shim: Move pprof server to plugin

Makes the pprof server a plugin and also gates by the `shim_tracing`
build tag (like otel is).
With this change, `net/http` is no longer a dependency in the shim.

Signed-off-by: Brian Goff <cpuguy83@gmail.com>

internal/pprof/plugin.go

@@ -0,0 +1,55 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package pprof
+
+import (
+	"expvar"
+	"net/http"
+	"net/http/pprof"
+	"time"
+
+	"github.com/containerd/containerd/v2/plugins"
+	"github.com/containerd/plugin"
+	"github.com/containerd/plugin/registry"
+)
+
+const pluginName = "pprof"
+
+func init() {
+	registry.Register(&plugin.Registration{
+		ID:   pluginName,
+		Type: plugins.HTTPHandler,
+		InitFn: func(ic *plugin.InitContext) (interface{}, error) {
+			return newHandler(), nil
+		},
+	})
+}
+
+func newHandler() *http.Server {
+	m := http.NewServeMux()
+	m.Handle("/debug/vars", expvar.Handler())
+	m.Handle("/debug/pprof/", http.HandlerFunc(pprof.Index))
+	m.Handle("/debug/pprof/cmdline", http.HandlerFunc(pprof.Cmdline))
+	m.Handle("/debug/pprof/profile", http.HandlerFunc(pprof.Profile))
+	m.Handle("/debug/pprof/symbol", http.HandlerFunc(pprof.Symbol))
+	m.Handle("/debug/pprof/trace", http.HandlerFunc(pprof.Trace))
+
+	return &http.Server{
+		Handler:           m,
+		ReadHeaderTimeout: 5 * time.Minute,
+	}
+}