Add rate limiter, rename maxConn into inFlightReq

Co-authored-by: Julien Salleyron <julien.salleyron@gmail.com>
Co-authored-by: Jean-Baptiste Doumenjou <jb.doumenjou@gmail.com>

pkg/middlewares/ratelimiter/rate_limiter_test.go

@@ -0,0 +1,160 @@
+package ratelimiter
+
+import (
+	"context"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/containous/traefik/v2/pkg/config/dynamic"
+	"github.com/containous/traefik/v2/pkg/testhelpers"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"github.com/vulcand/oxy/utils"
+)
+
+func TestNewRateLimiter(t *testing.T) {
+	testCases := []struct {
+		desc             string
+		config           dynamic.RateLimit
+		expectedMaxDelay time.Duration
+		expectedSourceIP string
+	}{
+		{
+			desc: "maxDelay computation",
+			config: dynamic.RateLimit{
+				Average: 200,
+				Burst:   10,
+			},
+			expectedMaxDelay: 2500 * time.Microsecond,
+		},
+		{
+			desc: "default SourceMatcher is remote address ip strategy",
+			config: dynamic.RateLimit{
+				Average: 200,
+				Burst:   10,
+			},
+			expectedSourceIP: "127.0.0.1",
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {})
+
+			h, err := New(context.Background(), next, test.config, "rate-limiter")
+			require.NoError(t, err)
+
+			rtl, _ := h.(*rateLimiter)
+			if test.expectedMaxDelay != 0 {
+				assert.Equal(t, test.expectedMaxDelay, rtl.maxDelay)
+			}
+
+			if test.expectedSourceIP != "" {
+				extractor, ok := rtl.sourceMatcher.(utils.ExtractorFunc)
+				require.True(t, ok, "Not an ExtractorFunc")
+
+				req := http.Request{
+					RemoteAddr: fmt.Sprintf("%s:1234", test.expectedSourceIP),
+				}
+
+				ip, _, err := extractor(&req)
+				assert.NoError(t, err)
+				assert.Equal(t, test.expectedSourceIP, ip)
+			}
+		})
+	}
+}
+
+func TestRateLimit(t *testing.T) {
+	testCases := []struct {
+		desc     string
+		config   dynamic.RateLimit
+		reqCount int
+	}{
+		{
+			desc: "Average is respected",
+			config: dynamic.RateLimit{
+				Average: 100,
+				Burst:   1,
+			},
+			reqCount: 200,
+		},
+		{
+			desc: "Burst is taken into account",
+			config: dynamic.RateLimit{
+				Average: 100,
+				Burst:   200,
+			},
+			reqCount: 300,
+		},
+		{
+			desc: "Zero average ==> no rate limiting",
+			config: dynamic.RateLimit{
+				Average: 0,
+				Burst:   1,
+			},
+			reqCount: 100,
+		},
+	}
+
+	for _, test := range testCases {
+		test := test
+		t.Run(test.desc, func(t *testing.T) {
+			t.Parallel()
+
+			reqCount := 0
+			next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				reqCount++
+			})
+
+			h, err := New(context.Background(), next, test.config, "rate-limiter")
+			require.NoError(t, err)
+
+			start := time.Now()
+			for {
+				if reqCount >= test.reqCount {
+					break
+				}
+
+				req := testhelpers.MustNewRequest(http.MethodGet, "http://localhost", nil)
+				req.RemoteAddr = "127.0.0.1:1234"
+				w := httptest.NewRecorder()
+
+				h.ServeHTTP(w, req)
+				// TODO(mpl): predict and count the 200 VS the 429?
+			}
+
+			stop := time.Now()
+			elapsed := stop.Sub(start)
+			if test.config.Average == 0 {
+				if elapsed > time.Millisecond {
+					t.Fatalf("rate should not have been limited, but: %d requests in %v", reqCount, elapsed)
+				}
+				return
+			}
+
+			// Assume allowed burst is initially consumed in an infinitesimal period of time
+			var expectedDuration time.Duration
+			if test.config.Average != 0 {
+				expectedDuration = time.Duration((int64(test.reqCount)-test.config.Burst+1)/test.config.Average) * time.Second
+			}
+
+			// Allow for a 2% leeway
+			minDuration := expectedDuration * 98 / 100
+			maxDuration := expectedDuration * 102 / 100
+
+			if elapsed < minDuration {
+				t.Fatalf("rate was faster than expected: %d requests in %v", reqCount, elapsed)
+			}
+			if elapsed > maxDuration {
+				t.Fatalf("rate was slower than expected: %d requests in %v", reqCount, elapsed)
+			}
+		})
+	}
+}