smallwebwaf/internal/servewaf/bytelimits_test.go

package servewaf_test

import (
	"bufio"
	"io"
	"net"
	"net/http"
	"net/netip"
	"reflect"
	"strconv"
	"strings"
	"testing"
	"time"

	"sneak.berlin/go/smallwebwaf/internal/alerts"
	"sneak.berlin/go/smallwebwaf/internal/bans"
	"sneak.berlin/go/smallwebwaf/internal/requestlog"
)

// The byte limit settings.
const (
	bytesLimitPerMinute = "SWWAF_BYTES_LIMIT_PER_MINUTE"
	bytesLimitPerHour   = "SWWAF_BYTES_LIMIT_PER_HOUR"
	bytesLimitPerDay    = "SWWAF_BYTES_LIMIT_PER_DAY"
	bytesCount          = "SWWAF_BYTES_COUNT"
)

// The values of SWWAF_BYTES_COUNT.
const (
	countResponse = "response"
	countRequest  = "request"
	countBoth     = "both"
)

const (
	// bodyBytes is the size of the body of each request these tests send
	// with one, and answerBytes that of each answer of the app.
	bodyBytes   = 30
	answerBytes = 70
	// byteLimit is the byte limit these tests set, as a setting: a request
	// with a body and its answer, 100 bytes, go over it.
	byteLimit = "99"
	// minuteBytes is limit_hit for SWWAF_BYTES_LIMIT_PER_MINUTE.
	minuteBytes = "minute_bytes"
)

func TestEachByteLimitBansOnceTheResponseHasEnded(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		setting, window string
		// apart is the time between the two requests, which the window
		// still covers.
		apart time.Duration
	}{
		{bytesLimitPerMinute, minute, 0},
		{bytesLimitPerHour, "hour", 2 * time.Minute},
		{bytesLimitPerDay, "day", 2 * time.Hour},
	} {
		t.Run(tc.setting, func(t *testing.T) {
			t.Parallel()

			s, clk := startWithAnswers(t, map[string]string{
				tc.setting: byteLimit, metricsToken: token,
			})

			// 70 bytes are within the limit of 99.
			line, _ := s.download()
			if line.LimitHit != "" || line.Offence != "" {
				t.Errorf("log line has limit_hit %q and offence %q, want neither",
					line.LimitHit, line.Offence)
			}

			// 140 bytes are over it. The response is passed on whole, and
			// then bans the client for an hour.
			clk.advance(tc.apart)
			expires := requestlog.FormatTime(clk.Now().Add(time.Hour))

			line, got := s.download()
			if got.err != nil || len(got.body) != answerBytes ||
				line.ResponseBytes != answerBytes {
				t.Errorf("got %d bytes (%v), and the log line has response_bytes %d, "+
					"want %d", len(got.body), got.err, line.ResponseBytes, answerBytes)
			}

			if line.LimitHit != tc.window+"_bytes" || line.Offence != requestlog.OffenceLimit ||
				line.BanExpires != expires {
				t.Errorf("log line has limit_hit %q, offence %q and ban_expires %q, "+
					"want %s_bytes, limit and %s", line.LimitHit, line.Offence,
					line.BanExpires, tc.window, expires)
			}

			s.get(client, http.StatusForbidden, requestlog.ActionBanned)

			wantMetric(t, s.scrape(), `smallwebwaf_rate_limit_hits_total{`+
				`instance="`+alertInstance+`",kind="bytes",window="`+tc.window+`"}`, 1)
		})
	}
}

func TestByteLimitBanNamesItsHeuristicWindowCountAndLimit(t *testing.T) {
	t.Parallel()

	s, _ := startWithAnswers(t, map[string]string{bytesLimitPerMinute: byteLimit})

	line, _ := s.download()
	wantAfterAnswerHeuristic(t, line, "", "null")

