netwatch/backend/internal/middleware/middleware_test.go

package middleware_test

import (
	"bytes"
	"encoding/json"
	"errors"
	"log/slog"
	"net/http"
	"net/http/httptest"
	"net/netip"
	"strings"
	"testing"
	"testing/synctest"
	"time"

	"sneak.berlin/go/netwatch/internal/middleware"
)

const (
	// loopbackPeer is a remote address inside the trusted-proxy allowlist.
	loopbackPeer = "127.0.0.1:5000"
	// forwardedIP is the client address presented via X-Forwarded-For.
	forwardedIP = "203.0.113.7"
	// realIP is the client address presented via X-Real-IP.
	realIP = "203.0.113.9"
)

func mustPrefixes(t *testing.T, cidrs ...string) []netip.Prefix {
	t.Helper()

	prefixes, err := middleware.ParseTrustedProxies(cidrs)
	if err != nil {
		t.Fatalf("ParseTrustedProxies(%v): %v", cidrs, err)
	}

	return prefixes
}

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

	_, err := middleware.ParseTrustedProxies([]string{"not-a-cidr"})
	if err == nil {
		t.Fatal("expected error for malformed CIDR, got nil")
	}
}

type clientIPCase struct {
	name       string
	remoteAddr string
	xff        string
	xRealIP    string
	want       string
}

func clientIPCases() []clientIPCase {
	return []clientIPCase{
		{
			name:       "trusted proxy uses forwarded-for",
			remoteAddr: loopbackPeer,
			xff:        forwardedIP,
			want:       forwardedIP,
		},
		{
			name:       "trusted proxy uses left-most of chain",
			remoteAddr: "10.1.2.3:5000",
			xff:        forwardedIP + ", 10.1.2.3",
			want:       forwardedIP,
		},
		{
			name:       "trusted proxy falls back to x-real-ip",
			remoteAddr: loopbackPeer,
			xRealIP:    realIP,
			want:       realIP,
		},
		{
			name:       "untrusted peer ignores forwarded-for",
			remoteAddr: "198.51.100.4:5000",
			xff:        forwardedIP,
			want:       "198.51.100.4",
		},
		{
			name:       "untrusted peer ignores x-real-ip",
			remoteAddr: "198.51.100.4:5000",
			xRealIP:    realIP,
			want:       "198.51.100.4",
		},
		{
			name:       "trusted proxy with no headers uses peer",
			remoteAddr: "10.1.2.3:5000",
			want:       "10.1.2.3",
		},
		{
			name:       "trusted proxy with garbage header uses peer",
			remoteAddr: loopbackPeer,
			xff:        "not-an-ip",
			want:       "127.0.0.1",
		},
	}
}

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

	trusted := mustPrefixes(t, "127.0.0.1/32", "::1/128", "10.0.0.0/8")

	for _, tc := range clientIPCases() {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			header := http.Header{}
			if tc.xff != "" {
				header.Set("X-Forwarded-For", tc.xff)
			}

			if tc.xRealIP != "" {
				header.Set("X-Real-IP", tc.xRealIP)
			}

			got := middleware.ClientIP(tc.remoteAddr, header, trusted)
			if got != tc.want {
				t.Errorf("ClientIP() = %q, want %q", got, tc.want)
			}
		})
	}
}

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

	handler := (&middleware.Middleware{}).SecurityHeaders()(
		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
			w.WriteHeader(http.StatusOK)
		}),
	)

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
	handler.ServeHTTP(rec, req)

	want := map[string]string{
		"Strict-Transport-Security": "max-age=31536000; includeSubDomains",
		"Content-Security-Policy":   "default-src 'none'; frame-ancestors 'none'",
		"X-Frame-Options":           "DENY",
		"X-Content-Type-Options":    "nosniff",
		"Referrer-Policy":           "no-referrer",
		"Permissions-Policy":        "camera=(), microphone=(), geolocation=()",
	}

	for name, value := range want {
		if got := rec.Header().Get(name); got != value {
			t.Errorf("header %s = %q, want %q", name, got, value)
		}
	}
}

// TestMaxBodyBytesRejectsOversizeOnNonReadingRoute confirms the
// limit is enforced even for a handler that never reads the body
// (for example the health check), via the Content-Length check.
func TestMaxBodyBytesRejectsOversizeOnNonReadingRoute(t *testing.T) {
	t.Parallel()

	const limit = 16

	called := false
	handler := (&middleware.Middleware{}).MaxBodyBytes(limit)(
		http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
			called = true
		}),
	)

