Say that losing the state directory forgets the latest logout (part of #256)

The state directory bullet in README.md and the session package doc now
say that the time of the latest logout is kept in the database, which a
restart without a persistent volume loses.

Model: opus-5-5

README.md

@@ -26,6 +26,11 @@ make docker
 docker run -p 8080:8080 -e PIXA_SIGNING_KEY="$(openssl rand -base64 32)" pixa:latest
 ```
 
+The example config allowlists no host (`allowlist_hosts`), so pixa serves an
+image only for a signed or encrypted URL. Every image on an allowlisted host is
+served to anyone without a signature, at any size and in any format, so
+allowlist only hosts you control, where nobody else can put images.
+
 A container takes its settings from environment variables (see Configuration
 below for the list). Only `PIXA_SIGNING_KEY` is required; if it is unset the
 container exits at startup naming the variable. Everything else has a built-in
@@ -66,9 +71,10 @@ The state directory (`state_dir`, `/var/lib/pixa` in the container) holds the
 database and the disk cache:
 
 - It needs a persistent volume: without one, every restart starts with an empty
-  cache. In the container, the startup script gives the directory to the user
-  pixa runs as (uid 65532) and sets its mode to `750`; outside it, that user
-  must be able to write the directory.
+  cache and forgets the latest logout, so the login sessions that logout ended
+  work again (see Encrypted URLs). In the container, the startup script gives
+  the directory to the user pixa runs as (uid 65532) and sets its mode to `750`;
+  outside it, that user must be able to write the directory.
 - `cache_max_bytes` limits the source and transformed images together. The
   database, the metadata files, the `.meta` file beside each transformed image
   and files still being written come on top, and eviction runs in the
@@ -115,7 +121,9 @@ What the [upaas](https://git.eeqj.de/sneak/upaas) app for pixa needs:
     - `PIXA_SIGNING_KEY` (required): secret for signed and encrypted URLs and
       login, 32+ characters, for example from `openssl rand -base64 32`
     - `PIXA_ALLOWLIST_HOSTS`: upstream hosts served without a signature,
-      comma-separated
+      comma-separated; default none. Every image on a listed host is served to
+      anyone without a signature, so list only hosts you control, where nobody
+      else can put images.
     - `PIXA_CACHE_MAX_BYTES`: disk cache limit in bytes; `0` disables it;
       default 75% of (free space + what the cache holds)
     - the rest are in the table under Configuration below
@@ -177,7 +185,10 @@ path under `/v1/` answers 200, in maintenance mode too.
   session it answers 303 to `/`. Answers: 200 with the page showing the URL; 400
   with the page naming a field that is not valid; 500 when the URL cannot be
   made.
-- `GET /logout` — end the login session. Needs: nothing. Answers: 303 to `/`.
+- `GET /logout` — end every login session, in every browser (see Encrypted
+  URLs), and remove the session cookie. Needs: a login session; without one it
+  only removes the cookie. Answers: 303 to `/`; 500 when the logout cannot be
+  saved in the database.
 - `GET` or `HEAD` `/v1/image/<host>/<path>/<size>.<format>`, or
   `/v1/image/<host>/<path>/<size>` with no format — an image, fetched, resized
   and converted (below). Needs: a signature, unless the host is allowlisted (see
@@ -263,6 +274,12 @@ once, is refused with 400.
   both optional (values under Signature Specification). Both are part of what is
   cached, so each value of either is a separate cached image.
 
+A size with one side `0` has that side scaled to keep the source's proportions,
+and is refused with 400 when that side would come out above 8192, the most
+either side may be; so is a size with `fit=outside`, which scales the image to
+cover the size and so past it on one side, when that side would come out
+above 8192.
+
 The source image may be JPEG, PNG, GIF, WebP, AVIF or JPEG XL. The upstream's
 `Content-Type` must name its format, and the image's first bytes must match it.
 An upstream answering with any other `Content-Type`, SVG included, is refused
@@ -339,13 +356,18 @@ nor change what it asks for.
 
 1. Open `/` in a browser over HTTPS (or over plain HTTP while `debug` is on, see
    Routes) and log in with the signing key (`signing_key`). The login session
-   lasts 30 days, or until `/logout`.
+   lasts 30 days, or until someone logs out at `/logout`. Every login is made
+   with the one signing key, so logging out ends every login session, in every
+   browser: pixa saves the time of the latest logout in its database and refuses
+   a login session made before it, a copy of the session cookie included, also
+   after a restart that keeps the state directory (see Deployment).
 2. On the generator page, give the source image's URL, the width and height, the
    format, quality and fit, and how long the URL lasts, then submit the form
    (`POST /generate`). The format is JPEG XL unless another is chosen; a form
    sent with an empty format, or none, also makes a JPEG XL URL. Width and
    height both empty or `0` keep the original size; if only one of them is empty
-   or `0`, that side is scaled to keep the image's proportions.
+   or `0`, that side is scaled to keep the image's proportions. A URL whose
+   scaled side would come out above 8192 answers 400.
 3. The page shows the URL, `https://<host>/v1/e/<token>/img.<format>`, and when
    it expires. `<host>` is the host the page was opened on, and the URL starts
    with `http` instead while `debug` is on. The name after the token is ignored

TODO.md

@@ -30,6 +30,51 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
+- 2026-10-15 logging out ends every login session (closes #256): a login session
+  was a cookie with nothing kept on the server, so `/logout` removed it from one
+  browser and a copy of it kept working for its 30 days. Every login is made
+  with the one signing key, so `/logout` now ends them all: the session manager
+  keeps the time of the latest logout, saves it in the new `logout` table so
+  that it outlasts a restart, and refuses a session made before it. A restart
+  without a persistent volume for the state directory forgets it. A `/logout`
+  without a valid login session, such as one another site makes a browser send
+  without the `SameSite=Strict` cookie, ends none and only removes the cookie. A
+  logout that cannot be saved answers 500. `session.NewManager`, which the tests
+  use, keeps logouts in memory only; pixad uses
+  `session.NewManagerWithDatabase`.
+- 2026-10-15 the example config allowlists no host (closes #249): it allowlisted
+  `github.com` and `user-images.githubusercontent.com`, where anyone can put an
+  image, so a deployment set up as Getting Started says served those images to
+  anyone without a signature, at any size and in any format.
+  `configs/config.example.yml` now leaves `allowlist_hosts` out, with one
+  commented entry under `example.com`. Getting Started and "Running under upaas"
+  in `README.md` say that every image on an allowlisted host is served without a
+  signature, so an allowlisted host must be one the operator controls.
