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/httpx/httpx_test.go

@@ -0,0 +1,84 @@
+package httpx
+
+import (
+	"context"
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+func TestWriteProblem(t *testing.T) {
+	req := httptest.NewRequest("GET", "/api/items/1", nil)
+	req = req.WithContext(WithRequestID(req.Context(), "req-123"))
+	rec := httptest.NewRecorder()
+	WriteProblem(rec, req, http.StatusNotFound, "no such item")
+
+	if rec.Code != http.StatusNotFound {
+		t.Errorf("status = %d; want 404", rec.Code)
+	}
+	if ct := rec.Header().Get("Content-Type"); ct != "application/problem+json" {
+		t.Errorf("Content-Type = %q", ct)
+	}
+	if nosniff := rec.Header().Get("X-Content-Type-Options"); nosniff != "nosniff" {
+		t.Errorf("X-Content-Type-Options = %q", nosniff)
+	}
+	var p Problem
+	if err := json.Unmarshal(rec.Body.Bytes(), &p); err != nil {
+		t.Fatalf("body %q: %v", rec.Body, err)
+	}
+	want := Problem{
+		Type:      "about:blank",
+		Status:    http.StatusNotFound,
+		Title:     "Not Found",
+		Detail:    "no such item",
+		RequestID: "req-123",
+	}
+	if p != want {
+		t.Errorf("problem = %+v; want %+v", p, want)
+	}
+}
+
+// Without a request (or a request ID) the problem has no requestId, and an
+// empty detail is left out.
+func TestWriteProblemMinimal(t *testing.T) {
+	for _, req := range []*http.Request{nil, httptest.NewRequest("GET", "/", nil)} {
+		rec := httptest.NewRecorder()
+		WriteProblem(rec, req, http.StatusTooManyRequests, "")
+		var body map[string]any
+		if err := json.Unmarshal(rec.Body.Bytes(), &body); err != nil {
+			t.Fatalf("body %q: %v", rec.Body, err)
+		}
+		want := map[string]any{
+			"type":   "about:blank",
+			"status": float64(http.StatusTooManyRequests),
+			"title":  "Too Many Requests",
+		}
+		if len(body) != len(want) {
+			t.Errorf("request %v: body = %v; want %v", req != nil, body, want)
+		}
+		for k, v := range want {
+			if body[k] != v {
+				t.Errorf("request %v: %s = %v; want %v", req != nil, k, body[k], v)
+			}
+		}
+	}
+}
+
+func TestRequestID(t *testing.T) {
+	ctx := context.Background()
+	if id := RequestID(ctx); id != "" {
+		t.Errorf("RequestID(empty) = %q; want empty", id)
+	}
+	ctx = WithRequestID(ctx, "abc")
+	if id := RequestID(ctx); id != "abc" {
+		t.Errorf("RequestID = %q; want abc", id)
+	}
+	// The latest ID wins; a value of another type under the key is ignored.
+	if id := RequestID(WithRequestID(ctx, "def")); id != "def" {
+		t.Errorf("RequestID after replacing = %q; want def", id)
+	}
+	if id := RequestID(context.WithValue(ctx, requestIDKey, 42)); id != "" {
+		t.Errorf("RequestID(int) = %q; want empty", id)
+	}
+}

internal/httpx/problem.go

@@ -0,0 +1,34 @@
+// Package httpx holds small HTTP helpers shared by middleware and handlers.
+package httpx
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// Problem is an RFC 9457 problem details body.
+type Problem struct {
+	Type      string `json:"type,omitempty"`
+	Status    int    `json:"status"`
+	Title     string `json:"title"`
+	Detail    string `json:"detail,omitempty"`
+	Instance  string `json:"instance,omitempty"`
+	RequestID string `json:"requestId,omitempty"`
+}
+
+// WriteProblem writes a problem+json error response.
+func WriteProblem(w http.ResponseWriter, r *http.Request, status int, detail string) {
+	p := Problem{
+		Type:   "about:blank",
+		Title:  http.StatusText(status),
+		Status: status,
+		Detail: detail,
+	}
+	if r != nil {
+		p.RequestID = RequestID(r.Context())
+	}
+	w.Header().Set("Content-Type", "application/problem+json")
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	w.WriteHeader(status)
+	json.NewEncoder(w).Encode(p) //nolint:errcheck,gosec // the client may have gone; nothing to do
+}

internal/httpx/request_id.go

@@ -0,0 +1,20 @@
+package httpx
+
+import (
+	"context"
+)
+
+type ctxKey int
+
+const requestIDKey ctxKey = iota
+
+// WithRequestID stores a request ID in the context.
+func WithRequestID(ctx context.Context, id string) context.Context {
+	return context.WithValue(ctx, requestIDKey, id)
+}
+
+// RequestID returns the request ID stored in ctx, or "".
+func RequestID(ctx context.Context) string {
+	id, _ := ctx.Value(requestIDKey).(string)
+	return id
+}