feat: add security response headers middleware (closes #98)

Add SecurityHeaders() to internal/middleware and register it in the
global middleware stack so every response - dashboard, embedded static
assets, healthchecks, JSON API, and metrics - carries the six response
headers required by REPO_POLICIES.md before tagging 1.0:

  Strict-Transport-Security: max-age=31536000; includeSubDomains
  Content-Security-Policy:   default-src 'self'; script-src 'none';
                             style-src 'self'; img-src 'self';
                             font-src 'none'; connect-src 'none';
                             object-src 'none'; base-uri 'none';
                             form-action 'none'; frame-ancestors 'none'
  X-Frame-Options:           DENY
  X-Content-Type-Options:    nosniff
  Referrer-Policy:           no-referrer
  Permissions-Policy:        unused browser features denied

The dashboard template ships no JavaScript, no inline styles, no inline
event handlers and no images, and its only subresource is the embedded
stylesheet at /s/css/tailwind.min.css, so the policy needs neither
unsafe-inline nor unsafe-eval. frame-ancestors 'none' is the primary
anti-framing control with X-Frame-Options as the legacy fallback.

HSTS is emitted unconditionally rather than gated on r.TLS, because the
service runs behind a TLS-terminating proxy and the browser must still
enforce HTTPS end to end.

The headers are set before the request reaches the next handler, so
they are present on error responses too, including recovered panics and
request timeouts.

Tests cover each header's exact value, the CSP's required and forbidden
directives, presence on a 500 response, and a render of the real
dashboard through the middleware confirming the page still references
its stylesheet.

README.md

@@ -203,6 +203,46 @@ are read, so a smaller value would sever the connection before a handler
 using its full budget could respond. `IdleTimeout` exceeds common
 Prometheus scrape intervals so the scraper reuses its connection.
 
+### Security Headers
+
+Every response — the dashboard, the static assets under `/s/...`, the
+healthchecks, the JSON API, and `/metrics` — carries the following
+headers, set by a global middleware:
+
+| Header                      | Value                                 |
+|-----------------------------|---------------------------------------|
+| `Strict-Transport-Security` | `max-age=31536000; includeSubDomains` |
+| `Content-Security-Policy`   | see below                             |
+| `X-Frame-Options`           | `DENY`                                |
+| `X-Content-Type-Options`    | `nosniff`                             |
+| `Referrer-Policy`           | `no-referrer`                         |
+| `Permissions-Policy`        | all unused browser features denied    |
+
+The content security policy is:
+
+```
+default-src 'self'; script-src 'none'; style-src 'self'; img-src 'self';
+font-src 'none'; connect-src 'none'; object-src 'none'; base-uri 'none';
+form-action 'none'; frame-ancestors 'none'
+```
+
+The dashboard ships no JavaScript (the 30-second refresh is a
+`<meta http-equiv="refresh">`), no inline styles, no inline event
+handlers, and no images; its only subresource is the embedded stylesheet
+at `/s/css/tailwind.min.css`, which `style-src 'self'` permits. The
+policy therefore needs neither `unsafe-inline` nor `unsafe-eval`.
+`frame-ancestors 'none'` is the primary anti-framing control, with
+`X-Frame-Options: DENY` retained as the legacy fallback.
+
+HSTS is emitted unconditionally, including over plain HTTP. dnswatcher is
+expected to run behind a TLS-terminating reverse proxy, and the browser
+must still be told to enforce HTTPS end to end, so the header is never
+gated on whether the request itself arrived over TLS.
+
+`Referrer-Policy: no-referrer` is stricter than the
+`strict-origin-when-cross-origin` baseline: the dashboard has no
+cross-origin navigation needs, and its URL may name internal hosts.
+
 ---
 
 ## Architecture
@@ -215,7 +255,8 @@ internal/
   globals/globals.go           Build-time variables (version)
   logger/logger.go             slog structured logging (TTY detection)
   healthcheck/healthcheck.go   Health check service
-  middleware/middleware.go      HTTP middleware (logging, CORS, metrics auth)
+  middleware/middleware.go      HTTP middleware (logging, CORS, security
+                               headers, metrics auth)
   handlers/handlers.go         HTTP request handlers
   server/
     server.go                  HTTP server lifecycle

TODO.md

@@ -23,13 +23,8 @@ Rationale, Design, TODO, License, Author) if any are still missing.
 
