build: move e2e dependencies into e2e/go.mod

Several packages are only used while running the e2e suite. These
packages are less important to update, as the they can not influence the
final executable that is part of the Ceph-CSI container-image.

By moving these dependencies out of the main Ceph-CSI go.mod, it is
easier to identify if a reported CVE affects Ceph-CSI, or only the
testing (like most of the Kubernetes CVEs).

Signed-off-by: Niels de Vos <ndevos@ibm.com>

e2e/vendor/github.com/felixge/httpsnoop/LICENSE.txt

@@ -0,0 +1,19 @@
+Copyright (c) 2016 Felix Geisendörfer (felix@debuggable.com)
+
+ Permission is hereby granted, free of charge, to any person obtaining a copy
+ of this software and associated documentation files (the "Software"), to deal
+ in the Software without restriction, including without limitation the rights
+ to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ copies of the Software, and to permit persons to whom the Software is
+ furnished to do so, subject to the following conditions:
+
+ The above copyright notice and this permission notice shall be included in
+ all copies or substantial portions of the Software.
+
+ THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ THE SOFTWARE.

e2e/vendor/github.com/felixge/httpsnoop/Makefile

@@ -0,0 +1,10 @@
+.PHONY: ci generate clean
+
+ci: clean generate
+	go test -race -v ./...
+
+generate:
+	go generate .
+
+clean:
+	rm -rf *_generated*.go

e2e/vendor/github.com/felixge/httpsnoop/README.md

@@ -0,0 +1,95 @@
+# httpsnoop
+
+Package httpsnoop provides an easy way to capture http related metrics (i.e.
+response time, bytes written, and http status code) from your application's
+http.Handlers.
+
+Doing this requires non-trivial wrapping of the http.ResponseWriter interface,
+which is also exposed for users interested in a more low-level API.
+
+[![Go Reference](https://pkg.go.dev/badge/github.com/felixge/httpsnoop.svg)](https://pkg.go.dev/github.com/felixge/httpsnoop)
+[![Build Status](https://github.com/felixge/httpsnoop/actions/workflows/main.yaml/badge.svg)](https://github.com/felixge/httpsnoop/actions/workflows/main.yaml)
+
+## Usage Example
+
+```go
+// myH is your app's http handler, perhaps a http.ServeMux or similar.
+var myH http.Handler
+// wrappedH wraps myH in order to log every request.
+wrappedH := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+	m := httpsnoop.CaptureMetrics(myH, w, r)
+	log.Printf(
+		"%s %s (code=%d dt=%s written=%d)",
+		r.Method,
+		r.URL,
+		m.Code,
+		m.Duration,
+		m.Written,
+	)
+})
+http.ListenAndServe(":8080", wrappedH)
+```
+
+## Why this package exists
+
+Instrumenting an application's http.Handler is surprisingly difficult.
+
+However if you google for e.g. "capture ResponseWriter status code" you'll find
+lots of advise and code examples that suggest it to be a fairly trivial
+undertaking. Unfortunately everything I've seen so far has a high chance of
+breaking your application.
+
+The main problem is that a `http.ResponseWriter` often implements additional
+interfaces such as `http.Flusher`, `http.CloseNotifier`, `http.Hijacker`, `http.Pusher`, and
+`io.ReaderFrom`. So the naive approach of just wrapping `http.ResponseWriter`
+in your own struct that also implements the `http.ResponseWriter` interface
+will hide the additional interfaces mentioned above. This has a high change of
+introducing subtle bugs into any non-trivial application.
+
+Another approach I've seen people take is to return a struct that implements
+all of the interfaces above. However, that's also problematic, because it's
+difficult to fake some of these interfaces behaviors when the underlying
+`http.ResponseWriter` doesn't have an implementation. It's also dangerous,
+because an application may choose to operate differently, merely because it
+detects the presence of these additional interfaces.
+
+This package solves this problem by checking which additional interfaces a
+`http.ResponseWriter` implements, returning a wrapped version implementing the
+exact same set of interfaces.
+
+Additionally this package properly handles edge cases such as `WriteHeader` not
+being called, or called more than once, as well as concurrent calls to
+`http.ResponseWriter` methods, and even calls happening after the wrapped
+`ServeHTTP` has already returned.
+
+Unfortunately this package is not perfect either. It's possible that it is
+still missing some interfaces provided by the go core (let me know if you find
+one), and it won't work for applications adding their own interfaces into the
+mix. You can however use `httpsnoop.Unwrap(w)` to access the underlying
+`http.ResponseWriter` and type-assert the result to its other interfaces.
+
+However, hopefully the explanation above has sufficiently scared you of rolling
+your own solution to this problem. httpsnoop may still break your application,
+but at least it tries to avoid it as much as possible.
+
+Anyway, the real problem here is that smuggling additional interfaces inside
+`http.ResponseWriter` is a problematic design choice, but it probably goes as
+deep as the Go language specification itself. But that's okay, I still prefer
+Go over the alternatives ;).
+
+## Performance
+
+```
+BenchmarkBaseline-8      	   20000	     94912 ns/op
+BenchmarkCaptureMetrics-8	   20000	     95461 ns/op
+```
+
+As you can see, using `CaptureMetrics` on a vanilla http.Handler introduces an
+overhead of ~500 ns per http request on my machine. However, the margin of
+error appears to be larger than that, therefor it should be reasonable to
+assume that the overhead introduced by `CaptureMetrics` is absolutely
+negligible.
+
+## License
+
+MIT

