/
block_read_stream.go
183 lines (150 loc) · 4.12 KB
/
block_read_stream.go
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package rpc
import (
"bytes"
"encoding/binary"
"errors"
"hash/crc32"
"io"
"math"
hdfs "github.com/colinmarc/hdfs/protocol/hadoop_hdfs"
"github.com/golang/protobuf/proto"
)
var errInvalidChecksum = errors.New("Invalid checksum")
// blockReadStream implements io.Reader for reading a packet stream for a single
// block from a single datanode.
type blockReadStream struct {
reader io.Reader
checksumTab *crc32.Table
chunkSize int
checksums bytes.Buffer
chunk bytes.Buffer
packetLength int
chunkIndex int
numChunks int
lastPacket bool
}
func newBlockReadStream(reader io.Reader, chunkSize int, checksumTab *crc32.Table) *blockReadStream {
return &blockReadStream{
reader: reader,
chunkSize: chunkSize,
checksumTab: checksumTab,
}
}
func (s *blockReadStream) Read(b []byte) (int, error) {
if s.chunkIndex == s.numChunks {
if s.lastPacket {
return 0, io.EOF
}
err := s.startPacket()
if err != nil {
return 0, err
}
}
remainingInPacket := (s.packetLength - (s.chunkIndex * s.chunkSize))
// For small reads, we need to buffer a single chunk. If we did that
// previously, read the rest of the buffer, so we're aligned back on a
// chunk boundary.
if s.chunk.Len() > 0 {
n, _ := s.chunk.Read(b)
return n, nil
} else if len(b) < s.chunkSize {
chunkSize := s.chunkSize
if chunkSize > remainingInPacket {
chunkSize = remainingInPacket
}
_, err := io.CopyN(&s.chunk, s.reader, int64(chunkSize))
if err != nil {
return 0, err
}
err = s.validateChecksum(s.chunk.Bytes())
if err != nil {
return 0, nil
}
s.chunkIndex++
n, _ := s.chunk.Read(b)
return n, nil
}
// Always align reads to a chunk boundary. This makes the code much simpler,
// and with readers that pick sane read sizes (like io.Copy), should be
// efficient.
var amountToRead int
var chunksToRead int
if len(b) > remainingInPacket {
chunksToRead = s.numChunks - s.chunkIndex
amountToRead = remainingInPacket
} else {
chunksToRead = len(b) / s.chunkSize
amountToRead = chunksToRead * s.chunkSize
}
n, err := io.ReadFull(s.reader, b[:amountToRead])
if err != nil {
return n, err
}
// Validate the bytes we just read into b against the packet checksums.
for i := 0; i < chunksToRead; i++ {
chunkOff := i * s.chunkSize
chunkEnd := chunkOff + s.chunkSize
if chunkEnd >= len(b) {
chunkEnd = len(b)
}
err := s.validateChecksum(b[chunkOff:chunkEnd])
if err != nil {
return n, err
}
s.chunkIndex++
}
// EOF would be returned by the next call to Read anyway, but it's nice to
// return it here.
if s.chunkIndex == s.numChunks && s.lastPacket {
err = io.EOF
}
return n, err
}
func (s *blockReadStream) validateChecksum(b []byte) error {
checksumOffset := 4 * s.chunkIndex
checksumBytes := s.checksums.Bytes()[checksumOffset : checksumOffset+4]
checksum := binary.BigEndian.Uint32(checksumBytes)
crc := crc32.Checksum(b, s.checksumTab)
if crc != checksum {
return errInvalidChecksum
}
return nil
}
func (s *blockReadStream) startPacket() error {
header, err := s.readPacketHeader()
if err != nil {
return err
}
dataLength := int(header.GetDataLen())
numChunks := int(math.Ceil(float64(dataLength) / float64(s.chunkSize)))
// TODO don't assume checksum size is 4
checksumsLength := numChunks * 4
s.checksums.Reset()
s.checksums.Grow(checksumsLength)
_, err = io.CopyN(&s.checksums, s.reader, int64(checksumsLength))
if err != nil {
return err
}
s.packetLength = dataLength
s.numChunks = numChunks
s.chunkIndex = 0
s.lastPacket = header.GetLastPacketInBlock()
return nil
}
func (s *blockReadStream) readPacketHeader() (*hdfs.PacketHeaderProto, error) {
lengthBytes := make([]byte, 6)
_, err := io.ReadFull(s.reader, lengthBytes)
if err != nil {
return nil, err
}
// We don't actually care about the total length.
packetHeaderLength := binary.BigEndian.Uint16(lengthBytes[4:])
packetHeaderBytes := make([]byte, packetHeaderLength)
_, err = io.ReadFull(s.reader, packetHeaderBytes)
if err != nil {
return nil, err
}
packetHeader := &hdfs.PacketHeaderProto{}
err = proto.Unmarshal(packetHeaderBytes, packetHeader)
return packetHeader, nil
}