Added websocket hub for handling websocket clients, with a wsserve command

which runs a plain TCP server for receiving websocket hub clients, with
server config, CSRF and rate limit middleware.

- internal/websocket: Hub pushing messages to WebSocket clients (ServeHTTP,
  example.com/ws upgrade with optional CSRF check) and plain TCP clients (ServeTCP,
  newline-delimited JSON envelopes); ping/pong keepalive, per-client message
  rate limit, slow consumer handling, graceful Shutdown, debug logging of
  messages sent and received
- internal/websocket/tcpserver: standalone TCP server for a hub, with accept
  back-off, a per-IP connection limit (server.websocket.connection_limit) and
  graceful shutdown
- internal/cli/wsserve: `wsserve` command running the TCP server, with
  --listen/--host/--port overrides
- internal/middleware: keyed token bucket rate limiter, real client IP from
  trusted proxies
- internal/httpx: RFC 9457 problem responses, request IDs in context
- internal/config: server section (host, port, shutdown timeout, rate limiter
  idle TTL, websocket); util.ByteSize settings (e.g. "32KiB"); lists of
  sections as single keys; empty lists stored as nil; isExplicitlySet for
  printLoadedConfig; JobSearchConfigSource renamed to JSCSourcesSource;
  TestSections checks every section's methods
- internal/util: ByteSize, parsed and formatted with go-humanize

internal/middleware/real_ip_test.go

@@ -0,0 +1,56 @@
+package middleware
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"testing"
+)
+
+// serveRealIP runs a request from peer with the given headers through RealIP
+// and returns the ClientInfo the next handler sees.
+func serveRealIP(t *testing.T, opts RealIPOptions, peer string, h map[string]string) ClientInfo {
+	t.Helper()
+	var got ClientInfo
+	next := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) { got = Client(r) })
+	req := httptest.NewRequest("GET", "/", nil)
+	req.RemoteAddr = peer
+	for k, v := range h {
+		req.Header.Set(k, v)
+	}
+	RealIP(opts)(next).ServeHTTP(httptest.NewRecorder(), req)
+	return got
+}
+
+var defaultHeaders = []string{"X-Forwarded-For", "Forwarded", "X-Real-IP"}
+
+func TestRealIP(t *testing.T) {
+	opts := RealIPOptions{
+		Trusted: []netip.Prefix{netip.MustParsePrefix("127.0.0.0/8")},
+		Headers: defaultHeaders,
+	}
+	// Spoofed left-most entry is ignored; right-most untrusted wins.
+	c := serveRealIP(t, opts, "127.0.0.1:1234", map[string]string{
+		"X-Forwarded-For": "6.6.6.6, 203.0.113.9, 127.0.0.1", "X-Forwarded-Proto": "https",
+	})
+	if c.IP.String() != "203.0.113.9" || c.Scheme != "https" || !c.ViaProxy {
+		t.Fatalf("xff: %+v", c)
+	}
+	c = serveRealIP(t, opts, "127.0.0.1:1234", map[string]string{
+		"Forwarded": `for="[2001:db8::7]:4711";proto=https`,
+	})
+	if c.IP.String() != "2001:db8::7" {
+		t.Fatalf("forwarded: %+v", c)
+	}
+}
+
+func TestUntrustedPeerHeadersIgnored(t *testing.T) {
+	opts := RealIPOptions{
+		Trusted: []netip.Prefix{netip.MustParsePrefix("10.0.0.0/8")},
+		Headers: defaultHeaders,
+	}
+	c := serveRealIP(t, opts, "127.0.0.1:1234", map[string]string{"X-Forwarded-For": "203.0.113.9"})
+	if c.IP.String() != "127.0.0.1" || c.ViaProxy {
+		t.Fatalf("untrusted XFF honoured: %+v", c)
+	}
+}