
+// (we just need to return *any* error ID, this will do)
+const errorID = "951c03eadb6b474db35c23d47a10f6c0"
+
+type Handler struct {
+	Port        int    `json:"port"`
+	ProxyTarget string `json:"proxy_target"`
+	Debug       bool   `json:"debug"`
+
+	limiter *Limiter
+	proxy   *httputil.ReverseProxy
+	client  *http.Client
+}
+
+func (hn *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// all public api endpoints are prefixed with this
+	if !strings.HasPrefix(r.URL.Path, "/api/v2") {
+		w.WriteHeader(http.StatusNotFound)
+		return
+	}
+
+	data, err := hn.requestData(r)
+	if err != nil {
+		if rde, ok := err.(requestDataError); ok {
+			switch rde.Type {
+			case "badRequest":
+				if hn.Debug {
+					log.Printf("Bad request error for path %v\n", r.URL.Path)
+				}
+
+				w.Header().Set("Content-Type", "application/json; charset=utf-8")
+				w.Header().Set("Content-Length", strconv.Itoa(len(notFoundError)))
+				w.WriteHeader(http.StatusNotFound)
+				_, _ = w.Write([]byte(notFoundError))
+
+				return
+			case "internalServerError":
+				respBody := fmt.Sprintf(internalServerErrorTemplate, rde.ErrorID)
+				w.Header().Set("Content-Type", "application/json; charset=utf-8")
+				w.Header().Set("Content-Length", strconv.Itoa(len(respBody)))
+				w.WriteHeader(http.StatusInternalServerError)
+				_, _ = w.Write([]byte(respBody))
+
+				return
+			}
+		}
+
+		log.Printf("internal error while parsing request data response: %v\n", err)
+
+		respBody := fmt.Sprintf(internalServerErrorTemplate, errorID)
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		w.Header().Set("Content-Length", strconv.Itoa(len(respBody)))
+		w.WriteHeader(http.StatusInternalServerError)
+		_, _ = w.Write([]byte(respBody))
+
+		return
+	}
+
+	if hn.Debug {
+		log.Printf("proxying request to %v %v", r.Method, data.Template)
+	}
+
+	isLimited, err := hn.limiter.TryLimit(w, r, data.UserID, data.Template)
+	if err != nil {
+		log.Printf("error checking rate limit: %v\n", err)
+
+		respBody := fmt.Sprintf(internalServerErrorTemplate, errorID)
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		w.Header().Set("Content-Length", strconv.Itoa(len(respBody)))
+		w.WriteHeader(http.StatusInternalServerError)
+		_, _ = w.Write([]byte(respBody))
+		return
+	}
+
+	if isLimited {
+		var resetTime time.Time
+		if reset := getReset(w); reset == 0 {
+			resetTime = time.Now().UTC().Add(10 * time.Second)
+		} else {
+			resetTime = time.Unix(reset, 0)
+		}
+
+		respBody := fmt.Sprintf(rateLimitedErrorTemplate, resetTime.UnixMilli())
+		w.Header().Set("Content-Type", "application/json; charset=utf-8")
+		w.Header().Set("Content-Length", strconv.Itoa(len(respBody)))
+		w.WriteHeader(http.StatusTooManyRequests)
+		_, _ = w.Write([]byte(respBody))
+		return
+	}
+
+	hn.proxy.ServeHTTP(w, r)
+}
+
+func (hn *Handler) requestData(r *http.Request) (data requestDataResponse, err error) {
+	var token *string
+	if header := r.Header.Get("Authorization"); header != "" {
+		token = &header
+	}
+
+	url := hn.ProxyTarget + "/api/internal/request-data"
+
+	reqData, err := json.Marshal(requestDataRequest{Token: token, Method: r.Method, Path: r.URL.Path})
+	if err != nil {
+		return data, fmt.Errorf("marshaling request json: %w", err)
+	}
+
+	req, err := http.NewRequestWithContext(r.Context(), "POST", url, bytes.NewReader(reqData))
+	if err != nil {
+		return data, fmt.Errorf("creating request: %w", err)
+	}
+	req.Header.Set("User-Agent", "Foxnouns.NET/rate")
+	req.Header.Set("Content-Type", "application/json; charset=utf-8")
+
+	resp, err := hn.client.Do(req)
+	if err != nil {
+		return data, fmt.Errorf("making request: %w", err)
+	}
+	defer resp.Body.Close()
+
+	// If we got a bad request error, that means the endpoint wasn't found, and we should tell the client that
+	if resp.StatusCode == http.StatusBadRequest {
+		return data, requestDataError{Type: "badRequest"}
+	}
+
+	// If we got an internal server error we have to forward the error ID
+	if resp.StatusCode == http.StatusInternalServerError {
+		b, err := io.ReadAll(resp.Body)
+		if err != nil {
+			return data, fmt.Errorf("reading internal server error body: %w", err)
+		}
+
+		var fne foxnounsError
+		err = json.Unmarshal(b, &fne)
+		if err != nil {
+			return data, fmt.Errorf("unmarshaling internal server error: %w", err)
+		}
+
+		return data, requestDataError{Type: "internalServerError", ErrorID: fne.ErrorId}
+	}
+
+	b, err := io.ReadAll(resp.Body)
+	if err != nil {
+		return data, fmt.Errorf("reading body: %w", err)
+	}
+
+	err = json.Unmarshal(b, &data)
+	if err != nil {
+		return data, fmt.Errorf("unmarshaling data: %w", err)
+	}
+	return data, nil
+}
+
+type requestDataRequest struct {
+	Token  *string `json:"token"`
+	Method string  `json:"method"`
+	Path   string  `json:"path"`
+}
+
+type requestDataResponse struct {
+	UserID   *string `json:"user_id"`
+	Template string  `json:"template"`
+}
+
+type foxnounsError struct {
+	ErrorId string `json:"error_id"`
+}
+
+type requestDataError struct {
+	Type    string
+	ErrorID string
+}
+
+func (e requestDataError) Error() string { return "request data error: " + e.Type }

