webhooker/internal/middleware/middleware.go

// Package middleware provides HTTP middleware for logging, auth,
// CORS, and metrics.
package middleware

import (
	"log/slog"
	"net"
	"net/http"
	"time"

	basicauth "github.com/99designs/basicauth-go"
	"github.com/go-chi/chi/middleware"
	"github.com/go-chi/cors"
	metrics "github.com/slok/go-http-metrics/metrics/prometheus"
	ghmm "github.com/slok/go-http-metrics/middleware"
	"github.com/slok/go-http-metrics/middleware/std"
	"go.uber.org/fx"
	"sneak.berlin/go/webhooker/internal/config"
	"sneak.berlin/go/webhooker/internal/globals"
	"sneak.berlin/go/webhooker/internal/logger"
	"sneak.berlin/go/webhooker/internal/session"
)

const (
	// corsMaxAge is the maximum time (in seconds) that a
	// preflight response can be cached.
	corsMaxAge = 300
)

//nolint:revive // MiddlewareParams is a standard fx naming convention.
type MiddlewareParams struct {
	fx.In

	Logger  *logger.Logger
	Globals *globals.Globals
	Config  *config.Config
	Session *session.Session
}

// Middleware provides HTTP middleware for logging, CORS, auth, and
// metrics.
type Middleware struct {
	log     *slog.Logger
	params  *MiddlewareParams
	session *session.Session
}

// New creates a Middleware from the provided fx parameters.
//
//nolint:revive // lc parameter is required by fx even if unused.
func New(
	lc fx.Lifecycle,
	params MiddlewareParams,
) (*Middleware, error) {
	s := new(Middleware)
	s.params = &params
	s.log = params.Logger.Get()
	s.session = params.Session

	return s, nil
}

// the following is from
// https://learning-cloud-native-go.github.io/docs/a6.adding_zerolog_logger/

func ipFromHostPort(hp string) string {
	h, _, err := net.SplitHostPort(hp)
	if err != nil {
		return ""
	}

	if len(h) > 0 && h[0] == '[' {
		return h[1 : len(h)-1]
	}

	return h
}

type loggingResponseWriter struct {
	http.ResponseWriter

	statusCode int
}

// newLoggingResponseWriter wraps w and records status codes.
func newLoggingResponseWriter(
	w http.ResponseWriter,
) *loggingResponseWriter {
	return &loggingResponseWriter{w, http.StatusOK}
}

func (lrw *loggingResponseWriter) WriteHeader(code int) {
	lrw.statusCode = code
	lrw.ResponseWriter.WriteHeader(code)
}

// Logging returns middleware that logs each HTTP request with
// timing and metadata.
func (s *Middleware) Logging() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			w http.ResponseWriter,
			r *http.Request,
		) {
			start := time.Now()
			lrw := newLoggingResponseWriter(w)
			ctx := r.Context()

			defer func() {
				latency := time.Since(start)
				requestID := ""

				if reqID := ctx.Value(
					middleware.RequestIDKey,
				); reqID != nil {
					if id, ok := reqID.(string); ok {
						requestID = id
					}
				}

				s.log.Info("http request",
					"request_start", start,
					"method", r.Method,
					"url", r.URL.String(),
					"useragent", r.UserAgent(),
					"request_id", requestID,
					"referer", r.Referer(),
					"proto", r.Proto,
					"remoteIP", ipFromHostPort(r.RemoteAddr),
					"status", lrw.statusCode,
					"latency_ms", latency.Milliseconds(),
				)
			}()

			next.ServeHTTP(lrw, r)
		})
	}
}

// CORS returns middleware that sets CORS headers (permissive in
// dev, no-op in prod).
func (s *Middleware) CORS() func(http.Handler) http.Handler {
	if s.params.Config.IsDev() {
		// In development, allow any origin for local testing.
		return cors.Handler(cors.Options{
			AllowedOrigins: []string{"*"},
			AllowedMethods: []string{
				"GET", "POST", "PUT", "DELETE", "OPTIONS",
			},
			AllowedHeaders: []string{
				"Accept", "Authorization",
				"Content-Type", "X-CSRF-Token",
			},
			ExposedHeaders:   []string{"Link"},
			AllowCredentials: false,
			MaxAge:           corsMaxAge,
		})
	}

	// In production, the web UI is server-rendered so
	// cross-origin requests are not expected. Return a no-op
	// middleware.
	return func(next http.Handler) http.Handler {
		return next
	}
}

