tsweb: replace NewMux with a more flexible DebugHandler.

Signed-off-by: David Anderson <danderson@tailscale.com>
2025-08-13 06:07:34 +00:00 · 2021-06-15 23:38:19 -07:00
parent b461ba9554
commit 0022c3d2e2
5 changed files with 339 additions and 83 deletions
--- a/tsweb/debug.go
+++ b/tsweb/debug.go
@@ -0,0 +1,136 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package tsweb
+
+import (
+	"expvar"
+	"fmt"
+	"html"
+	"io"
+	"net/http"
+	"net/http/pprof"
+	"net/url"
+	"os"
+	"runtime"
+
+	"tailscale.com/version"
+)
+
+// DebugHandler is an http.Handler that serves a debugging "homepage",
+// and provides helpers to register more debug endpoints and reports.
+//
+// The rendered page consists of three sections: informational
+// key/value pairs, links to other pages, and additional
+// program-specific HTML. Callers can add to these sections using the
+// KV, URL and Section helpers respectively.
+//
+// Additionally, the Handle method offers a shorthand for correctly
+// registering debug handlers and cross-linking them from /debug/.
+type DebugHandler struct {
+	mux      *http.ServeMux                   // where this handler is registered
+	kvs      []func(io.Writer)                // output one <li>...</li> each, see KV()
+	urls     []string                         // one <li>...</li> block with link each
+	sections []func(io.Writer, *http.Request) // invoked in registration order prior to outputting </body>
+}
+
+// Debugger returns the DebugHandler registered on mux at /debug/,
+// creating it if necessary.
+func Debugger(mux *http.ServeMux) *DebugHandler {
+	h, pat := mux.Handler(&http.Request{URL: &url.URL{Path: "/debug/"}})
+	if d, ok := h.(*DebugHandler); ok && pat == "/debug/" {
+		return d
+	}
+	ret := &DebugHandler{
+		mux: mux,
+	}
+	mux.Handle("/debug/", ret)
+
+	ret.KVFunc("Uptime", func() interface{} { return Uptime() })
+	ret.KV("Version", version.Long)
+	ret.Handle("vars", "Metrics (Go)", expvar.Handler())
+	ret.Handle("varz", "Metrics (Prometheus)", http.HandlerFunc(VarzHandler))
+	ret.Handle("pprof/", "pprof", http.HandlerFunc(pprof.Index))
+	ret.URL("/debug/pprof/goroutine?debug=1", "Goroutines (collapsed)")
+	ret.URL("/debug/pprof/goroutine?debug=2", "Goroutines (full)")
+	ret.Handle("gc", "force GC", http.HandlerFunc(gcHandler))
+	hostname, err := os.Hostname()
+	if err == nil {
+		ret.KV("Machine", hostname)
+	}
+	return ret
+}
+
+// ServeHTTP implements http.Handler.
+func (d *DebugHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	if !AllowDebugAccess(r) {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	if r.URL.Path != "/debug/" {
+		// Sub-handlers are handled by the parent mux directly.
+		http.NotFound(w, r)
+		return
+	}
+
+	f := func(format string, args ...interface{}) { fmt.Fprintf(w, format, args...) }
+	f("<html><body><h1>%s debug</h1><ul>", version.CmdName())
+	for _, kv := range d.kvs {
+		kv(w)
+	}
+	for _, url := range d.urls {
+		io.WriteString(w, url)
+	}
+	for _, section := range d.sections {
+		section(w, r)
+	}
+}
+
+// Handle registers handler at /debug/<slug> and creates a descriptive
+// entry in /debug/ for it.
+func (d *DebugHandler) Handle(slug, desc string, handler http.Handler) {
+	href := "/debug/" + slug
+	d.mux.Handle(href, Protected(handler))
+	d.URL(href, desc)
+}
+
+// KV adds a key/value list item to /debug/.
+func (d *DebugHandler) KV(k string, v interface{}) {
+	val := html.EscapeString(fmt.Sprintf("%v", v))
+	d.kvs = append(d.kvs, func(w io.Writer) {
+		fmt.Fprintf(w, "<li><b>%s:</b> %s</li>", k, val)
+	})
+}
+
+// KVFunc adds a key/value list item to /debug/. v is called on every
+// render of /debug/.
+func (d *DebugHandler) KVFunc(k string, v func() interface{}) {
+	d.kvs = append(d.kvs, func(w io.Writer) {
+		val := html.EscapeString(fmt.Sprintf("%v", v()))
+		fmt.Fprintf(w, "<li><b>%s:</b> %s</li>", k, val)
+	})
+}
+
+// URL adds a URL and description list item to /debug/.
+func (d *DebugHandler) URL(url, desc string) {
+	if desc != "" {
+		desc = " (" + desc + ")"
+	}
+	d.urls = append(d.urls, fmt.Sprintf(`<li><a href="%s">%s</a>%s</li>`, url, url, html.EscapeString(desc)))
+}
+
+// Section invokes f on every render of /debug/ to add supplemental
+// HTML to the page body.
+func (d *DebugHandler) Section(f func(w io.Writer, r *http.Request)) {
+	d.sections = append(d.sections, f)
+}
+
+func gcHandler(w http.ResponseWriter, r *http.Request) {
+	w.Write([]byte("running GC...\n"))
+	if f, ok := w.(http.Flusher); ok {
+		f.Flush()
+	}
+	runtime.GC()
+	w.Write([]byte("Done.\n"))
+}