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(),
		http.MethodPost, "/.well-known/healthcheck",
		strings.NewReader(strings.Repeat("x", limit+1)),
	)
	handler.ServeHTTP(rec, req)

	if rec.Code != http.StatusRequestEntityTooLarge {
		t.Fatalf("status = %d, want %d",
			rec.Code, http.StatusRequestEntityTooLarge)
	}

	if called {
		t.Fatal("handler ran despite oversize body")
	}

	if got := rec.Body.String(); got != "{\"status\":\"error\"}\n" {
		t.Errorf("body = %q, want %q", got, "{\"status\":\"error\"}\n")
	}

	got := rec.Header().Get("Content-Type")
	if got != "application/json; charset=utf-8" {
		t.Errorf("Content-Type = %q, want a JSON content type", got)
	}
}

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

	const limit = 64

	handler := (&middleware.Middleware{}).MaxBodyBytes(limit)(
		http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
			w.WriteHeader(http.StatusOK)
		}),
	)

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(),
		http.MethodPost, "/api/v1/reports",
		strings.NewReader(`{"clientId":"c1"}`),
	)
	handler.ServeHTTP(rec, req)

	if rec.Code != http.StatusOK {
		t.Fatalf("status = %d, want %d", rec.Code, http.StatusOK)
	}
}

func TestRecovererReturns500AndLogsThroughSlog(t *testing.T) {
	t.Parallel()

	var logbuf bytes.Buffer

	mw := middleware.NewWithLogger(
		slog.New(slog.NewJSONHandler(&logbuf, nil)),
	)

	handler := mw.Recoverer()(
		http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
			panic("boom")
		}),
	)

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)
	handler.ServeHTTP(rec, req)

	if rec.Code != http.StatusInternalServerError {
		t.Fatalf("status = %d, want %d",
			rec.Code, http.StatusInternalServerError)
	}

	var record map[string]any

	err := json.Unmarshal(logbuf.Bytes(), &record)
	if err != nil {
		t.Fatalf("panic log is not one JSON record: %v (%q)", err, logbuf.String())
	}

	if record["msg"] != "panic recovered" || record["level"] != "ERROR" {
		t.Errorf("log record = %v, want msg %q at level ERROR",
			record, "panic recovered")
	}

	if record["panic"] != "boom" {
		t.Errorf("panic field = %v, want %q", record["panic"], "boom")
	}

	stack, _ := record["stack"].(string)
	if !strings.HasPrefix(stack, "goroutine ") {
		t.Errorf("stack field = %q, want a stack trace", stack)
	}
}

// TestRecovererRepanicsOnAbortHandler checks that a handler aborting
// with http.ErrAbortHandler is not treated as a crash: Recoverer
// panics again so the server aborts the response, and logs nothing.
func TestRecovererRepanicsOnAbortHandler(t *testing.T) {
	t.Parallel()

	var logbuf bytes.Buffer

	mw := middleware.NewWithLogger(
		slog.New(slog.NewJSONHandler(&logbuf, nil)),
	)

	handler := mw.Recoverer()(
		http.HandlerFunc(func(_ http.ResponseWriter, _ *http.Request) {
			panic(http.ErrAbortHandler)
		}),
	)

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", http.NoBody)

	var recovered any

	func() {
		defer func() { recovered = recover() }()

		handler.ServeHTTP(rec, req)
	}()

	err, _ := recovered.(error)
	if !errors.Is(err, http.ErrAbortHandler) {
		t.Errorf("Recoverer panicked with %v, want http.ErrAbortHandler", recovered)
	}

	if logbuf.Len() != 0 {
		t.Errorf("abort was logged: %q", logbuf.String())
	}
}

// okHandler stands in for the route a middleware guards.
func okHandler() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, _ *http.Request) {
		w.WriteHeader(http.StatusOK)
	})
}

// TestRateLimitRefusesPastAllowanceThenResets checks one client
// address: it may use its whole allowance at once, the next request
// is refused with 429, and later it may send again.
func TestRateLimitRefusesPastAllowanceThenResets(t *testing.T) {
	t.Parallel()

	// synctest runs this on a fake clock: time.Sleep returns at once,
	// with the clock moved on.
	synctest.Test(t, func(t *testing.T) {
		const perMinute = 2

		handler := (&middleware.Middleware{}).RateLimit(perMinute)(okHandler())

		post := func() *httptest.ResponseRecorder {
			rec := httptest.NewRecorder()
			req := httptest.NewRequestWithContext(t.Context(),
				http.MethodPost, "/api/v1/reports", http.NoBody)
			handler.ServeHTTP(rec, req)

			return rec
		}

		for i := range perMinute {
			if code := post().Code; code != http.StatusOK {
				t.Fatalf("request %d: status = %d, want %d",
					i+1, code, http.StatusOK)
			}
		}

		rec := post()
		if rec.Code != http.StatusTooManyRequests {
			t.Fatalf("request past the allowance: status = %d, want %d",
				rec.Code, http.StatusTooManyRequests)
		}

		if got := rec.Body.String(); got != "{\"status\":\"error\"}\n" {
			t.Errorf("body = %q, want %q", got, "{\"status\":\"error\"}\n")
		}

		if got := rec.Header().Get("Retry-After"); got != "60" {
			t.Fatalf("Retry-After = %q, want %q", got, "60")
		}

