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/client_test.go

@@ -44,7 +44,7 @@ func (f *fakeConn) CloseNow() error { return nil }
 // newTestClient returns a client of a new hub on f, with no loops running,
 // and its context.
 func newTestClient(f *fakeConn) (*client, context.Context) {
-	h := NewHub(config.JSCServerWebSocket{}, discardLog)
+	h := NewHub(config.JSCServerWebSocket{}, WithLogger(discardLog))
 	ctx, cancel := context.WithCancel(context.Background())
 	return newClient(h, f, "192.0.2.1", cancel), ctx
 }
@@ -114,7 +114,7 @@ func TestClientMessageRateLimit(t *testing.T) {
 		{config.JSCRateLimitRule{Enabled: true, PerSecond: 1, Burst: 1}, true},
 	}
 	for _, tt := range tests {
-		h := NewHub(config.JSCServerWebSocket{MessageRateLimit: tt.rule}, discardLog)
+		h := NewHub(config.JSCServerWebSocket{MessageRateLimit: tt.rule}, WithLogger(discardLog))
 		c := newClient(h, newFakeConn(), "", func() {})
 		c.limiter.Allow()
 		if limited := !c.limiter.Allow(); limited != tt.limited {
@@ -193,7 +193,7 @@ func jsonLog(level slog.Level) (*slog.Logger, *syncBuffer) {
 // At debug level, messages received from and sent to a client are logged.
 func TestLogMessages(t *testing.T) {
 	log, buf := jsonLog(slog.LevelDebug)
-	h := NewHub(config.JSCServerWebSocket{WriteTimeout: time.Second}, log)
+	h := NewHub(config.JSCServerWebSocket{WriteTimeout: time.Second}, WithLogger(log))
 	peer, _ := pipeClient(t, h)
 
 	ping := `{"type":"ping","id":"1"}`
@@ -235,7 +235,7 @@ func TestLogMessages(t *testing.T) {
 // unless debug logging is on.
 func TestLogMessageLimit(t *testing.T) {
 	log, buf := jsonLog(slog.LevelDebug)
-	h := NewHub(config.JSCServerWebSocket{}, log)
+	h := NewHub(config.JSCServerWebSocket{}, WithLogger(log))
 	c := newClient(h, newFakeConn(), "", func() {})
 	long := strings.Repeat("x", logMessageLimit+100)
 	c.logMessage(context.Background(), "message sent", []byte(long))
@@ -251,7 +251,7 @@ func TestLogMessageLimit(t *testing.T) {
 	}
 
 	log, buf = jsonLog(slog.LevelInfo)
-	c.hub = NewHub(config.JSCServerWebSocket{}, log)
+	c.hub = NewHub(config.JSCServerWebSocket{}, WithLogger(log))
 	c.logMessage(context.Background(), "message sent", []byte("x"))
 	if entries := buf.entries(t); len(entries) != 0 {
 		t.Errorf("logged %v at info level", entries)