net/http: Server fails to clean up MultipartForm files when Request.WithContext is used

[JellyZero]

What version of Go are you using (go version)?

$ go version
go version go1.19.5 darwin/arm64

Does this issue reproduce with the latest release?

yes

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE="on"
GOARCH="arm64"
GOBIN="/Users/jeffreybool/code/go/bin"
GOCACHE="/Users/jeffreybool/Library/Caches/go-build"
GOENV="/Users/jeffreybool/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/jeffreybool/code/go/pkg/mod"
GONOPROXY="git.xxx.com"
GONOSUMDB="git.xxx.com"
GOOS="darwin"
GOPATH="/Users/jeffreybool/code/go"
GOPRIVATE="git.xxx.com"
GOPROXY="https://goproxy.cn,direct"
GOROOT="/opt/homebrew/Cellar/go/1.19.5/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.19.5/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.19.5"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/1b/9qbcfwxs19g5k9_5h05_9h9m0000gn/T/go-build2306283356=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

request, err := http.NewRequest(http.MethodGet,"/test",nil)
	if err != nil {
		return 
	}
	request.WithContext(request.Context())

What did you expect to see?

labstack/echo#2413

What did you see instead?

The pointer address changes after calling the WithContext method, which causes the server. go finishRequest() method to fail to execute normally

[bcmills]

causes the server. go finishRequest() method to fail to execute normally

Causes it to fail in what way? (What are the symptoms you actually saw?)

[JellyZero]

causes the server. go finishRequest() method to fail to execute normally

Causes it to fail in what way? (What are the symptoms you actually saw?)

package main

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"os"
)

func main() {
	http.HandleFunc("/upload", foo(bar(upload)))
	http.ListenAndServe(":1323", nil)
}

func foo(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("foo("))

		// do something before
		ctx := context.WithValue(r.Context(), "foo", "bar")
		r = r.WithContext(ctx)

		next(w, r)
		w.Write([]byte(")"))
	}
}

func bar(next http.HandlerFunc) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		w.Write([]byte("bar("))
		next(w, r)
		w.Write([]byte(")"))
	}
}

func upload(w http.ResponseWriter, r *http.Request) {
	r.ParseMultipartForm(32 << 20)
	file, handler, err := r.FormFile("file")
	if err != nil {
		fmt.Println(err)
		return
	}
	defer file.Close()
	f, err := os.OpenFile(handler.Filename, os.O_WRONLY|os.O_CREATE, 0666)
	if err != nil {
		fmt.Println(err)
		return
	}
	defer f.Close()
	io.Copy(f, file)
	fmt.Fprintln(w, "upload ok!")
}

After calling WithContext with 'r=r.WithContext (ctx)', the request variable pointer address was changed, so it was not executed finishRequest() method, resulting in temporary files not being cleared

[seankhliao]

WithContext makes a shallow copy of Request, with MultiPartForm == nil
ParseForm changes the value of MultiPartForm from nil to a parsed form, but only on the new copy.
Once the request is completed, finishRequest is run on the original Request, where MultiPartForm is nil, so nothing gets cleaned up.

[JellyZero]

How to solve it?

[seankhliao]

call ParseForm before WithContext, or call RemoveAll yourself.

[JellyZero]

You mean that the middleware implements req ParseForm method