 # Completed Steps
 
-- 2026-09-21: server timeout test now drives `Run` and asserts the
-  served `http.Server` carries the timeouts; corrected the inverted
-  `ReadTimeout` rationale note (#120).
-
 - 2026-09-21: `go mod tidy` dropped the redundant `golang.org/x/sync`
   `// indirect` line so `script/bootstrap` leaves a clean tree (#132)
-
 - 2026-08-10: comment-only corrections to `script/bootstrap`,
   `script/cibuild`, and `Dockerfile.lint`. The `goimports` pin in
   `script/bootstrap` was justified by a claim that `script/fmt-check`
@@ -116,6 +111,16 @@ Rationale, Design, TODO, License, Author) if any are still missing.
   than the 60s `chimw.Timeout` handler budget so that budget stays
   reachable, and tests in `internal/server` pin both the non-zero
   values and that relationship (#99)
+- 2026-08-09: security response headers middleware
+  (`SecurityHeaders()` in `internal/middleware/middleware.go`)
+  registered globally in `internal/server/routes.go`, so HSTS, CSP,
+  `X-Frame-Options`, `X-Content-Type-Options`, `Referrer-Policy`, and
+  `Permissions-Policy` are set on every response including `/s/...` and
+  `/metrics`; the CSP needs no `unsafe-inline`/`unsafe-eval` because the
+  dashboard ships no JavaScript and no inline styles; HSTS is emitted
+  unconditionally per policy (TLS-terminating proxy in front). Remaining
+  1.0 hardening items — `http.Server` timeouts, request body limits,
+  rate limiting, CORS scoping — are tracked separately
 - 2026-08-07: golangci-lint bumped to v2.12.2 (commit-pinned installs
   in `Dockerfile` and `script/bootstrap`); `.golangci.yml` set to the
   org-standard v2-schema config used across the org's repos

internal/middleware/middleware.go

@@ -21,6 +21,60 @@ import (
 // corsMaxAge is the maximum age for CORS preflight responses.
 const corsMaxAge = 300
 
+// Security response header values applied to every response.
+//
+// The CSP is as strict as the dashboard allows: the template ships no
+// JavaScript, no inline styles, no inline event handlers and no images,
+// and its only subresource is the embedded stylesheet at
+// /s/css/tailwind.min.css, which style-src 'self' permits. Neither
+// unsafe-inline nor unsafe-eval is used. frame-ancestors 'none' is the
+// primary anti-framing control; X-Frame-Options is the legacy fallback.
+const (
+	// hstsValue is emitted unconditionally, including over plain HTTP,
+	// because the service runs behind a TLS-terminating proxy and the
+	// browser must still enforce HTTPS end to end.
+	hstsValue = "max-age=31536000; includeSubDomains"
+
+	cspValue = "default-src 'self'; " +
+		"script-src 'none'; " +
+		"style-src 'self'; " +
+		"img-src 'self'; " +
+		"font-src 'none'; " +
+		"connect-src 'none'; " +
+		"object-src 'none'; " +
+		"base-uri 'none'; " +
+		"form-action 'none'; " +
+		"frame-ancestors 'none'"
+
+	frameOptionsValue = "DENY"
+
+	contentTypeOptionsValue = "nosniff"
+
+	// referrerPolicyValue is stricter than the policy minimum of
+	// strict-origin-when-cross-origin: the dashboard has no
+	// cross-origin navigation needs and its URL may name internal
+	// hosts.
+	referrerPolicyValue = "no-referrer"
+
+	permissionsPolicyValue = "accelerometer=(), " +
+		"autoplay=(), " +
+		"camera=(), " +
+		"display-capture=(), " +
+		"encrypted-media=(), " +
+		"fullscreen=(), " +
+		"geolocation=(), " +
+		"gyroscope=(), " +
+		"magnetometer=(), " +
+		"microphone=(), " +
+		"midi=(), " +
+		"payment=(), " +
+		"picture-in-picture=(), " +
+		"publickey-credentials-get=(), " +
+		"screen-wake-lock=(), " +
+		"usb=(), " +
+		"xr-spatial-tracking=()"
+)
+
 // Params contains dependencies for Middleware.
 type Params struct {
 	fx.In
@@ -186,6 +240,37 @@ func (m *Middleware) CORS() func(http.Handler) http.Handler {
 	})
 }
 
