Fix export segfault

Closes #1834

server/export.go

@@ -9,6 +9,8 @@ import (
 
 	"github.com/cosmos/cosmos-sdk/wire"
 	tmtypes "github.com/tendermint/tendermint/types"
+	"io/ioutil"
+	"path"
 )
 
 // ExportCmd dumps app state to JSON.
@@ -19,6 +21,21 @@ func ExportCmd(ctx *Context, cdc *wire.Codec, appExporter AppExporter) *cobra.Co
 		RunE: func(cmd *cobra.Command, args []string) error {
 			home := viper.GetString("home")
 			traceStore := viper.GetString(flagTraceStore)
+			emptyState, err := isEmptyState(home)
+			if err != nil {
+				return err
+			}
+
+			if emptyState {
+				fmt.Println("WARNING: State is not initialized. Returning genesis file.")
+				genesisFile := path.Join(home, "config", "genesis.json")
+				genesis, err := ioutil.ReadFile(genesisFile)
+				if err != nil {
+					return err
+				}
+				fmt.Println(string(genesis))
+				return nil
+			}
 
 			appState, validators, err := appExporter(home, ctx.Logger, traceStore)
 			if err != nil {
@@ -43,3 +60,12 @@ func ExportCmd(ctx *Context, cdc *wire.Codec, appExporter AppExporter) *cobra.Co
 		},
 	}
 }
+
+func isEmptyState(home string) (bool, error) {
+	files, err := ioutil.ReadDir(path.Join(home, "data"))
+	if err != nil {
+		return false, err
+	}
+
+	return len(files) == 0, nil
+}

server/export_test.go

@@ -0,0 +1,53 @@
+package server
+
+import (
+	"testing"
+	"github.com/stretchr/testify/require"
+	"github.com/cosmos/cosmos-sdk/wire"
+	"github.com/tendermint/tendermint/libs/log"
+	tcmd "github.com/tendermint/tendermint/cmd/tendermint/commands"
+	"os"
+	"bytes"
+	"io"
+		"github.com/cosmos/cosmos-sdk/server/mock"
+	)
+
+func TestEmptyState(t *testing.T) {
+	defer setupViper(t)()
+	logger := log.NewNopLogger()
+	cfg, err := tcmd.ParseConfig()
+	require.Nil(t, err)
+	ctx := NewContext(cfg, logger)
+	cdc := wire.NewCodec()
+	appInit := AppInit{
+		AppGenTx:    mock.AppGenTx,
+		AppGenState: mock.AppGenStateEmpty,
+	}
+	cmd := InitCmd(ctx, cdc, appInit)
+	err = cmd.RunE(nil, nil)
+	require.NoError(t, err)
+
+	old := os.Stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w
+	cmd = ExportCmd(ctx, cdc, nil)
+	err = cmd.RunE(nil, nil)
+	require.NoError(t, err)
+
+	outC := make(chan string)
+	go func() {
+		var buf bytes.Buffer
+		io.Copy(&buf, r)
+		outC <- buf.String()
+	}()
+
+	w.Close()
+	os.Stdout = old
+	out := <-outC
+	require.Contains(t, out, "WARNING: State is not initialized")
+	require.Contains(t, out, "genesis_time")
+	require.Contains(t, out, "chain_id")
+	require.Contains(t, out, "consensus_params")
+	require.Contains(t, out, "validators")
+	require.Contains(t, out, "app_hash")
+}

server/mock/app.go

@@ -121,9 +121,15 @@ func AppGenState(_ *wire.Codec, _ []json.RawMessage) (appState json.RawMessage,
 	return
 }
 
+// AppGenStateEmpty returns an empty transaction state for mocking.
+func AppGenStateEmpty(_ *wire.Codec, _ []json.RawMessage) (appState json.RawMessage, err error) {
+	appState = json.RawMessage(``)
+	return
+}
+
 // Return a validator, not much else
 func AppGenTx(_ *wire.Codec, pk crypto.PubKey, genTxConfig gc.GenTx) (
-	appGenTx, cliPrint json.RawMessage, validator tmtypes.GenesisValidator, err error) {
+		appGenTx, cliPrint json.RawMessage, validator tmtypes.GenesisValidator, err error) {
 
 	validator = tmtypes.GenesisValidator{
 		PubKey: pk,