pixa/internal/handlers/bodylimit_internal_test.go

package handlers

import (
	"log/slog"
	"net/http"
	"net/url"
	"strings"
	"testing"

	"github.com/go-chi/chi/v5"

	"sneak.berlin/go/pixa/internal/config"
	"sneak.berlin/go/pixa/internal/encurl"
	"sneak.berlin/go/pixa/internal/seal"
	"sneak.berlin/go/pixa/internal/session"
)

// Form field names and a throwaway source image URL for the body-limit
// tests.
const (
	sourceURLField = "url"
	testSourceURL  = "https://example.com/a.jpg"
)

// newBodyLimitTestRouter mirrors the production wiring for the form POST
// routes (see server.SetupRoutes): LimitBody sits in front of the CSRF
// middleware, which sits in front of the handlers. maxBytes is the body
// cap under test, so a test can trip the limit with a small body.
func newBodyLimitTestRouter(
	t *testing.T, maxBytes int64,
) (*Handlers, http.Handler) {
	t.Helper()

	cfg := &config.Config{SigningKey: testSigningKey, Debug: true}

	keys, err := seal.DeriveKeys(testSigningKey)
	if err != nil {
		t.Fatalf("seal.DeriveKeys() error = %v", err)
	}

	h := &Handlers{
		log:         slog.New(slog.DiscardHandler),
		config:      cfg,
		sessMgr:     session.NewManager(keys.SessionHashKey, keys.SessionBlockKey),
		encGen:      encurl.NewGenerator(keys.EncryptedURLKey),
		csrfProtect: newCSRFProtect(keys.CSRFKey, cfg.Debug),
	}

	r := chi.NewRouter()
	r.Group(func(r chi.Router) {
		r.Use(h.LimitBody(maxBytes))
		r.Use(h.CSRF())
		r.Get("/", h.HandleRoot())
		r.Post("/", h.HandleRoot())
		r.Post("/generate", h.HandleGenerateURL())
	})

	return h, r
}

// TestOversizedLoginPostRejectedBeforeCSRF is the core regression: an
// oversized POST / carrying an otherwise valid CSRF cookie and token must
// be rejected with 413. If the body limit ran after CSRF, the truncated
// body would read as a missing token and return 403; if it ran after the
// handler, a valid token would return 303. Getting 413 proves the limit
// fires before CSRF parses the form.
func TestOversizedLoginPostRejectedBeforeCSRF(t *testing.T) {
	t.Parallel()

	_, srv := newBodyLimitTestRouter(t, 16)

	cookies, token := csrfCredentials(t, srv, nil)

	rec := postForm(srv, "/", cookies, url.Values{
		loginKeyField:  {testSigningKey},
		csrfTokenField: {token},
	})

	if rec.Code != http.StatusRequestEntityTooLarge {
		t.Errorf("oversized POST / status = %d, want %d",
			rec.Code, http.StatusRequestEntityTooLarge)
	}
}

// TestOversizedGeneratePostRejectedBeforeCSRF is the same regression for
// POST /generate, which also parses a form behind CSRF.
func TestOversizedGeneratePostRejectedBeforeCSRF(t *testing.T) {
	t.Parallel()

	h, srv := newBodyLimitTestRouter(t, 16)

	sessionCookie := newSessionCookie(t, h)

	cookies, token := csrfCredentials(t, srv, []*http.Cookie{sessionCookie})
	cookies = append(cookies, sessionCookie)

	rec := postForm(srv, "/generate", cookies, url.Values{
		sourceURLField: {testSourceURL},
		csrfTokenField: {token},
	})

	if rec.Code != http.StatusRequestEntityTooLarge {
		t.Errorf("oversized POST /generate status = %d, want %d",
			rec.Code, http.StatusRequestEntityTooLarge)
	}
}

// TestWithinLimitLoginPostSucceeds verifies the limit does not disturb a
// normal request: under the production cap, a valid login still parses and
// establishes a session (303). This guards against the body limit
// consuming or corrupting the form the CSRF check and handler depend on.
func TestWithinLimitLoginPostSucceeds(t *testing.T) {
	t.Parallel()

	_, srv := newBodyLimitTestRouter(t, MaxFormBytes)

	cookies, token := csrfCredentials(t, srv, nil)

	rec := postForm(srv, "/", cookies, url.Values{
		loginKeyField:  {testSigningKey},
		csrfTokenField: {token},
	})

	if rec.Code != http.StatusSeeOther {
		t.Fatalf("within-limit POST / status = %d, want %d",
			rec.Code, http.StatusSeeOther)
	}

	var authed bool

	for _, c := range rec.Result().Cookies() {
		if c.Name == session.CookieName && c.Value != "" {
			authed = true
		}
	}

	if !authed {
		t.Error("within-limit valid login did not set a session cookie")
	}
}

// TestWithinLimitGeneratePostSucceeds is the same non-regression check for
// POST /generate.
func TestWithinLimitGeneratePostSucceeds(t *testing.T) {
	t.Parallel()

	h, srv := newBodyLimitTestRouter(t, MaxFormBytes)

	sessionCookie := newSessionCookie(t, h)

	cookies, token := csrfCredentials(t, srv, []*http.Cookie{sessionCookie})
	cookies = append(cookies, sessionCookie)

	rec := postForm(srv, "/generate", cookies, url.Values{
		sourceURLField: {testSourceURL},
		"format":       {"jpeg"},
		csrfTokenField: {token},
	})

	if rec.Code != http.StatusOK {
		t.Fatalf("within-limit POST /generate status = %d, want %d",
			rec.Code, http.StatusOK)
	}

	if !strings.Contains(rec.Body.String(), "/v1/e/") {
		t.Error("within-limit generate response did not contain a generated URL")
	}
}