+// SecurityHeaders returns middleware that sets the security response
+// headers required for production internet exposure on every response.
+//
+// The headers are set before the request reaches the next handler so
+// that they are present on every response, including panics recovered
+// by chi's Recoverer and timeouts produced by chi's Timeout.
+func (m *Middleware) SecurityHeaders() func(http.Handler) http.Handler {
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(
+			writer http.ResponseWriter,
+			request *http.Request,
+		) {
+			header := writer.Header()
+			header.Set("Strict-Transport-Security", hstsValue)
+			header.Set("Content-Security-Policy", cspValue)
+			header.Set("X-Frame-Options", frameOptionsValue)
+			header.Set(
+				"X-Content-Type-Options",
+				contentTypeOptionsValue,
+			)
+			header.Set("Referrer-Policy", referrerPolicyValue)
+			header.Set(
+				"Permissions-Policy",
+				permissionsPolicyValue,
+			)
+
+			next.ServeHTTP(writer, request)
+		})
+	}
+}
+
 // MetricsAuth returns basic auth middleware for /metrics.
 func (m *Middleware) MetricsAuth() func(http.Handler) http.Handler {
 	if m.params.Config.MetricsUsername == "" {

internal/middleware/middleware_test.go

@@ -0,0 +1,334 @@
+package middleware_test
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+	"go.uber.org/fx/fxtest"
+
+	"sneak.berlin/go/dnswatcher/internal/config"
+	"sneak.berlin/go/dnswatcher/internal/globals"
+	"sneak.berlin/go/dnswatcher/internal/handlers"
+	"sneak.berlin/go/dnswatcher/internal/logger"
+	"sneak.berlin/go/dnswatcher/internal/middleware"
+	"sneak.berlin/go/dnswatcher/internal/notify"
+	"sneak.berlin/go/dnswatcher/internal/state"
+)
+
+// Expected security header values, spelled out literally so that any
+// change to the middleware has to be made deliberately here as well.
+const (
+	wantHSTS = "max-age=31536000; includeSubDomains"
+
+	wantCSP = "default-src 'self'; " +
+		"script-src 'none'; " +
+		"style-src 'self'; " +
+		"img-src 'self'; " +
+		"font-src 'none'; " +
+		"connect-src 'none'; " +
+		"object-src 'none'; " +
+		"base-uri 'none'; " +
+		"form-action 'none'; " +
+		"frame-ancestors 'none'"
+
+	wantFrameOptions = "DENY"
+
+	wantContentTypeOptions = "nosniff"
+
+	wantReferrerPolicy = "no-referrer"
+
+	wantPermissionsPolicy = "accelerometer=(), " +
+		"autoplay=(), " +
+		"camera=(), " +
+		"display-capture=(), " +
+		"encrypted-media=(), " +
+		"fullscreen=(), " +
+		"geolocation=(), " +
+		"gyroscope=(), " +
+		"magnetometer=(), " +
+		"microphone=(), " +
+		"midi=(), " +
+		"payment=(), " +
+		"picture-in-picture=(), " +
+		"publickey-credentials-get=(), " +
+		"screen-wake-lock=(), " +
+		"usb=(), " +
+		"xr-spatial-tracking=()"
+)
+
+// stylesheetPath is the only subresource the dashboard loads.
+const stylesheetPath = "/s/css/tailwind.min.css"
+
+// newTestLogger builds a logger for direct component construction.
+func newTestLogger(t *testing.T) *logger.Logger {
+	t.Helper()
+
+	glob, err := globals.New(nil)
+	if err != nil {
+		t.Fatalf("globals.New: %v", err)
+	}
+
+	log, err := logger.New(nil, logger.Params{Globals: glob})
+	if err != nil {
+		t.Fatalf("logger.New: %v", err)
+	}
+
+	return log
+}
+
+// newTestMiddleware builds a Middleware without an fx application.
+func newTestMiddleware(t *testing.T) *middleware.Middleware {
+	t.Helper()
+
+	glob, err := globals.New(nil)
+	if err != nil {
+		t.Fatalf("globals.New: %v", err)
+	}
+
+	mw, err := middleware.New(nil, middleware.Params{
+		Logger:  newTestLogger(t),
+		Globals: glob,
+		Config:  &config.Config{},
+	})
+	if err != nil {
+		t.Fatalf("middleware.New: %v", err)
+	}
+
+	return mw
+}
+
+// serveWithSecurityHeaders runs a GET through SecurityHeaders and
+// returns the recorded response.
+func serveWithSecurityHeaders(
+	t *testing.T,
+	target string,
+	handler http.Handler,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	mw := newTestMiddleware(t)
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, target, nil,
+	)
+
+	mw.SecurityHeaders()(handler).ServeHTTP(rec, req)
+
+	return rec
+}
+
+// okHandler writes a trivial 200 response.
+func okHandler() http.Handler {
+	return http.HandlerFunc(func(
+		writer http.ResponseWriter,
+		_ *http.Request,
+	) {
+		writer.WriteHeader(http.StatusOK)
+	})
+}
+
+func TestSecurityHeaders(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name   string
+		header string
+		want   string
