httplibp2p: cannot mount a protocol at the root

[aschmahmann]

It seems from the spec PR that it should be possible to mount a protocol at the root (i.e. /).

However, from what I can tell though this will cause problems in go-libp2p because the / will be sliced off the prefix

go-libp2p/p2p/http/libp2phttp.go

Line 371 in 87a8d4e

h.ServeMux.Handle(path, http.StripPrefix(path, handler))

which will result in some infinite looping if you follow redirects (e.g. curl -L ) https://cs.opensource.google/go/go/+/refs/tags/go1.21.0:src/net/http/server.go;l=2475-2479 since path != r.URL.Path will always be the case due to slicing the / off the front.

[sukunrt]

Can you elaborate here? I'm not sure if this is a problem, but my understanding of the http work is not great.

I'm using this example host and making requests via curl:

func Test_ExampleHost_RootPath(t *testing.T) {
	// Create the server
	server := libp2phttp.Host{
		InsecureAllowHTTP: true, // For our example, we'll allow insecure HTTP
		ListenAddrs:       []ma.Multiaddr{ma.StringCast("/ip4/127.0.0.1/tcp/50221/http")},
	}

	server.SetHTTPHandlerAtPath("/hello/1", "/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		fmt.Println(r.URL.Path)
		w.Header().Add("Content-Type", "text/plain")
		w.Write([]byte("Hello World"))
	}))
	
	server.Serve()
}

This works fine with curl:
curl -Lv http://127.0.0.1:50221/ curl -Lv http://127.0.0.1:50221

This also works with:
curl -Lv --path-as-is "http://127.0.0.1:50221/abc/../"

using libp2phost.Host.NewConstrainedRoundTripper also works fine for me.

In https://cs.opensource.google/go/go/+/refs/tags/go1.21.0:src/net/http/server.go;l=2475-2479
both path and r.URL.Path are the same unless r.URL.Path has . and .. elements like the example above(/abc/../).

[aschmahmann]

both path and r.URL.Path are the same unless r.URL.Path has . and .. elements like the example above(/abc/../).

They are also not the same if r.URL.Path does not start with a / which is what I'm running into here.

---

Maybe I'm misunderstanding how the composition is supposed to work here, but my understanding is that the httplibp2p.Host is supposed to operate roughly like a ServeMux itself.

Thanks for your test example, it gives something to write against. Here's a similar example demonstrating an infinite loop issue that comes up with nested ServeMux's.

Using standard HTTP ServeMux:

func Test_StandardHTTPNestedMux(t *testing.T) {
	rootMx := http.NewServeMux()
	nestedMx := http.NewServeMux()
	nestedMx.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Println(r.URL.Path)
		w.Header().Add("Content-Type", "text/plain")
		w.Write([]byte("Hello World"))
	})
	rootMx.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		nestedMx.ServeHTTP(w, r)
	})

	l, err := net.Listen("tcp", "127.0.0.1:50221")
	if err != nil {
		t.Fatal(err)
	}
	http.Serve(l, rootMx)
}

❯ curl 127.0.0.1:50221/abc/def
Hello World

Using an httplibp2p host as the root:

func Test_HTTPLibp2pNestedMux(t *testing.T) {
	// Create the server
	server := libp2phttp.Host{
		InsecureAllowHTTP: true, // For our example, we'll allow insecure HTTP
		ListenAddrs:       []ma.Multiaddr{ma.StringCast("/ip4/127.0.0.1/tcp/50221/http")},
	}

	nestedMux := http.NewServeMux()
	nestedMux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Println(r.URL.Path)
		w.Header().Add("Content-Type", "text/plain")
		w.Write([]byte("Hello World"))
	})

	server.SetHTTPHandlerAtPath("/hello/1", "/", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		nestedMux.ServeHTTP(w, r)
	}))

	server.Serve()
}

❯ curl 127.0.0.1:50221/abc/def
<a href="/abc/def">Moved Permanently</a>.

❯ curl -L 127.0.0.1:50221/abc/def
curl: (47) Maximum (50) redirects followed

[sukunrt]

Thanks! This clarified the issue. There is a bug in the happy case too here. See the PR.