mempool: implement Mempool.CloseWAL

Fixes https://github.com/tendermint/tendermint/issues/890

Add a CloseWAL method to Mempool to close the underlying WAL file
and then discard it so that further writes to it will have no effect.

mempool/mempool.go

@@ -110,6 +110,26 @@ func (mem *Mempool) SetLogger(l log.Logger) {
 	mem.logger = l
 }
 
+// CloseWAL closes and discards the underlying WAL file.
+// Any further writes will not be relayed to disk.
+func (mem *Mempool) CloseWAL() bool {
+	if mem == nil {
+		return false
+	}
+
+	mem.proxyMtx.Lock()
+	defer mem.proxyMtx.Unlock()
+
+	if mem.wal == nil {
+		return false
+	}
+	if err := mem.wal.Close(); err != nil && mem.logger != nil {
+		mem.logger.Error("Mempool.CloseWAL", "err", err)
+	}
+	mem.wal = nil
+	return true
+}
+
 func (mem *Mempool) initWAL() {
 	walDir := mem.config.WalDir()
 	if walDir != "" {

mempool/mempool_test.go

@@ -1,8 +1,13 @@
 package mempool
 
 import (
+	"crypto/md5"
 	"crypto/rand"
 	"encoding/binary"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"testing"
 	"time"
 
@@ -13,6 +18,8 @@ import (
 	cfg "github.com/tendermint/tendermint/config"
 	"github.com/tendermint/tendermint/proxy"
 	"github.com/tendermint/tendermint/types"
+
+	"github.com/stretchr/testify/require"
 )
 
 func newMempoolWithApp(cc proxy.ClientCreator) *Mempool {
@@ -57,7 +64,7 @@ func checkTxs(t *testing.T, mempool *Mempool, count int) types.Txs {
 			t.Error(err)
 		}
 		if err := mempool.CheckTx(txBytes, nil); err != nil {
-			t.Fatal("Error after CheckTx: %v", err)
+			t.Fatalf("Error after CheckTx: %v", err)
 		}
 	}
 	return txs
@@ -127,7 +134,7 @@ func TestSerialReap(t *testing.T) {
 			binary.BigEndian.PutUint64(txBytes, uint64(i))
 			err := mempool.CheckTx(txBytes, nil)
 			if err != nil {
-				t.Fatal("Error after CheckTx: %v", err)
+				t.Fatalf("Error after CheckTx: %v", err)
 			}
 
 			// This will fail because not serial (incrementing)
@@ -135,7 +142,7 @@ func TestSerialReap(t *testing.T) {
 			// It just won't show up on Reap().
 			err = mempool.CheckTx(txBytes, nil)
 			if err != nil {
-				t.Fatal("Error after CheckTx: %v", err)
+				t.Fatalf("Error after CheckTx: %v", err)
 			}
 
 		}
@@ -211,3 +218,63 @@ func TestSerialReap(t *testing.T) {
 	// We should have 600 now.
 	reapCheck(600)
 }
+
+func TestMempoolCloseWAL(t *testing.T) {
+	// 1. Create the temporary directory for mempool and WAL testing.
+	rootDir, err := ioutil.TempDir("", "mempool-test")
+	require.Nil(t, err, "expecting successful tmpdir creation")
+	defer os.RemoveAll(rootDir)
+
+	// 2. Ensure that it doesn't contain any elements -- Sanity check
+	m1, err := filepath.Glob(filepath.Join(rootDir, "*"))
+	require.Nil(t, err, "successful globbing expected")
+	require.Equal(t, 0, len(m1), "no matches yet")
+
+	// 3. Create the mempool
+	wcfg := *(cfg.DefaultMempoolConfig())
+	wcfg.RootDir = rootDir
+	app := dummy.NewDummyApplication()
+	cc := proxy.NewLocalClientCreator(app)
+	appConnMem, _ := cc.NewABCIClient()
+	mempool := NewMempool(&wcfg, appConnMem, 10)
+
+	// 4. Ensure that the directory contains the WAL file
+	m2, err := filepath.Glob(filepath.Join(rootDir, "*"))
+	require.Nil(t, err, "successful globbing expected")
+	require.Equal(t, 1, len(m2), "expecting the wal match in")
+
+	// 5. Write some contents to the WAL
+	mempool.CheckTx(types.Tx([]byte("foo")), nil)
+	walFilepath := mempool.wal.Path
+	sum1 := checksumFile(walFilepath, t)
+
+	// 6. Sanity check to ensure that the written TX matches the expectation.
+	require.Equal(t, sum1, checksumIt([]byte("foo\n")), "foo with a newline should be written")
+
+	// 7. Invoke CloseWAL() and ensure it discards the
+	// WAL thus any other write won't go through.
+	require.True(t, mempool.CloseWAL(), "CloseWAL should CloseWAL")
+	mempool.CheckTx(types.Tx([]byte("bar")), nil)
+	sum2 := checksumFile(walFilepath, t)
+	require.Equal(t, sum1, sum2, "expected no change to the WAL after invoking CloseWAL() since it was discarded")
+
+	// 8. Second CloseWAL should do nothing
+	require.False(t, mempool.CloseWAL(), "CloseWAL should CloseWAL")
+
+	// 9. Sanity check to ensure that the WAL file still exists
+	m3, err := filepath.Glob(filepath.Join(rootDir, "*"))
+	require.Nil(t, err, "successful globbing expected")
+	require.Equal(t, 1, len(m3), "expecting the wal match in")
+}
+
+func checksumIt(data []byte) string {
+	h := md5.New()
+	h.Write(data)
+	return fmt.Sprintf("%x", h.Sum(nil))
+}
+
+func checksumFile(p string, t *testing.T) string {
+	data, err := ioutil.ReadFile(p)
+	require.Nil(t, err, "expecting successful read of %q", p)
+	return checksumIt(data)
+}