+- 2026-10-15 a chunked upstream body of exactly `upstream_max_response_size`
+  bytes is accepted (closes #248): once the limit was used up, the fetcher's
+  next read refused the body without looking for its end. Go's HTTP client
+  returns the end of a body sent with a `Content-Length` together with its last
+  bytes, but the end of a chunked body can come in a later read, so such a body
+  was refused after it had been downloaded whole, and the image routes
+  answered 500. Once the limit is used up, the fetcher now reads one more byte:
+  if the body has ended it is accepted, and if there is more it is refused with
+  `ErrResponseTooLarge`, as before.
+- 2026-10-13 `fit=outside` no longer makes an output above 8192 on a side
+  (closes #257): it scales the image to cover the requested size, and the side
+  scaled past that size was held to no maximum, so `1x8192?fit=outside` of a
+  3000x600 source was resized to 40960x8192 and encoded. The image processor now
+  refuses such a size with `ErrOutputTooLarge` before resizing, and both image
+  routes answer it 400, as for a size with one side `0`. The other fit modes
+  make the requested size or one within it, so none can go above 8192.
+- 2026-10-13 a size with one side `0` no longer makes an output above 8192 on a
+  side (closes #241): that side is computed from the source's proportions, and
+  nothing held it to the 8192 a requested side is held to, so `0x8192` of a
+  3000x600 source was resized to 40960x8192 and encoded. The image processor now
+  refuses such a size with `ErrOutputTooLarge` once it knows the source's
+  dimensions, before resizing, and both image routes answer it 400 with the JSON
+  error body. The refusal is not cached as a failed fetch, so the same source is
+  still served at other sizes. `imgcache.MaxDimension` is now the image
+  processor's `MaxOutputDimension`, so the two cannot differ.
 - 2026-10-13 the unused cache lifetime is removed (closes #69):
   `CacheConfig.CacheTTL`, which pixad set to `DefaultCacheTTL` (24 hours), was
   never read, so cached images never expired. The field and the constant are

configs/config.example.yml

@@ -45,15 +45,14 @@ state_dir: ./data
 signing_key: "CHANGE_ME_generate_with_openssl_rand_base64_32"
 
 # Hosts that don't require signatures (default: none)
+# Every image on an allowlisted host is served to anyone without a
+# signature, at any size and in any format, so list only hosts you
+# control, where nobody else can put images.
 # Use "." prefix for wildcard subdomain matching (e.g., ".example.com" matches "cdn.example.com")
 # An entry that is neither a host name nor an IP address (IPv6 without
 # brackets), such as one with a port or a "*." wildcard, aborts startup.
-allowlist_hosts:
-  - s3.sneak.cloud
-  - static.sneak.cloud
-  - sneak.berlin
-  - github.com
-  - user-images.githubusercontent.com
+# allowlist_hosts:
+#   - images.example.com
 
 # Hosts whose pages may not show pixa's images, written as for
 # allowlist_hosts. A request to /v1/image/ or /v1/e/ whose Referer header

internal/config/config_internal_test.go

@@ -92,6 +92,32 @@ func TestGetStringSlice_Empty(t *testing.T) {
 	}
 }
 
+// TestExampleConfigAllowlistsNoHost loads configs/config.example.yml
+// with a real signing key, as Getting Started in README.md has it copied
+// and edited, and checks that it allowlists no host: every image on an
+// allowlisted host is served to anyone without a signature.
+func TestExampleConfigAllowlistsNoHost(t *testing.T) {
+	t.Setenv("PIXA_SIGNING_KEY", validTestSigningKey)
+
+	examplePath := filepath.Join("..", "..", "configs", "config.example.yml")
+
+	sc, err := loadTestConfig(examplePath)
+	if err != nil {
+		t.Fatalf("failed to load %s: %v", examplePath, err)
+	}
+
+	c, err := newFromSmartConfig(sc)
+	if err != nil {
+		t.Fatalf("%s is not a valid config: %v", examplePath, err)
+	}
+
+	t.Logf("allowlist_hosts in %s: %v", examplePath, c.AllowlistHosts)
+
+	if len(c.AllowlistHosts) != 0 {
+		t.Errorf("%s allowlists %v, want no host", examplePath, c.AllowlistHosts)
+	}
+}
+
 // loadTestConfig is a helper to load a config file for testing.
 func loadTestConfig(path string) (*smartconfig.Config, error) {
 	return smartconfig.NewFromConfigPath(path)

internal/db/migrations/001_schema.sql

@@ -176,3 +176,10 @@ CREATE TABLE IF NOT EXISTS cache_stats (
     last_updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
 );
 INSERT OR IGNORE INTO cache_stats (id) VALUES (1);
+
+-- Time of the latest logout. A login session made before it is refused,
+-- so logging out ends every login session. No row: nobody has logged out.
+CREATE TABLE IF NOT EXISTS logout (
+    id INTEGER PRIMARY KEY CHECK (id = 1),
+    logged_out_at DATETIME NOT NULL
+);

internal/handlers/auth.go

@@ -89,10 +89,18 @@ func (s *Handlers) handleLoginPost(w http.ResponseWriter, r *http.Request) {
 	http.Redirect(w, r, "/", http.StatusSeeOther)
 }
 
-// HandleLogout clears the session and redirects to login.
+// HandleLogout logs out, which ends every login session (see
+// session.Manager.Logout), and redirects to login.
 func (s *Handlers) HandleLogout() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		s.sessMgr.ClearSession(w)
+		err := s.sessMgr.Logout(w, r)
+		if err != nil {
+			s.log.Error("failed to log out", "error", err)
+			http.Error(w, "Failed to log out", http.StatusInternalServerError)
+
+			return
+		}
+
 		http.Redirect(w, r, "/", http.StatusSeeOther)
 	}
 }

internal/handlers/auth_session_internal_test.go

@@ -185,6 +185,98 @@ func TestHandleLogout_ClearsSessionCookie(t *testing.T) {
 	}
 }
 
+// TestHandleLogout_EndsCopiedSession verifies that after GET /logout a copy
+// of the session cookie taken before it shows the login page, not the
+// generator page.
+func TestHandleLogout_EndsCopiedSession(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newCSRFTestRouter(t)
+
+	copied := newSessionCookie(t, h)
+
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/logout", nil)
+	req.AddCookie(copied)
+
+	rec := httptest.NewRecorder()
+	h.HandleLogout().ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusSeeOther {
+		t.Fatalf("GET /logout status = %d, want %d",
+			rec.Code, http.StatusSeeOther)
+	}
+
+	req = httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
+	req.AddCookie(copied)
+
+	rec = httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+
+	body := rec.Body.String()
+	t.Logf("GET / with the copied cookie: status %d, login page %v",
+		rec.Code, strings.Contains(body, loginForm))
+
+	if !strings.Contains(body, loginForm) || strings.Contains(body, generatorForm) {
+		t.Error("a cookie copied before /logout still opens the generator page")
+	}
+}
+
+// TestHandleLogout_SaveFails_Answers500 verifies that when the logout cannot
+// be saved in the database, GET /logout answers 500, leaves the session
+// cookie in place and ends no session.
