proposal: net/http/pprof: function to register all profiles to a mux

[DerekTBrown]

User Story

• I have an application that has mux instances.
• I want to enable net/http/pprof on a specific mux instance.
• net/http/pprof does not provide an ergonomic interface for attaching the handlers to a specific mux.

Current Options / Alternatives Considered

The net/http/pprof package init function is the recommended path for enabling the pprof handler.¹ This method uses the DefaultServeMux:

go/src/net/http/pprof/pprof.go

Lines 95 to 105 in 46b576b

	func init() {
	prefix := ""
	if godebug.New("httpmuxgo121").Value() != "1" {
	prefix = "GET "
	}
	http.HandleFunc(prefix+"/debug/pprof/", Index)
	http.HandleFunc(prefix+"/debug/pprof/cmdline", Cmdline)
	http.HandleFunc(prefix+"/debug/pprof/profile", Profile)
	http.HandleFunc(prefix+"/debug/pprof/symbol", Symbol)
	http.HandleFunc(prefix+"/debug/pprof/trace", Trace)
	}

If the user wants to mount the pprof handlers using a non-default mux, they must do this by manually enumerating all of the available profilers². For example:

	mux := http.NewServeMux()
	mux.HandleFunc("/debug/pprof/", pprof.Index)
	mux.HandleFunc("/debug/pprof/cmdline/", pprof.Cmdline)
	mux.HandleFunc("/debug/pprof/profile/", pprof.Profile)
	mux.HandleFunc("/debug/pprof/symbol/", pprof.Symbol)
	mux.HandleFunc("/debug/pprof/trace/", pprof.Trace)

Proposal

This experience could be made better for users by moving the logic in the init function into a separate method (with the mux as an argument), then invoking this within the default package init function.

Footnotes

1. https://pkg.go.dev/net/http/pprof#:~:text=To%20use%20pprof%2C%20link%20this%20package%20into%20your%20program%3A ↩

2. https://pkg.go.dev/net/http/pprof#:~:text=If%20you%20are%20not%20using%20DefaultServeMux%2C%20you%20will%20have%20to%20register%20handlers%20with%20the%20mux%20you%20are%20using. ↩

[DerekTBrown]

Here is an example of where a re-implementation of this handler caused issues:

argoproj/argo-rollouts#4038

[gabyhelp]

Related Issues

• proposal: net/http/pprof/v2: disallow package to register to the default mux #42834

Related Code Changes

• doc: make it clear which pprof package is used
• net/http/pprof: explicitly mention DefaultServeMux for default handlers

Related Discussions

• Custom ServeMux and pprof

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

[ianlancetaylor]

Closely related to #42834.

[tmthrgd]

A relatively straight forward way to do this currently is:

import _ "net/http/pprof"

...

mux.Handle("/debug/pprof/", http.DefaultServerMux)

and then rely on the init registration against DefaultServerMux.

[seankhliao]

CL 641858 proposes

func AttachHandlers(prefix string, mux *http.ServeMux)

But I don't think it's necessary to expose prefix as:

1. it's an implementation detail for optional method scoping that can't effectively be used outside of the standard library
2. using any other non-method prefix will likely break the index page.

#42834 (comment) proposes a simpler:

func RegisterHandlers(mux *http.ServeMux)

[DerekTBrown]

Closely related to #42834.

IIUC, this issue (#71213) is somewhat of a pre-requisite to taking action on #42834. We need an ergonomic way to initialize a non-default mux before we can stop using the default mux.

[DerekTBrown]

CL 641858 proposes

func AttachHandlers(prefix string, mux *http.ServeMux)
But I don't think it's necessary to expose prefix as:

1. it's an implementation detail for optional method scoping that can't effectively be used outside of the standard library
2. using any other non-method prefix will likely break the index page.

#42834 (comment) proposes a simpler:

func RegisterHandlers(mux *http.ServeMux)

Makes sense. I revised the CL to not expose prefix.

[ianlancetaylor]

CC @neild