forked from mirror/afero
272 lines
8.7 KiB
Markdown
272 lines
8.7 KiB
Markdown
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A FileSystem Abstraction System for Go
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[](https://travis-ci.org/spf13/afero) [](https://ci.appveyor.com/project/mbertschler/afero) [](https://godoc.org/github.com/spf13/afero)
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# Overview
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Afero is an filesystem framework providing a simple, uniform and universal API
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interacting with any filesystem, as an abstraction layer providing interfaces,
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types and methods. Afero has an exceptionally clean interface and simple design
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without needless constructors or initialization methods.
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Afero is also a library providing a base set of interoperable backend
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filesystems that make it easy to work with afero while retaining all the power
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and benefit of the os and ioutil packages.
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Afero provides significant improvements over using the os package alone, most
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notably the ability to create mock and testing filesystems without relying on the disk.
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It is suitable for use in a any situation where you would consider using the OS
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package as it provides an additional abstraction that makes it easy to use a
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memory backed file system during testing. It also adds support for the http
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filesystem for full interoperability.
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## Afero Features
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* A single consistent API for accessing a variety of filesystems
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* Interoperation between a variety of file system types
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* A set of interfaces to encourage and enforce interoperability between backends
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* An atomic cross platform memory backed file system
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* Support for compositional file systems by joining various different file systems (see httpFs)
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# Using Afero
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Afero is easy to use and easier to adopt.
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A few different ways you could use Afero:
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* Use the interfaces alone to define you own file system.
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* Wrap for the OS packages.
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* Define different filesystems for different parts of your application.
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* Use Afero for mock filesystems while testing
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## Step 1: Install Afero
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First use go get to install the latest version of the library.
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$ go get github.com/spf13/afero
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Next include Afero in your application.
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```go
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import "github.com/spf13/afero"
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```
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## Step 2: Declare a backend
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First define a package variable and set it to a pointer to a filesystem.
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```go
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var AppFs afero.Fs = &afero.MemMapFs{}
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or
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var AppFs afero.Fs = &afero.OsFs{}
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```
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It is important to note that if you repeat the composite literal you
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will be using a completely new and isolated filesystem. In the case of
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OsFs it will still use the same underlying filesystem but will reduce
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the ability to drop in other filesystems as desired.
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## Step 3: Use it like you would the OS package
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Throughout your application use any function and method like you normally
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would.
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So if my application before had:
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```go
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os.Open('/tmp/foo')
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```
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We would replace it with a call to `AppFs.Open('/tmp/foo')`.
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`AppFs` being the variable we defined above.
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## List of all available functions
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File System Methods Available:
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```go
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Chmod(name string, mode os.FileMode) : error
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Chtimes(name string, atime time.Time, mtime time.Time) : error
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Create(name string) : File, error
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Mkdir(name string, perm os.FileMode) : error
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MkdirAll(path string, perm os.FileMode) : error
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Name() : string
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Open(name string) : File, error
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OpenFile(name string, flag int, perm os.FileMode) : File, error
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Remove(name string) : error
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RemoveAll(path string) : error
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Rename(oldname, newname string) : error
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Stat(name string) : os.FileInfo, error
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```
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File Interfaces and Methods Available:
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```go
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io.Closer
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io.Reader
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io.ReaderAt
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io.Seeker
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io.Writer
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io.WriterAt
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Name() : string
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Readdir(count int) : []os.FileInfo, error
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Readdirnames(n int) : []string, error
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Stat() : os.FileInfo, error
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Sync() : error
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Truncate(size int64) : error
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WriteString(s string) : ret int, err error
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```
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In some applications it may make sense to define a new package that
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simply exports the file system variable for easy access from anywhere.
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## Using Afero for Testing
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There is a large benefit to using a mock filesystem for testing. It has a
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completely blank state every time it is initialized and can be easily
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reproducible regardless of OS. You could create files to your heart’s content
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and the file access would be fast while also saving you from all the annoying
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issues with deleting temporary files, Windows file locking, etc. The MemMapFs
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backend is perfect for testing.
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* Much faster than performing I/O operations on disk
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* Avoid security issues and permissions
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* Far more control. 'rm -rf /' with confidence
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* Test setup is far more easier to do
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* No test cleanup needed
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One way to accomplish this is to define a variable as mentioned above.