// RequireAuth returns middleware that checks for a valid session.
// Unauthenticated users are redirected to the login page.
func (s *Middleware) RequireAuth() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			w http.ResponseWriter,
			r *http.Request,
		) {
			sess, err := s.session.Get(r)
			if err != nil {
				s.log.Debug(
					"auth middleware: failed to get session",
					"error", err,
				)
				http.Redirect(
					w, r, "/pages/login", http.StatusSeeOther,
				)

				return
			}

			if !s.session.IsAuthenticated(sess) {
				s.log.Debug(
					"auth middleware: unauthenticated request",
					"path", r.URL.Path,
					"method", r.Method,
				)
				http.Redirect(
					w, r, "/pages/login", http.StatusSeeOther,
				)

				return
			}

			next.ServeHTTP(w, r)
		})
	}
}

// Metrics returns middleware that records Prometheus HTTP metrics.
func (s *Middleware) Metrics() func(http.Handler) http.Handler {
	mdlw := ghmm.New(ghmm.Config{
		Recorder: metrics.NewRecorder(metrics.Config{}),
	})

	return func(next http.Handler) http.Handler {
		return std.Handler("", mdlw, next)
	}
}

// MetricsAuth returns middleware that protects metrics endpoints
// with basic auth.
func (s *Middleware) MetricsAuth() func(http.Handler) http.Handler {
	return basicauth.New(
		"metrics",
		map[string][]string{
			s.params.Config.MetricsUsername: {
				s.params.Config.MetricsPassword,
			},
		},
	)
}

// SecurityHeaders returns middleware that sets production security
// headers on every response: HSTS, X-Content-Type-Options,
// X-Frame-Options, CSP, Referrer-Policy, and Permissions-Policy.
func (s *Middleware) SecurityHeaders() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			w http.ResponseWriter,
			r *http.Request,
		) {
			w.Header().Set(
				"Strict-Transport-Security",
				"max-age=63072000; includeSubDomains; preload",
			)
			w.Header().Set(
				"X-Content-Type-Options", "nosniff",
			)
			w.Header().Set("X-Frame-Options", "DENY")
			w.Header().Set(
				"Content-Security-Policy",
				"default-src 'self'; "+
					"script-src 'self' 'unsafe-inline'; "+
					"style-src 'self' 'unsafe-inline'",
			)
			w.Header().Set(
				"Referrer-Policy",
				"strict-origin-when-cross-origin",
			)
			w.Header().Set(
				"Permissions-Policy",
				"camera=(), microphone=(), geolocation=()",
			)

			next.ServeHTTP(w, r)
		})
	}
}

// NoCache returns middleware that instructs browsers and
// intermediary proxies not to cache the response. It sets
// Cache-Control: no-store and Pragma: no-cache (the latter for
// older HTTP/1.0 intermediaries). Apply it to authenticated pages
// so webhook configuration and captured event data are not stored
// by caches.
func (s *Middleware) NoCache() func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			w http.ResponseWriter,
			r *http.Request,
		) {
			w.Header().Set("Cache-Control", "no-store")
			w.Header().Set("Pragma", "no-cache")

			next.ServeHTTP(w, r)
		})
	}
}

// bodyLimitedMethod reports whether the request method carries a
// body that the MaxBodySize middleware should cap.
func bodyLimitedMethod(method string) bool {
	return method == http.MethodPost ||
		method == http.MethodPut ||
		method == http.MethodPatch
}

// MaxBodySize returns middleware that limits the size of
// POST/PUT/PATCH request bodies to maxBytes. It must be registered
// before any middleware that parses the body — notably CSRF, which
// calls r.PostFormValue — so that form parsing happens under this
// cap rather than net/http's 10 MB default.
//
// Two enforcement paths exist, because http.MaxBytesReader alone
// cannot produce a 413: it reports the overflow as an error from
// Read, by which point the body parser downstream has already
// converted that error into its own response.
//
//   - Declared oversize: the request announces a Content-Length
//     greater than maxBytes. The middleware answers 413 Request
//     Entity Too Large immediately and does not call the next
//     handler, so neither CSRF nor the endpoint handler runs.
//   - Undeclared oversize: the request is chunked (Content-Length
//     of -1) or lies about its Content-Length. There is nothing to
//     check up front, so http.MaxBytesReader hard-caps the body at
//     maxBytes and the request fails downstream — the form parse
//     errors out and CSRF rejects it with 403. The response is less
//     precise than a 413, but the body is still never buffered
//     beyond the cap, which is the property that matters.
func (s *Middleware) MaxBodySize(
	maxBytes int64,
) func(http.Handler) http.Handler {
	return func(next http.Handler) http.Handler {
		return http.HandlerFunc(func(
			w http.ResponseWriter,
			r *http.Request,
		) {
			if !bodyLimitedMethod(r.Method) {
				next.ServeHTTP(w, r)

				return
			}

			if r.ContentLength > maxBytes {
				s.log.Warn(
					"request body exceeds limit",
					"method", r.Method,
					"path", r.URL.Path,
					"content_length", r.ContentLength,
					"limit", maxBytes,
				)
				http.Error(
					w,
					"Request Entity Too Large",
					http.StatusRequestEntityTooLarge,
				)

				return
			}

			r.Body = http.MaxBytesReader(w, r.Body, maxBytes)

			next.ServeHTTP(w, r)
		})
	}
}