+func TestHandleLogout_SaveFails_Answers500(t *testing.T) {
+	t.Parallel()
+
+	h, srv := newCSRFTestRouter(t)
+
+	db := setupTestDB(t)
+
+	sessMgr, err := session.NewManagerWithDatabase(
+		t.Context(), testSigningKey, db)
+	if err != nil {
+		t.Fatalf("session.NewManagerWithDatabase() error = %v", err)
+	}
+
+	h.sessMgr = sessMgr
+	cookie := newSessionCookie(t, h)
+
+	// Saving the logout fails on a closed database.
+	err = db.Close()
+	if err != nil {
+		t.Fatalf("closing the database: %v", err)
+	}
+
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/logout", nil)
+	req.AddCookie(cookie)
+
+	rec := httptest.NewRecorder()
+	h.HandleLogout().ServeHTTP(rec, req)
+
+	t.Logf("GET /logout: status %d, Set-Cookie %q",
+		rec.Code, rec.Header().Get("Set-Cookie"))
+
+	if rec.Code != http.StatusInternalServerError {
+		t.Errorf("GET /logout status = %d, want %d",
+			rec.Code, http.StatusInternalServerError)
+	}
+
+	if c := findSessionCookie(rec); c != nil {
+		t.Errorf("a logout that failed set the session cookie: %s", c)
+	}
+
+	req = httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
+	req.AddCookie(cookie)
+
+	rec = httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+
+	if !strings.Contains(rec.Body.String(), generatorForm) {
+		t.Error("a logout that failed ended the session")
+	}
+}
+
 // TestGeneratePost_NoSession_RedirectsToLogin verifies that POST /generate
 // with a valid CSRF token but no login session answers 303 to / and makes no
 // URL.

internal/handlers/handlers.go

@@ -163,7 +163,9 @@ func (s *Handlers) initImageService() error {
 
 	// Initialize session manager (signing key is validated at config load
 	// time). Session cookies are always Secure/HttpOnly/SameSite=Strict.
-	sessMgr, err := session.NewManager(s.config.SigningKey)
+	// Logouts are saved in the database, so they outlast a restart.
+	sessMgr, err := session.NewManagerWithDatabase(
+		context.Background(), s.config.SigningKey, s.db.DB())
 	if err != nil {
 		return err
 	}

internal/handlers/image.go

@@ -255,6 +255,14 @@ func (s *Handlers) respondImageError(
 		return
 	}
 
+	if errors.Is(err, imageprocessor.ErrOutputTooLarge) {
+		s.respondError(w, fmt.Sprintf("size too large for the source: the side "+
+			"computed from its proportions is above %d",
+			imageprocessor.MaxOutputDimension), http.StatusBadRequest)
+
+		return
+	}
+
 	s.respondError(w, "internal error", http.StatusInternalServerError)
 }
 

internal/handlers/imageenc.go

@@ -165,6 +165,10 @@ func (s *Handlers) handleImageError(w http.ResponseWriter, err error) {
 		errors.Is(err, imageprocessor.ErrUnsupportedInputFormat):
 		s.respondError(w, "unsupported source format",
 			http.StatusUnsupportedMediaType)
+	case errors.Is(err, imageprocessor.ErrOutputTooLarge):
+		s.respondError(w, fmt.Sprintf("size too large for the source: the side "+
+			"computed from its proportions is above %d",
+			imageprocessor.MaxOutputDimension), http.StatusBadRequest)
 	default:
 		s.log.Error("image request failed", "error", err)
 		s.respondError(w, "internal error", http.StatusInternalServerError)

internal/httpfetcher/fetch_internal_test.go

@@ -9,6 +9,7 @@ import (
 	"net/http"
 	"net/http/httptest"
 	"slices"
+	"strconv"
 	"strings"
 	"sync"
 	"testing"
@@ -297,6 +298,139 @@ func TestFetchMaxResponseSizeEnforced(t *testing.T) {
 	}
 }
 
+// fetchWithMaxResponseSize serves handler as the fake upstream and fetches
+// its /image route with MaxResponseSize set to maxResponseSize.
+func fetchWithMaxResponseSize(
+	t *testing.T,
+	maxResponseSize int64,
+	handler http.HandlerFunc,
+) *FetchResult {
+	t.Helper()
+
+	srv := httptest.NewServer(handler)
+	t.Cleanup(srv.Close)
+
+	cfg := DefaultConfig()
+	cfg.MaxResponseSize = maxResponseSize
+
+	f, _ := newServerFetcher(t, srv, cfg)
+
+	res := fetchImage(t, f, "/image")
+	t.Cleanup(func() { _ = res.Content.Close() })
+
+	return res
+}
+
+// TestFetchContentLengthBodyAtMaxResponseSize checks that a body sent with a
+// Content-Length is read whole at exactly MaxResponseSize bytes and refused
+// at one byte more.
+func TestFetchContentLengthBodyAtMaxResponseSize(t *testing.T) {
+	t.Parallel()
+
+	const maxResponseSize = 8
+
+	for _, tc := range []struct {
+		size    int
+		wantErr error
+	}{
+		{maxResponseSize, nil},
+		{maxResponseSize + 1, ErrResponseTooLarge},
+	} {
+		t.Run(strconv.Itoa(tc.size)+" bytes", func(t *testing.T) {
+			t.Parallel()
+
+			body := strings.Repeat("x", tc.size)
+
+			res := fetchWithMaxResponseSize(t, maxResponseSize,
+				func(w http.ResponseWriter, _ *http.Request) {
+					w.Header().Set("Content-Type", contentTypeJPEG)
+					w.Header().Set("Content-Length", strconv.Itoa(tc.size))
+					_, _ = io.WriteString(w, body)
+				})
+
+			if res.ContentLength != int64(tc.size) {
+				t.Fatalf("ContentLength = %d, want %d", res.ContentLength, tc.size)
+			}
+
+			data, err := io.ReadAll(res.Content)
+			t.Logf("body of %d bytes: read %d, error %v", tc.size, len(data), err)
+
+			if !errors.Is(err, tc.wantErr) {
+				t.Fatalf("read error = %v, want %v", err, tc.wantErr)
+			}
+
+			if err == nil && string(data) != body {
+				t.Errorf("read %q, want %q", data, body)
+			}
+		})
+	}
+}
+
+// TestFetchChunkedBodyAtMaxResponseSize checks that a chunked body is read
+// whole at exactly MaxResponseSize bytes and refused at one byte more. The
+// upstream sends the end of the body only once the test has read
+// MaxResponseSize bytes, so the read after them comes before the end of the
+// body has arrived, as it can from a real upstream.
