net/http: request.Clone doesn't deep copy TransferEncoding

[dqu123]

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

$ go version
go version go1.14.5 darwin/amd64

Does this issue reproduce with the latest release?

yes, bug exists in master: https://github.com/golang/go/blob/master/src/net/http/request.go#L385

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

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/david/Library/Caches/go-build"
GOENV="/Users/david/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/david/cs/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/local/Cellar/go/1.14.5/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.14.5/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/5r/35kn30hd119486nmd0sjcy8c0000gn/T/go-build221526405=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

• initialize http.Request with TransferEncoding
• clone request
• modify original request TransferEncoding
  https://play.golang.org/p/aSFm22u_TGZ

What did you expect to see?

cloned request TransferEncoding should not changed by changes to the original request after it has been copied.

What did you see instead?

cloned request TransferEncoding was modified by changing original request TransferEncoding

[gopherbot]

Change https://golang.org/cl/261258 mentions this issue: net/http: deep copy Request.TransferEncoding

[odeke-em]

Thank you for catching this @dqu123 and welcome to the Go project! Good eyes.

@gopherbot please backport this issue.

[gopherbot]

Backport issue(s) opened: #41913 (for 1.14), #41914 (for 1.15).

Remember to create the cherry-pick CL(s) as soon as the patch is submitted to master, according to https://golang.org/wiki/MinorReleases.

[gopherbot]

Change https://golang.org/cl/261377 mentions this issue: net/http: deep copy Request.TransferEncoding

[gopherbot]

Change https://golang.org/cl/261378 mentions this issue: net/http: deep copy Request.TransferEncoding