Properly escape strings during export. (#3429)

Same change as #3424 but for the release/v1.0 branch. The changes could
not be cherry-picked since the code has since been heavily refactored.

worker/export.go

@@ -20,11 +20,11 @@ import (
 	"bufio"
 	"bytes"
 	"compress/gzip"
+	"encoding/json"
 	"fmt"
 	"os"
 	"path"
 	"path/filepath"
-	"strconv"
 	"strings"
 	"time"
 
@@ -54,6 +54,20 @@ var rdfTypeMap = map[types.TypeID]string{
 	types.PasswordID: "xs:password",
 }
 
+// escapedString converts a string into an escaped string for exporting.
+func escapedString(str string) string {
+	// We use the Marshal function in the JSON package for all export formats
+	// because it properly escapes strings.
+	byt, err := json.Marshal(str)
+	if err != nil {
+		// All valid stings should be able to be escaped to a JSON string so
+		// it's safe to panic here. Marshal has to return an error because it
+		// accepts an interface.
+		panic("Could not marshal string to JSON string")
+	}
+	return string(byt)
+}
+
 func toRDF(pl *posting.List, prefix string, readTs uint64) (*bpb.KVList, error) {
 	var buf bytes.Buffer
 
@@ -76,7 +90,7 @@ func toRDF(pl *posting.List, prefix string, readTs uint64) (*bpb.KVList, error)
 
 			// trim null character at end
 			trimmed := strings.TrimRight(str.Value.(string), "\x00")
-			buf.WriteString(strconv.Quote(trimmed))
+			buf.WriteString(escapedString(trimmed))
 			if p.PostingType == pb.Posting_VALUE_LANG {
 				buf.WriteByte('@')
 				buf.WriteString(string(p.LangTag))
@@ -121,7 +135,7 @@ func toRDF(pl *posting.List, prefix string, readTs uint64) (*bpb.KVList, error)
 				}
 
 				if facetTid == types.StringID {
-					buf.WriteString(strconv.Quote(fStringVal.Value.(string)))
+					buf.WriteString(escapedString(fStringVal.Value.(string)))
 				} else {
 					buf.WriteString(fStringVal.Value.(string))
 				}

worker/export_test.go

@@ -54,13 +54,15 @@ func populateGraphExport(t *testing.T) {
 		`<3> <name> "First Line\nSecondLine" .`,
 		"<1> <friend_not_served> <5> <author0> .",
 		`<5> <name> "" .`,
+		`<6> <name> "Ding!\u0007Ding!\u0007Ding!\u0007" .`,
 	}
 	idMap := map[string]uint64{
 		"1": 1,
 		"2": 2,
 		"3": 3,
 		"4": 4,
 		"5": 5,
+		"6": 6,
 	}
 
 	for _, edge := range rdfEdges {
@@ -149,7 +151,8 @@ func TestExport(t *testing.T) {
 	for scanner.Scan() {
 		nq, err := rdf.Parse(scanner.Text())
 		require.NoError(t, err)
-		require.Contains(t, []string{"_:uid1", "_:uid2", "_:uid3", "_:uid4", "_:uid5"}, nq.Subject)
+		require.Contains(t, []string{"_:uid1", "_:uid2", "_:uid3", "_:uid4", "_:uid5", "_:uid6"},
+			nq.Subject)
 		if nq.ObjectValue != nil {
 			switch nq.Subject {
 			case "_:uid1", "_:uid2":
@@ -161,6 +164,9 @@ func TestExport(t *testing.T) {
 			case "_:uid4":
 			case "_:uid5":
 				require.Equal(t, `<_:uid5> <name> "" .`, scanner.Text())
+			case "_:uid6":
+				require.Equal(t, `<_:uid6> <name> "Ding!\u0007Ding!\u0007Ding!\u0007" .`,
+					scanner.Text())
 			default:
 				t.Errorf("Unexpected subject: %v", nq.Subject)
 			}
@@ -203,7 +209,7 @@ func TestExport(t *testing.T) {
 	}
 	require.NoError(t, scanner.Err())
 	// This order will be preserved due to file naming.
-	require.Equal(t, 8, count)
+	require.Equal(t, 9, count)
 
 	require.Equal(t, 1, len(schemaFileList))
 	file = schemaFileList[0]