+	}{
+		{
+			"hsts",
+			"Strict-Transport-Security",
+			wantHSTS,
+		},
+		{
+			"csp",
+			"Content-Security-Policy",
+			wantCSP,
+		},
+		{
+			"frame options",
+			"X-Frame-Options",
+			wantFrameOptions,
+		},
+		{
+			"content type options",
+			"X-Content-Type-Options",
+			wantContentTypeOptions,
+		},
+		{
+			"referrer policy",
+			"Referrer-Policy",
+			wantReferrerPolicy,
+		},
+		{
+			"permissions policy",
+			"Permissions-Policy",
+			wantPermissionsPolicy,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			rec := serveWithSecurityHeaders(t, "/", okHandler())
+
+			got := rec.Header().Get(tt.header)
+			if got != tt.want {
+				t.Errorf(
+					"%s = %q, want %q",
+					tt.header, got, tt.want,
+				)
+			}
+		})
+	}
+}
+
+// TestSecurityHeadersCSPDirectives guards the properties the repo
+// policy requires of the content security policy itself.
+func TestSecurityHeadersCSPDirectives(t *testing.T) {
+	t.Parallel()
+
+	rec := serveWithSecurityHeaders(t, "/", okHandler())
+	csp := rec.Header().Get("Content-Security-Policy")
+
+	forbidden := []string{"unsafe-inline", "unsafe-eval"}
+	for _, directive := range forbidden {
+		if strings.Contains(csp, directive) {
+			t.Errorf("CSP must not contain %q: %q", directive, csp)
+		}
+	}
+
+	required := []string{
+		"default-src 'self'",
+		"script-src 'none'",
+		"style-src 'self'",
+		"frame-ancestors 'none'",
+	}
+	for _, directive := range required {
+		if !strings.Contains(csp, directive) {
+			t.Errorf("CSP must contain %q: %q", directive, csp)
+		}
+	}
+}
+
+// TestSecurityHeadersOnErrorResponse verifies the headers are emitted
+// even when the wrapped handler fails, since they are set before the
+// handler runs.
+func TestSecurityHeadersOnErrorResponse(t *testing.T) {
+	t.Parallel()
+
+	failing := http.HandlerFunc(func(
+		writer http.ResponseWriter,
+		_ *http.Request,
+	) {
+		http.Error(
+			writer,
+			"boom",
+			http.StatusInternalServerError,
+		)
+	})
+
+	rec := serveWithSecurityHeaders(t, "/api/v1/status", failing)
+
+	if rec.Code != http.StatusInternalServerError {
+		t.Fatalf("status = %d, want 500", rec.Code)
+	}
+
+	if got := rec.Header().Get(
+		"X-Content-Type-Options",
+	); got != wantContentTypeOptions {
+		t.Errorf(
+			"X-Content-Type-Options = %q, want %q",
+			got, wantContentTypeOptions,
+		)
+	}
+
+	if got := rec.Header().Get(
+		"Strict-Transport-Security",
+	); got != wantHSTS {
+		t.Errorf(
+			"Strict-Transport-Security = %q, want %q",
+			got, wantHSTS,
+		)
+	}
+}
+
+// newTestHandlers builds real Handlers with empty monitoring state.
+func newTestHandlers(t *testing.T) *handlers.Handlers {
+	t.Helper()
+
+	glob, err := globals.New(nil)
+	if err != nil {
+		t.Fatalf("globals.New: %v", err)
+	}
+
+	log := newTestLogger(t)
+
+	notifier, err := notify.New(fxtest.NewLifecycle(t), notify.Params{
+		Logger: log,
+		Config: &config.Config{},
+	})
+	if err != nil {
+		t.Fatalf("notify.New: %v", err)
+	}
+
+	hnd, err := handlers.New(nil, handlers.Params{
+		Logger:  log,
+		Globals: glob,
+		State:   state.NewForTest(),
+		Notify:  notifier,
+	})
+	if err != nil {
+		t.Fatalf("handlers.New: %v", err)
+	}
+
+	return hnd
+}
+
+// TestDashboardRendersWithSecurityHeaders renders the real dashboard
+// through the middleware and checks that the policy still permits the
+// one stylesheet the page loads.
+func TestDashboardRendersWithSecurityHeaders(t *testing.T) {
+	t.Parallel()
+
+	mw := newTestMiddleware(t)
+	hnd := newTestHandlers(t)
+
+	router := chi.NewRouter()
+	router.Use(mw.SecurityHeaders())
+	router.Get("/", hnd.HandleDashboard())
+
+	rec := httptest.NewRecorder()
+	req := httptest.NewRequestWithContext(
+		t.Context(), http.MethodGet, "/", nil,
+	)
+
+	router.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusOK {
+		t.Fatalf("status = %d, want 200", rec.Code)
+	}
+
+	body := rec.Body.String()
+	if !strings.Contains(body, stylesheetPath) {
+		t.Errorf("dashboard does not reference %q", stylesheetPath)
+	}
+
+	if !strings.Contains(body, "dnswatcher") {
+		t.Errorf("dashboard body looks empty: %d bytes", len(body))
+	}
+
+	csp := rec.Header().Get("Content-Security-Policy")
+	if csp != wantCSP {
+		t.Errorf("CSP = %q, want %q", csp, wantCSP)
+	}
+
+	// The stylesheet is same-origin, so style-src 'self' allows it.
+	if !strings.Contains(csp, "style-src 'self'") {
+		t.Errorf("CSP would block %q: %q", stylesheetPath, csp)
+	}
+}