	// Two answers of 70 bytes are over the limit of 99.
	line, _ = s.download()
	wantHeuristic(t, line, "", "null")
	wantAfterAnswerHeuristic(t, line, "byte_limits",
		`{"window": "minute", "count": 140, "limit": 99}`)
}

func TestResponseOverAByteLimitByItselfIsPassedOnWhole(t *testing.T) {
	t.Parallel()

	s, _ := startWithAnswers(t, map[string]string{bytesLimitPerMinute: "50"})

	// The answer's 70 bytes are over the limit of 50 on their own.
	line, got := s.download()
	if got.err != nil || len(got.body) != answerBytes || line.LimitHit != minuteBytes {
		t.Errorf("got %d bytes (%v), and the log line has limit_hit %q, want %d and %s",
			len(got.body), got.err, line.LimitHit, answerBytes, minuteBytes)
	}

	s.get(client, http.StatusForbidden, requestlog.ActionBanned)
}

func TestBytesOfAnAnswerThatBreaksOffAreCounted(t *testing.T) {
	t.Parallel()

	s, clk, _, _ := startAppWithAlerts(t, breakOff, map[string]string{
		bytesLimitPerMinute: "50",
	})
	expires := requestlog.FormatTime(clk.Now().Add(time.Hour))

	// The 70 bytes passed on before the app broke off are over the limit of
	// 50, and ban the client for an hour.
	line, got := s.requestWithBody(http.MethodGet, client, "/", "", "", http.StatusOK,
		requestlog.ActionForward)
	if len(got.body) != answerBytes || line.LimitHit != minuteBytes ||
		line.BanExpires != expires {
		t.Errorf("got %d bytes, and the log line has limit_hit %q and ban_expires %q, "+
			"want %d, %s and %s", len(got.body), line.LimitHit, line.BanExpires,
			answerBytes, minuteBytes, expires)
	}

	s.get(client, http.StatusForbidden, requestlog.ActionBanned)
}

func TestWebSocketBytesAreCountedOnceItCloses(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		setting string
		counted float64
	}{
		{countResponse, answerBytes},
		{countRequest, bodyBytes},
		{countBoth, bodyBytes + answerBytes},
	} {
		t.Run(tc.setting, func(t *testing.T) {
			t.Parallel()

			s, _, _, _ := startAppWithAlerts(t, answerAfterUpgrade, map[string]string{
				bytesLimitPerMinute: "29", bytesCount: tc.setting,
			})

			// The client sends 30 bytes and the app 70, each over the limit
			// of 29, which bans the client once the WebSocket has closed.
			line := s.webSocket()
			if line.LimitHit != minuteBytes || line.Counts.MinuteBytes != tc.counted {
				t.Errorf("log line has limit_hit %q and minute_bytes %v, want %s and %v",
					line.LimitHit, line.Counts.MinuteBytes, minuteBytes, tc.counted)
			}

			s.get(client, http.StatusForbidden, requestlog.ActionBanned)
		})
	}
}

func TestBytesCountSaysWhichBytesCount(t *testing.T) {
	t.Parallel()

	for _, tc := range []struct {
		setting string
		// each is the bytes each request counts, and breaking the request
		// that goes over the limit of 99.
		each     float64
		breaking int
	}{
		{countResponse, answerBytes, 2},
		{countRequest, bodyBytes, 4},
		{countBoth, bodyBytes + answerBytes, 1},
	} {
		t.Run(tc.setting, func(t *testing.T) {
			t.Parallel()

			s, _ := startWithAnswers(t, map[string]string{
				bytesLimitPerMinute: byteLimit, bytesCount: tc.setting,
			})

			for i := 1; i <= tc.breaking; i++ {
				line := s.upload()

				want := ""
				if i == tc.breaking {
					want = minuteBytes
				}

				counted := float64(i) * tc.each
				if line.LimitHit != want || line.Counts.MinuteBytes != counted {
					t.Errorf("request %d: log line has limit_hit %q and minute_bytes %v, "+
						"want %q and %v", i, line.LimitHit, line.Counts.MinuteBytes,
						want, counted)
				}
			}

