// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package tsweb
import (
"expvar"
"fmt"
"html"
"io"
"net/http"
"net/url"
"os"
"runtime"
"tailscale.com/feature"
"tailscale.com/tsweb/varz"
"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>
title string // title displayed on index page
}
// PrometheusHandler is an optional hook to enable native Prometheus
// support in the debug handler. It is disabled by default. Import the
// tailscale.com/tsweb/promvarz package to enable this feature.
var PrometheusHandler feature.Hook[func(*DebugHandler)]
// 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,
title: fmt.Sprintf("%s debug", version.CmdName()),
}
mux.Handle("/debug/", ret)
ret.KVFunc("Uptime", func() any { return varz.Uptime() })
ret.KV("Version", version.Long())
ret.Handle("vars", "Metrics (Go)", expvar.Handler())
if PrometheusHandler.IsSet() {
PrometheusHandler.Get()(ret)
} else {
ret.Handle("varz", "Metrics (Prometheus)", http.HandlerFunc(varz.Handler))
}
addProfilingHandlers(ret)
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
}
AddBrowserHeaders(w)
f := func(format string, args ...any) { fmt.Fprintf(w, format, args...) }
f("<html><body><h1>%s</h1><ul>", html.EscapeString(d.title))
for _, kv := range d.kvs {
kv(w)
}
for _, url := range d.urls {
io.WriteString(w, url)
}
for _, section := range d.sections {
section(w, r)
}
}
func (d *DebugHandler) handle(slug string, handler http.Handler) string {
href := "/debug/" + slug
d.mux.Handle(href, Protected(debugBrowserHeaderHandler(handler)))
return href
}
// Handle registers handler at /debug/<slug> and adds a link to it
// on /debug/ with the provided description.
func (d *DebugHandler) Handle(slug, desc string, handler http.Handler) {
href := d.handle(slug, handler)
d.URL(href, desc)
}
// Handle registers handler at /debug/<slug> and adds a link to it
// on /debug/ with the provided description.
func (d *DebugHandler) HandleFunc(slug, desc string, handler http.HandlerFunc) {
d.Handle(slug, desc, handler)
}
// HandleSilent registers handler at /debug/<slug>. It does not add
// a descriptive entry in /debug/ for it. This should be used
// sparingly, for things that need to be registered but would pollute
// the list of debug links.
func (d *DebugHandler) HandleSilent(slug string, handler http.Handler) {
d.handle(slug, handler)
}
// HandleSilent registers handler at /debug/<slug>. It does not add
// a descriptive entry in /debug/ for it. This should be used
// sparingly, for things that need to be registered but would pollute
// the list of debug links.
func (d *DebugHandler) HandleSilentFunc(slug string, handler http.HandlerFunc) {
d.HandleSilent(slug, handler)
}
// KV adds a key/value list item to /debug/.
func (d *DebugHandler) KV(k string, v any) {
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() any) {
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)
}
// Title sets the title at the top of the debug page.
func (d *DebugHandler) Title(title string) {
d.title = title
}
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"))
}
// debugBrowserHeaderHandler is a wrapper around BrowserHeaderHandler with a
// more relaxed Content-Security-Policy that's acceptable for internal debug
// pages. It should not be used on any public-facing handlers!
func debugBrowserHeaderHandler(h http.Handler) http.Handler {
return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
AddBrowserHeaders(w)
// The only difference from AddBrowserHeaders is that this policy
// allows inline CSS styles. They make debug pages much easier to
// prototype, while the risk of user-injected CSS is relatively low.
w.Header().Set("Content-Security-Policy", "default-src 'self'; frame-ancestors 'none'; form-action 'self'; base-uri 'self'; block-all-mixed-content; object-src 'none'; style-src 'self' 'unsafe-inline'")
h.ServeHTTP(w, r)
})
}