Merge pull request #93 from travisgrigsby/master

encoding/mvt: stable marshalling
paulmach · Apr 2, 2022 · a24e53a · a24e53a
2 parents 8add77b + 4408fe0
commit a24e53a
Show file tree

Hide file tree

Showing 3 changed files with 30 additions and 2 deletions.
diff --git a/encoding/mvt/geometry.go b/encoding/mvt/geometry.go
@@ -138,6 +138,8 @@ type keyValueEncoder struct {
 
 	Values   []*vectortile.Tile_Value
 	valueMap map[interface{}]uint32
+
+	keySortBuffer []string
 }
 
 func newKeyValueEncoder() *keyValueEncoder {

diff --git a/encoding/mvt/marshal.go b/encoding/mvt/marshal.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"compress/gzip"
 	"fmt"
+	"sort"
 	"strconv"
 
 	"github.com/paulmach/orb/encoding/mvt/vectortile"
@@ -84,9 +85,16 @@ func Marshal(layers Layers) ([]byte, error) {
 
 func encodeProperties(kve *keyValueEncoder, properties geojson.Properties) ([]uint32, error) {
 	tags := make([]uint32, 0, 2*len(properties))
-	for k, v := range properties {
+
+	kve.keySortBuffer = kve.keySortBuffer[:0]
+	for k := range properties {
+		kve.keySortBuffer = append(kve.keySortBuffer, k)
+	}
+	sort.Strings(kve.keySortBuffer)
+
+	for _, k := range kve.keySortBuffer {
 		ki := kve.Key(k)
-		vi, err := kve.Value(v)
+		vi, err := kve.Value(properties[k])
 		if err != nil {
 			return nil, fmt.Errorf("property %s: %v", k, err)
 		}

diff --git a/encoding/mvt/marshal_test.go b/encoding/mvt/marshal_test.go
@@ -1,6 +1,8 @@
 package mvt
 
 import (
+	"crypto/md5"
+	"encoding/hex"
 	"encoding/json"
 	"fmt"
 	"io/ioutil"
@@ -469,6 +471,22 @@ func TestMarshal_ID(t *testing.T) {
 	})
 }
 
+func TestStableMarshalling(t *testing.T) {
+	layers := NewLayers(loadGeoJSON(t, maptile.New(17896, 24449, 16)))
+	values := make(map[string]bool)
+
+	for i := 0; i < 100; i++ {
+		marshal, _ := Marshal(layers)
+		checksum := md5.Sum(marshal)
+		sum := hex.EncodeToString(checksum[:])
+		values[sum] = true
+	}
+
+	if len(values) != 1 {
+		t.Errorf("multiple values (%d) for marshalled bytes", len(values))
+	}
+}
+
 func BenchmarkMarshal(b *testing.B) {
 	layers := NewLayers(loadGeoJSON(b, maptile.New(17896, 24449, 16)))