distribution/testutil/tarfile.go

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package testutil
import (
"archive/tar"
"bytes"
"crypto/rand"
"fmt"
"io"
"io/ioutil"
mrand "math/rand"
"time"
"github.com/docker/docker/pkg/tarsum"
)
// CreateRandomTarFile creates a random tarfile, returning it as an
// io.ReadSeeker along with its tarsum. An error is returned if there is a
// problem generating valid content.
func CreateRandomTarFile() (rs io.ReadSeeker, tarSum string, err error) {
nFiles := mrand.Intn(10) + 10
target := &bytes.Buffer{}
wr := tar.NewWriter(target)
// Perturb this on each iteration of the loop below.
header := &tar.Header{
Mode: 0644,
ModTime: time.Now(),
Typeflag: tar.TypeReg,
Uname: "randocalrissian",
Gname: "cloudcity",
AccessTime: time.Now(),
ChangeTime: time.Now(),
}
for fileNumber := 0; fileNumber < nFiles; fileNumber++ {
fileSize := mrand.Int63n(1<<20) + 1<<20
header.Name = fmt.Sprint(fileNumber)
header.Size = fileSize
if err := wr.WriteHeader(header); err != nil {
return nil, "", err
}
randomData := make([]byte, fileSize)
// Fill up the buffer with some random data.
n, err := rand.Read(randomData)
if n != len(randomData) {
return nil, "", fmt.Errorf("short read creating random reader: %v bytes != %v bytes", n, len(randomData))
}
if err != nil {
return nil, "", err
}
nn, err := io.Copy(wr, bytes.NewReader(randomData))
if nn != fileSize {
return nil, "", fmt.Errorf("short copy writing random file to tar")
}
if err != nil {
return nil, "", err
}
if err := wr.Flush(); err != nil {
return nil, "", err
}
}
if err := wr.Close(); err != nil {
return nil, "", err
}
reader := bytes.NewReader(target.Bytes())
// A tar builder that supports tarsum inline calculation would be awesome
// here.
ts, err := tarsum.NewTarSum(reader, true, tarsum.Version1)
if err != nil {
return nil, "", err
}
nn, err := io.Copy(ioutil.Discard, ts)
if nn != int64(len(target.Bytes())) {
return nil, "", fmt.Errorf("short copy when getting tarsum of random layer: %v != %v", nn, len(target.Bytes()))
}
if err != nil {
return nil, "", err
}
return bytes.NewReader(target.Bytes()), ts.Sum(nil), nil
}