Stop the chat client only after the API has stopped (closes #4)

The chat client's context no longer follows the bot's, so a stop no
longer sends it SIGTERM while the API is still finishing its requests.
The deferred stop in Run, which runs after the API's, stops it instead,
so a request in progress at a stop gets its answer rather than a 500.
The README says so.

The new test runs the whole bot with the test binary itself standing in
for simplex-chat on PATH. The stand-in holds its answer to the contacts
request until the test has told the bot to stop.

Model: opus-5-5

README.md

@@ -228,7 +228,7 @@ container.
   Handlers call the chat client on the request's own goroutine, never on
   the one that delivers events, which also delivers the chat client's
   answers. When the bot stops, requests in progress get 5 seconds to
-  finish.
+  finish before the chat client is stopped.
 - **Replies**: for each text message a contact sends in a direct chat,
   the bot sends back the result, as a reply quoting the message. Group
   messages, files and the bot's own messages are ignored.

internal/bot/bot.go

@@ -67,7 +67,9 @@ func Run(ctx context.Context, log *slog.Logger, cfg *config.Config) error {
 
 	// Cancelling this stops the chat client; the deferred wait makes
 	// Run return only once it has exited, whatever path Run takes.
-	cliCtx, stopCLI := context.WithCancel(ctx)
+	// Cancelling ctx does not reach it, so that the API, stopped first,
+	// can finish its requests while the chat client still answers.
+	cliCtx, stopCLI := context.WithCancel(context.WithoutCancel(ctx))
 
 	cli, err := simplex.StartCLI(cliCtx, log, filepath.Join(cfg.DataDir, "simplex"),
 		DisplayName, chatPort)

