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blobs.go
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blobs.go
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package apk
import (
"bufio"
"bytes"
ogzip "compress/gzip"
"fmt"
"io"
"github.com/jonjohnsonjr/dagdotdev/internal/gzip"
"github.com/jonjohnsonjr/dagdotdev/internal/zstd"
)
// Pretends to implement Seek because ServeContent only cares about checking
// for the size by calling Seek(0, io.SeekEnd)
type sizeSeeker struct {
rc io.Reader
size int64
}
func (s *sizeSeeker) Seek(offset int64, whence int) (int64, error) {
return 0, fmt.Errorf("not implemented")
}
func (s *sizeSeeker) Read(p []byte) (int, error) {
return s.rc.Read(p)
}
func (s *sizeSeeker) Size() int64 {
return s.size
}
type sizeBlob struct {
io.ReadCloser
size int64
}
func (s *sizeBlob) Size() int64 {
return s.size
}
const (
magicGNU, versionGNU = "ustar ", " \x00"
magicUSTAR, versionUSTAR = "ustar\x00", "00"
)
func tarPeek(r io.Reader) (bool, gzip.PeekReader, error) {
// Make sure it's more than 512
var pr gzip.PeekReader
if p, ok := r.(gzip.PeekReader); ok {
pr = p
} else {
// For tar peek.
pr = bufio.NewReaderSize(r, 1<<16)
}
block, err := pr.Peek(512)
if err != nil {
// https://github.com/google/go-containerregistry/issues/367
if err == io.EOF {
return false, pr, nil
}
return false, pr, err
}
magic := string(block[257:][:6])
isTar := magic == magicGNU || magic == magicUSTAR
return isTar, pr, nil
}
func gztarPeek(r io.Reader) (bool, gzip.PeekReader, error) {
pr := bufio.NewReaderSize(r, 1<<16)
// Should be enough to read first block?
zb, err := pr.Peek(1024)
if err != nil {
if err != io.EOF {
return false, pr, err
}
}
br := bytes.NewReader(zb)
ok, zpr, err := gzip.Peek(br)
if !ok {
return ok, pr, err
}
zr, err := ogzip.NewReader(zpr)
if err != nil {
return false, pr, err
}
ok, _, err = tarPeek(zr)
return ok, pr, err
}
func zstdTarPeek(r io.Reader) (bool, gzip.PeekReader, error) {
pr := bufio.NewReaderSize(r, 1<<16)
// Should be enough to read first block?
zb, err := pr.Peek(1024)
if err != nil {
if err != io.EOF {
return false, pr, err
}
}
br := bytes.NewReader(zb)
ok, zpr, err := zstdPeek(br)
if !ok {
return ok, pr, err
}
zr, err := ogzip.NewReader(zpr)
if err != nil {
return false, pr, err
}
ok, _, err = tarPeek(zr)
return ok, pr, err
}
func zstdPeek(r io.Reader) (bool, gzip.PeekReader, error) {
// Make sure it's more than 512
var pr gzip.PeekReader
if p, ok := r.(gzip.PeekReader); ok {
pr = p
} else {
// For tar peek.
pr = bufio.NewReaderSize(r, 1<<16)
}
return checkHeader(pr, zstd.MagicHeader)
}
// CheckHeader checks whether the first bytes from a PeekReader match an expected header
func checkHeader(pr gzip.PeekReader, expectedHeader []byte) (bool, gzip.PeekReader, error) {
header, err := pr.Peek(len(expectedHeader))
if err != nil {
// https://github.com/google/go-containerregistry/issues/367
if err == io.EOF {
return false, pr, nil
}
return false, pr, err
}
return bytes.Equal(header, expectedHeader), pr, nil
}