+func TestFetchChunkedBodyAtMaxResponseSize(t *testing.T) {
+	t.Parallel()
+
+	const maxResponseSize = 8
+
+	for _, tc := range []struct {
+		size    int
+		wantErr error
+	}{
+		{maxResponseSize, nil},
+		{maxResponseSize + 1, ErrResponseTooLarge},
+	} {
+		t.Run(strconv.Itoa(tc.size)+" bytes", func(t *testing.T) {
+			t.Parallel()
+
+			body := strings.Repeat("x", tc.size)
+			endBody := make(chan struct{})
+
+			res := fetchWithMaxResponseSize(t, maxResponseSize,
+				func(w http.ResponseWriter, r *http.Request) {
+					w.Header().Set("Content-Type", contentTypeJPEG)
+					_, _ = io.WriteString(w, body)
+					// With no Content-Length, flushing sends the body
+					// chunked; its end is sent when the handler returns.
+					_ = http.NewResponseController(w).Flush()
+
+					select {
+					case <-endBody:
+					case <-r.Context().Done():
+					}
+				})
+
+			if res.ContentLength != -1 {
+				t.Fatalf("ContentLength = %d, want -1 (chunked)", res.ContentLength)
+			}
+
+			head := make([]byte, maxResponseSize)
+
+			_, err := io.ReadFull(res.Content, head)
+			if err != nil {
+				t.Fatalf("read the first %d bytes: %v", maxResponseSize, err)
+			}
+
+			close(endBody)
+
+			rest, err := io.ReadAll(res.Content)
+			data := string(head) + string(rest)
+			t.Logf("body of %d bytes: read %d, error %v", tc.size, len(data), err)
+
+			if !errors.Is(err, tc.wantErr) {
+				t.Fatalf("read error = %v, want %v", err, tc.wantErr)
+			}
+
+			if err == nil && data != body {
+				t.Errorf("read %q, want %q", data, body)
+			}
+		})
+	}
+}
+
 func TestFetchSemaphoreReleasedOnError(t *testing.T) {
 	t.Parallel()
 

internal/httpfetcher/httpfetcher.go

@@ -660,14 +660,33 @@ func dialSSRFSafe(
 	return nil, fmt.Errorf("%w to %s", errConnectFailed, host)
 }
 
-// limitedReader wraps a reader and limits the number of bytes read.
+// limitedReader wraps a reader and refuses a body longer than remaining
+// bytes with ErrResponseTooLarge. remaining goes below 0 once the body is
+// found to be longer.
 type limitedReader struct {
 	reader    io.Reader
 	remaining int64
 }
 
+// Read reads at most the remaining bytes. Once they are read, it reads one
+// more byte to tell the end of the body from more data: at the end it
+// returns the wrapped reader's error, io.EOF; with more data it returns
+// ErrResponseTooLarge, as does every later Read.
 func (r *limitedReader) Read(p []byte) (int, error) {
-	if r.remaining <= 0 {
+	if r.remaining < 0 {
+		return 0, ErrResponseTooLarge
+	}
+
+	if r.remaining == 0 {
+		var extra [1]byte
+
+		n, err := r.reader.Read(extra[:])
+		r.remaining -= int64(n)
+
+		if n == 0 {
+			return 0, err
+		}
+
 		return 0, ErrResponseTooLarge
 	}
 

internal/imageprocessor/computed_side_internal_test.go

@@ -0,0 +1,52 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+// TestImageProcessor_RefusesComputedSideAboveMaximum verifies that a size
+// with one side 0, which Process computes from the input's proportions, is
+// served when that side comes out at MaxOutputDimension and refused with
+// ErrOutputTooLarge when it would be above. A 4096x1 or 1x4096 input given
+// 2 for its short side has 8192 for its long side.
+func TestImageProcessor_RefusesComputedSideAboveMaximum(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name                    string
+		inputWidth, inputHeight int
+		size                    Size
+		wantErr                 error
+	}{
+		{"width at the maximum", 4096, 1, Size{Height: 2}, nil},
+		{"width above the maximum", 4096, 1, Size{Height: 3}, ErrOutputTooLarge},
+		{"height at the maximum", 1, 4096, Size{Width: 2}, nil},
+		{"height above the maximum", 1, 4096, Size{Width: 3}, ErrOutputTooLarge},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			input := createTestJPEG(t, tt.inputWidth, tt.inputHeight)
+
+			result, err := New(Params{}).Process(t.Context(),
+				bytes.NewReader(input),
+				&Request{Size: tt.size, Format: FormatJPEG, FitMode: FitCover})
+			if result != nil {
+				t.Logf("Process() made %dx%d", result.Width, result.Height)
+
+				if max(result.Width, result.Height) != MaxOutputDimension {
+					t.Errorf("Process() made %dx%d, want a side of %d",
+						result.Width, result.Height, MaxOutputDimension)
+				}
+			}
+
+			if !errors.Is(err, tt.wantErr) {
+				t.Errorf("Process() error = %v, want %v", err, tt.wantErr)
+			}
+		})
+	}
+}

internal/imageprocessor/fit_outside_internal_test.go

@@ -0,0 +1,62 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+)
+
+// TestImageProcessor_RefusesFitOutsideAboveMaximum verifies that FitOutside,
+// which scales the input to cover the requested size and so past it on one
+// side, is refused with ErrOutputTooLarge when that side would come out above
+// MaxOutputDimension, and otherwise makes the scaled size. A 1024x256 or
+// 256x1024 input scaled by 8 has 8192 for its long side.