e2e/vendor/github.com/felixge/httpsnoop/capture_metrics.go

@@ -0,0 +1,86 @@
+package httpsnoop
+
+import (
+	"io"
+	"net/http"
+	"time"
+)
+
+// Metrics holds metrics captured from CaptureMetrics.
+type Metrics struct {
+	// Code is the first http response code passed to the WriteHeader func of
+	// the ResponseWriter. If no such call is made, a default code of 200 is
+	// assumed instead.
+	Code int
+	// Duration is the time it took to execute the handler.
+	Duration time.Duration
+	// Written is the number of bytes successfully written by the Write or
+	// ReadFrom function of the ResponseWriter. ResponseWriters may also write
+	// data to their underlaying connection directly (e.g. headers), but those
+	// are not tracked. Therefor the number of Written bytes will usually match
+	// the size of the response body.
+	Written int64
+}
+
+// CaptureMetrics wraps the given hnd, executes it with the given w and r, and
+// returns the metrics it captured from it.
+func CaptureMetrics(hnd http.Handler, w http.ResponseWriter, r *http.Request) Metrics {
+	return CaptureMetricsFn(w, func(ww http.ResponseWriter) {
+		hnd.ServeHTTP(ww, r)
+	})
+}
+
+// CaptureMetricsFn wraps w and calls fn with the wrapped w and returns the
+// resulting metrics. This is very similar to CaptureMetrics (which is just
+// sugar on top of this func), but is a more usable interface if your
+// application doesn't use the Go http.Handler interface.
+func CaptureMetricsFn(w http.ResponseWriter, fn func(http.ResponseWriter)) Metrics {
+	m := Metrics{Code: http.StatusOK}
+	m.CaptureMetrics(w, fn)
+	return m
+}
+
+// CaptureMetrics wraps w and calls fn with the wrapped w and updates
+// Metrics m with the resulting metrics. This is similar to CaptureMetricsFn,
+// but allows one to customize starting Metrics object.
+func (m *Metrics) CaptureMetrics(w http.ResponseWriter, fn func(http.ResponseWriter)) {
+	var (
+		start         = time.Now()
+		headerWritten bool
+		hooks         = Hooks{
+			WriteHeader: func(next WriteHeaderFunc) WriteHeaderFunc {
+				return func(code int) {
+					next(code)
+
+					if !(code >= 100 && code <= 199) && !headerWritten {
+						m.Code = code
+						headerWritten = true
+					}
+				}
+			},
+
+			Write: func(next WriteFunc) WriteFunc {
+				return func(p []byte) (int, error) {
+					n, err := next(p)
+
+					m.Written += int64(n)
+					headerWritten = true
+					return n, err
+				}
+			},
+
+			ReadFrom: func(next ReadFromFunc) ReadFromFunc {
+				return func(src io.Reader) (int64, error) {
+					n, err := next(src)
+
+					headerWritten = true
+					m.Written += n
+					return n, err
+				}
+			},
+		}
+	)
+
+	fn(Wrap(w, hooks))
+	m.Duration += time.Since(start)
+}

