msgLogFP -> write ahead log

consensus/wal.go

@@ -0,0 +1,113 @@
+package consensus
+
+import (
+	"bufio"
+	"os"
+	"time"
+
+	. "github.com/tendermint/go-common"
+	"github.com/tendermint/go-wire"
+	"github.com/tendermint/tendermint/types"
+)
+
+//--------------------------------------------------------
+// types and functions for savings consensus messages
+
+type ConsensusLogMessage struct {
+	Time time.Time                    `json:"time"`
+	Msg  ConsensusLogMessageInterface `json:"msg"`
+}
+
+type ConsensusLogMessageInterface interface{}
+
+var _ = wire.RegisterInterface(
+	struct{ ConsensusLogMessageInterface }{},
+	wire.ConcreteType{&types.EventDataRoundState{}, 0x01},
+	wire.ConcreteType{msgInfo{}, 0x02},
+	wire.ConcreteType{timeoutInfo{}, 0x03},
+)
+
+//--------------------------------------------------------
+// Simple write-ahead logger
+
+// Write ahead logger writes msgs to disk before they are processed.
+// Can be used for crash-recovery and deterministic replay
+type WAL struct {
+	fp     *os.File
+	exists bool // if the file already existed (restarted process)
+}
+
+func NewWAL(file string) (*WAL, error) {
+	var walExists bool
+	if _, err := os.Stat(file); err == nil {
+		walExists = true
+	}
+	fp, err := os.OpenFile(file, os.O_RDWR|os.O_APPEND|os.O_CREATE, 0600)
+	if err != nil {
+		return nil, err
+	}
+	return &WAL{
+		fp:     fp,
+		exists: walExists,
+	}, nil
+}
+
+// called in newStep and for each pass in receiveRoutine
+func (wal *WAL) Save(msg ConsensusLogMessageInterface) {
+	if wal != nil {
+		var n int
+		var err error
+		wire.WriteJSON(ConsensusLogMessage{time.Now(), msg}, wal.fp, &n, &err)
+		wire.WriteTo([]byte("\n"), wal.fp, &n, &err) // one message per line
+		if err != nil {
+			PanicQ(Fmt("Error writing msg to consensus wal. Error: %v \n\nMessage: %v", err, msg))
+		}
+	}
+}
+
+// Must not be called concurrently.
+func (wal *WAL) Close() {
+	if wal != nil {
+		wal.fp.Close()
+	}
+}
+
+func (wal *WAL) SeekFromEnd(found func([]byte) bool) (nLines int, err error) {
+	var current int64
+	// start at the end
+	current, err = wal.fp.Seek(0, 2)
+	if err != nil {
+		return
+	}
+
+	// backup until we find the the right line
+	for {
+		current -= 1
+		if current < 0 {
+			return
+		}
+		// backup one and read a new byte
+		if _, err = wal.fp.Seek(current, 0); err != nil {
+			return
+		}
+		b := make([]byte, 1)
+		if _, err = wal.fp.Read(b); err != nil {
+			return
+		}
+		if b[0] == '\n' || len(b) == 0 {
+			// read a full line
+			reader := bufio.NewReader(wal.fp)
+			lineBytes, _ := reader.ReadBytes('\n')
+			if len(lineBytes) == 0 {
+				continue
+			}
+
+			nLines += 1
+			if found(lineBytes) {
+				wal.fp.Seek(0, 1) // (?)
+				wal.fp.Seek(current, 0)
+				return
+			}
+		}
+	}
+}