+func TestImageProcessor_RefusesFitOutsideAboveMaximum(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name                    string
+		inputWidth, inputHeight int
+		size                    Size
+		// wantWidth and wantHeight are the output's, 0 for a refusal
+		wantWidth, wantHeight int
+	}{
+		{"width above the maximum", 3000, 600, Size{Width: 1, Height: 8192}, 0, 0},
+		{"height above the maximum", 600, 3000, Size{Width: 8192, Height: 1}, 0, 0},
+		{"width at the maximum", 1024, 256, Size{Width: 1, Height: 2048}, 8192, 2048},
+		{"height at the maximum", 256, 1024, Size{Width: 2048, Height: 1}, 2048, 8192},
+		{"within the maximum", 3000, 600, Size{Width: 1, Height: 1200}, 6000, 1200},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			input := createTestJPEG(t, tt.inputWidth, tt.inputHeight)
+
+			result, err := New(Params{}).Process(t.Context(),
+				bytes.NewReader(input),
+				&Request{Size: tt.size, Format: FormatJPEG, FitMode: FitOutside})
+			if result != nil {
+				t.Logf("Process() made %dx%d", result.Width, result.Height)
+			}
+
+			if tt.wantWidth == 0 {
+				if !errors.Is(err, ErrOutputTooLarge) {
+					t.Errorf("Process() error = %v, want %v", err, ErrOutputTooLarge)
+				}
+
+				return
+			}
+
+			if err != nil {
+				t.Fatalf("Process() error = %v", err)
+			}
+
+			if result.Width != tt.wantWidth || result.Height != tt.wantHeight {
+				t.Errorf("Process() made %dx%d, want %dx%d",
+					result.Width, result.Height, tt.wantWidth, tt.wantHeight)
+			}
+		})
+	}
+}

internal/imageprocessor/imageprocessor.go

@@ -133,6 +133,16 @@ var ErrInputTooLarge = errors.New("input image dimensions exceed maximum")
 // configured byte limit.
 var ErrInputDataTooLarge = errors.New("input data exceeds maximum allowed size")
 
+// MaxOutputDimension is the maximum width or height of an output image, and
+// so of a requested size (imgcache.MaxDimension).
+const MaxOutputDimension = 8192
+
+// ErrOutputTooLarge is returned, before resizing, when the output would have a
+// side above MaxOutputDimension: the side of a size with one side 0, computed
+// from the input's proportions, or with FitOutside, the side scaled past the
+// requested size.
+var ErrOutputTooLarge = errors.New("output image dimensions exceed maximum")
+
 // ErrUnsupportedOutputFormat is returned when the requested output format is
 // not supported.
 var ErrUnsupportedOutputFormat = errors.New("unsupported output format")
@@ -259,8 +269,11 @@ func (p *ImageProcessor) Process(
 		return nil, ErrInputTooLarge
 	}
 
-	// Determine target dimensions
-	targetWidth, targetHeight := targetDimensions(req.Size, origWidth, origHeight)
+	// Determine target dimensions; too large ones are refused before resizing
+	targetWidth, targetHeight, err := targetDimensions(req.Size, origWidth, origHeight)
+	if err != nil {
+		return nil, err
+	}
 
 	// Resize if needed
 	if targetWidth != origWidth || targetHeight != origHeight {
@@ -296,21 +309,29 @@ func (p *ImageProcessor) Process(
 
 // targetDimensions calculates the output dimensions for a requested size,
 // scaling proportionally when only one dimension is given and keeping the
-// original dimensions when both are zero.
-func targetDimensions(size Size, origWidth, origHeight int) (int, int) {
+// original dimensions when both are zero. A side scaled proportionally can
+// come out above MaxOutputDimension, which is ErrOutputTooLarge.
+func targetDimensions(size Size, origWidth, origHeight int) (int, int, error) {
+	width, height := size.Width, size.Height
+
 	switch {
-	case size.Width == 0 && size.Height == 0:
+	case width == 0 && height == 0:
 		// Both are 0: keep original size
-		return origWidth, origHeight
-	case size.Width == 0:
+		return origWidth, origHeight, nil
+	case width == 0:
 		// Only height specified: calculate width proportionally
-		return origWidth * size.Height / origHeight, size.Height
-	case size.Height == 0:
+		width = origWidth * height / origHeight
+	case height == 0:
 		// Only width specified: calculate height proportionally
-		return size.Width, origHeight * size.Width / origWidth
-	default:
-		return size.Width, size.Height
+		height = origHeight * width / origWidth
 	}
+
+	if width > MaxOutputDimension || height > MaxOutputDimension {
+		return 0, 0, fmt.Errorf("%w: %dx%d is above %d", ErrOutputTooLarge,
+			width, height, MaxOutputDimension)
+	}
+
+	return width, height, nil
 }
 
 // MIME types for the supported image formats.
@@ -441,7 +462,9 @@ func (p *ImageProcessor) detectFormat(imageType vips.ImageType) string {
 	}
 }
 
-// resize resizes the image according to the fit mode.
+// resize resizes the image according to the fit mode. With FitOutside one
+// side can come out larger than requested; when it would be above
+// MaxOutputDimension, resize returns ErrOutputTooLarge without resizing.
 func (p *ImageProcessor) resize(
 	img *vips.ImageRef, width, height int, fit FitMode,
 ) error {
@@ -489,6 +512,12 @@ func (p *ImageProcessor) resize(
 		newW := int(float64(imgW) * scale)
 		newH := int(float64(imgH) * scale)
 
+		// The dimension that exceeds the target is held to the maximum too
+		if newW > MaxOutputDimension || newH > MaxOutputDimension {
+			return fmt.Errorf("%w: %dx%d is above %d", ErrOutputTooLarge,
+				newW, newH, MaxOutputDimension)
+		}
+
 		return img.Thumbnail(newW, newH, vips.InterestingNone)
 
 	default:

internal/imgcache/urlparser.go

@@ -7,6 +7,8 @@ import (
 	"regexp"
 	"strconv"
 	"strings"
+
+	"sneak.berlin/go/pixa/internal/imageprocessor"
 )
 
 // URL parsing errors.
@@ -20,8 +22,9 @@ var (
 	ErrPathTraversal     = errors.New("path traversal detected")
 )
 
-// MaxDimension is the maximum allowed width or height.
-const MaxDimension = 8192
+// MaxDimension is the maximum allowed width or height, the same as the image
+// processor's maximum for an output image.
+const MaxDimension = imageprocessor.MaxOutputDimension
 
 // ValidateDimension checks one requested width or height; name ("width" or
 // "height") appears in the error. 0 means "original size" and is valid.

internal/server/computed_side_internal_test.go

@@ -0,0 +1,153 @@
+package server
+
+import (
+	"bytes"
+	"encoding/json"
+	"image/jpeg"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// TestImageProxyRefusesComputedSideAboveMaximum requests sizes of a 3000x600
+// and a 600x3000 PNG through both image routes. A size with one side 0, whose
+// side computed from the source's proportions would be above 8192, is refused
+// with 400 and the JSON error body. The sizes after those refusals are served
+// as before, which also shows that a refusal is not cached as a failed fetch of
+// the source: orig, a size with both sides given, and a size with one side 0
+// whose computed side stays within 8192.