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In your application this will be set to &afero.OsFs{} during testing you
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can set it to &afero.MemMapFs{}.
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It wouldn't be uncommon to have each test initialize a blank slate memory
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backend. To do this I would define my `appFS = &afero.OsFs{}` somewhere
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appropriate in my application code. This approach ensures that Tests are order
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independent, with no test relying on the state left by an earlier test.
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Then in my tests I would initialize a new MemMapFs for each test:
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```go
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func TestExist(t *testing.T) {
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appFS = &afero.MemMapFs{}
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// create test files and directories
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appFS.MkdirAll("src/a", 0755))
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appFS.WriteFile("src/a/b", []byte("file b"), 0644)
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appFS.WriteFile("src/c", []byte("file c"), 0644)
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testExistence("src/c", true, t)
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}
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func testExistence(name string, e bool, t *testing.T) {
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_, err := appFS.Stat(name)
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if os.IsNotExist(err) {
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if e {
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t.Errorf("file \"%s\" does not exist.\n", name)
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}
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} else if err != nil {
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panic(err)
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} else {
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if !e {
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t.Errorf("file \"%s\" exists.\n", name)
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}
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}
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}
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```
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## Using Afero with Http
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Afero provides an http compatible backend which can wrap any of the existing
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backends.
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The Http package requires a slightly specific version of Open which
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returns an http.File type.
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Afero provides an httpFs file system which satisfies this requirement.
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Any Afero FileSystem can be used as an httpFs.
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```go
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httpFs := &afero.HttpFs{SourceFs: <ExistingFS>}
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fileserver := http.FileServer(httpFs.Dir(<PATH>)))
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http.Handle("/", fileserver)
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```
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# Available Backends
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## OsFs
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The first is simply a wrapper around the native OS calls. This makes it
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very easy to use as all of the calls are the same as the existing OS
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calls. It also makes it trivial to have your code use the OS during
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operation and a mock filesystem during testing or as needed.
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## MemMapFs
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Afero also provides a fully atomic memory backed filesystem perfect for use in
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mocking and to speed up unnecessary disk io when persistence isn’t
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necessary. It is fully concurrent and will work within go routines
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safely.
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### InMemoryFile
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As part of MemMapFs, Afero also provides an atomic, fully concurrent memory
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backed file implementation. This can be used in other memory backed file
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systems with ease. Plans are to add a radix tree memory stored file
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system using InMemoryFile.
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## Desired/possible backends
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The following is a short list of possible backends we hope someone will
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implement:
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* SSH/SCP
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* ZIP
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* TAR
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* S3
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* Mem buffering to disk/network
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* BasePath (where all paths are relative to a fixed basepath)
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# About the project
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## The name
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Initially this project was called fs. Unfortunately as I used it, the
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name proved confusing, there were too many fs’. In looking for
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alternatives I looked up the word 'abstract' in a variety of different
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languages. Afero is the Greek word for abstract and it seemed to be a
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fitting name for the project. It also means ‘to do’ or ‘thing’ in
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Esperanto which is also fitting.
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## Release Notes
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* **0.9.0** 2015.11.05
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* New Walk function similar to filepath.Walk
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* MemMapFs.OpenFile handles O_CREATE, O_APPEND, O_TRUNC
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* MemMapFs.Remove now really deletes the file
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* InMemoryFile.Readdir and Readdirnames work correctly
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* InMemoryFile functions lock it for concurrent access
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* Test suite improvements
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* **0.8.0** 2014.10.28
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* First public version
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* Interfaces feel ready for people to build using
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* Interfaces satisfy all known uses
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* MemMapFs passes the majority of the OS test suite
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* OsFs passes the majority of the OS test suite
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## Contributing
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1. Fork it
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2. Create your feature branch (`git checkout -b my-new-feature`)
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3. Commit your changes (`git commit -am 'Add some feature'`)
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4. Push to the branch (`git push origin my-new-feature`)
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5. Create new Pull Request
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## Contributors
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Names in no particular order:
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* [spf13](https://github.com/spf13)
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* [jaqx0r](https://github.com/jaqx0r)
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* [mbertschler](https://github.com/mbertschler)
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## License
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Afero is released under the Apache 2.0 license. See
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[LICENSE.txt](https://github.com/spf13/afero/blob/master/LICENSE.txt)
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