			s.get(client, http.StatusForbidden, requestlog.ActionBanned)
		})
	}
}

func TestByteLimitsLeaveOutWhatTheRateLimitsLeaveOut(t *testing.T) {
	t.Parallel()

	const (
		allowed = "192.0.2.7"  // in SWWAF_ALLOW_NETS
		exempt  = "192.0.2.10" // in SWWAF_RATE_LIMIT_EXEMPT_NETS
	)

	s, _ := startWithAnswers(t, map[string]string{
		bytesLimitPerMinute:  byteLimit,
		allowNets:            allowed,
		rateLimitExemptNets:  exempt,
		rateLimitExemptPaths: "/assets/",
	})

	// Each sends 200 bytes, none of which is counted.
	for _, sent := range []struct{ from, path string }{
		{allowed, "/"}, {exempt, "/"}, {client, "/assets/app.js"},
	} {
		for range 2 {
			line, _ := s.requestWithBody(http.MethodPost, sent.from, sent.path,
				uploadHeader, uploadBody, http.StatusOK, requestlog.ActionForward)
			if _, counted := line.fields["counts"]; counted || line.LimitHit != "" {
				t.Errorf("%s %s: log line has counts %v and limit_hit %q, want neither",
					sent.from, sent.path, line.fields["counts"], line.LimitHit)
			}
		}
	}

	// A path that is not exempt is counted, and breaks the limit.
	line := s.upload()
	if line.LimitHit != minuteBytes {
		t.Errorf("log line has limit_hit %q, want %s", line.LimitHit, minuteBytes)
	}
}

func TestByteLimitsOffCountTheBytesAndBanNoOne(t *testing.T) {
	t.Parallel()

	s, _ := startWithAnswers(t, map[string]string{
		bytesLimitPerMinute: off, bytesLimitPerHour: off, bytesLimitPerDay: off,
	})

	for i := 1; i <= 3; i++ {
		line := s.upload()

		counted := float64(i * (bodyBytes + answerBytes))
		if line.LimitHit != "" || line.Counts.MinuteBytes != counted ||
			line.Counts.HourBytes != counted || line.Counts.DayBytes != counted {
			t.Errorf("request %d: log line has limit_hit %q and counts %+v, "+
				"want none and %v bytes in each window", i, line.LimitHit,
				line.Counts, counted)
		}
	}
}

func TestBanForABrokenByteLimitHasItsNotesAndItsAlert(t *testing.T) {
	t.Parallel()

	s, clk, server, queue := startAppWithAlerts(t, readAndAnswer, map[string]string{
		bytesLimitPerMinute: byteLimit,
	})
	start := clk.Now()

	s.requestWithBody(http.MethodPost, client, "/upload?part=1", uploadHeader,
		uploadBody, http.StatusOK, requestlog.ActionForward)

	netblock := netip.MustParsePrefix(client + "/32")
	want := bans.Ban{
		Netblock: netblock,
		Start:    start,
		Expires:  start.Add(time.Hour),
		Cause:    bans.CauseLimit,
		Reason:   "bytes per minute over the limit of " + byteLimit,
		Notes: bans.Notes{
			Kind:   "bytes",
			Limit:  99,
			Window: minute,
			Count:  bodyBytes + answerBytes,
			// The request as it was answered, by the app.
			Request: bans.Request{
				Time:      start,
				Method:    http.MethodPost,
				Host:      appHost,
				Path:      "/upload?part=1",
				Status:    http.StatusOK,
				UserAgent: userAgent,
			},
			Requests: 1,
		},
	}

	got := server.Ledger.Bans(netblock)
	if len(got) != 1 || !reflect.DeepEqual(got[0], want) {
		t.Fatalf("bans\n%+v\nwant\n%+v", got, want)
	}

	wantAlerts(t, queue, banAlert(alerts.EventBan, start, client, want,
		requestlog.FormatTime(want.Expires)))

	if offences := historyOf(t, server, client).Offences.Limit; offences != 1 {
		t.Errorf("history counts %d offences for a limit, want 1", offences)
	}
}

func TestObserveModeLogsAndAlertsAByteLimitAndBansNoOne(t *testing.T) {
	t.Parallel()

	s, clk, server, queue := startAppWithAlerts(t, readAndAnswer, map[string]string{
		mode:                observe,
		bytesLimitPerMinute: byteLimit,
	})
	start := clk.Now()