+func TestImageProxyRefusesComputedSideAboveMaximum(t *testing.T) {
+	t.Parallel()
+
+	// The upstream paths of the two sources
+	const (
+		widePath = "/wide.png"
+		tallPath = "/tall.png"
+	)
+
+	wide := encodeTestPNG(t, 3000, 600)
+	tall := encodeTestPNG(t, 600, 3000)
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "image/png")
+
+			if r.URL.Path == tallPath {
+				_, _ = w.Write(tall)
+
+				return
+			}
+
+			_, _ = w.Write(wide)
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	generator, err := encurl.NewGenerator(testSigningKey)
+	if err != nil {
+		t.Fatalf("encurl.NewGenerator: %v", err)
+	}
+
+	tests := []struct {
+		path string
+		// size is the size of the /v1/image/ URL, and width and height are
+		// those of the encrypted URL
+		size          string
+		width, height int
+		// wantWidth and wantHeight are the served image's, 0 for a refusal
+		wantWidth, wantHeight int
+	}{
+		{widePath, "0x8192", 0, 8192, 0, 0},
+		{tallPath, "8192x0", 8192, 0, 0, 0},
+		{widePath, "orig", 0, 0, 3000, 600},
+		{widePath, "300x200", 300, 200, 300, 200},
+		{widePath, "0x300", 0, 300, 1500, 300},
+		{tallPath, "300x0", 300, 0, 300, 1500},
+	}
+
+	for _, tt := range tests {
+		token, err := generator.Generate(&encurl.Payload{
+			SourceHost: upstreamHost, SourcePath: tt.path,
+			Width: tt.width, Height: tt.height, Format: imgcache.FormatJPEG,
+		})
+		if err != nil {
+			t.Fatalf("encurl Generate: %v", err)
+		}
+
+		for _, target := range []string{
+			"/v1/image/" + upstreamHost + tt.path + "/" + tt.size + ".jpeg",
+			"/v1/e/" + token + "/img.jpg",
+		} {
+			rec := httptest.NewRecorder()
+			s.ServeHTTP(rec, httptest.NewRequestWithContext(
+				t.Context(), http.MethodGet, target, nil))
+			t.Logf("GET %s: %d, Content-Type %s",
+				target, rec.Code, rec.Header().Get("Content-Type"))
+
+			if tt.wantWidth == 0 {
+				checkSizeRefused(t, rec)
+			} else {
+				checkServedSize(t, rec, tt.wantWidth, tt.wantHeight)
+			}
+		}
+	}
+}
+
+// checkSizeRefused checks that rec answers 400 with the JSON error body that
+// refuses a size whose side computed from the source's proportions is above
+// 8192.
+func checkSizeRefused(t *testing.T, rec *httptest.ResponseRecorder) {
+	t.Helper()
+
+	const wantError = "size too large for the source: " +
+		"the side computed from its proportions is above 8192"
+
+	var body struct {
+		Error  string `json:"error"`
+		Status int    `json:"status"`
+	}
+
+	err := json.Unmarshal(rec.Body.Bytes(), &body)
+	if err != nil {
+		t.Errorf("status %d, body is not JSON: %v", rec.Code, err)
+
+		return
+	}
+
+	if rec.Code != http.StatusBadRequest || body.Status != http.StatusBadRequest ||
+		body.Error != wantError {
+		t.Errorf("status %d, body %+v, want %d and the error %q",
+			rec.Code, body, http.StatusBadRequest, wantError)
+	}
+}
+
+// checkServedSize checks that rec answers 200 with a JPEG of wantWidth by
+// wantHeight.
+func checkServedSize(
+	t *testing.T, rec *httptest.ResponseRecorder, wantWidth, wantHeight int,
+) {
+	t.Helper()
+
+	if rec.Code != http.StatusOK {
+		t.Errorf("status %d, want %d; body %s",
+			rec.Code, http.StatusOK, rec.Body.String())
+
+		return
+	}
+
+	served, err := jpeg.DecodeConfig(bytes.NewReader(rec.Body.Bytes()))
+	if err != nil {
+		t.Errorf("decoding the served JPEG: %v", err)
+
+		return
+	}
+
+	if served.Width != wantWidth || served.Height != wantHeight {
+		t.Errorf("served %dx%d, want %dx%d",
+			served.Width, served.Height, wantWidth, wantHeight)
+	}
+}

internal/server/fit_outside_internal_test.go

@@ -0,0 +1,91 @@
+package server
+
+import (
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// TestImageProxyRefusesFitOutsideAboveMaximum requests sizes with fit=outside
+// through both image routes. fit=outside scales the source to cover the size,
+// and so past it on one side: a size for which that side would be above 8192
+// is refused with 400 and the JSON error body, whether it is the width or the
+// height, and a size for which it stays within 8192 is served at the scaled
+// size.
+func TestImageProxyRefusesFitOutsideAboveMaximum(t *testing.T) {
+	t.Parallel()
+
+	// The upstream paths of the sources
+	const (
+		widePath   = "/wide.png"
+		rowPath    = "/row.png"
+		columnPath = "/column.png"
+	)
+
+	sources := map[string][]byte{
+		widePath:   encodeTestPNG(t, 3000, 600),
+		rowPath:    encodeTestPNG(t, 8192, 1),
+		columnPath: encodeTestPNG(t, 1, 8192),
+	}
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, r *http.Request) {
+			w.Header().Set("Content-Type", "image/png")
+			_, _ = w.Write(sources[r.URL.Path])
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	generator, err := encurl.NewGenerator(testSigningKey)
+	if err != nil {
+		t.Fatalf("encurl.NewGenerator: %v", err)
+	}
+
+	tests := []struct {
+		path          string
+		width, height int
+		// wantWidth and wantHeight are the served image's, 0 for a refusal
+		wantWidth, wantHeight int
+	}{
+		{widePath, 1, 8192, 0, 0},
+		{rowPath, 1, 8192, 0, 0},
+		{columnPath, 8192, 1, 0, 0},
+		{widePath, 1, 1200, 6000, 1200},
+	}
+
+	for _, tt := range tests {
+		token, err := generator.Generate(&encurl.Payload{
+			SourceHost: upstreamHost, SourcePath: tt.path,
+			Width: tt.width, Height: tt.height, Format: imgcache.FormatJPEG,
+			FitMode: imgcache.FitOutside,
+		})
+		if err != nil {
+			t.Fatalf("encurl Generate: %v", err)
+		}
+
+		size := fmt.Sprintf("%dx%d", tt.width, tt.height)
+
+		for _, target := range []string{
+			"/v1/image/" + upstreamHost + tt.path + "/" + size +
+				".jpeg?fit=outside",
+			"/v1/e/" + token + "/img.jpg",
+		} {
+			rec := httptest.NewRecorder()
+			s.ServeHTTP(rec, httptest.NewRequestWithContext(
+				t.Context(), http.MethodGet, target, nil))
+			t.Logf("GET %s: %d, Content-Type %s",
+				target, rec.Code, rec.Header().Get("Content-Type"))
+
+			if tt.wantWidth == 0 {
+				checkSizeRefused(t, rec)
+			} else {
+				checkServedSize(t, rec, tt.wantWidth, tt.wantHeight)
+			}
+		}
+	}
+}

internal/server/logout_internal_test.go

@@ -0,0 +1,112 @@
+package server
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"go.uber.org/fx"
+	"go.uber.org/fx/fxtest"
+
+	"sneak.berlin/go/pixa/internal/config"
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/globals"
+	"sneak.berlin/go/pixa/internal/handlers"
+	"sneak.berlin/go/pixa/internal/healthcheck"
+	"sneak.berlin/go/pixa/internal/logger"
+	"sneak.berlin/go/pixa/internal/middleware"
+	"sneak.berlin/go/pixa/internal/session"
+)
+
+// startPixa starts the components pixad's fx app builds, from cfg, and
+// returns the server with its routes, as newTestServer does.
