open-consul/agent/consul/fsm/log_verification_chunking_s...

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package fsm
import (
"bytes"
"encoding/binary"
"io"
"github.com/hashicorp/go-raftchunking"
"github.com/hashicorp/raft"
"github.com/hashicorp/raft-wal/verifier"
"github.com/hashicorp/consul/agent/structs"
)
type logVerificationChunkingShim struct {
chunker *raftchunking.ChunkingFSM
}
var logVerifierMagicBytes [8]byte
func init() {
binary.LittleEndian.PutUint64(logVerifierMagicBytes[:], verifier.ExtensionMagicPrefix)
}
// Apply implements raft.FSM.
func (s *logVerificationChunkingShim) Apply(l *raft.Log) interface{} {
// This is a hack because raftchunking doesn't play nicely with lower-level
// usage of Extensions field like we need for LogStore verification. We might
// change that instead but just seeing if I can get this to work here without
// upstream changes for now.
// We rely on the way we encode a checkpoint message being distinguishable
// from any valid chunked log entry. The type byte alone or the fact there is
// only one byte of data is not quite enough because it's just possible that
// chunking might split a larger log such that its final chunk was just a
// single byte, and if so there is a 1 in 256 chance it collides with our type
// byte! But we specially chose a magic value for verifier.LogStore to use
// that would never be the first 8 bytes of a valid proto encoding. See the
// docs on that value for more detail on why not. Note the data length for a
// checkpoint is actually 2 because msgpack encodes the nil slice as a typed
// nil byte (0xc0).
if len(l.Data) == 2 &&
structs.MessageType(l.Data[0]) == (structs.RaftLogVerifierCheckpoint|structs.IgnoreUnknownTypeFlag) &&
len(l.Extensions) > 8 &&
bytes.Equal(logVerifierMagicBytes[:], l.Extensions[0:8]) {
// Handle the checkpoint here since the lower level FSM doesn't know
// anything about it! The LogStore has already done what we need, we just
// need to return the index so that the caller can know which index the
// checkpoint ended up at.
return l.Index
}
return s.chunker.Apply(l)
}
// Snapshot implements raft.FSM
func (s *logVerificationChunkingShim) Snapshot() (raft.FSMSnapshot, error) {
return s.chunker.Snapshot()
}
// Restore implements raft.FSM
func (s *logVerificationChunkingShim) Restore(snapshot io.ReadCloser) error {
return s.chunker.Restore(snapshot)
}