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Another Virtual File System for Go

AVFS is a virtual file system abstraction, inspired mostlybyAfero and Go standard library. It providesan abstraction layer to emulate the behavior of a file system that provides several features :

• a set ofconstants,interfaces andtypes for all file systems
• atest suite for all file systems (emulated or real)
• each file system has itsown package
• a very basicidentity manager allows testing of user related functions(Chown, Lchown) and file system permissions

Additionally, some file systems support :

• user file creation mode mask (Umask) (MemFS, OrefaFS)
• chroot (OSFS on Linux)
• hard links (MemFS, OrefaFS)
• symbolic links (MemFS)
• multiple users concurrently (MemFS)
• Linux andWindows emulation regardless of host operating system (MemFS, OrefaFS)

This package can be installed with the go install command :

go install github.com/avfs/avfs@latest

It is only tested with Go version >= 1.18

To make an existing code work withAVFS :

• replace all references ofos,path/filepathwith the variable used to initialize the file system (vfs in the followingexamples)
• import the packages of the file systems and, if necessary, theavfs packageand initialize the file system variable.
• some file systems provide specific options available at initialization. ForinstanceMemFS needsWithSystemDirs option to create/home,/rootand/tmp directories.

The example below demonstrates the creation of a file, a symbolic link to thisfile, for a different file systems (depending on an environment variable). Errormanagement has been omitted for the sake of simplicity :

package mainimport ("bytes""log""os""github.com/avfs/avfs""github.com/avfs/avfs/vfs/memfs""github.com/avfs/avfs/vfs/osfs")funcmain() {varvfs avfs.VFSswitchos.Getenv("ENV") {case"PROD":// The real file system for production.vfs=osfs.NewWithNoIdm()default:// in memory for tests.vfs=memfs.New()}// From this point all references of 'os', 'path/filepath'// should be replaced by 'vfs'rootDir,_:=vfs.MkdirTemp("","avfs")defervfs.RemoveAll(rootDir)aFilePath:=vfs.Join(rootDir,"aFile.txt")content:= []byte("randomContent")_=vfs.WriteFile(aFilePath,content,0o644)aFilePathSl:=vfs.Join(rootDir,"aFileSymlink.txt")_=vfs.Symlink(aFilePath,aFilePathSl)gotContentSl,_:=vfs.ReadFile(aFilePathSl)if!bytes.Equal(content,gotContentSl) {log.Fatalf("Symlink %s : want content to be %v, got %v",aFilePathSl,content,gotContentSl)}log.Printf("content from symbolic link %s : %s",aFilePathSl,gotContentSl)}

The example below demonstrates the concurrent creation of subdirectories under aroot directory by several users in different goroutines (works only withMemFS) :

package mainimport ("fmt""log""sync""github.com/avfs/avfs""github.com/avfs/avfs/idm/memidm""github.com/avfs/avfs/vfs/memfs")funcmain() {const (maxUsers=100groupName="test_users")idm:=memidm.New()vfs:=memfs.New()rootDir,_:=vfs.MkdirTemp("","avfs")vfs.Chmod(rootDir,0o777)g,_:=idm.GroupAdd(groupName)varwg sync.WaitGroupwg.Add(maxUsers)fori:=0;i<maxUsers;i++ {gofunc(iint) {deferwg.Done()userName:=fmt.Sprintf("user_%08d",i)idm.UserAdd(userName,g.Name())vfsU,_:=vfs.Sub("/")vfsU.SetUser(userName)path:=vfsU.Join(rootDir,userName)vfsU.Mkdir(path,avfs.DefaultDirPerm)}(i)}wg.Wait()entries,_:=vfs.ReadDir(rootDir)log.Println("number of dirs :",len(entries))for_,entry:=rangeentries {info,_:=entry.Info()sst:=vfs.ToSysStat(info)u,_:=idm.LookupUserId(sst.Uid())log.Println("dir :",info.Name(),", mode :",info.Mode(),", owner :",u.Name())}}

Almost ready for Windows.

All file systems implement at leastavfs.FS andavfs.File interfaces.By default, each file system supported methods are the most commonly used frompackagesos andpath/filepath. All methods have identical names as theirfunctions counterparts.The following file systems are currently available :

Identity managers allow users and groups management. The ones implementedinavfs are just here to allow testing of functions related to users (Chown,Lchown) and access rights, so they just allow one default group per user.

All file systems supporting identity manager implement by default the identitymanagerDummyIdmwhere all functions returnsavfs.ErrPermDenied.