rate/main.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+	"os"
+	"strconv"
+)
+
+func main() {
+	// read config file and parse it
+	confB, err := os.ReadFile("proxy-config.json")
+	if err != nil {
+		log.Fatalf("reading config.json: %v", err)
+	}
+
+	hn := &Handler{}
+	err = json.Unmarshal(confB, hn)
+	if err != nil {
+		log.Fatalf("unmarshaling config.json: %v", err)
+	}
+
+	proxyURL, err := url.Parse(hn.ProxyTarget)
+	if err != nil {
+		log.Fatalf("parsing proxy_target as URL: %v", err)
+	}
+	hn.proxy = &httputil.ReverseProxy{
+		Rewrite: func(pr *httputil.ProxyRequest) {
+			pr.SetURL(proxyURL)
+			pr.Out.Host = pr.In.Host
+		},
+	}
+	hn.limiter = NewLimiter()
+	hn.client = &http.Client{}
+
+	log.Printf("serving on port %v", hn.Port)
+
+	err = http.ListenAndServe(":"+strconv.Itoa(hn.Port), hn)
+	if err != nil {
+		log.Fatalf("listening on port %v: %v", hn.Port, err)
+	}
+
+}

rate/proxy-config.example.json

@@ -0,0 +1,5 @@
+{
+    "port": 5003,
+    "proxy_target": "http://localhost:5000",
+    "debug": true
+}

