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+![afero logo-sm](https://cloud.githubusercontent.com/assets/173412/11490338/d50e16dc-97a5-11e5-8b12-019a300d0fcb.png)
+
+A FileSystem Abstraction System for Go
+
+[![Build Status](https://travis-ci.org/spf13/afero.svg)](https://travis-ci.org/spf13/afero) [![Build status](https://ci.appveyor.com/api/projects/status/github/spf13/afero?branch=master&svg=true)](https://ci.appveyor.com/project/spf13/afero) [![GoDoc](https://godoc.org/github.com/spf13/afero?status.svg)](https://godoc.org/github.com/spf13/afero) [![Join the chat at https://gitter.im/spf13/afero](https://badges.gitter.im/Dev%20Chat.svg)](https://gitter.im/spf13/afero?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
+
+# Overview
+
+Afero is an filesystem framework providing a simple, uniform and universal API
+interacting with any filesystem, as an abstraction layer providing interfaces,
+types and methods. Afero has an exceptionally clean interface and simple design
+without needless constructors or initialization methods.
+
+Afero is also a library providing a base set of interoperable backend
+filesystems that make it easy to work with afero while retaining all the power
+and benefit of the os and ioutil packages.
+
+Afero provides significant improvements over using the os package alone, most
+notably the ability to create mock and testing filesystems without relying on the disk.
+
+It is suitable for use in a any situation where you would consider using the OS
+package as it provides an additional abstraction that makes it easy to use a
+memory backed file system during testing. It also adds support for the http
+filesystem for full interoperability.
+
+
+## Afero Features
+
+* A single consistent API for accessing a variety of filesystems
+* Interoperation between a variety of file system types
+* A set of interfaces to encourage and enforce interoperability between backends
+* An atomic cross platform memory backed file system
+* Support for compositional (union) file systems by combining multiple file systems acting as one
+* Specialized backends which modify existing filesystems (Read Only, Regexp filtered)
+* A set of utility functions ported from io, ioutil & hugo to be afero aware
+
+
+# Using Afero
+
+Afero is easy to use and easier to adopt.
+
+A few different ways you could use Afero:
+
+* Use the interfaces alone to define you own file system.
+* Wrap for the OS packages.
+* Define different filesystems for different parts of your application.
+* Use Afero for mock filesystems while testing
+
+## Step 1: Install Afero
+
+First use go get to install the latest version of the library.
+
+    $ go get github.com/spf13/afero
+
+Next include Afero in your application.
+```go
+import "github.com/spf13/afero"
+```
+
+## Step 2: Declare a backend
+
+First define a package variable and set it to a pointer to a filesystem.
+```go
+var AppFs = afero.NewMemMapFs()
+
+or
+
+var AppFs = afero.NewOsFs()
+```
+It is important to note that if you repeat the composite literal you
+will be using a completely new and isolated filesystem. In the case of
+OsFs it will still use the same underlying filesystem but will reduce
+the ability to drop in other filesystems as desired.
+
+## Step 3: Use it like you would the OS package
+
+Throughout your application use any function and method like you normally
+would.
+
+So if my application before had:
+```go
+os.Open('/tmp/foo')
+```
+We would replace it with:
+```go
+AppFs.Open('/tmp/foo')
+```
+
+`AppFs` being the variable we defined above.
+
+
+## List of all available functions
+
+File System Methods Available:
+```go
+Chmod(name string, mode os.FileMode) : error
+Chtimes(name string, atime time.Time, mtime time.Time) : error
+Create(name string) : File, error
+Mkdir(name string, perm os.FileMode) : error
+MkdirAll(path string, perm os.FileMode) : error
+Name() : string
+Open(name string) : File, error
+OpenFile(name string, flag int, perm os.FileMode) : File, error
+Remove(name string) : error
+RemoveAll(path string) : error
+Rename(oldname, newname string) : error
+Stat(name string) : os.FileInfo, error
+```
+File Interfaces and Methods Available:
+```go
+io.Closer
+io.Reader
+io.ReaderAt
+io.Seeker
+io.Writer
+io.WriterAt
+
+Name() : string
+Readdir(count int) : []os.FileInfo, error
+Readdirnames(n int) : []string, error
+Stat() : os.FileInfo, error
+Sync() : error
+Truncate(size int64) : error
+WriteString(s string) : ret int, err error
+```
+In some applications it may make sense to define a new package that
+simply exports the file system variable for easy access from anywhere.
+
+## Using Afero's utility functions
+
+Afero provides a set of functions to make it easier to use the underlying file systems.
+These functions have been primarily ported from io & ioutil with some developed for Hugo.
+
+The afero utilities support all afero compatible backends.
