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|
package transfer
import (
"context"
"errors"
"io"
"net"
"time"
hdfs "github.com/colinmarc/hdfs/v2/internal/protocol/hadoop_hdfs"
)
// 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 is the block location provided by the namenode.
Block *hdfs.LocatedBlockProto
// UseDatanodeHostname specifies whether the datanodes should be connected to
// via their hostnames (if true) or IP addresses (if false).
UseDatanodeHostname bool
// DialFunc is used to connect to the datanodes. If nil, then (&net.Dialer{}).DialContext is used
DialFunc func(ctx context.Context, network, addr string) (net.Conn, error)
deadline time.Time
datanodes *datanodeFailover
}
// SetDeadline sets the deadline for future ReadChecksum calls. A zero value
// for t means Read will not time out.
func (cr *ChecksumReader) SetDeadline(t time.Time) error {
cr.deadline = t
// Return the error at connection time.
return nil
}
// ReadChecksum returns the checksum of the block.
func (cr *ChecksumReader) ReadChecksum() ([]byte, error) {
if cr.datanodes == nil {
locs := cr.Block.GetLocs()
datanodes := make([]string, len(locs))
for i, loc := range locs {
dn := loc.GetId()
datanodes[i] = getDatanodeAddress(dn, cr.UseDatanodeHostname)
}
cr.datanodes = newDatanodeFailover(datanodes)
}
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) {
if cr.DialFunc == nil {
cr.DialFunc = (&net.Dialer{}).DialContext
}
conn, err := cr.DialFunc(context.Background(), "tcp", address)
if err != nil {
return nil, err
}
err = conn.SetDeadline(cr.deadline)
if err != nil {
return nil, err
}
err = cr.writeBlockChecksumRequest(conn)
if err != nil {
return nil, err
}
resp, err := cr.readBlockChecksumResponse(conn)
if err != nil {
return nil, err
}
return resp.GetChecksumResponse().GetBlockChecksum(), 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(w io.Writer) error {
header := []byte{0x00, dataTransferVersion, checksumBlockOp}
op := newChecksumBlockOp(cr.Block)
opBytes, err := makePrefixedMessage(op)
if err != nil {
return err
}
req := append(header, opBytes...)
_, err = w.Write(req)
if err != nil {
return err
}
return nil
}
// The response from the datanode:
// +-----------------------------------------------------------+
// | varint length + BlockOpResponseProto |
// +-----------------------------------------------------------+
func (cr *ChecksumReader) readBlockChecksumResponse(r io.Reader) (*hdfs.BlockOpResponseProto, error) {
resp := &hdfs.BlockOpResponseProto{}
err := readPrefixedMessage(r, resp)
return resp, err
}
func newChecksumBlockOp(block *hdfs.LocatedBlockProto) *hdfs.OpBlockChecksumProto {
return &hdfs.OpBlockChecksumProto{
Header: &hdfs.BaseHeaderProto{
Block: block.GetB(),
Token: block.GetBlockToken(),
},
}
}
|
