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package ingest
import (
"errors"
"hash"
"io"
"os"
)
const streamScannerBufferSize = 64 << 10
// streamScanner incrementally reads/consumes one pack stream while mirroring
// consumed bytes into one destination pack file.
type streamScanner struct {
src io.Reader
dstFile *os.File
// Input buffer window: buf[off:n] is unread.
buf []byte
off int
n int
// Absolute consumed stream bytes.
consumed uint64
// Running pack hash over consumed bytes while hashEnabled is true.
hash hash.Hash
hashSize int
hashEnabled bool
// Entry CRC state while one entry is being consumed.
entryCRC uint32
inEntryCRC bool
packTrailer []byte
}
// newStreamScanner constructs one scanner with fixed input buffering.
func newStreamScanner(src io.Reader, dstFile *os.File, hash hash.Hash, hashSize int) *streamScanner {
return &streamScanner{
src: src,
dstFile: dstFile,
buf: make([]byte, streamScannerBufferSize),
hash: hash,
hashSize: hashSize,
hashEnabled: true,
}
}
// Read implements io.Reader.
func (scanner *streamScanner) Read(dst []byte) (int, error) {
if len(dst) == 0 {
return 0, nil
}
if scanner.n-scanner.off == 0 {
err := scanner.fill(1)
if err != nil {
if errors.Is(err, io.EOF) {
return 0, io.EOF
}
return 0, err
}
}
unread := scanner.n - scanner.off
if unread == 0 {
return 0, io.EOF
}
n := min(len(dst), unread)
copy(dst, scanner.buf[scanner.off:scanner.off+n])
err := scanner.use(n)
if err != nil {
return 0, err
}
return n, nil
}
// ReadByte implements io.ByteReader without allocation.
func (scanner *streamScanner) ReadByte() (byte, error) {
if scanner.n-scanner.off == 0 {
err := scanner.fill(1)
if err != nil {
return 0, err
}
}
b := scanner.buf[scanner.off]
err := scanner.use(1)
if err != nil {
return 0, err
}
return b, nil
}
// readFull reads exactly len(dst) bytes through receiver.
func (scanner *streamScanner) readFull(dst []byte) error {
_, err := io.ReadFull(scanner, dst)
if err != nil {
return err
}
return nil
}
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