rate/rate_limiter.go

@@ -0,0 +1,145 @@
+package main
+
+import (
+	"crypto/sha256"
+	"encoding/hex"
+	"fmt"
+	"net/http"
+	"strconv"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/go-chi/httprate"
+)
+
+func userOrIp(r *http.Request, userId *string) (string, error) {
+	if userId != nil {
+		return *userId, nil
+	}
+
+	return httprate.KeyByRealIP(r)
+}
+
+type Limiter struct {
+	bucketRateLimiters map[bucketKey]*httprate.RateLimiter
+	globalRateLimiters map[string]*httprate.RateLimiter
+
+	bucketMu *sync.Mutex
+	globalMu *sync.Mutex
+}
+
+type LimitData struct {
+	Global    bool
+	Bucket    string
+	Remaining int
+	Reset     int
+}
+
+type bucketKey struct {
+	user, bucket string
+}
+
+func NewLimiter() *Limiter {
+	return &Limiter{
+		bucketRateLimiters: make(map[bucketKey]*httprate.RateLimiter),
+		globalRateLimiters: make(map[string]*httprate.RateLimiter),
+
+		bucketMu: new(sync.Mutex),
+		globalMu: new(sync.Mutex),
+	}
+}
+
+// TryLimit handles rate limiting for a request.
+// If this function returns true, a rate limit was hit, and the request should be aborted with a 429 status.
+func (l *Limiter) TryLimit(w http.ResponseWriter, r *http.Request, userID *string, template string) (bool, error) {
+	user, err := userOrIp(r, userID)
+	if err != nil {
+		return false, fmt.Errorf("getting user or IP: %w", err)
+	}
+
+	// Check the globalLimiter rate limit for this user
+	globalLimiter := l.globalLimiter(user)
+	if globalLimiter.OnLimit(w, r, "") {
+		w.Header().Add("X-RateLimit-Global", "true")
+		return true, nil
+	}
+
+	bucket := requestBucket(r.Method, template)
+	w.Header().Add("X-RateLimit-Bucket", bucket)
+
+	bucketLimiter := l.bucketLimiter(user, r.Method, bucket)
+	if bucketLimiter.OnLimit(w, r, "") {
+		return true, nil
+	}
+
+	return false, nil
+}
+
+func getReset(w http.ResponseWriter) int64 {
+	header := w.Header().Get("X-RateLimit-Reset")
+	if header == "" {
+		return 0
+	}
+
+	i, err := strconv.ParseInt(header, 10, 64)
+	if err != nil {
+		return 0
+	}
+
+	return i
+}
+
+func requestBucket(method, template string) string {
+	hasher := sha256.New()
+	_, err := hasher.Write([]byte(method + "-" + template))
+	if err != nil {
+		panic(err)
+	}
+	return hex.EncodeToString(hasher.Sum(nil))
+}
+
+func (l *Limiter) globalLimiter(user string) *httprate.RateLimiter {
+	l.globalMu.Lock()
+	defer l.globalMu.Unlock()
+
+	limiter, ok := l.globalRateLimiters[user]
+	if ok {
+		return limiter
+	}
+
+	limiter = httprate.NewRateLimiter(20, time.Second)
+	l.globalRateLimiters[user] = limiter
+	return limiter
+}
+
+func (l *Limiter) bucketLimiter(user, method, bucket string) *httprate.RateLimiter {
+	l.bucketMu.Lock()
+	defer l.bucketMu.Unlock()
+
+	limiter, ok := l.bucketRateLimiters[bucketKey{user, bucket}]
+	if ok {
+		return limiter
+	}
+
+	requestLimit, windowLength := requestLimitFor(method)
+
+	limiter = httprate.NewRateLimiter(requestLimit, windowLength)
+	l.bucketRateLimiters[bucketKey{user, bucket}] = limiter
+	return limiter
+}
+
+// returns the request limit and window length for the given method.
+// methods that change state have lower rate limits
+func requestLimitFor(method string) (int, time.Duration) {
+	switch strings.ToUpper(method) {
+	case "PATCH", "POST":
+		return 1, time.Second
+	case "DELETE":
+		return 1, 5 * time.Second
+	case "GET":
+		return 3, time.Second
+	default:
+		return 2, time.Second
+	}
+}