internal/server/export_test.go

@@ -5,20 +5,15 @@ import (
 	"time"
 )
 
+// NewHTTPServer exports newHTTPServer for testing.
+func NewHTTPServer(
+	listenAddr string,
+	handler http.Handler,
+) *http.Server {
+	return newHTTPServer(listenAddr, handler)
+}
+
 // RequestTimeout exports the handler execution budget applied by
 // chimw.Timeout in SetupRoutes, so tests can assert the relationship
 // between it and the server's WriteTimeout.
 const RequestTimeout time.Duration = requestTimeout
-
-// SetListenPort overrides the port Run binds. A test uses it to hand
-// Run an unbindable port so ListenAndServe fails immediately and Run
-// returns after storing its http.Server.
-func SetListenPort(s *Server, port int) {
-	s.port = port
-}
-
-// HTTPServerOf returns the http.Server that Run built and stored, so a
-// test can inspect the timeouts the running server actually carries.
-func HTTPServerOf(s *Server) *http.Server {
-	return s.httpServer
-}

internal/server/routes.go

@@ -21,6 +21,7 @@ func (s *Server) SetupRoutes() {
 	// Global middleware
 	s.router.Use(chimw.Recoverer)
 	s.router.Use(chimw.RequestID)
+	s.router.Use(s.mw.SecurityHeaders())
 	s.router.Use(s.mw.Logging())
 	s.router.Use(s.mw.CORS())
 	s.router.Use(chimw.Timeout(requestTimeout))

internal/server/server_test.go

@@ -1,136 +1,112 @@
 package server_test
 
 import (
+	"net/http"
 	"testing"
 
