Closed
Description
What version of Go are you using (go version)?
$ go version go version devel go1.19-3e387528e5 Fri Apr 8 14:13:32 2022 +0000 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="" GOARCH="arm64" GOBIN="" GOCACHE="/Users/bpowers/Library/Caches/go-build" GOENV="/Users/bpowers/Library/Application Support/go/env" GOEXE="" GOEXPERIMENT="" GOFLAGS="" GOHOSTARCH="arm64" GOHOSTOS="darwin" GOINSECURE="" GOMODCACHE="/Users/bpowers/pkg/mod" GONOPROXY="" GONOSUMDB="" GOOS="darwin" GOPATH="/Users/bpowers" GOPRIVATE="" GOPROXY="https://proxy.golang.org,direct" GOROOT="/Users/bpowers/go" GOSUMDB="sum.golang.org" GOTMPDIR="" GOTOOLDIR="/Users/bpowers/go/pkg/tool/darwin_arm64" GOVCS="" GOVERSION="devel go1.19-3e387528e5 Fri Apr 8 14:13:32 2022 +0000" GCCGO="gccgo" AR="ar" CC="clang" CXX="clang++" CGO_ENABLED="1" GOMOD="/Users/bpowers/go/src/go.mod" 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/8t/qj6z573x0gvdm6s6krh_9qvw0000gn/T/go-build1085205980=/tmp/go-build -gno-record-gcc-switches -fno-common"
What did you do?
A common pattern in HTTP middleware is to compute a value, derive a new context with Context.WithValue (or WithDeadline, etc), attach the context to the request using WithContext, and invoke the next handler (https://goji.io/ in particular encourages this pattern for middleware, but I think it is generally common).
WithContext has a TODO around trying to remove the not-quite-deep-but-not-quite-shallow behavior of copying the URL now that additional NewRequestWithContext and Clone methods exist for http.Requests:
func (r *Request) WithContext(ctx context.Context) *Request {
if ctx == nil {
panic("nil context")
}
r2 := new(Request)
*r2 = *r
r2.ctx = ctx
r2.URL = cloneURL(r.URL) // legacy behavior; TODO: try to remove. Issue 23544
return r2
}I'd like to remove this copy, as users now have Clone to get real deep-copy semantics.
What did you expect to see?
One less allocation in this common hot-path function.
What did you see instead?
An allocation for legacy behavior with a TODO to remove it.