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174 lines
5.9 KiB
Go
174 lines
5.9 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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package tsweb
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import (
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"expvar"
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"fmt"
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"html"
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"io"
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"net/http"
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"net/http/pprof"
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"net/url"
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"os"
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"runtime"
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"tailscale.com/tsweb/promvarz"
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"tailscale.com/tsweb/varz"
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"tailscale.com/version"
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)
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// DebugHandler is an http.Handler that serves a debugging "homepage",
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// and provides helpers to register more debug endpoints and reports.
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//
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// The rendered page consists of three sections: informational
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// key/value pairs, links to other pages, and additional
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// program-specific HTML. Callers can add to these sections using the
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// KV, URL and Section helpers respectively.
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//
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// Additionally, the Handle method offers a shorthand for correctly
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// registering debug handlers and cross-linking them from /debug/.
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type DebugHandler struct {
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mux *http.ServeMux // where this handler is registered
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kvs []func(io.Writer) // output one <li>...</li> each, see KV()
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urls []string // one <li>...</li> block with link each
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sections []func(io.Writer, *http.Request) // invoked in registration order prior to outputting </body>
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}
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// Debugger returns the DebugHandler registered on mux at /debug/,
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// creating it if necessary.
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func Debugger(mux *http.ServeMux) *DebugHandler {
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h, pat := mux.Handler(&http.Request{URL: &url.URL{Path: "/debug/"}})
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if d, ok := h.(*DebugHandler); ok && pat == "/debug/" {
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return d
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}
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ret := &DebugHandler{
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mux: mux,
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}
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mux.Handle("/debug/", ret)
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ret.KVFunc("Uptime", func() any { return varz.Uptime() })
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ret.KV("Version", version.Long())
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ret.Handle("vars", "Metrics (Go)", expvar.Handler())
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ret.Handle("varz", "Metrics (Prometheus)", http.HandlerFunc(promvarz.Handler))
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ret.Handle("pprof/", "pprof (index)", http.HandlerFunc(pprof.Index))
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// the CPU profile handler is special because it responds
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// streamily, unlike every other pprof handler. This means it's
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// not made available through pprof.Index the way all the other
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// pprof types are, you have to register the CPU profile handler
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// separately. Use HandleSilent for that to not pollute the human
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// debug list with a link that produces streaming line noise if
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// you click it.
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ret.HandleSilent("pprof/profile", http.HandlerFunc(pprof.Profile))
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ret.URL("/debug/pprof/goroutine?debug=1", "Goroutines (collapsed)")
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ret.URL("/debug/pprof/goroutine?debug=2", "Goroutines (full)")
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ret.Handle("gc", "force GC", http.HandlerFunc(gcHandler))
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hostname, err := os.Hostname()
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if err == nil {
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ret.KV("Machine", hostname)
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}
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return ret
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}
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// ServeHTTP implements http.Handler.
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func (d *DebugHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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if !AllowDebugAccess(r) {
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http.Error(w, "debug access denied", http.StatusForbidden)
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return
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}
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if r.URL.Path != "/debug/" {
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// Sub-handlers are handled by the parent mux directly.
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http.NotFound(w, r)
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return
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}
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AddBrowserHeaders(w)
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f := func(format string, args ...any) { fmt.Fprintf(w, format, args...) }
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f("<html><body><h1>%s debug</h1><ul>", version.CmdName())
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for _, kv := range d.kvs {
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kv(w)
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}
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for _, url := range d.urls {
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io.WriteString(w, url)
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}
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for _, section := range d.sections {
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section(w, r)
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}
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}
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func (d *DebugHandler) handle(slug string, handler http.Handler) string {
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href := "/debug/" + slug
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d.mux.Handle(href, Protected(debugBrowserHeaderHandler(handler)))
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return href
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}
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// Handle registers handler at /debug/<slug> and creates a descriptive
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// entry in /debug/ for it.
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func (d *DebugHandler) Handle(slug, desc string, handler http.Handler) {
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href := d.handle(slug, handler)
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d.URL(href, desc)
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}
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// HandleSilent registers handler at /debug/<slug>. It does not create
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// a descriptive entry in /debug/ for it. This should be used
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// sparingly, for things that need to be registered but would pollute
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// the list of debug links.
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func (d *DebugHandler) HandleSilent(slug string, handler http.Handler) {
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d.handle(slug, handler)
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}
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// KV adds a key/value list item to /debug/.
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func (d *DebugHandler) KV(k string, v any) {
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val := html.EscapeString(fmt.Sprintf("%v", v))
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d.kvs = append(d.kvs, func(w io.Writer) {
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fmt.Fprintf(w, "<li><b>%s:</b> %s</li>", k, val)
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})
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}
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// KVFunc adds a key/value list item to /debug/. v is called on every
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// render of /debug/.
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func (d *DebugHandler) KVFunc(k string, v func() any) {
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d.kvs = append(d.kvs, func(w io.Writer) {
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val := html.EscapeString(fmt.Sprintf("%v", v()))
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fmt.Fprintf(w, "<li><b>%s:</b> %s</li>", k, val)
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})
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}
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// URL adds a URL and description list item to /debug/.
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func (d *DebugHandler) URL(url, desc string) {
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if desc != "" {
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desc = " (" + desc + ")"
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}
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d.urls = append(d.urls, fmt.Sprintf(`<li><a href="%s">%s</a>%s</li>`, url, url, html.EscapeString(desc)))
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}
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// Section invokes f on every render of /debug/ to add supplemental
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// HTML to the page body.
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func (d *DebugHandler) Section(f func(w io.Writer, r *http.Request)) {
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d.sections = append(d.sections, f)
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}
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func gcHandler(w http.ResponseWriter, r *http.Request) {
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w.Write([]byte("running GC...\n"))
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if f, ok := w.(http.Flusher); ok {
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f.Flush()
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}
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runtime.GC()
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w.Write([]byte("Done.\n"))
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}
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// debugBrowserHeaderHandler is a wrapper around BrowserHeaderHandler with a
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// more relaxed Content-Security-Policy that's acceptable for internal debug
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// pages. It should not be used on any public-facing handlers!
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func debugBrowserHeaderHandler(h http.Handler) http.Handler {
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return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
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AddBrowserHeaders(w)
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// The only difference from AddBrowserHeaders is that this policy
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// allows inline CSS styles. They make debug pages much easier to
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// prototype, while the risk of user-injected CSS is relatively low.
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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'")
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h.ServeHTTP(w, r)
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})
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}
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