-	"github.com/spf13/viper"
-	"go.uber.org/fx"
-
-	"sneak.berlin/go/dnswatcher/internal/config"
-	"sneak.berlin/go/dnswatcher/internal/globals"
-	"sneak.berlin/go/dnswatcher/internal/handlers"
-	"sneak.berlin/go/dnswatcher/internal/healthcheck"
-	"sneak.berlin/go/dnswatcher/internal/logger"
-	"sneak.berlin/go/dnswatcher/internal/middleware"
-	"sneak.berlin/go/dnswatcher/internal/notify"
 	"sneak.berlin/go/dnswatcher/internal/server"
-	"sneak.berlin/go/dnswatcher/internal/state"
 )
 
-// buildServer wires a *server.Server exactly as cmd/dnswatcher does,
+// noopHandler stands in for the router; newHTTPServer only stores it.
-// minus the watcher/resolver subtree that would touch live DNS. fx
+func noopHandler() http.Handler {
-// builds the object graph but the lifecycle is never started, so no
+	return http.HandlerFunc(
-// OnStart hook runs and nothing listens or resolves. The caller must
+		func(w http.ResponseWriter, _ *http.Request) {
-// first configure viper (config.New reads it), which is also why the
+			w.WriteHeader(http.StatusOK)
-// caller cannot run in parallel.
+		},
-func buildServer(t *testing.T) *server.Server {
-	t.Helper()
-
-	var srv *server.Server
-
-	app := fx.New(
-		fx.NopLogger,
-		fx.Provide(
-			globals.New,
-			logger.New,
-			config.New,
-			state.New,
-			healthcheck.New,
-			notify.New,
-			middleware.New,
-			handlers.New,
-			server.New,
-		),
-		fx.Populate(&srv),
 	)
-
-	err := app.Err()
-	if err != nil {
-		t.Fatalf("building server graph: %v", err)
-	}
-
-	return srv
 }
 
-// TestRunWiresSocketTimeouts pins that the http.Server the running
+// TestHTTPServerTimeoutsAreSet asserts that every socket-level
-// server actually serves — the one Run builds and hands to
+// timeout is configured. A zero value in net/http means "no limit",
-// ListenAndServe — carries every socket-level timeout, plus the two
+// so a refactor that silently drops one of these reintroduces the
-// relationships the values must satisfy. Earlier tests asserted these
+// slowloris / unreaped-keep-alive exposure this guards against.
-// on newHTTPServer directly, which left the call site unguarded: a Run
-// that built its http.Server inline would drop every timeout with the
-// suite still green (https://git.eeqj.de/sneak/dnswatcher/issues/120).
 //
-// Run is driven to completion with an unbindable port: it builds and
+// The assertions are on the configured field values only; nothing
-// stores s.httpServer, then ListenAndServe fails at once and Run
+// here measures elapsed time, so the test cannot flake on timing.
-// returns without ever listening. The assertions run in the same
+func TestHTTPServerTimeoutsAreSet(t *testing.T) {
-// goroutine after Run returns, so reading s.httpServer is free of any
+	t.Parallel()
-// data race. Nothing here measures elapsed time.
-//
-// On the ReadTimeout >= ReadHeaderTimeout relationship: a smaller
-// ReadTimeout does NOT make the header phase unreachable. net/http's
-// (*Server).readHeaderTimeout applies ReadHeaderTimeout directly, so
-// the header read keeps its full budget. What breaks is the
-// whole-request deadline: once the headers are read, readRequest
-// installs a read deadline of t0+ReadTimeout, which is already in the
-// past when ReadTimeout is the smaller value, severing the request.
-// Verified against the pinned go1.25 net/http (Dockerfile golang
-// 1.25-alpine; go.mod go 1.25.5): src/net/http/server.go readRequest
-// and (*Server).readHeaderTimeout.
-func TestRunWiresSocketTimeouts(t *testing.T) {
-	// Sets an env var and touches viper global state, so like the
-	// config tests it cannot use t.Parallel.
-	viper.Reset()
-	t.Setenv("DNSWATCHER_TARGETS", "example.com")
 
