feat: mount pprof and metrics to /api/v2/debug for admins (#20353)

Adds the following debug routes for people with the `debug_info:read`
permission:
- `/api/v2/debug/pprof` for `net/http/pprof`
    - `/`
    - `/cmdline`
    - `/profile`
    - `/symbol`
    - `/trace`
    - `/*`
- `/api/v2/debug/metrics` for Prometheus metrics

coderd/coderd.go

@@ -11,6 +11,7 @@ import (
 	"fmt"
 	"io"
 	"net/http"
+	httppprof "net/http/pprof"
 	"net/url"
 	"path/filepath"
 	"regexp"
@@ -32,6 +33,7 @@ import (
 	"github.com/google/uuid"
 	"github.com/klauspost/compress/zstd"
 	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
 	httpSwagger "github.com/swaggo/http-swagger/v2"
 	"go.opentelemetry.io/otel/trace"
 	"golang.org/x/xerrors"
@@ -1512,7 +1514,8 @@ func New(options *Options) *API {
 		r.Route("/debug", func(r chi.Router) {
 			r.Use(
 				apiKeyMiddleware,
-				// Ensure only owners can access debug endpoints.
+				// Ensure only users with the debug_info:read (e.g. only owners)
+				// can view debug endpoints.
 				func(next http.Handler) http.Handler {
 					return http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
 						if !api.Authorize(r, policy.ActionRead, rbac.ResourceDebugInfo) {
@@ -1545,6 +1548,41 @@ func New(options *Options) *API {
 				})
 			}
 			r.Method("GET", "/expvar", expvar.Handler()) // contains DERP metrics as well as cmdline and memstats
+
+			r.Route("/pprof", func(r chi.Router) {
+				r.Use(func(next http.Handler) http.Handler {
+					// Some of the pprof handlers strip the `/debug/pprof`
+					// prefix, so we need to strip our additional prefix as
+					// well.
+					return http.StripPrefix("/api/v2", next)
+				})
+
+				// Serve the index HTML page.
+				r.Get("/", func(w http.ResponseWriter, r *http.Request) {
+					// Redirect to include a trailing slash, otherwise links on
+					// the generated HTML page will be broken.
+					if !strings.HasSuffix(r.URL.Path, "/") {
+						http.Redirect(w, r, "/api/v2/debug/pprof/", http.StatusTemporaryRedirect)
+						return
+					}
+					httppprof.Index(w, r)
+				})
+
+				// Handle any out of the box pprof handlers that don't get
+				// dealt with by the default index handler. See httppprof.init.
+				r.Get("/cmdline", httppprof.Cmdline)
+				r.Get("/profile", httppprof.Profile)
+				r.Get("/symbol", httppprof.Symbol)
+				r.Get("/trace", httppprof.Trace)
+
+				// Index will handle any standard and custom runtime/pprof
+				// profiles.
+				r.Get("/*", httppprof.Index)
+			})
+
+			r.Get("/metrics", promhttp.InstrumentMetricHandler(
+				options.PrometheusRegistry, promhttp.HandlerFor(options.PrometheusRegistry, promhttp.HandlerOpts{}),
+			).ServeHTTP)
 		})
 		// Manage OAuth2 applications that can use Coder as an OAuth2 provider.
 		r.Route("/oauth2-provider", func(r chi.Router) {