Logging: structured slog messages throughout, and WithLogger options so callers choose the logger

Log messages are lower-case event names with their details as key/value
attributes ("error" for errors), in place of formatted strings.

Loggable package take a WithLogger option as part of their "New*" call,
defaulting to slog.Default(). Each tags its lines with its `component`.

Some debug loggers print directly rather than using slog when in
terminal logging mode.

internal/websocket/http_test.go

@@ -46,7 +46,7 @@ func dialWS(t *testing.T, ctx context.Context, url string) *ws.Conn {
 // A client upgraded over HTTP gets replies. A max_message_size of 0 uses the
 // default limit rather than refusing every message.
 func TestHTTPMessages(t *testing.T) {
-	h := NewHub(config.JSCServerWebSocket{WriteTimeout: time.Second}, discardLog)
+	h := NewHub(config.JSCServerWebSocket{WriteTimeout: time.Second}, WithLogger(discardLog))
 	url := wsHub(t, h)
 	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 	defer cancel()
@@ -98,7 +98,7 @@ func TestPushBadPayload(t *testing.T) {
 
 // A binary frame closes the connection with 1003 (unsupported data).
 func TestHTTPBinaryFrame(t *testing.T) {
-	h := NewHub(config.JSCServerWebSocket{WriteTimeout: time.Second}, discardLog)
+	h := NewHub(config.JSCServerWebSocket{WriteTimeout: time.Second}, WithLogger(discardLog))
 	url := wsHub(t, h)
 	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 	defer cancel()
@@ -120,7 +120,7 @@ func TestHTTPMessageRateLimit(t *testing.T) {
 		WriteTimeout:     time.Second,
 		MessageRateLimit: config.JSCRateLimitRule{Enabled: true, PerSecond: 1, Burst: 1},
 	}
-	h := NewHub(conf, discardLog)
+	h := NewHub(conf, WithLogger(discardLog))
 	url := wsHub(t, h)
 	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
 	defer cancel()
@@ -147,7 +147,7 @@ func TestHTTPMessageRateLimit(t *testing.T) {
 // A request that isn't a WebSocket upgrade is refused by the upgrade and no
 // client is registered.
 func TestHTTPNotAnUpgrade(t *testing.T) {
-	h := NewHub(config.JSCServerWebSocket{}, discardLog)
+	h := NewHub(config.JSCServerWebSocket{}, WithLogger(discardLog))
 	srv := httptest.NewServer(h)
 	defer srv.Close()
 	res, err := http.Get(srv.URL)
@@ -166,7 +166,7 @@ func TestHTTPNotAnUpgrade(t *testing.T) {
 // After Shutdown, an upgrade succeeds but the client is closed at once with
 // 1001 (going away).
 func TestHTTPRefusedAfterShutdown(t *testing.T) {
-	h := NewHub(config.JSCServerWebSocket{}, discardLog)
+	h := NewHub(config.JSCServerWebSocket{}, WithLogger(discardLog))
 	url := wsHub(t, h)
 	if err := h.Shutdown(context.Background()); err != nil {
 		t.Fatal(err)