-	srv := buildServer(t)
+	srv := server.NewHTTPServer(":8080", noopHandler())
-	server.SetListenPort(srv, -1)
 
-	srv.Run()
+	if srv.ReadTimeout <= 0 {
-
-	hs := server.HTTPServerOf(srv)
-	if hs == nil {
-		t.Fatal("Run did not build an http.Server")
-	}
-
-	if hs.ReadTimeout <= 0 {
-		t.Errorf("ReadTimeout must be non-zero, got %v", hs.ReadTimeout)
-	}
-
-	if hs.ReadHeaderTimeout <= 0 {
 		t.Errorf(
-			"ReadHeaderTimeout must be non-zero, got %v",
+			"ReadTimeout must be non-zero, got %v",
-			hs.ReadHeaderTimeout,
+			srv.ReadTimeout,
 		)
 	}
 
-	if hs.WriteTimeout <= 0 {
+	if srv.ReadHeaderTimeout <= 0 {
-		t.Errorf("WriteTimeout must be non-zero, got %v", hs.WriteTimeout)
+		t.Errorf(
+			"ReadHeaderTimeout must be non-zero, got %v",
+			srv.ReadHeaderTimeout,
+		)
 	}
 
-	if hs.IdleTimeout <= 0 {
+	if srv.WriteTimeout <= 0 {
-		t.Errorf("IdleTimeout must be non-zero, got %v", hs.IdleTimeout)
+		t.Errorf(
+			"WriteTimeout must be non-zero, got %v",
+			srv.WriteTimeout,
+		)
 	}
 
-	if hs.WriteTimeout <= server.RequestTimeout {
+	if srv.IdleTimeout <= 0 {
+		t.Errorf(
+			"IdleTimeout must be non-zero, got %v",
+			srv.IdleTimeout,
+		)
+	}
+}
+
+// TestWriteTimeoutExceedsHandlerBudget pins the one relationship the
+// values must satisfy. net/http arms the write deadline once request
+// headers are read, so it covers handler execution plus the response
+// flush. If WriteTimeout were not greater than the chimw.Timeout
+// handler budget, the connection would be severed before a handler
+// that used its full budget could respond, making that budget
+// unreachable.
+func TestWriteTimeoutExceedsHandlerBudget(t *testing.T) {
+	t.Parallel()
+
+	srv := server.NewHTTPServer(":8080", noopHandler())
+
+	if srv.WriteTimeout <= server.RequestTimeout {
 		t.Errorf(
 			"WriteTimeout (%v) must exceed handler budget (%v)",
-			hs.WriteTimeout,
+			srv.WriteTimeout,
 			server.RequestTimeout,
 		)
 	}
+}
 
-	if hs.ReadTimeout < hs.ReadHeaderTimeout {
+// TestReadTimeoutCoversHeaderTimeout asserts the read deadline for
+// the whole request is at least as long as the header-only deadline;
+// a smaller ReadTimeout would make ReadHeaderTimeout unreachable.
+func TestReadTimeoutCoversHeaderTimeout(t *testing.T) {
+	t.Parallel()
+
+	srv := server.NewHTTPServer(":8080", noopHandler())
+
+	if srv.ReadTimeout < srv.ReadHeaderTimeout {
 		t.Errorf(
 			"ReadTimeout (%v) must be >= ReadHeaderTimeout (%v)",
-			hs.ReadTimeout,
+			srv.ReadTimeout,
-			hs.ReadHeaderTimeout,
+			srv.ReadHeaderTimeout,
-		)
-	}
-
-	if hs.Handler != srv {
-		t.Errorf(
-			"Run wired handler %T, want the *server.Server",
-			hs.Handler,
 		)
 	}
 }
+
+// TestHTTPServerAddrAndHandler covers the rest of the constructor so
+// a future edit cannot drop the listen address or the handler.
+func TestHTTPServerAddrAndHandler(t *testing.T) {
+	t.Parallel()
+
+	srv := server.NewHTTPServer(":9999", noopHandler())
+
+	if srv.Addr != ":9999" {
+		t.Errorf("Addr = %q, want %q", srv.Addr, ":9999")
+	}
+
+	if srv.Handler == nil {
+		t.Error("Handler must not be nil")
+	}
+}