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package objects
import (
"bufio"
"bytes"
"errors"
"strconv"
)
// FileFragment describes a fragment of a file. It consists of the ID of a blob and the size of the blob.
// The size is not necessary for reconstruction (the blob object already has a size)
// but it can speed up random access to the whole file by skipping previous fragments.
// It is serialized as `Properties` (see there) with the keys `blob` (ID of blob object) and `size` (decimal size of the blob)
type FileFragment struct {
Blob ObjectId
Size uint64
}
func (ff FileFragment) toProperties() Properties {
return Properties{"blob": ff.Blob.String(), "size": strconv.FormatUint(ff.Size, 10)}
}
func (ff *FileFragment) fromProperties(p Properties) error {
blob, ok := p["blob"]
if !ok {
return errors.New("Field `blob` is missing")
}
var err error
ff.Blob, err = ParseObjectId(blob)
if err != nil {
return err
}
size, ok := p["size"]
if !ok {
return errors.New("Field `size` is missing")
}
ff.Size, err = strconv.ParseUint(size, 10, 64)
return err
}
func (a FileFragment) Equals(b FileFragment) bool {
return a.Blob.Equals(b.Blob) && a.Size == b.Size
}
// File describes a file object which ties together multiple Blob objects to a file.
// It is an ordered list of `FileFragment`s. The referenced blobs concatencated in the given order are the content of the file.
//
// Example:
//
// blob=sha3-256:1111111111111111111111111111111111111111111111111111111111111111&size=123
// blob=sha3-256:1111111111111111111111111111111111111111111111111111111111111111&size=123
// blob=sha3-256:2222222222222222222222222222222222222222222222222222222222222222&size=10
//
// The file described by this object is 123+123+10 = 256 bytes long and consists of the blobs 111... (two times) and 222...
//
// Since the blob IDs and sizes don't change unless the file itself changes and the format will always serialize the same,
// serializing the same file twice results in exactly the same object with exactly the same ID. It will therefor only be stored once.
type File []FileFragment
func (f File) Type() ObjectType {
return OTFile
}
func (f File) Payload() []byte {
out := []byte{}
for _, ff := range f {
b, err := ff.toProperties().MarshalText()
if err != nil {
panic(err)
}
out = append(out, b...)
out = append(out, '\n')
}
return out
}
func (f *File) FromPayload(payload []byte) error {
sc := bufio.NewScanner(bytes.NewReader(payload))
for sc.Scan() {
line := sc.Bytes()
if len(line) == 0 {
continue
}
props := make(Properties)
if err := props.UnmarshalText(line); err != nil {
return nil
}
ff := FileFragment{}
if err := ff.fromProperties(props); err != nil {
return err
}
*f = append(*f, ff)
}
return sc.Err()
}
func (a File) Equals(b File) bool {
if len(a) != len(b) {
return false
}
for i := range a {
if !a[i].Equals(b[i]) {
return false
}
}
return true
}
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