+func startPixa(t *testing.T, cfg *config.Config) *Server {
+	t.Helper()
+
+	var (
+		h  *handlers.Handlers
+		mw *middleware.Middleware
+	)
+
+	app := fxtest.New(t,
+		fx.Supply(cfg),
+		fx.Provide(
+			globals.New,
+			logger.New,
+			database.New,
+			healthcheck.New,
+			handlers.New,
+			middleware.New,
+		),
+		fx.Populate(&h, &mw),
+	)
+	app.RequireStart()
+	t.Cleanup(app.RequireStop)
+
+	s := &Server{config: cfg, mw: mw, h: h}
+	s.SetupRoutes()
+
+	return s
+}
+
+// opensGeneratorPage reports whether GET / with cookie shows s's generator
+// page, which only a valid login session opens.
+func opensGeneratorPage(t *testing.T, s *Server, cookie *http.Cookie) bool {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
+	req.AddCookie(cookie)
+
+	rec := httptest.NewRecorder()
+	s.ServeHTTP(rec, req)
+
+	return rec.Code == http.StatusOK &&
+		strings.Contains(rec.Body.String(), `action="/generate"`)
+}
+
+// TestLogoutOutlastsRestart verifies that a copy of the session cookie taken
+// before /logout is still refused by a pixa started again on the same state
+// directory, as pixad is after a restart.
+func TestLogoutOutlastsRestart(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+
+	login := postLogin(t, s, firstClient, "", testSigningKey)
+
+	var copied *http.Cookie
+
+	for _, c := range login.Result().Cookies() {
+		if c.Name == session.CookieName {
+			copied = c
+		}
+	}
+
+	if copied == nil || !opensGeneratorPage(t, s, copied) {
+		t.Fatal("logging in gave no session cookie that opens the generator page")
+	}
+
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/logout", nil)
+	req.AddCookie(copied)
+
+	logout := httptest.NewRecorder()
+	s.ServeHTTP(logout, req)
+
+	if logout.Code != http.StatusSeeOther {
+		t.Fatalf("GET /logout status = %d, want %d",
+			logout.Code, http.StatusSeeOther)
+	}
+
+	restarted := startPixa(t, s.config)
+
+	opens := opensGeneratorPage(t, restarted, copied)
+	t.Logf("after the restart, the copied cookie opens the generator page: %v",
+		opens)
+
+	if opens {
+		t.Error("after a restart, a cookie copied before /logout " +
+			"still opens the generator page")
+	}
+}

internal/session/session.go

@@ -1,9 +1,15 @@
-// Package session provides encrypted session cookie management.
+// Package session provides encrypted session cookie management, and keeps the
+// time of the latest logout in the database so that a logout ends every
+// session made before it.
 package session
 
 import (
+	"context"
+	"database/sql"
 	"errors"
+	"fmt"
 	"net/http"
+	"sync"
 	"time"
 
 	"github.com/gorilla/securecookie"
@@ -35,11 +41,25 @@ type Data struct {
 }
 
 // Manager handles session creation and validation using encrypted cookies.
+//
+// Every login is made with the one signing key, so a logout ends every
+// session made before it, in every browser. The Manager keeps the time of
+// the latest logout in memory, so checking a session reads no database; a
+// Manager from NewManagerWithDatabase also saves it in the database, so that
+// it outlasts a restart.
 type Manager struct {
 	sc *securecookie.SecureCookie
+	db *sql.DB
+
+	// mu guards latestLogout, and is held while a logout is saved, so that
+	// the database and latestLogout agree.
+	mu           sync.Mutex
+	latestLogout time.Time
 }
 
 // NewManager creates a session manager with keys derived from the signing key.
+// It keeps logouts in memory only, so a restart forgets them;
+// NewManagerWithDatabase keeps them in the database.
 //
 // Session cookies always carry the Secure, HttpOnly, and SameSite=Strict
 // attributes; this cannot be configured. Browsers treat http://localhost as a
@@ -67,6 +87,29 @@ func NewManager(signingKey string) (*Manager, error) {
 	}, nil
 }
 
+// NewManagerWithDatabase creates a session manager like NewManager that saves
+// each logout in db, which must have pixa's schema, and starts from the
+// latest logout saved there.
+func NewManagerWithDatabase(
+	ctx context.Context, signingKey string, db *sql.DB,
+) (*Manager, error) {
+	m, err := NewManager(signingKey)
+	if err != nil {
+		return nil, err
+	}
+
+	err = db.QueryRowContext(ctx,
+		"SELECT logged_out_at FROM logout WHERE id = 1",
+	).Scan(&m.latestLogout)
+	if err != nil && !errors.Is(err, sql.ErrNoRows) {
+		return nil, fmt.Errorf("failed to read the latest logout: %w", err)
+	}
+
+	m.db = db
+
+	return m, nil
+}
+
 // CreateSession creates a new authenticated session and sets the cookie.
 func (m *Manager) CreateSession(w http.ResponseWriter) error {
 	now := time.Now()
@@ -122,9 +165,31 @@ func (m *Manager) ValidateSession(r *http.Request) (*Data, error) {
 		return nil, ErrInvalidSession
 	}
 
+	// A session made before the latest logout has ended.