	// No ban sets the client's counters back to zero, so each request
	// breaks the limit again. The answer is the app's either way, and the
	// alert for the ban is not sent twice within the cooldown.
	for range 2 {
		line := s.upload()
		wantWouldAction(t, line, "")

		if line.LimitHit != minuteBytes || line.Offence != requestlog.OffenceLimit ||
			line.BanExpires != "" {
			t.Errorf("log line has limit_hit %q, offence %q and ban_expires %q, "+
				"want %s, limit and none", line.LimitHit, line.Offence, line.BanExpires,
				minuteBytes)
		}
	}

	if held := server.Ledger.Snapshot(); len(held) != 0 {
		t.Errorf("the ledger holds %+v, want no ban", held)
	}

	waiting := queue.Snapshot().Waiting[alerts.DestinationWebhook]
	if len(waiting) != 1 {
		t.Fatalf("%d alerts wait, want 1: %+v", len(waiting), waiting)
	}

	notes, _ := waiting[0].Detail["notes"].(bans.Notes)
	alert := banAlert(alerts.EventBan, start, client, bans.Ban{
		Netblock: netip.MustParsePrefix(client + "/32"), Cause: bans.CauseLimit,
		Reason: "bytes per minute over the limit of " + byteLimit, Notes: notes,
	}, requestlog.FormatTime(start.Add(time.Hour)))
	alert.Detail["mode"] = observe
	wantAlerts(t, queue, alert)
}

func TestObserveModeLeavesOutTheBytesOfARequestEnforceModeRefuses(t *testing.T) {
	t.Parallel()

	s, _ := startWithAnswers(t, map[string]string{
		mode:                observe,
		rateLimitPerMinute:  "1",
		bytesLimitPerMinute: "150",
	})

	s.upload()

	// The second request breaks the rate limit, which in enforce mode would
	// refuse it before the app sent anything, so its 100 bytes are not
	// counted, and the byte limit is not broken. Its line gives the bytes
	// counted before it.
	line := s.upload()
	wantWouldAction(t, line, requestlog.ActionRateLimited)

	if line.LimitHit != minute || line.Counts.MinuteBytes != bodyBytes+answerBytes {
		t.Errorf("log line has limit_hit %q and minute_bytes %v, want minute and %d",
			line.LimitHit, line.Counts.MinuteBytes, bodyBytes+answerBytes)
	}
}

// uploadHeader and uploadBody are the header and the body of a request
// with a body of bodyBytes.
//
//nolint:gochecknoglobals // a constant cannot call strings.Repeat
var (
	uploadHeader = "Content-Length: " + strconv.Itoa(bodyBytes)
	uploadBody   = strings.Repeat("u", bodyBytes)
)

// readAndAnswer is the app of these tests: it reads each request's whole
// body and answers with answerBytes bytes.
func readAndAnswer(w http.ResponseWriter, r *http.Request) {
	_, _ = io.Copy(io.Discard, r.Body)
	_, _ = io.WriteString(w, strings.Repeat("a", answerBytes))
}

// breakOff is an app that announces an answer of twice answerBytes, and
// breaks off after answerBytes.
func breakOff(w http.ResponseWriter, _ *http.Request) {
	w.Header().Set("Content-Length", strconv.Itoa(2*answerBytes))
	_, _ = io.WriteString(w, strings.Repeat("a", answerBytes))
}

