[performance] simpler throttling logic (#2407)

* reduce complexity of throttling logic to use 1 queue and an atomic int

* use atomic add instead of CAS, add throttling test

internal/middleware/throttling_test.go

@@ -0,0 +1,149 @@
+// GoToSocial
+// Copyright (C) GoToSocial Authors admin@gotosocial.org
+// SPDX-License-Identifier: AGPL-3.0-or-later
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+/*
+	The code in this file is adapted from MIT-licensed code in github.com/go-chi/chi. Thanks chi (thi)!
+
+	See: https://github.com/go-chi/chi/blob/e6baba61759b26ddf7b14d1e02d1da81a4d76c08/middleware/throttle.go
+
+	And: https://github.com/sponsors/pkieltyka
+*/
+
+package middleware_test
+
+import (
+	"context"
+	"net/http"
+	"net/http/httptest"
+	"runtime"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/gin-gonic/gin"
+	"github.com/superseriousbusiness/gotosocial/internal/middleware"
+)
+
+func TestThrottlingMiddleware(t *testing.T) {
+	testThrottlingMiddleware(t, 2, time.Second*10)
+	testThrottlingMiddleware(t, 4, time.Second*15)
+	testThrottlingMiddleware(t, 8, time.Second*30)
+}
+
+func testThrottlingMiddleware(t *testing.T, cpuMulti int, retryAfter time.Duration) {
+	// Calculate expected request limit + queue.
+	limit := runtime.GOMAXPROCS(0) * cpuMulti
+	queueLimit := limit * cpuMulti
+
+	// Calculate expected retry-after header string.
+	retryAfterStr := strconv.FormatUint(uint64(retryAfter/time.Second), 10)
+
+	// Gin test http engine
+	// (used for ctx init).
+	e := gin.New()
+
+	// Add middleware to the gin engine handler stack.
+	middleware := middleware.Throttle(cpuMulti, retryAfter)
+	e.Use(middleware)
+
+	// Set the blocking gin handler.
+	handler := blockingHandler()
+	e.Handle("GET", "/", handler)
+
+	var cncls []func()
+
+	for i := 0; i < queueLimit+limit; i++ {
+		// Prepare a gin test context.
+		r := httptest.NewRequest("GET", "/", nil)
+		rw := httptest.NewRecorder()
+
+		// Wrap request with new cancel context.
+		ctx, cncl := context.WithCancel(r.Context())
+		r = r.WithContext(ctx)
+
+		// Pass req through
+		// engine handler.
+		go e.ServeHTTP(rw, r)
+		time.Sleep(time.Millisecond)
+
+		// Get http result.
+		res := rw.Result()
+
+		if i < queueLimit {
+
+			// Check status == 200 (default, i.e not set).
+			if res.StatusCode != http.StatusOK {
+				t.Fatalf("status code was set (%d) with queueLimit=%d and request=%d", res.StatusCode, queueLimit, i)
+			}
+
+			// Add cancel to func slice.
+			cncls = append(cncls, cncl)
+
+		} else {
+
+			// Check the returned status code is expected.
+			if res.StatusCode != http.StatusTooManyRequests {
+				t.Fatalf("did not return status 429 (%d) with queueLimit=%d and request=%d", res.StatusCode, queueLimit, i)
+			}
+
+			// Check the returned retry-after header is set.
+			if res.Header.Get("Retry-After") != retryAfterStr {
+				t.Fatalf("did not return retry-after %s with queueLimit=%d and request=%d", retryAfterStr, queueLimit, i)
+			}
+
+			// Cancel on return.
+			defer cncl()
+
+		}
+	}
+
+	// Cancel all blocked reqs.
+	for _, cncl := range cncls {
+		cncl()
+	}
+	time.Sleep(time.Second)
+
+	// Check a bunchh more requests
+	// can now make it through after
+	// previous requests were released!
+	for i := 0; i < limit; i++ {
+
+		// Prepare a gin test context.
+		r := httptest.NewRequest("GET", "/", nil)
+		rw := httptest.NewRecorder()
+
+		// Pass req through
+		// engine handler.
+		go e.ServeHTTP(rw, r)
+		time.Sleep(time.Millisecond)
+
+		// Get http result.
+		res := rw.Result()
+
+		// Check status == 200 (default, i.e not set).
+		if res.StatusCode != http.StatusOK {
+			t.Fatalf("status code was set (%d) with queueLimit=%d and request=%d", res.StatusCode, queueLimit, i)
+		}
+	}
+}
+
+func blockingHandler() gin.HandlerFunc {
+	return func(ctx *gin.Context) {
+		<-ctx.Done()
+		ctx.Status(201) // specifically not 200
+	}
+}