+
+The list of utilities includes:
+
+```go
+DirExists(path string) (bool, error)
+Exists(path string) (bool, error)
+FileContainsBytes(filename string, subslice []byte) (bool, error)
+GetTempDir(subPath string) string
+IsDir(path string) (bool, error)
+IsEmpty(path string) (bool, error)
+ReadDir(dirname string) ([]os.FileInfo, error)
+ReadFile(filename string) ([]byte, error)
+SafeWriteReader(path string, r io.Reader) (err error)
+TempDir(dir, prefix string) (name string, err error)
+TempFile(dir, prefix string) (f File, err error)
+Walk(root string, walkFn filepath.WalkFunc) error
+WriteFile(filename string, data []byte, perm os.FileMode) error
+WriteReader(path string, r io.Reader) (err error)
+```
+For a complete list see [Afero's GoDoc](https://godoc.org/github.com/spf13/afero)
+
+They are available under two different approaches to use. You can either call
+them directly where the first parameter of each function will be the file
+system, or you can declare a new `Afero`, a custom type used to bind these
+functions as methods to a given filesystem.
+
+### Calling utilities directly
+
+```go
+fs := new(afero.MemMapFs)
+f, err := afero.TempFile(fs,"", "ioutil-test")
+
+```
+
+### Calling via Afero
+
+```go
+fs := afero.NewMemMapFs()
+afs := &afero.Afero{Fs: fs}
+f, err := afs.TempFile("", "ioutil-test")
+```
+
+## Using Afero for Testing
+
+There is a large benefit to using a mock filesystem for testing. It has a
+completely blank state every time it is initialized and can be easily
+reproducible regardless of OS. You could create files to your heart’s content
+and the file access would be fast while also saving you from all the annoying
+issues with deleting temporary files, Windows file locking, etc. The MemMapFs
+backend is perfect for testing.
+
+* Much faster than performing I/O operations on disk
+* Avoid security issues and permissions
+* Far more control. 'rm -rf /' with confidence
+* Test setup is far more easier to do
+* No test cleanup needed
+
+One way to accomplish this is to define a variable as mentioned above.
+In your application this will be set to afero.NewOsFs() during testing you
+can set it to afero.NewMemMapFs().
+
+It wouldn't be uncommon to have each test initialize a blank slate memory
+backend. To do this I would define my `appFS = afero.NewOsFs()` somewhere
+appropriate in my application code. This approach ensures that Tests are order
+independent, with no test relying on the state left by an earlier test.
+
+Then in my tests I would initialize a new MemMapFs for each test:
+```go
+func TestExist(t *testing.T) {
+        appFS := afero.NewMemMapFs()
+        // create test files and directories
+        appFS.MkdirAll("src/a", 0755)
+        afero.WriteFile(appFS, "src/a/b", []byte("file b"), 0644)
+        afero.WriteFile(appFS, "src/c", []byte("file c"), 0644)
+        name := "src/c"
+        _, err := appFS.Stat(name)
+        if os.IsNotExist(err) {
+                t.Errorf("file \"%s\" does not exist.\n", name)
+        }
+}
+```
+
+# Available Backends
+
+## Operating System Native
+
+### OsFs
+
+The first is simply a wrapper around the native OS calls. This makes it
+very easy to use as all of the calls are the same as the existing OS
+calls. It also makes it trivial to have your code use the OS during
+operation and a mock filesystem during testing or as needed.
+
+```go
+appfs := afero.NewOsFs()
+appfs.MkdirAll("src/a", 0755))
+```
+
+## Memory Backed Storage
+
+### MemMapFs
+
+Afero also provides a fully atomic memory backed filesystem perfect for use in
+mocking and to speed up unnecessary disk io when persistence isn’t
+necessary. It is fully concurrent and will work within go routines
+safely.
+
+```go
+mm := afero.NewMemMapFs()
+mm.MkdirAll("src/a", 0755))
+```
+
+#### InMemoryFile
+
+As part of MemMapFs, Afero also provides an atomic, fully concurrent memory
+backed file implementation. This can be used in other memory backed file
+systems with ease. Plans are to add a radix tree memory stored file
+system using InMemoryFile.
+
+## Network Interfaces
+
+### SftpFs
+
+Afero has experimental support for secure file transfer protocol (sftp). Which can
+be used to perform file operations over a encrypted channel.
+
+## Filtering Backends
+
+### BasePathFs
+
+The BasePathFs restricts all operations to a given path within an Fs.
+The given file name to the operations on this Fs will be prepended with
+the base path before calling the source Fs.
+
+```go
+bp := afero.NewBasePathFs(afero.NewOsFs(), "/base/path")
+```
+
+### ReadOnlyFs
+
+A thin wrapper around the source Fs providing a read only view.
+
+```go
+fs := afero.NewReadOnlyFs(afero.NewOsFs())
+_, err := fs.Create("/file.txt")
+// err = syscall.EPERM
+```
+
+# RegexpFs
+
+A filtered view on file names, any file NOT matching
+the passed regexp will be treated as non-existing.
+Files not matching the regexp provided will not be created.
+Directories are not filtered.
+
+```go
+fs := afero.NewRegexpFs(afero.NewMemMapFs(), regexp.MustCompile(`\.txt$`))
+_, err := fs.Create("/file.html")
+// err = syscall.ENOENT
+```
+
+### HttpFs
+
+Afero provides an http compatible backend which can wrap any of the existing
+backends.
