fix: decode in the case of field missing in both writer binary and re…

…ader struct (#452)

codec_record.go

@@ -76,9 +76,17 @@ func decoderOfStruct(d *decoderContext, schema Schema, typ reflect2.Type) ValDec
  }
  }
  }
-
- // Skip field if it doesnt exist
+ // Skip field if it doesn't exist
  if sf == nil {
+ // If the field value doesn't exist in the binary, ignore it instead of
+ // appending a 'SkipDecoder'.
+ //
+ // Note: 'SkipDecoder' performs a read and moves the cursor, which,
+ // in this case, will lead to a dirty read.
+ if field.action == FieldSetDefault {
+ continue
+ }
+
  fields = append(fields, &structFieldDecoder{
  decoder: createSkipDecoder(field.Type()),
  })

schema_compatibility_test.go

@@ -976,3 +976,44 @@ func TestSchemaCompatibility_ResolveWithComplexUnion(t *testing.T) {
  want := map[string]any{"b": []byte("foo")}
  assert.Equal(t, want, result)
 }
+
+func TestSchemaCompatibility_ResolveWithFieldMissingInWriterAndReaderStruct(t *testing.T) {
+ w := avro.MustParse(`{
+ "type":"record", "name":"test", "namespace": "org.hamba.avro", 
+ "fields":[
+ {"name": "a", "type": "string"}
+ ]
+ }`)
+
+ r := avro.MustParse(`{
+ "type":"record", "name":"test", "namespace": "org.hamba.avro", 
+ "fields":[
+ {"name": "a", "type": "string"},
+ {"name": "b", "type": "int", "default": 10},
+ {"name": "c", "type": "string", "default": "foo"}
+ ]
+ }`)
+
+ type TestW struct {
+ A string `avro:"a"`
+ }
+ value := TestW{A: "abc"}
+
+ b, err := avro.Marshal(w, value)
+ assert.NoError(t, err)
+
+ schema, err := avro.NewSchemaCompatibility().Resolve(r, w)
+ assert.NoError(t, err)
+
+ type TestR struct {
+ A string `avro:"a"`
+ C string `avro:"c"`
+ }
+ want := TestR{A: "abc", C: "foo"}
+
+ var result TestR
+ err = avro.Unmarshal(schema, b, &result)
+ assert.NoError(t, err)
+
+ assert.Equal(t, want, result)
+}