feat: add rate limiter proxy

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 }