+
+The Http package requires a slightly specific version of Open which
+returns an http.File type.
+
+Afero provides an httpFs file system which satisfies this requirement.
+Any Afero FileSystem can be used as an httpFs.
+
+```go
+httpFs := afero.NewHttpFs(<ExistingFS>)
+fileserver := http.FileServer(httpFs.Dir(<PATH>)))
+http.Handle("/", fileserver)
+```
+
+## Composite Backends
+
+Afero provides the ability have two filesystems (or more) act as a single
+file system.
+
+### CacheOnReadFs
+
+The CacheOnReadFs will lazily make copies of any accessed files from the base
+layer into the overlay. Subsequent reads will be pulled from the overlay
+directly permitting the request is within the cache duration of when it was
+created in the overlay.
+
+If the base filesystem is writeable, any changes to files will be
+done first to the base, then to the overlay layer. Write calls to open file
+handles like `Write()` or `Truncate()` to the overlay first.
+
+To writing files to the overlay only, you can use the overlay Fs directly (not
+via the union Fs).
+
+Cache files in the layer for the given time.Duration, a cache duration of 0
+means "forever" meaning the file will not be re-requested from the base ever.
+
+A read-only base will make the overlay also read-only but still copy files
+from the base to the overlay when they're not present (or outdated) in the
+caching layer.
+
+```go
+base := afero.NewOsFs()
+layer := afero.NewMemMapFs()
+ufs := afero.NewCacheOnReadFs(base, layer, 100 * time.Second)
+```
+
+### CopyOnWriteFs()
+
+The CopyOnWriteFs is a read only base file system with a potentially
+writeable layer on top.
+
+Read operations will first look in the overlay and if not found there, will
+serve the file from the base.
+
+Changes to the file system will only be made in the overlay.
+
+Any attempt to modify a file found only in the base will copy the file to the
+overlay layer before modification (including opening a file with a writable
+handle).
+
+Removing and Renaming files present only in the base layer is not currently
+permitted. If a file is present in the base layer and the overlay, only the
+overlay will be removed/renamed.
+
+```go
+        base := afero.NewOsFs()
+        roBase := afero.NewReadOnlyFs(base)
+        ufs := afero.NewCopyOnWriteFs(roBase, afero.NewMemMapFs())
+
+        fh, _ = ufs.Create("/home/test/file2.txt")
+        fh.WriteString("This is a test")
+        fh.Close()
+```
+
+In this example all write operations will only occur in memory (MemMapFs)
+leaving the base filesystem (OsFs) untouched.
+
+
+## Desired/possible backends
+
+The following is a short list of possible backends we hope someone will
+implement:
+
+* SSH
+* ZIP
+* TAR
+* S3
+
+# About the project
+
+## What's in the name
+
+Afero comes from the latin roots Ad-Facere.
+
+**"Ad"** is a prefix meaning "to".
+
+**"Facere"** is a form of the root "faciō" making "make or do".
+
+The literal meaning of afero is "to make" or "to do" which seems very fitting
+for a library that allows one to make files and directories and do things with them.
+
+The English word that shares the same roots as Afero is "affair". Affair shares
+the same concept but as a noun it means "something that is made or done" or "an
+object of a particular type".
+
+It's also nice that unlike some of my other libraries (hugo, cobra, viper) it
+Googles very well.
+
+## Release Notes
+
+* **0.10.0** 2015.12.10
+  * Full compatibility with Windows
+  * Introduction of afero utilities
+  * Test suite rewritten to work cross platform
+  * Normalize paths for MemMapFs
+  * Adding Sync to the file interface
+  * **Breaking Change** Walk and ReadDir have changed parameter order
+  * Moving types used by MemMapFs to a subpackage
+  * General bugfixes and improvements
+* **0.9.0** 2015.11.05
+  * New Walk function similar to filepath.Walk
+  * MemMapFs.OpenFile handles O_CREATE, O_APPEND, O_TRUNC
+  * MemMapFs.Remove now really deletes the file
+  * InMemoryFile.Readdir and Readdirnames work correctly
+  * InMemoryFile functions lock it for concurrent access
+  * Test suite improvements
+* **0.8.0** 2014.10.28
+  * First public version
+  * Interfaces feel ready for people to build using
+  * Interfaces satisfy all known uses
+  * MemMapFs passes the majority of the OS test suite
+  * OsFs passes the majority of the OS test suite
+
+## Contributing
+
+1. Fork it
+2. Create your feature branch (`git checkout -b my-new-feature`)
+3. Commit your changes (`git commit -am 'Add some feature'`)
+4. Push to the branch (`git push origin my-new-feature`)
+5. Create new Pull Request
+
+## Contributors
+
+Names in no particular order:
+
+* [spf13](https://github.com/spf13)
+* [jaqx0r](https://github.com/jaqx0r)
+* [mbertschler](https://github.com/mbertschler)
+* [xor-gate](https://github.com/xor-gate)
+
+## License
+
+Afero is released under the Apache 2.0 license. See
+[LICENSE.txt](https://github.com/spf13/afero/blob/master/LICENSE.txt)