e2e/vendor/github.com/felixge/httpsnoop/docs.go

@@ -0,0 +1,10 @@
+// Package httpsnoop provides an easy way to capture http related metrics (i.e.
+// response time, bytes written, and http status code) from your application's
+// http.Handlers.
+//
+// Doing this requires non-trivial wrapping of the http.ResponseWriter
+// interface, which is also exposed for users interested in a more low-level
+// API.
+package httpsnoop
+
+//go:generate go run codegen/main.go

e2e/vendor/github.com/felixge/httpsnoop/wrap_generated_gteq_1.8.go

@@ -0,0 +1,436 @@
+// +build go1.8
+// Code generated by "httpsnoop/codegen"; DO NOT EDIT.
+
+package httpsnoop
+
+import (
+	"bufio"
+	"io"
+	"net"
+	"net/http"
+)
+
+// HeaderFunc is part of the http.ResponseWriter interface.
+type HeaderFunc func() http.Header
+
+// WriteHeaderFunc is part of the http.ResponseWriter interface.
+type WriteHeaderFunc func(code int)
+
+// WriteFunc is part of the http.ResponseWriter interface.
+type WriteFunc func(b []byte) (int, error)
+
+// FlushFunc is part of the http.Flusher interface.
+type FlushFunc func()
+
+// CloseNotifyFunc is part of the http.CloseNotifier interface.
+type CloseNotifyFunc func() <-chan bool
+
+// HijackFunc is part of the http.Hijacker interface.
+type HijackFunc func() (net.Conn, *bufio.ReadWriter, error)
+
+// ReadFromFunc is part of the io.ReaderFrom interface.
+type ReadFromFunc func(src io.Reader) (int64, error)
+
+// PushFunc is part of the http.Pusher interface.
+type PushFunc func(target string, opts *http.PushOptions) error
+
+// Hooks defines a set of method interceptors for methods included in
+// http.ResponseWriter as well as some others. You can think of them as
+// middleware for the function calls they target. See Wrap for more details.
+type Hooks struct {
+	Header      func(HeaderFunc) HeaderFunc
+	WriteHeader func(WriteHeaderFunc) WriteHeaderFunc
+	Write       func(WriteFunc) WriteFunc
+	Flush       func(FlushFunc) FlushFunc
+	CloseNotify func(CloseNotifyFunc) CloseNotifyFunc
+	Hijack      func(HijackFunc) HijackFunc
+	ReadFrom    func(ReadFromFunc) ReadFromFunc
+	Push        func(PushFunc) PushFunc
+}
+
+// Wrap returns a wrapped version of w that provides the exact same interface
+// as w. Specifically if w implements any combination of:
+//
+// - http.Flusher
+// - http.CloseNotifier
+// - http.Hijacker
+// - io.ReaderFrom
+// - http.Pusher
+//
+// The wrapped version will implement the exact same combination. If no hooks
+// are set, the wrapped version also behaves exactly as w. Hooks targeting
+// methods not supported by w are ignored. Any other hooks will intercept the
+// method they target and may modify the call's arguments and/or return values.
+// The CaptureMetrics implementation serves as a working example for how the
+// hooks can be used.
+func Wrap(w http.ResponseWriter, hooks Hooks) http.ResponseWriter {
+	rw := &rw{w: w, h: hooks}
+	_, i0 := w.(http.Flusher)
+	_, i1 := w.(http.CloseNotifier)
+	_, i2 := w.(http.Hijacker)
+	_, i3 := w.(io.ReaderFrom)
+	_, i4 := w.(http.Pusher)
+	switch {
+	// combination 1/32
+	case !i0 && !i1 && !i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+		}{rw, rw}
+	// combination 2/32
+	case !i0 && !i1 && !i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Pusher
+		}{rw, rw, rw}
+	// combination 3/32
+	case !i0 && !i1 && !i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			io.ReaderFrom
+		}{rw, rw, rw}
+	// combination 4/32
+	case !i0 && !i1 && !i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw}
+	// combination 5/32
+	case !i0 && !i1 && i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Hijacker
+		}{rw, rw, rw}
+	// combination 6/32
+	case !i0 && !i1 && i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Hijacker
+			http.Pusher
+		}{rw, rw, rw, rw}
+	// combination 7/32
+	case !i0 && !i1 && i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw}
+	// combination 8/32
+	case !i0 && !i1 && i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Hijacker
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw}
+	// combination 9/32
+	case !i0 && i1 && !i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+		}{rw, rw, rw}
+	// combination 10/32
+	case !i0 && i1 && !i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Pusher
+		}{rw, rw, rw, rw}
+	// combination 11/32
+	case !i0 && i1 && !i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			io.ReaderFrom
+		}{rw, rw, rw, rw}
+	// combination 12/32
