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checksum_reader.go
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/
checksum_reader.go
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package rpc
import (
"bufio"
"encoding/binary"
"errors"
"fmt"
"io"
"net"
hdfs "github.com/capsule8/hdfs/protocol/hadoop_hdfs"
"github.com/golang/protobuf/proto"
)
// ChecksumReader provides an interface for reading the "MD5CRC32" checksums of
// individual blocks. It abstracts over reading from multiple datanodes, in
// order to be robust to failures.
type ChecksumReader struct {
block *hdfs.LocatedBlockProto
datanodes *datanodeFailover
conn net.Conn
reader *bufio.Reader
}
// NewChecksumReader creates a new ChecksumReader for the given block.
func NewChecksumReader(block *hdfs.LocatedBlockProto) *ChecksumReader {
hdfs.LoadAPI()
locs := block.GetLocs()
datanodes := make([]string, len(locs))
for i, loc := range locs {
dn := loc.GetId()
datanodes[i] = fmt.Sprintf("%s:%d", dn.GetHostName(), dn.GetXferPort())
}
return &ChecksumReader{
block: block,
datanodes: newDatanodeFailover(datanodes),
}
}
// ReadChecksum returns the checksum of the block.
func (cr *ChecksumReader) ReadChecksum() ([]byte, error) {
for cr.datanodes.numRemaining() > 0 {
address := cr.datanodes.next()
checksum, err := cr.readChecksum(address)
if err != nil {
cr.datanodes.recordFailure(err)
continue
}
return checksum, nil
}
err := cr.datanodes.lastError()
if err != nil {
err = errors.New("No available datanodes for block.")
}
return nil, err
}
func (cr *ChecksumReader) readChecksum(address string) ([]byte, error) {
conn, err := net.DialTimeout("tcp", address, connectTimeout)
if err != nil {
return nil, err
}
cr.conn = conn
err = cr.writeBlockChecksumRequest()
if err != nil {
return nil, err
}
cr.reader = bufio.NewReader(conn)
resp, err := cr.readBlockChecksumResponse()
if err != nil {
return nil, err
}
return resp.GetChecksumResponse().GetMd5(), nil
}
// A checksum request to a datanode:
// +-----------------------------------------------------------+
// | Data Transfer Protocol Version, int16 |
// +-----------------------------------------------------------+
// | Op code, 1 byte (CHECKSUM_BLOCK = 0x55) |
// +-----------------------------------------------------------+
// | varint length + OpReadBlockProto |
// +-----------------------------------------------------------+
func (cr *ChecksumReader) writeBlockChecksumRequest() error {
header := []byte{0x00, dataTransferVersion, checksumBlockOp}
op := newChecksumBlockOp(cr.block)
opBytes, err := makePrefixedMessage(op)
if err != nil {
return err
}
req := append(header, opBytes...)
_, err = cr.conn.Write(req)
if err != nil {
return err
}
return nil
}
// The response from the datanode:
// +-----------------------------------------------------------+
// | varint length + BlockOpResponseProto |
// +-----------------------------------------------------------+
func (cr *ChecksumReader) readBlockChecksumResponse() (*hdfs.BlockOpResponseProto, error) {
respLength, err := binary.ReadUvarint(cr.reader)
if err != nil {
if err == io.EOF {
err = io.ErrUnexpectedEOF
}
return nil, err
}
respBytes := make([]byte, respLength)
_, err = io.ReadFull(cr.reader, respBytes)
if err != nil {
return nil, err
}
resp := &hdfs.BlockOpResponseProto{}
err = proto.Unmarshal(respBytes, resp)
if err != nil {
return nil, err
}
return resp, nil
}
func newChecksumBlockOp(block *hdfs.LocatedBlockProto) *hdfs.OpBlockChecksumProto {
return &hdfs.OpBlockChecksumProto{
Header: &hdfs.BaseHeaderProto{
Block: block.GetB(),
Token: block.GetBlockToken(),
},
}
}