func New()

in web/web.go [250:436]
151 lines of code
10 McCabe index (conditional complexity)

func New(logger log.Logger, o *Options) *Handler {
	if logger == nil {
		logger = log.NewNopLogger()
	}

	m := newMetrics(o.Registerer)
	router := route.New().
		WithInstrumentation(m.instrumentHandler).
		WithInstrumentation(setPathWithPrefix(""))

	cwd, err := os.Getwd()
	if err != nil {
		cwd = "<error retrieving current working directory>"
	}

	h := &Handler{
		logger: logger,

		gatherer: o.Gatherer,
		metrics:  m,

		router:      router,
		quitCh:      make(chan struct{}),
		reloadCh:    make(chan chan error),
		options:     o,
		versionInfo: o.Version,
		birth:       time.Now(),
		cwd:         cwd,
		flagsMap:    o.Flags,

		context:       o.Context,
		scrapeManager: o.ScrapeManager,
		ruleManager:   o.RuleManager,
		queryEngine:   o.QueryEngine,
		tsdb:          o.TSDB,
		storage:       o.Storage,
		notifier:      o.Notifier,

		now: model.Now,

		ready: 0,
	}

	h.apiV1 = api_v1.NewAPI(h.queryEngine, h.storage, h.scrapeManager, h.notifier,
		func() config.Config {
			h.mtx.RLock()
			defer h.mtx.RUnlock()
			return *h.config
		},
		o.Flags,
		h.testReady,
		func() api_v1.TSDBAdmin {
			return h.options.TSDB()
		},
		h.options.EnableAdminAPI,
		logger,
		h.ruleManager,
		h.options.RemoteReadSampleLimit,
		h.options.RemoteReadConcurrencyLimit,
		h.options.RemoteReadBytesInFrame,
		h.options.CORSOrigin,
		h.runtimeInfo,
		h.versionInfo,
	)

	if o.RoutePrefix != "/" {
		// If the prefix is missing for the root path, prepend it.
		router.Get("/", func(w http.ResponseWriter, r *http.Request) {
			http.Redirect(w, r, o.RoutePrefix, http.StatusFound)
		})
		router = router.WithPrefix(o.RoutePrefix)
	}

	readyf := h.testReady

	router.Get("/", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, path.Join(o.ExternalURL.Path, "/graph"), http.StatusFound)
	})

	router.Get("/alerts", readyf(h.alerts))
	router.Get("/graph", readyf(h.graph))
	router.Get("/status", readyf(h.status))
	router.Get("/flags", readyf(h.flags))
	router.Get("/config", readyf(h.serveConfig))
	router.Get("/rules", readyf(h.rules))
	router.Get("/targets", readyf(h.targets))
	router.Get("/version", readyf(h.version))
	router.Get("/service-discovery", readyf(h.serviceDiscovery))

	router.Get("/metrics", promhttp.Handler().ServeHTTP)

	router.Get("/federate", readyf(httputil.CompressionHandler{
		Handler: http.HandlerFunc(h.federation),
	}.ServeHTTP))

	router.Get("/consoles/*filepath", readyf(h.consoles))

	router.Get("/static/*filepath", func(w http.ResponseWriter, r *http.Request) {
		r.URL.Path = path.Join("/static", route.Param(r.Context(), "filepath"))
		fs := server.StaticFileServer(ui.Assets)
		fs.ServeHTTP(w, r)
	})

	// Make sure that "<path-prefix>/new" is redirected to "<path-prefix>/new/" and
	// not just the naked "/new/", which would be the default behavior of the router
	// with the "RedirectTrailingSlash" option (https://godoc.org/github.com/julienschmidt/httprouter#Router.RedirectTrailingSlash),
	// and which breaks users with a --web.route-prefix that deviates from the path derived
	// from the external URL.
	router.Get("/new", func(w http.ResponseWriter, r *http.Request) {
		http.Redirect(w, r, path.Join(o.ExternalURL.Path, "new")+"/", http.StatusFound)
	})

	router.Get("/new/*filepath", func(w http.ResponseWriter, r *http.Request) {
		p := route.Param(r.Context(), "filepath")

		// For paths that the React/Reach router handles, we want to serve the
		// index.html, but with replaced path prefix placeholder.
		for _, rp := range reactRouterPaths {
			if p != rp {
				continue
			}

			f, err := ui.Assets.Open("/static/react/index.html")
			if err != nil {
				w.WriteHeader(http.StatusInternalServerError)
				fmt.Fprintf(w, "Error opening React index.html: %v", err)
				return
			}
			idx, err := ioutil.ReadAll(f)
			if err != nil {
				w.WriteHeader(http.StatusInternalServerError)
				fmt.Fprintf(w, "Error reading React index.html: %v", err)
				return
			}
			prefixedIdx := bytes.ReplaceAll(idx, []byte("PATH_PREFIX_PLACEHOLDER"), []byte(o.ExternalURL.Path))
			w.Write(prefixedIdx)
			return
		}

		// For all other paths, serve auxiliary assets.
		r.URL.Path = path.Join("/static/react/", p)
		fs := server.StaticFileServer(ui.Assets)
		fs.ServeHTTP(w, r)
	})

	if o.UserAssetsPath != "" {
		router.Get("/user/*filepath", route.FileServe(o.UserAssetsPath))
	}

	if o.EnableLifecycle {
		router.Post("/-/quit", h.quit)
		router.Put("/-/quit", h.quit)
		router.Post("/-/reload", h.reload)
		router.Put("/-/reload", h.reload)
	} else {
		forbiddenAPINotEnabled := func(w http.ResponseWriter, _ *http.Request) {
			w.WriteHeader(http.StatusForbidden)
			w.Write([]byte("Lifecycle API is not enabled."))
		}
		router.Post("/-/quit", forbiddenAPINotEnabled)
		router.Put("/-/quit", forbiddenAPINotEnabled)
		router.Post("/-/reload", forbiddenAPINotEnabled)
		router.Put("/-/reload", forbiddenAPINotEnabled)
	}
	router.Get("/-/quit", func(w http.ResponseWriter, _ *http.Request) {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write([]byte("Only POST or PUT requests allowed"))
	})
	router.Get("/-/reload", func(w http.ResponseWriter, _ *http.Request) {
		w.WriteHeader(http.StatusMethodNotAllowed)
		w.Write([]byte("Only POST or PUT requests allowed"))
	})

	router.Get("/debug/*subpath", serveDebug)
	router.Post("/debug/*subpath", serveDebug)

	router.Get("/-/healthy", func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		fmt.Fprintf(w, "Prometheus is Healthy.\n")
	})
	router.Get("/-/ready", readyf(func(w http.ResponseWriter, r *http.Request) {
		w.WriteHeader(http.StatusOK)
		fmt.Fprintf(w, "Prometheus is Ready.\n")
	}))

	return h
}