internal/bot/run_test.go

@@ -0,0 +1,233 @@
+package bot_test
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"log/slog"
+	"net"
+	"net/http"
+	"net/netip"
+	"os"
+	"path/filepath"
+	"slices"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"github.com/gorilla/websocket"
+	"sneak.berlin/go/simplexcalc/internal/bot"
+	"sneak.berlin/go/simplexcalc/internal/config"
+	"sneak.berlin/go/simplexcalc/internal/simplex"
+)
+
+const (
+	// credential is what the bot's API is configured with here.
+	credential = "a-credential-for-these-tests" //nolint:gosec // G101: invented for tests
+
+	// asked is the file the stand-in chat client creates in the data
+	// directory when it is asked for the contacts.
+	asked = "asked-for-contacts"
+
+	// contactsDelay is how long the stand-in then holds its answer:
+	// long enough for the test to stop the bot meanwhile, and well
+	// within the 5 seconds the API gets to finish its requests.
+	contactsDelay = time.Second
+)
+
+// TestMain lets this test binary be the chat client as well: started
+// under the chat client's name, as TestStopDuringRequest arranges, it is
+// the stand-in instead of running the tests.
+func TestMain(m *testing.M) {
+	if filepath.Base(os.Args[0]) == simplex.Binary {
+		standIn() // never returns
+	}
+
+	m.Run()
+}
+
+// standIn plays the chat client: it serves the WebSocket API on the
+// port it is given, on localhost, and answers the commands the bot
+// sends. SIGTERM ends it, as it ends the real client. Unlike the real
+// client, it also exits when the bot hangs up, so that it never
+// outlives a test run that was cut short. It takes port 5225, the chat
+// client's fixed port, so this test cannot run twice at once on one
+// machine.
+func standIn() {
+	arg := func(name string) string {
+		return os.Args[slices.Index(os.Args, name)+1]
+	}
+
+	marker := filepath.Join(filepath.Dir(arg("--database")), asked)
+
+	srv := &http.Server{
+		Addr:              "127.0.0.1:" + arg("--chat-server-port"),
+		ReadHeaderTimeout: time.Second,
+		Handler: http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			answer(w, r, marker)
+		}),
+	}
+
+	err := srv.ListenAndServe()
+	_, _ = fmt.Fprintln(os.Stderr, err)
+
+	os.Exit(1)
+}
+
+// answer answers the commands on one connection with records reduced to
+// the fields the bot reads. Asked for the contacts, it first creates
+// the file marker, then holds its answer for contactsDelay.
+func answer(w http.ResponseWriter, r *http.Request, marker string) {
+	conn, err := (&websocket.Upgrader{}).Upgrade(w, r, nil)
+	if err != nil {
+		return
+	}
+
+	records := map[string]string{
+		"/user":              `{"type":"activeUser","user":{"userId":1}}`,
+		"/_show_address":     `{"type":"userContactLink","contactLink":{}}`,
+		"/_address_settings": `{"type":"userContactLinkUpdated"}`,
+		"/_contacts": `{"type":"contactsList","contacts":[{"contactId":3,` +
+			`"profile":{"displayName":"tester"},"contactStatus":"active"}]}`,
+	}
+
+	for {
+		var cmd map[string]string
+
+		err = conn.ReadJSON(&cmd)
+		if err != nil {
+			os.Exit(0)
+		}
+
+		name, _, _ := strings.Cut(cmd["cmd"], " ")
+
+		record, ok := records[name]
+		if !ok {
+			continue
+		}
+
+		if name == "/_contacts" {
+			_ = os.WriteFile(marker, nil, 0o600)
+
+			time.Sleep(contactsDelay)
+		}
+
+		_ = conn.WriteJSON(map[string]any{
+			"corrId": cmd["corrId"],
+			"resp":   json.RawMessage(record),
+		})
+	}
+}
+
+// TestStopDuringRequest: a request that is waiting on the chat client
+// when the bot is told to stop still gets the chat client's answer,
+// because the chat client is stopped only once the API has stopped.
+func TestStopDuringRequest(t *testing.T) {
+	// Run starts the chat client from PATH: put this test binary there
+	// under the chat client's name.
+	bin := t.TempDir()
+
+	exe, err := os.Executable()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = os.Symlink(exe, filepath.Join(bin, simplex.Binary))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Setenv("PATH", bin)
+
+	cfg := &config.Config{DataDir: t.TempDir(), Port: freePort(t), APIToken: credential}
+	ctx, stop := context.WithCancel(t.Context())
+	done := make(chan struct{})
+
+	var runErr error
+
+	go func() {
+		defer close(done)
+
+		runErr = bot.Run(ctx, slog.New(slog.DiscardHandler), cfg)
+	}()
+
+	t.Cleanup(func() {
+		stop()
+		<-done
+
+		if runErr != nil {
+			t.Errorf("Run: %v", runErr)
+		}
+	})
+
+	// Stop the bot once the request below is waiting on the chat client.
+	go func() {
+		for ctx.Err() == nil {
+			_, err := os.Stat(filepath.Join(cfg.DataDir, asked))
+			if err == nil {
+				stop()
+			}
+
+			time.Sleep(10 * time.Millisecond)
+		}
+	}()
+
+	status, body := getChats(t, cfg.Port, done)
+
+	want := `{"chats":[{"id":3,"display_name":"tester","contact_deleted":false}]}` + "\n"
+	if status != http.StatusOK || body != want {
+		t.Errorf("GET /api/v1/chats = %d %q, want 200 %q", status, body, want)
+	}
+}
+
+// freePort returns a TCP port that nothing listens on at the moment.
+func freePort(t *testing.T) int {
+	t.Helper()
+
+	l, err := (&net.ListenConfig{}).Listen(t.Context(), "tcp", ":0")
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() { _ = l.Close() }()
+
+	return int(netip.MustParseAddrPort(l.Addr().String()).Port())
+}
+
+// getChats asks the bot's API for the chats, trying again while the API
+// is not listening yet, and returns the answer's status and body. It
+// fails the test if Run returns first, which closes done.
+func getChats(t *testing.T, port int, done <-chan struct{}) (int, string) {
+	t.Helper()
+
+	url := "http://127.0.0.1:" + strconv.Itoa(port) + "/api/v1/chats"
+
+	for {
+		req, err := http.NewRequestWithContext(t.Context(), http.MethodGet, url, nil)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		req.Header.Set("Authorization", "Bearer "+credential)
+
+		resp, err := http.DefaultClient.Do(req)
+		if err == nil {
+			body, err := io.ReadAll(resp.Body)
+			_ = resp.Body.Close()
+
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			return resp.StatusCode, string(body)
+		}
+
+		select {
+		case <-done:
+			t.Fatal("Run returned before the API answered")
+		case <-time.After(50 * time.Millisecond):
+		}
+	}
+}