Make TextualFromNative output deterministic

map.go

@@ -15,6 +15,7 @@ import (
 	"io"
 	"math"
 	"reflect"
+	"sort"
 )
 
 func makeMapCodec(st map[string]*Codec, namespace string, schemaMap map[string]interface{}, cb *codecBuilder) (*Codec, error) {
@@ -243,8 +244,10 @@ func genericMapTextEncoder(buf []byte, datum interface{}, defaultCodec *Codec, c
 	var atLeastOne bool
 
 	buf = append(buf, '{')
+	sortedKeys := sortKeys(mapValues)
 
-	for key, value := range mapValues {
+	for _, key := range sortedKeys {
+		value := mapValues[key]
 		atLeastOne = true
 
 		// Find a codec for the key
@@ -305,3 +308,12 @@ func convertMap(datum interface{}) (map[string]interface{}, error) {
 	}
 	return mapValues, nil
 }
+
+func sortKeys(m map[string]interface{}) (keys []string) {
+	for key, _ := range m {
+		keys = append(keys, key)
+	}
+
+	sort.Slice(keys, func(i, j int) bool { return keys[i] < keys[j] })
+	return keys
+}

map_test.go

@@ -173,3 +173,62 @@ func ExampleMap() {
 	fmt.Println(string(buf))
 	// Output: {"f1":{"k1":3.5}}
 }
+
+func exampleMapDeterministic() {
+	codec, err := NewCodec(`{
+   "name":"r1",
+   "type":"record",
+   "fields":[
+      {
+         "name":"f1",
+         "type":{
+            "type":"double"
+         }
+      },
+      {
+         "name":"a1",
+         "type":{
+            "type":"double"
+         }
+      },
+      {
+         "name":"b2",
+         "type":{
+            "type":"double"
+         }
+      },
+      {
+         "name":"c3",
+         "type":{
+            "type":"double"
+         }
+      },
+      {
+         "name":"d4",
+         "type":{
+            "type":"double"
+         }
+      }
+   ]
+}`)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	_, err = codec.TextualFromNative(nil, map[string]interface{}{
+		"f1": 3.5,
+		"a1": 3.5,
+		"b2": 3.5,
+		"c3": 3.5,
+		"d4": 3.5,
+	})
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func BenchmarkMapDeterministic(b *testing.B) {
+	b.Run("TextualFromNative deterministic map ", func(b *testing.B) {
+		exampleMapDeterministic()
+	})
+}