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mirror of https://github.com/octoleo/restic.git synced 2024-11-10 23:31:09 +00:00
restic/backend/generic.go
2015-05-02 16:13:56 +02:00

136 lines
2.6 KiB
Go

package backend
import (
"crypto/sha256"
"errors"
"io"
)
const (
MinPrefixLength = 8
)
var (
ErrNoIDPrefixFound = errors.New("no ID found")
ErrMultipleIDMatches = errors.New("multiple IDs with prefix found")
)
var (
hashData = sha256.Sum256
)
const hashSize = sha256.Size
// Hash returns the ID for data.
func Hash(data []byte) ID {
h := hashData(data)
id := make([]byte, IDSize)
copy(id, h[:])
return id
}
// Find loads the list of all blobs of type t and searches for names which
// start with prefix. If none is found, nil and ErrNoIDPrefixFound is returned.
// If more than one is found, nil and ErrMultipleIDMatches is returned.
func Find(be Lister, t Type, prefix string) (string, error) {
done := make(chan struct{})
defer close(done)
match := ""
// TODO: optimize by sorting list etc.
for name := range be.List(t, done) {
if prefix == name[:len(prefix)] {
if match == "" {
match = name
} else {
return "", ErrMultipleIDMatches
}
}
}
if match != "" {
return match, nil
}
return "", ErrNoIDPrefixFound
}
// FindSnapshot takes a string and tries to find a snapshot whose ID matches
// the string as closely as possible.
func FindSnapshot(be Lister, s string) (string, error) {
// find snapshot id with prefix
name, err := Find(be, Snapshot, s)
if err != nil {
return "", err
}
return name, nil
}
// PrefixLength returns the number of bytes required so that all prefixes of
// all names of type t are unique.
func PrefixLength(be Lister, t Type) (int, error) {
done := make(chan struct{})
defer close(done)
// load all IDs of the given type
list := make([]string, 0, 100)
for name := range be.List(t, done) {
list = append(list, name)
}
// select prefixes of length l, test if the last one is the same as the current one
outer:
for l := MinPrefixLength; l < IDSize; l++ {
var last string
for _, name := range list {
if last == name[:l] {
continue outer
}
last = name[:l]
}
return l, nil
}
return IDSize, nil
}
// wrap around io.LimitedReader that implements io.ReadCloser
type blobReader struct {
cl io.Closer
rd io.Reader
closed bool
}
func (l *blobReader) Read(p []byte) (int, error) {
n, err := l.rd.Read(p)
if err == io.EOF {
l.Close()
}
return n, err
}
func (l *blobReader) Close() error {
if l == nil {
return nil
}
if !l.closed {
err := l.cl.Close()
l.closed = true
return err
}
return nil
}
// LimitReadCloser returns a new reader wraps r in an io.LimitReader, but also
// implements the Close() method.
func LimitReadCloser(r io.ReadCloser, n int64) *blobReader {
return &blobReader{cl: r, rd: io.LimitReader(r, n)}
}