		// httprate also counts the previous minute's requests, fading
		// them out over the current one, so two minutes on the whole
		// allowance is back.
		time.Sleep(2 * time.Minute)

		for i := range perMinute {
			if code := post().Code; code != http.StatusOK {
				t.Fatalf("two minutes later, request %d: status = %d, want %d",
					i+1, code, http.StatusOK)
			}
		}
	})
}

// postForwarded sends handler a report from peer that names client in
// X-Forwarded-For, and returns the status.
func postForwarded(
	t *testing.T,
	handler http.Handler,
	peer, client string,
) int {
	t.Helper()

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(),
		http.MethodPost, "/api/v1/reports", http.NoBody)
	req.RemoteAddr = peer
	req.Header.Set("X-Forwarded-For", client)
	handler.ServeHTTP(rec, req)

	return rec.Code
}

// TestRateLimitIsPerForwardedClient checks that clients behind a
// trusted proxy each get their own allowance: the limit is keyed on
// the client address clientIP resolves, not on the proxy's.
func TestRateLimitIsPerForwardedClient(t *testing.T) {
	t.Parallel()

	const otherClient = "203.0.113.8"

	mw := middleware.NewWithTrustedProxies(mustPrefixes(t, "127.0.0.1/32"))
	handler := mw.RateLimit(1)(okHandler())

	code := postForwarded(t, handler, loopbackPeer, forwardedIP)
	if code != http.StatusOK {
		t.Fatalf("first request: status = %d, want %d", code, http.StatusOK)
	}

	code = postForwarded(t, handler, loopbackPeer, forwardedIP)
	if code != http.StatusTooManyRequests {
		t.Fatalf("same client again: status = %d, want %d",
			code, http.StatusTooManyRequests)
	}

	code = postForwarded(t, handler, loopbackPeer, otherClient)
	if code != http.StatusOK {
		t.Fatalf("other client behind the same proxy: status = %d, want %d",
			code, http.StatusOK)
	}
}

// TestRateLimitIgnoresForwardedForFromUntrustedPeer checks that a
// peer that is not a trusted proxy cannot get a fresh allowance by
// naming a different client in X-Forwarded-For on each request.
func TestRateLimitIgnoresForwardedForFromUntrustedPeer(t *testing.T) {
	t.Parallel()

	const untrustedPeer = "198.51.100.4:5000"

	mw := middleware.NewWithTrustedProxies(mustPrefixes(t, "127.0.0.1/32"))
	handler := mw.RateLimit(1)(okHandler())

	code := postForwarded(t, handler, untrustedPeer, "203.0.113.8")
	if code != http.StatusOK {
		t.Fatalf("first request: status = %d, want %d", code, http.StatusOK)
	}

	code = postForwarded(t, handler, untrustedPeer, "203.0.113.9")
	if code != http.StatusTooManyRequests {
		t.Fatalf("same peer naming another client: status = %d, want %d",
			code, http.StatusTooManyRequests)
	}
}

// preflight sends cors the preflight request a browser makes before
// it POSTs JSON from origin.
func preflight(
	t *testing.T,
	cors func(http.Handler) http.Handler,
	origin string,
) *httptest.ResponseRecorder {
	t.Helper()

	rec := httptest.NewRecorder()
	req := httptest.NewRequestWithContext(t.Context(),
		http.MethodOptions, "/api/v1/reports", http.NoBody)
	req.Header.Set("Origin", origin)
	req.Header.Set("Access-Control-Request-Method", http.MethodPost)
	req.Header.Set("Access-Control-Request-Headers", "content-type")
	cors(okHandler()).ServeHTTP(rec, req)

	return rec
}

// TestCORSWithoutOriginsAddsNoHeaders checks the default: with no
// origins configured, no origin is given any CORS header.
func TestCORSWithoutOriginsAddsNoHeaders(t *testing.T) {
	t.Parallel()

	rec := preflight(t,
		(&middleware.Middleware{}).CORS(nil), "https://elsewhere.example")

	for name := range rec.Header() {
		if strings.HasPrefix(name, "Access-Control-") {
			t.Errorf("CORS header %s set with no origins configured", name)
		}
	}
}

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

	const listed = "https://netwatch.example"

	cors := (&middleware.Middleware{}).CORS([]string{listed})

	cases := []struct {
		name   string
		origin string
		want   string
	}{
		{name: "listed origin allowed", origin: listed, want: listed},
		{name: "other origin refused", origin: "https://elsewhere.example"},
	}

	for _, tc := range cases {
		t.Run(tc.name, func(t *testing.T) {
			t.Parallel()

			rec := preflight(t, cors, tc.origin)

			got := rec.Header().Get("Access-Control-Allow-Origin")
			if got != tc.want {
				t.Errorf("Access-Control-Allow-Origin = %q, want %q",
					got, tc.want)
			}
		})
	}
}