logicalTypes: fix alternative encoding for decimal types

The alternative is an explicit codec decimal type, additionally, this
only worked for a small subset of values that were both valid native
and valid binary encoding. Since we want to stay in the native value
space, we just need to convert from native primative to native logical
type. In order to do this we just do an encode/decode step for decimal
logical types.

record.go

@@ -117,20 +117,23 @@ func makeRecordCodec(st map[string]*Codec, enclosingNamespace string, schemaMap
 				// TODO: change to schemaCanonical below
 				defaultValue = Union(fieldCodec.schemaOriginal, defaultValue)
 			default:
-				debug("fieldName: %q; type: %q; defaultValue: %T(%#v)\n", fieldName, c.typeName, defaultValue, defaultValue)
-
 				// Support defaults for logical types
-				if logicalType, ok := fieldSchemaMap["logicalType"]; ok {
-					if logicalType == "decimal" {
-						v, ok := defaultValue.(string)
-						if !ok {
-							return nil, fmt.Errorf("Record %q field %q: default value ought to have a string type got: %T", c.typeName, fieldName, defaultValue)
-						}
-						defaultValue, _, err = fieldCodec.nativeFromBinary([]byte(v))
-						if err != nil {
-							return nil, fmt.Errorf("Record %q field %q: default value ought to decode from textual: %w", c.typeName, fieldName, err)
-						}
+				if fieldSchemaMap["logicalType"] == "decimal" || typeNameShort == "decimal" {
+					v, ok := defaultValue.(string)
+					if !ok {
+						return nil, fmt.Errorf("Record %q field %q: default value ought to have a string type got: %T", c.typeName, fieldName, defaultValue)
+					}
+					// the default is a native byte array, we need to encode it first, then we can decode it into a *big.Rat
+					encoded, err := bytesBinaryFromNative(nil, v)
+					if err != nil {
+						return nil, fmt.Errorf("Record %q field %q: default value ought to be encodable from native binary: %w", c.typeName, fieldName, err)
+					}
+					defaultValue, _, err = fieldCodec.nativeFromBinary(encoded)
+					if err != nil {
+						return nil, fmt.Errorf("Record %q field %q: default value ought to decode from textual: %w", c.typeName, fieldName, err)
 					}
+				} else {
+					debug("fieldName: %q; type: %q; defaultValue: %T(%#v)\n", fieldName, c.typeName, defaultValue, defaultValue)
 				}
 			}
 

record_test.go

@@ -617,6 +617,10 @@ func TestRecordFieldFixedDefaultValue(t *testing.T) {
 	testSchemaValid(t, `{"type": "record", "name": "r1", "fields":[{"name": "f1", "type": {"type": "fixed", "name": "someFixed", "size": 1}, "default": "\u0000"}]}`)
 }
 
+func TestRecordFieldDecimalDefaultValue(t *testing.T) {
+	testSchemaValid(t, `{"type": "record", "name": "r1", "fields":[{"name": "f1", "type": {"type": "bytes", "scale": 2, "precision":10, "logicalType":"deicmal"}, "default": "d"}]}`)
+}
+
 func TestRecordFieldDefaultValueTypes(t *testing.T) {
 	t.Run("success", func(t *testing.T) {
 		codec, err := NewCodec(`{"type": "record", "name": "r1", "fields":[{"name": "someBoolean", "type": "boolean", "default": true},{"name": "someBytes", "type": "bytes", "default": "0"},{"name": "someDouble", "type": "double", "default": 0},{"name": "someFloat", "type": "float", "default": 0},{"name": "someInt", "type": "int", "default": 0},{"name": "someLong", "type": "long", "default": 0},{"name": "someString", "type": "string", "default": "0"}, {"name":"someTimestamp", "type":"long", "logicalType":"timestamp-millis","default":0}, {"name": "someDecimal", "type": "bytes", "logicalType": "decimal", "precision": 4, "scale": 2, "default":"\u0000"}]}`)