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/bot/bot.go

@@ -8,12 +8,15 @@ import (
 	"errors"
 	"fmt"
 	"log/slog"
+	"net/http"
 	"os"
 	"path/filepath"
 	"strconv"
 	"time"
 
+	"sneak.berlin/go/simplexcalc/internal/api"
 	"sneak.berlin/go/simplexcalc/internal/calc"
+	"sneak.berlin/go/simplexcalc/internal/config"
 	"sneak.berlin/go/simplexcalc/internal/simplex"
 )
 
@@ -42,17 +45,22 @@ const (
 	// retryInterval paces the connection attempts.
 	retryInterval = 250 * time.Millisecond
 
+	// apiStopTimeout is how long API requests in progress get to finish
+	// when the bot stops, before their connections are closed.
+	apiStopTimeout = 5 * time.Second
+
 	dataDirMode = 0o700
 )
 
 var errExited = errors.New("simplex-chat exited")
 
-// Run starts the chat client with its database in dataDir, connects to
-// it, sets up the bot's address, and answers messages until ctx is
-// cancelled — which is a clean stop and returns nil — or until the chat
-// client or the connection to it fails, which returns the error.
-func Run(ctx context.Context, log *slog.Logger, dataDir string) error {
-	err := os.MkdirAll(dataDir, dataDirMode)
+// Run starts the chat client with its database in cfg.DataDir, connects
+// to it, sets up the bot's address, then answers messages and serves the
+// API until ctx is cancelled — which is a clean stop and returns nil —
+// or until the chat client, the connection to it or the API's listener
+// fails, which returns the error.
+func Run(ctx context.Context, log *slog.Logger, cfg *config.Config) error {
+	err := os.MkdirAll(cfg.DataDir, dataDirMode)
 	if err != nil {
 		return fmt.Errorf("creating data directory: %w", err)
 	}
@@ -61,7 +69,7 @@ func Run(ctx context.Context, log *slog.Logger, dataDir string) error {
 	// Run return only once it has exited, whatever path Run takes.
 	cliCtx, stopCLI := context.WithCancel(ctx)
 
-	cli, err := simplex.StartCLI(cliCtx, log, filepath.Join(dataDir, "simplex"),
+	cli, err := simplex.StartCLI(cliCtx, log, filepath.Join(cfg.DataDir, "simplex"),
 		DisplayName, chatPort)
 	if err != nil {
 		stopCLI()
@@ -81,11 +89,31 @@ func Run(ctx context.Context, log *slog.Logger, dataDir string) error {
 
 	defer func() { _ = client.Close() }()
 
-	err = setUp(ctx, log, client)
+	user, err := setUp(ctx, log, client)
 	if err != nil {
 		return err
 	}
 
+	srv := api.New(api.Params{
+		Log:    log,
+		Client: client,
+		UserID: user.UserID,
+		Port:   cfg.Port,
+		Token:  cfg.APIToken,
+	})
+
+	served := make(chan error, 1)
+
+	go func() {
+		served <- srv.ListenAndServe()
+	}()
+
+	// Deferred last, so it runs first: requests in progress finish while
+	// the chat client is still there to answer them.
+	defer stopAPI(ctx, log, srv)
+
+	log.Info("starting the API", "port", cfg.Port)
+
 	select {
 	case <-ctx.Done():
 		return nil
@@ -93,6 +121,23 @@ func Run(ctx context.Context, log *slog.Logger, dataDir string) error {
 		return fmt.Errorf("%w: %w", simplex.ErrClosed, client.Err())
 	case <-cli.Done():
 		return fmt.Errorf("%w: %w", errExited, cli.Err())
+	case err := <-served:
+		return fmt.Errorf("serving the API: %w", err)
+	}
+}
+
+// stopAPI stops the API server, giving requests in progress up to
+// apiStopTimeout to finish before closing their connections.
+func stopAPI(ctx context.Context, log *slog.Logger, srv *http.Server) {
+	// ctx is usually cancelled by now: that is why the bot is stopping.
+	ctx, cancel := context.WithTimeout(context.WithoutCancel(ctx), apiStopTimeout)
+	defer cancel()
+
+	err := srv.Shutdown(ctx)
+	if err != nil {
+		log.Warn("stopping the API", "error", err)
+
+		_ = srv.Close()
 	}
 }
 
@@ -125,19 +170,22 @@ func connect(
 // setUp gives the bot a long-term contact address, creating it on the
 // first start, and sets it to accept every contact request and to greet
 // each new contact. The settings are written on every start, so an
-// address whose settings were changed by hand is put right.
-func setUp(ctx context.Context, log *slog.Logger, client *simplex.Client) error {
+// address whose settings were changed by hand is put right. It returns
+// the bot's user profile.
+func setUp(
+	ctx context.Context, log *slog.Logger, client *simplex.Client,
+) (simplex.User, error) {
 	ctx, cancel := context.WithTimeout(ctx, setupTimeout)
 	defer cancel()
 
 	user, err := client.ActiveUser(ctx)
 	if err != nil {
-		return fmt.Errorf("reading the bot's profile: %w", err)
+		return user, fmt.Errorf("reading the bot's profile: %w", err)
 	}
 
 	link, ok, err := client.Address(ctx, user.UserID)
 	if err != nil {
-		return fmt.Errorf("reading the bot's address: %w", err)
+		return user, fmt.Errorf("reading the bot's address: %w", err)
 	}
 
 	if !ok {
@@ -145,7 +193,7 @@ func setUp(ctx context.Context, log *slog.Logger, client *simplex.Client) error
 
 		link, err = client.CreateAddress(ctx, user.UserID)
 		if err != nil {
-			return fmt.Errorf("creating the bot's address: %w", err)
+			return user, fmt.Errorf("creating the bot's address: %w", err)
 		}
 	}
 
@@ -154,7 +202,7 @@ func setUp(ctx context.Context, log *slog.Logger, client *simplex.Client) error
 		AutoReply:  &simplex.MsgContent{Type: "text", Text: Welcome},
 	})
 	if err != nil {
-		return fmt.Errorf("setting the bot's address to accept everyone: %w", err)
+		return user, fmt.Errorf("setting the bot's address to accept everyone: %w", err)
 	}
 
 	log.Info("ready",
@@ -163,7 +211,7 @@ func setUp(ctx context.Context, log *slog.Logger, client *simplex.Client) error
 		"full_address", link.FullLink,
 	)
 
-	return nil
+	return user, nil
 }
 
 // handle answers each text message a contact sends.