+	case !i0 && i1 && !i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw}
+	// combination 13/32
+	case !i0 && i1 && i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Hijacker
+		}{rw, rw, rw, rw}
+	// combination 14/32
+	case !i0 && i1 && i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Hijacker
+			http.Pusher
+		}{rw, rw, rw, rw, rw}
+	// combination 15/32
+	case !i0 && i1 && i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw}
+	// combination 16/32
+	case !i0 && i1 && i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Hijacker
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw, rw}
+	// combination 17/32
+	case i0 && !i1 && !i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+		}{rw, rw, rw}
+	// combination 18/32
+	case i0 && !i1 && !i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Pusher
+		}{rw, rw, rw, rw}
+	// combination 19/32
+	case i0 && !i1 && !i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			io.ReaderFrom
+		}{rw, rw, rw, rw}
+	// combination 20/32
+	case i0 && !i1 && !i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw}
+	// combination 21/32
+	case i0 && !i1 && i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Hijacker
+		}{rw, rw, rw, rw}
+	// combination 22/32
+	case i0 && !i1 && i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Hijacker
+			http.Pusher
+		}{rw, rw, rw, rw, rw}
+	// combination 23/32
+	case i0 && !i1 && i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw}
+	// combination 24/32
+	case i0 && !i1 && i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Hijacker
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw, rw}
+	// combination 25/32
+	case i0 && i1 && !i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+		}{rw, rw, rw, rw}
+	// combination 26/32
+	case i0 && i1 && !i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Pusher
+		}{rw, rw, rw, rw, rw}
+	// combination 27/32
+	case i0 && i1 && !i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw}
+	// combination 28/32
+	case i0 && i1 && !i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw, rw}
+	// combination 29/32
+	case i0 && i1 && i2 && !i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Hijacker
+		}{rw, rw, rw, rw, rw}
+	// combination 30/32
+	case i0 && i1 && i2 && !i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Hijacker
+			http.Pusher
+		}{rw, rw, rw, rw, rw, rw}
+	// combination 31/32
+	case i0 && i1 && i2 && i3 && !i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw, rw}
+	// combination 32/32
+	case i0 && i1 && i2 && i3 && i4:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Hijacker
+			io.ReaderFrom
+			http.Pusher
+		}{rw, rw, rw, rw, rw, rw, rw}
+	}
+	panic("unreachable")
+}
+
+type rw struct {
+	w http.ResponseWriter
+	h Hooks
+}
+
+func (w *rw) Unwrap() http.ResponseWriter {
+	return w.w
+}
+
+func (w *rw) Header() http.Header {
+	f := w.w.(http.ResponseWriter).Header
+	if w.h.Header != nil {
+		f = w.h.Header(f)
+	}
+	return f()
+}
+
+func (w *rw) WriteHeader(code int) {
+	f := w.w.(http.ResponseWriter).WriteHeader
+	if w.h.WriteHeader != nil {
+		f = w.h.WriteHeader(f)
+	}
+	f(code)
+}
+
+func (w *rw) Write(b []byte) (int, error) {
+	f := w.w.(http.ResponseWriter).Write
+	if w.h.Write != nil {
+		f = w.h.Write(f)
+	}
+	return f(b)
+}
+
+func (w *rw) Flush() {
+	f := w.w.(http.Flusher).Flush
+	if w.h.Flush != nil {
+		f = w.h.Flush(f)
+	}
+	f()
+}
+
+func (w *rw) CloseNotify() <-chan bool {
+	f := w.w.(http.CloseNotifier).CloseNotify
+	if w.h.CloseNotify != nil {
+		f = w.h.CloseNotify(f)
+	}
+	return f()
+}
+
+func (w *rw) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	f := w.w.(http.Hijacker).Hijack
+	if w.h.Hijack != nil {
+		f = w.h.Hijack(f)
+	}
+	return f()
+}
+
+func (w *rw) ReadFrom(src io.Reader) (int64, error) {
+	f := w.w.(io.ReaderFrom).ReadFrom
+	if w.h.ReadFrom != nil {
+		f = w.h.ReadFrom(f)
+	}
+	return f(src)
+}
+
+func (w *rw) Push(target string, opts *http.PushOptions) error {
+	f := w.w.(http.Pusher).Push
+	if w.h.Push != nil {
+		f = w.h.Push(f)
+	}
+	return f(target, opts)
+}
+
+type Unwrapper interface {
+	Unwrap() http.ResponseWriter
+}
+
+// Unwrap returns the underlying http.ResponseWriter from within zero or more
+// layers of httpsnoop wrappers.
+func Unwrap(w http.ResponseWriter) http.ResponseWriter {
+	if rw, ok := w.(Unwrapper); ok {
+		// recurse until rw.Unwrap() returns a non-Unwrapper
+		return Unwrap(rw.Unwrap())
+	} else {
+		return w
+	}
+}

