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peek.go
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/
peek.go
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package soci
import (
"bufio"
"bytes"
"io"
ogzip "compress/gzip"
kzstd "github.com/klauspost/compress/zstd"
"github.com/google/go-containerregistry/pkg/logs"
"github.com/jonjohnsonjr/dagdotdev/internal/and"
"github.com/jonjohnsonjr/dagdotdev/internal/gzip"
"github.com/jonjohnsonjr/dagdotdev/internal/zstd"
)
const (
magicGNU, versionGNU = "ustar ", " \x00"
magicUSTAR, versionUSTAR = "ustar\x00", "00"
)
type PeekReader interface {
io.Reader
Peek(n int) ([]byte, error)
}
// Peek detects streams of:
// tar
// tar+gzip
// tar+zstd
// gzip
// zstd
func Peek(rc io.ReadCloser) (string, io.ReadCloser, io.ReadCloser, error) {
logs.Debug.Printf("Peek")
buf := bufio.NewReaderSize(rc, 1<<16)
pr := &and.ReadCloser{Reader: buf, CloseFunc: rc.Close}
// Should be enough to read first block?
zb, err := buf.Peek(1024)
if err != nil {
if err != io.EOF {
return "", pr, nil, err
}
}
br := bytes.NewReader(zb)
if ok, zpr, err := gzip.Peek(br); err != nil {
return "", pr, nil, err
} else if ok {
zr, err := ogzip.NewReader(zpr)
if err != nil {
return "", pr, nil, err
}
ok, tpr, err := tarPeek(zr)
if err != nil {
return "", pr, nil, err
}
if ok {
return "tar+gzip", pr, tpr, nil
} else {
return "gzip", pr, tpr, nil
}
}
br = bytes.NewReader(zb)
if ok, zpr, err := zstdPeek(br); err != nil {
return "", pr, nil, err
} else if ok {
zr, err := kzstd.NewReader(zpr)
if err != nil {
return "", pr, nil, err
}
ok, tpr, err := tarPeek(zr.IOReadCloser())
if err != nil {
return "", pr, nil, err
}
if ok {
return "tar+zstd", pr, tpr, nil
} else {
return "zstd", pr, tpr, nil
}
}
br = bytes.NewReader(zb)
if ok, tpr, err := tarPeek(io.NopCloser(br)); err != nil {
return "", pr, nil, err
} else if ok {
return "tar", pr, tpr, nil
}
return "", pr, nil, nil
}
func zstdPeek(r io.Reader) (bool, 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 PeekReader, expectedHeader []byte) (bool, 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
}
func tarPeek(rc io.ReadCloser) (bool, io.ReadCloser, error) {
// Make sure it's more than 512
var pr PeekReader
if p, ok := rc.(PeekReader); ok {
pr = p
} else {
// For tar peek.
pr = bufio.NewReaderSize(rc, 1<<16)
}
prc := &and.ReadCloser{Reader: pr, CloseFunc: rc.Close}
block, err := pr.Peek(512)
if err != nil {
// https://github.com/google/go-containerregistry/issues/367
if err == io.EOF {
return false, prc, nil
}
return false, prc, err
}
magic := string(block[257:][:6])
isTar := magic == magicGNU || magic == magicUSTAR
return isTar, prc, nil
}