+	if !data.CreatedAt.After(m.latestLogoutTime()) {
+		return nil, ErrInvalidSession
+	}
+
 	return &data, nil
 }
 
+// Logout removes the session cookie and, when r has a valid session, ends
+// every session made until now. A request without one ends no session:
+// another site can make a browser request /logout, but the browser leaves
+// the SameSite=Strict session cookie out of that request.
+func (m *Manager) Logout(w http.ResponseWriter, r *http.Request) error {
+	if m.IsAuthenticated(r) {
+		err := m.saveLogout(r.Context())
+		if err != nil {
+			return err
+		}
+	}
+
+	m.ClearSession(w)
+
+	return nil
+}
+
 // ClearSession removes the session cookie.
 func (m *Manager) ClearSession(w http.ResponseWriter) {
 	http.SetCookie(w, &http.Cookie{
@@ -145,3 +210,34 @@ func (m *Manager) IsAuthenticated(r *http.Request) bool {
 
 	return err == nil && data != nil && data.Authenticated
 }
+
+// saveLogout makes now the time of the latest logout, saving it in the
+// database first when the Manager has one.
+func (m *Manager) saveLogout(ctx context.Context) error {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	now := time.Now().UTC()
+
+	if m.db != nil {
+		_, err := m.db.ExecContext(ctx,
+			"INSERT OR REPLACE INTO logout (id, logged_out_at) VALUES (1, ?)",
+			now)
+		if err != nil {
+			return fmt.Errorf("failed to save the logout: %w", err)
+		}
+	}
+
+	m.latestLogout = now
+
+	return nil
+}
+
+// latestLogoutTime returns the time of the latest logout, or the zero time
+// when there has been none.
+func (m *Manager) latestLogoutTime() time.Time {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	return m.latestLogout
+}

internal/session/session_logout_test.go

@@ -0,0 +1,149 @@
+package session_test
+
+import (
+	"database/sql"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/session"
+)
+
+const logoutTestSigningKey = "test-signing-key-12345"
+
+// newTestDatabase opens an empty in-memory database with pixa's schema. It
+// has one connection, as pixad's has: each connection to ":memory:" would
+// open a database of its own.
+func newTestDatabase(t *testing.T) *sql.DB {
+	t.Helper()
+
+	db, err := sql.Open("sqlite", ":memory:")
+	if err != nil {
+		t.Fatalf("sql.Open() error = %v", err)
+	}
+
+	db.SetMaxOpenConns(1)
+	t.Cleanup(func() { _ = db.Close() })
+
+	err = database.ApplyMigrations(t.Context(), db, nil)
+	if err != nil {
+		t.Fatalf("ApplyMigrations() error = %v", err)
+	}
+
+	return db
+}
+
+// createSessionCookie logs in with mgr and returns the session cookie it
+// sets.
+func createSessionCookie(t *testing.T, mgr *session.Manager) *http.Cookie {
+	t.Helper()
+
+	rec := httptest.NewRecorder()
+
+	err := mgr.CreateSession(rec)
+	if err != nil {
+		t.Fatalf("CreateSession() error = %v", err)
+	}
+
+	for _, c := range rec.Result().Cookies() {
+		if c.Name == session.CookieName {
+			return c
+		}
+	}
+
+	t.Fatalf("CreateSession() did not set a %q cookie", session.CookieName)
+
+	return nil
+}
+
+// requestWithCookie returns a GET request carrying cookie, or no cookie when
+// cookie is nil.
+func requestWithCookie(t *testing.T, cookie *http.Cookie) *http.Request {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, "/", nil)
+	if cookie != nil {
+		req.AddCookie(cookie)
+	}
+
+	return req
+}
+
+// TestLogout_EndsEverySessionMadeBeforeIt verifies that after a logout a
+// copy of the session cookie taken before it is refused and a login after it
+// works, and that both still hold for a new Manager on the same database, as
+// after a restart.
+func TestLogout_EndsEverySessionMadeBeforeIt(t *testing.T) {
+	t.Parallel()
+
+	db := newTestDatabase(t)
+
+	mgr, err := session.NewManagerWithDatabase(
+		t.Context(), logoutTestSigningKey, db)
+	if err != nil {
+		t.Fatalf("NewManagerWithDatabase() error = %v", err)
+	}
+
+	copied := createSessionCookie(t, mgr)
+
+	err = mgr.Logout(httptest.NewRecorder(), requestWithCookie(t, copied))
+	if err != nil {
+		t.Fatalf("Logout() error = %v", err)
+	}
+
+	_, err = mgr.ValidateSession(requestWithCookie(t, copied))
+	t.Logf("cookie copied before the logout: ValidateSession() error = %v", err)
+
+	if !errors.Is(err, session.ErrInvalidSession) {
+		t.Errorf("cookie copied before the logout: error = %v, want %v",
+			err, session.ErrInvalidSession)
+	}
+
+	loginAfter := createSessionCookie(t, mgr)
+
+	_, err = mgr.ValidateSession(requestWithCookie(t, loginAfter))
+	if err != nil {
+		t.Errorf("login after the logout: ValidateSession() error = %v", err)
+	}
+
+	restarted, err := session.NewManagerWithDatabase(
+		t.Context(), logoutTestSigningKey, db)
+	if err != nil {
+		t.Fatalf("NewManagerWithDatabase() after restart error = %v", err)
+	}
+
+	if restarted.IsAuthenticated(requestWithCookie(t, copied)) {
+		t.Error("after a restart, a cookie copied before the logout is accepted")
+	}
+
+	if !restarted.IsAuthenticated(requestWithCookie(t, loginAfter)) {
+		t.Error("after a restart, a login made after the logout is refused")
+	}
+}
+
+// TestLogout_WithoutSession_EndsNoSession verifies that a logout from a
+// request without a session cookie ends no session. Another site can make a
+// browser request /logout, but the browser leaves the SameSite=Strict
+// session cookie out of that request.
+func TestLogout_WithoutSession_EndsNoSession(t *testing.T) {
+	t.Parallel()
+
+	mgr, err := session.NewManagerWithDatabase(
+		t.Context(), logoutTestSigningKey, newTestDatabase(t))
+	if err != nil {
+		t.Fatalf("NewManagerWithDatabase() error = %v", err)
+	}
+
+	cookie := createSessionCookie(t, mgr)
+
+	err = mgr.Logout(httptest.NewRecorder(), requestWithCookie(t, nil))
+	if err != nil {
+		t.Fatalf("Logout() error = %v", err)
+	}
+
+	if !mgr.IsAuthenticated(requestWithCookie(t, cookie)) {
+		t.Error("a logout without a session cookie ended a session")
+	}
+}