e2e/vendor/github.com/felixge/httpsnoop/wrap_generated_lt_1.8.go

@@ -0,0 +1,278 @@
+// +build !go1.8
+// Code generated by "httpsnoop/codegen"; DO NOT EDIT.
+
+package httpsnoop
+
+import (
+	"bufio"
+	"io"
+	"net"
+	"net/http"
+)
+
+// HeaderFunc is part of the http.ResponseWriter interface.
+type HeaderFunc func() http.Header
+
+// WriteHeaderFunc is part of the http.ResponseWriter interface.
+type WriteHeaderFunc func(code int)
+
+// WriteFunc is part of the http.ResponseWriter interface.
+type WriteFunc func(b []byte) (int, error)
+
+// FlushFunc is part of the http.Flusher interface.
+type FlushFunc func()
+
+// CloseNotifyFunc is part of the http.CloseNotifier interface.
+type CloseNotifyFunc func() <-chan bool
+
+// HijackFunc is part of the http.Hijacker interface.
+type HijackFunc func() (net.Conn, *bufio.ReadWriter, error)
+
+// ReadFromFunc is part of the io.ReaderFrom interface.
+type ReadFromFunc func(src io.Reader) (int64, error)
+
+// Hooks defines a set of method interceptors for methods included in
+// http.ResponseWriter as well as some others. You can think of them as
+// middleware for the function calls they target. See Wrap for more details.
+type Hooks struct {
+	Header      func(HeaderFunc) HeaderFunc
+	WriteHeader func(WriteHeaderFunc) WriteHeaderFunc
+	Write       func(WriteFunc) WriteFunc
+	Flush       func(FlushFunc) FlushFunc
+	CloseNotify func(CloseNotifyFunc) CloseNotifyFunc
+	Hijack      func(HijackFunc) HijackFunc
+	ReadFrom    func(ReadFromFunc) ReadFromFunc
+}
+
+// Wrap returns a wrapped version of w that provides the exact same interface
+// as w. Specifically if w implements any combination of:
+//
+// - http.Flusher
+// - http.CloseNotifier
+// - http.Hijacker
+// - io.ReaderFrom
+//
+// The wrapped version will implement the exact same combination. If no hooks
+// are set, the wrapped version also behaves exactly as w. Hooks targeting
+// methods not supported by w are ignored. Any other hooks will intercept the
+// method they target and may modify the call's arguments and/or return values.
+// The CaptureMetrics implementation serves as a working example for how the
+// hooks can be used.
+func Wrap(w http.ResponseWriter, hooks Hooks) http.ResponseWriter {
+	rw := &rw{w: w, h: hooks}
+	_, i0 := w.(http.Flusher)
+	_, i1 := w.(http.CloseNotifier)
+	_, i2 := w.(http.Hijacker)
+	_, i3 := w.(io.ReaderFrom)
+	switch {
+	// combination 1/16
+	case !i0 && !i1 && !i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+		}{rw, rw}
+	// combination 2/16
+	case !i0 && !i1 && !i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			io.ReaderFrom
+		}{rw, rw, rw}
+	// combination 3/16
+	case !i0 && !i1 && i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Hijacker
+		}{rw, rw, rw}
+	// combination 4/16
+	case !i0 && !i1 && i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw}
+	// combination 5/16
+	case !i0 && i1 && !i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+		}{rw, rw, rw}
+	// combination 6/16
