xdr: Add function to obtain the type of a binary-compressed key (#5026)

xdr/main.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 
 	xdr "github.com/stellar/go-xdr/xdr3"
+
 	"github.com/stellar/go/support/errors"
 )
 
@@ -230,6 +231,18 @@ func (e *EncodingBuffer) LedgerKeyUnsafeMarshalBinaryCompress(key LedgerKey) ([]
 	return e.xdrEncoderBuf.Bytes(), nil
 }
 
+// GetBinaryCompressedLedgerKeyType gets the key type from the result of LedgerKeyUnsafeMarshalBinaryCompress
+func GetBinaryCompressedLedgerKeyType(compressedKey []byte) (LedgerEntryType, error) {
+	if len(compressedKey) < 1 {
+		return 0, errors.New("empty compressed ledger key")
+	}
+	result := LedgerEntryType(compressedKey[0])
+	if int(result) > len(ledgerEntryTypeMap)-1 {
+		return 0, fmt.Errorf("incorrect key type %d", result)
+	}
+	return result, nil
+}
+
 func (e *EncodingBuffer) MarshalBase64(encodable EncoderTo) (string, error) {
 	b, err := e.UnsafeMarshalBase64(encodable)
 	if err != nil {

xdr/main_test.go

@@ -217,8 +217,11 @@ func TestLedgerKeyBinaryCompressCoverage(t *testing.T) {
 		)
 		assert.NoError(t, gxdr.Convert(shape, &ledgerKey))
 
-		_, err := e.LedgerKeyUnsafeMarshalBinaryCompress(ledgerKey)
+		compressed, err := e.LedgerKeyUnsafeMarshalBinaryCompress(ledgerKey)
 		assert.NoError(t, err)
+		keyType, err := GetBinaryCompressedLedgerKeyType(compressed)
+		assert.NoError(t, err)
+		assert.Equal(t, ledgerKey.Type, keyType)
 	}
 }