forked from lug/matterbridge
431 lines
13 KiB
Markdown
431 lines
13 KiB
Markdown
|
||
|
||
A FileSystem Abstraction System for Go
|
||
|
||
[](https://travis-ci.org/spf13/afero) [](https://ci.appveyor.com/project/spf13/afero) [](https://godoc.org/github.com/spf13/afero) [](https://gitter.im/spf13/afero?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
|
||
|
||
# Overview
|
||
|
||
Afero is a 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 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
|
||
* Wrapper for go 1.16 filesystem abstraction `io/fs.FS`
|
||
|
||
# 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 your own file system.
|
||
* Wrapper 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
|
||
Chown(name string, uid, gid int) : 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
|
||
* 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
|
||
|
||
See the [Releases Page](https://github.com/spf13/afero/releases).
|
||
|
||
## 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)
|