HTTP API: server, credential and the list of chats (closes #4)

The bot now serves an HTTP API on PORT (default 8080) beside the chat
client. Every request needs the credential read at startup from the
file named by API_TOKEN_FILE, sent as a bearer token; without one,
every request is refused. Responses carry the security headers, bodies
are capped at 64 KiB and each request's work at 10 seconds.

GET /api/v1/chats lists the bot's contacts from the chat client's
/_contacts command, ordered by id, and marks the contacts who deleted
their chat with the bot, which the chat client keeps listing. bot.Run
starts the API after set-up and stops it within 5 seconds; a listener
failure ends the bot as a chat client failure does.

Model: opus-5-5

internal/api/api_test.go

@@ -0,0 +1,214 @@
+package api_test
+
+import (
+	"bytes"
+	"context"
+	"errors"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/simplexcalc/internal/api"
+	"sneak.berlin/go/simplexcalc/internal/simplex"
+)
+
+const (
+	// credential is what the API under test is configured with.
+	credential = "a-credential-for-these-tests" //nolint:gosec // G101: invented for tests
+	bearer     = "Bearer " + credential
+
+	chatsPath    = "/api/v1/chats"
+	unauthorized = `{"error":"unauthorized"}` + "\n"
+)
+
+var errChat = errors.New("sqlite: database is locked at /var/lib/simplexcalc")
+
+// fakeClient stands in for the chat client. It answers with contacts,
+// or with err, and remembers what it was asked.
+type fakeClient struct {
+	contacts []simplex.Contact
+	err      error
+
+	userID      int64
+	hadDeadline bool
+}
+
+func (f *fakeClient) Contacts(
+	ctx context.Context, userID int64,
+) ([]simplex.Contact, error) {
+	f.userID = userID
+	_, f.hadDeadline = ctx.Deadline()
+
+	return f.contacts, f.err
+}
+
+func newAPI(token string, client api.ChatClient) *http.Server {
+	return api.New(api.Params{
+		Log:    slog.New(slog.DiscardHandler),
+		Client: client,
+		UserID: 1,
+		Port:   8080,
+		Token:  token,
+	})
+}
+
+// request sends srv one request, with the Authorization header auth
+// unless that is empty.
+func request(
+	t *testing.T, srv *http.Server, method, path, auth string,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(t.Context(), method, path, nil)
+	if auth != "" {
+		req.Header.Set("Authorization", auth)
+	}
+
+	rec := httptest.NewRecorder()
+	srv.Handler.ServeHTTP(rec, req)
+
+	return rec
+}
+
+// TestCredential: only the configured credential, sent as a bearer,
+// gets in. With none configured, nothing does, an empty bearer
+// included.
+func TestCredential(t *testing.T) {
+	t.Parallel()
+
+	for name, tc := range map[string]struct {
+		token, auth string
+		in          bool
+	}{
+		"right":                         {credential, bearer, true},
+		"right, scheme in lower case":   {credential, "bearer " + credential, true},
+		"wrong":                         {credential, strings.ToUpper(bearer), false},
+		"missing":                       {credential, "", false},
+		"another scheme":                {credential, "Basic " + credential, false},
+		"no scheme":                     {credential, credential, false},
+		"empty bearer":                  {credential, "Bearer ", false},
+		"none configured":               {"", bearer, false},
+		"none configured, empty bearer": {"", "Bearer ", false},
+	} {
+		t.Run(name, func(t *testing.T) {
+			t.Parallel()
+
+			rec := request(t, newAPI(tc.token, &fakeClient{}),
+				http.MethodGet, chatsPath, tc.auth)
+
+			if tc.in {
+				if rec.Code != http.StatusOK {
+					t.Errorf("status = %d, want 200", rec.Code)
+				}
+
+				return
+			}
+
+			if rec.Code != http.StatusUnauthorized {
+				t.Fatalf("status = %d, want 401", rec.Code)
+			}
+
+			if got := rec.Header().Get("WWW-Authenticate"); got != "Bearer" {
+				t.Errorf("WWW-Authenticate = %q, want Bearer", got)
+			}
+
+			if rec.Body.String() != unauthorized {
+				t.Errorf("body = %q, want %q", rec.Body.String(), unauthorized)
+			}
+		})
+	}
+}
+
+// TestNoCredentialWarns: an API without a credential says at startup
+// that it refuses every request.
+func TestNoCredentialWarns(t *testing.T) {
+	t.Parallel()
+
+	var logged bytes.Buffer
+
+	api.New(api.Params{
+		Log:    slog.New(slog.NewJSONHandler(&logged, nil)),
+		Client: &fakeClient{},
+		Port:   8080,
+	})
+
+	if !strings.Contains(logged.String(), `"level":"WARN"`) ||
+		!strings.Contains(logged.String(), "API_TOKEN_FILE is not set") {
+		t.Errorf("log = %q, want a warning that API_TOKEN_FILE is not set",
+			logged.String())
+	}
+}
+
+// TestNoPathIsExempt: an unknown path or method needs the credential
+// like everything else, and then gets a JSON error.
+func TestNoPathIsExempt(t *testing.T) {
+	t.Parallel()
+
+	srv := newAPI(credential, &fakeClient{})
+
+	for _, tc := range []struct {
+		method, path, auth string
+		want               int
+		body               string
+	}{
+		{http.MethodGet, "/", "", http.StatusUnauthorized, unauthorized},
+		{
+			http.MethodGet, "/.well-known/healthcheck", "",
+			http.StatusUnauthorized, unauthorized,
+		},
+		{
+			http.MethodGet, "/api/v1/nothing", bearer,
+			http.StatusNotFound, `{"error":"not found"}` + "\n",
+		},
+		{
+			http.MethodPost, chatsPath, bearer,
+			http.StatusMethodNotAllowed, `{"error":"method not allowed"}` + "\n",
+		},
+	} {
+		rec := request(t, srv, tc.method, tc.path, tc.auth)
+		if rec.Code != tc.want || rec.Body.String() != tc.body {
+			t.Errorf("%s %s: %d %q, want %d %q", tc.method, tc.path,
+				rec.Code, rec.Body.String(), tc.want, tc.body)
+		}
+	}
+}
+
+// TestHeaders: every response, whatever its status, carries the
+// security headers, and none lets another origin in.
+func TestHeaders(t *testing.T) {
+	t.Parallel()
+
+	want := map[string]string{
+		"X-Content-Type-Options":    "nosniff",
+		"Content-Security-Policy":   "default-src 'none'; frame-ancestors 'none'",
+		"X-Frame-Options":           "DENY",
+		"Referrer-Policy":           "no-referrer",
+		"Strict-Transport-Security": "max-age=31536000; includeSubDomains",
+		"Cache-Control":             "no-store",
+	}
+
+	for _, tc := range []struct {
+		client     *fakeClient
+		path, auth string
+	}{
+		{&fakeClient{}, chatsPath, bearer},
+		{&fakeClient{}, chatsPath, ""},
+		{&fakeClient{}, "/nothing", bearer},
+		{&fakeClient{err: errChat}, chatsPath, bearer},
+	} {
+		rec := request(t, newAPI(credential, tc.client),
+			http.MethodGet, tc.path, tc.auth)
+
+		for key, value := range want {
+			if got := rec.Header().Get(key); got != value {
+				t.Errorf("%d response: %s = %q, want %q", rec.Code, key, got, value)
+			}
+		}
+
+		if got := rec.Header().Get("Access-Control-Allow-Origin"); got != "" {
+			t.Errorf("%d response: Access-Control-Allow-Origin = %q", rec.Code, got)
+		}
+	}
+}