// answerAfterUpgrade is an app that switches protocols, as for a
// WebSocket, and then answers each line it receives with a line of
// answerBytes.
func answerAfterUpgrade(w http.ResponseWriter, _ *http.Request) {
	conn, buffered, err := http.NewResponseController(w).Hijack()
	if err != nil {
		return
	}

	defer func() {
		_ = conn.Close()
	}()

	_, _ = buffered.WriteString("HTTP/1.1 101 Switching Protocols\r\n" +
		"Connection: Upgrade\r\nUpgrade: websocket\r\n\r\n")
	_ = buffered.Flush()

	for {
		_, err := buffered.ReadString('\n')
		if err != nil {
			return
		}

		_, _ = buffered.WriteString(strings.Repeat("a", answerBytes-1) + "\n")
		_ = buffered.Flush()
	}
}

// webSocket opens a WebSocket from client to answerAfterUpgrade, sends a
// line of bodyBytes on it, reads the answer, and closes it. It checks the
// answer, and the log line as request does, and returns the log line.
func (s *sender) webSocket() logLine {
	s.t.Helper()

	conn, reader := s.openWebSocket()
	send(s.t, conn, strings.Repeat("u", bodyBytes-1)+"\n")

	got, err := reader.ReadString('\n')
	if err != nil || len(got) != answerBytes {
		s.t.Errorf("got %d bytes (%v), want %d", len(got), err, answerBytes)
	}

	return s.closeWebSocket(conn)
}

// openWebSocket sends a request from client to switch protocols, as for a
// WebSocket, and checks that the app switches. It returns the connection,
// on which reading fails once waitLimit has passed, and a reader of what
// the app sends on it.
func (s *sender) openWebSocket() (net.Conn, *bufio.Reader) {
	s.t.Helper()

	conn := dial(s.t, s.addr)
	send(s.t, conn, "GET /socket HTTP/1.1\r\nHost: "+appHost+"\r\n"+forwardedFor+
		": "+client+"\r\nConnection: Upgrade\r\nUpgrade: websocket\r\n\r\n")

	err := conn.SetReadDeadline(time.Now().Add(waitLimit))
	if err != nil {
		s.t.Fatalf("set read deadline: %v", err)
	}

	reader := bufio.NewReader(conn)

	res, err := http.ReadResponse(reader, nil)
	if err != nil {
		s.t.Fatalf("read the answer to the upgrade: %v", err)
	}

	_ = res.Body.Close()

	if res.StatusCode != http.StatusSwitchingProtocols {
		s.t.Fatalf("status %d, want %d", res.StatusCode, http.StatusSwitchingProtocols)
	}

	return conn, reader
}

// closeWebSocket closes conn, a WebSocket openWebSocket opened, checks its
// log line as request does, and returns it.
func (s *sender) closeWebSocket(conn net.Conn) logLine {
	s.t.Helper()

	_ = conn.Close()

	line := s.out.endedLines(s.t, s.sent+1)[s.sent]
	s.sent++
	wantLine(s.t, line, http.StatusSwitchingProtocols, requestlog.ActionForward)

	return line
}

// startWithAnswers is startAppWithAlerts in front of readAndAnswer, for a
// test that looks at neither the server nor the alerts.
func startWithAnswers(t *testing.T, env map[string]string) (*sender, *clock) {
	t.Helper()

	s, clk, _, _ := startAppWithAlerts(t, readAndAnswer, env)

	return s, clk
}

// download sends a GET request for / from client, and checks that the
// app's answer is passed on, as request does. It returns the log line and
// the answer.
func (s *sender) download() (logLine, answer) {
	s.t.Helper()

	return s.requestWithBody(http.MethodGet, client, "/", "", "", http.StatusOK,
		requestlog.ActionForward)
}

// upload is download for a POST request with a body of bodyBytes, and
// returns the log line.
func (s *sender) upload() logLine {
	s.t.Helper()

	line, _ := s.requestWithBody(http.MethodPost, client, "/", uploadHeader,
		uploadBody, http.StatusOK, requestlog.ActionForward)

	return line
}