Golang net/http: Readdir method of DotFileHiding example does not conform to the doc

Go version

go version go1.22.3 windows/amd64

Output of go env in your module/workspace:

set GO111MODULE=
set GOARCH=amd64
set GOBIN=
set GOCACHE=C:\Users\user\AppData\Local\go-build
set GOENV=C:\Users\user\AppData\Roaming\go\env
set GOEXE=.exe
set GOEXPERIMENT=
set GOFLAGS=
set GOHOSTARCH=amd64
set GOHOSTOS=windows
set GOINSECURE=
set GOMODCACHE=C:\Users\user\go\pkg\mod
set GONOPROXY=
set GONOSUMDB=
set GOOS=windows
set GOPATH=C:\Users\user\go
set GOPRIVATE=
set GOPROXY=https://goproxy.cn,direct
set GOROOT=C:\Program Files\Go
set GOSUMDB=sum.golang.org
set GOTMPDIR=
set GOTOOLCHAIN=auto
set GOTOOLDIR=C:\Program Files\Go\pkg\tool\windows_amd64
set GOVCS=
set GOVERSION=go1.22.3
set GCCGO=gccgo
set GOAMD64=v1
set AR=ar
set CC=gcc
set CXX=g++
set CGO_ENABLED=1
set GOMOD=C:\Users\user\code\dotFileHidingFile\go.mod
set GOWORK=
set CGO_CFLAGS=-O2 -g
set CGO_CPPFLAGS=
set CGO_CXXFLAGS=-O2 -g
set CGO_FFLAGS=-O2 -g
set CGO_LDFLAGS=-O2 -g
set PKG_CONFIG=pkg-config
set GOGCCFLAGS=-m64 -mthreads -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=C:\Users\user\AppData\Local\Temp\go-build416355838=/tmp/go-build -gno-record-gcc-switches

What did you do?

Visit https://pkg.go.dev/net/http#example-FileServer-DotFileHiding

What did you see happen?

func (f dotFileHidingFile) Readdir(n int) (fis []fs.FileInfo, err error) {
    files, err := f.File.Readdir(n)
    for _, file := range files { // Filters out the dot files
        if !strings.HasPrefix(file.Name(), ".") {
            fis = append(fis, file)
        }
    }
    return
}

The implementation of dotFileHidingFile.Readdir method does not conform to the doc of *os.File.ReadDir:

If n > 0 ... if Readdir returns an empty slice, it will return a non-nil error explaining why ...

If n>0 and f.File.Readdir(n) returns dot files only, fis will be an empty slice while err is nil(not a non-nil error explaining why).

What did you expect to see?

Something like

func (f dotFileHidingFile) Readdir(n int) (fis []fs.FileInfo, err error) {
    var files []fs.FileInfo
    for {
        files, err = f.File.Readdir(n)
        // Filters out the dot files
        fis = slices.DeleteFunc(files, func(file fs.FileInfo) bool {
            return strings.HasPrefix(file.Name(), ".")
        })
        if err != nil || n <= 0 || (n > 0 && len(fis) > 0) {
            break
        }
    }
    return
}

Comment From: gopherbot

Change https://go.dev/cl/598075 mentions this issue: net/http: match os.File.Readdir behavior in DotFileHiding