+	case !i0 && i1 && !i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			io.ReaderFrom
+		}{rw, rw, rw, rw}
+	// combination 7/16
+	case !i0 && i1 && i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Hijacker
+		}{rw, rw, rw, rw}
+	// combination 8/16
+	case !i0 && i1 && i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.CloseNotifier
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw}
+	// combination 9/16
+	case i0 && !i1 && !i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+		}{rw, rw, rw}
+	// combination 10/16
+	case i0 && !i1 && !i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			io.ReaderFrom
+		}{rw, rw, rw, rw}
+	// combination 11/16
+	case i0 && !i1 && i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Hijacker
+		}{rw, rw, rw, rw}
+	// combination 12/16
+	case i0 && !i1 && i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw}
+	// combination 13/16
+	case i0 && i1 && !i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+		}{rw, rw, rw, rw}
+	// combination 14/16
+	case i0 && i1 && !i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw}
+	// combination 15/16
+	case i0 && i1 && i2 && !i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Hijacker
+		}{rw, rw, rw, rw, rw}
+	// combination 16/16
+	case i0 && i1 && i2 && i3:
+		return struct {
+			Unwrapper
+			http.ResponseWriter
+			http.Flusher
+			http.CloseNotifier
+			http.Hijacker
+			io.ReaderFrom
+		}{rw, rw, rw, rw, rw, rw}
+	}
+	panic("unreachable")
+}
+
+type rw struct {
+	w http.ResponseWriter
+	h Hooks
+}
+
+func (w *rw) Unwrap() http.ResponseWriter {
+	return w.w
+}
+
+func (w *rw) Header() http.Header {
+	f := w.w.(http.ResponseWriter).Header
+	if w.h.Header != nil {
+		f = w.h.Header(f)
+	}
+	return f()
+}
+
+func (w *rw) WriteHeader(code int) {
+	f := w.w.(http.ResponseWriter).WriteHeader
+	if w.h.WriteHeader != nil {
+		f = w.h.WriteHeader(f)
+	}
+	f(code)
+}
+
+func (w *rw) Write(b []byte) (int, error) {
+	f := w.w.(http.ResponseWriter).Write
+	if w.h.Write != nil {
+		f = w.h.Write(f)
+	}
+	return f(b)
+}
+
+func (w *rw) Flush() {
+	f := w.w.(http.Flusher).Flush
+	if w.h.Flush != nil {
+		f = w.h.Flush(f)
+	}
+	f()
+}
+
+func (w *rw) CloseNotify() <-chan bool {
+	f := w.w.(http.CloseNotifier).CloseNotify
+	if w.h.CloseNotify != nil {
+		f = w.h.CloseNotify(f)
+	}
+	return f()
+}
+
+func (w *rw) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	f := w.w.(http.Hijacker).Hijack
+	if w.h.Hijack != nil {
+		f = w.h.Hijack(f)
+	}
+	return f()
+}
+
+func (w *rw) ReadFrom(src io.Reader) (int64, error) {
+	f := w.w.(io.ReaderFrom).ReadFrom
+	if w.h.ReadFrom != nil {
+		f = w.h.ReadFrom(f)
+	}
+	return f(src)
+}
+
+type Unwrapper interface {
+	Unwrap() http.ResponseWriter
+}
+
+// Unwrap returns the underlying http.ResponseWriter from within zero or more
+// layers of httpsnoop wrappers.
+func Unwrap(w http.ResponseWriter) http.ResponseWriter {
+	if rw, ok := w.(Unwrapper); ok {
+		// recurse until rw.Unwrap() returns a non-Unwrapper
+		return Unwrap(rw.Unwrap())
+	} else {
+		return w
+	}
+}