refactor: decouple StrKey muxed helpers from xdr wrappers

src/main/java/org/stellar/sdk/Address.java

@@ -12,6 +12,9 @@
 import org.stellar.sdk.xdr.SCAddress;
 import org.stellar.sdk.xdr.SCVal;
 import org.stellar.sdk.xdr.SCValType;
+import org.stellar.sdk.xdr.Uint256;
+import org.stellar.sdk.xdr.Uint64;
+import org.stellar.sdk.xdr.XdrUnsignedHyperInteger;
 
 /**
  * Represents a single address in the Stellar network. An address can represent an account,
@@ -117,8 +120,8 @@ public static Address fromSCAddress(SCAddress scAddress) {
         return fromMuxedAccount(
             StrKey.toRawMuxedAccountStrKey(
                 new StrKey.RawMuxedAccountStrKeyParameter(
-                    scAddress.getMuxedAccount().getEd25519(),
-                    scAddress.getMuxedAccount().getId())));
+                    scAddress.getMuxedAccount().getEd25519().getUint256(),
+                    scAddress.getMuxedAccount().getId().getUint64().getNumber())));
       case SC_ADDRESS_TYPE_CLAIMABLE_BALANCE:
         if (scAddress.getClaimableBalanceId().getDiscriminant()
             != ClaimableBalanceIDType.CLAIMABLE_BALANCE_ID_TYPE_V0) {
@@ -174,8 +177,8 @@ public SCAddress toSCAddress() {
             StrKey.fromRawMuxedAccountStrKey(this.key);
         MuxedEd25519Account muxedEd25519Account =
             MuxedEd25519Account.builder()
-                .id(parameter.getId())
-                .ed25519(parameter.getEd25519())
+                .id(new Uint64(new XdrUnsignedHyperInteger(parameter.getId())))
+                .ed25519(new Uint256(parameter.getEd25519()))
                 .build();
         scAddress.setMuxedAccount(muxedEd25519Account);
         break;

src/main/java/org/stellar/sdk/MuxedAccount.java

@@ -70,8 +70,8 @@ public MuxedAccount(@NonNull String address) {
       byte[] rawMed25519 = StrKey.decodeMed25519PublicKey(address);
       StrKey.RawMuxedAccountStrKeyParameter parameter =
           StrKey.fromRawMuxedAccountStrKey(rawMed25519);
-      this.accountId = StrKey.encodeEd25519PublicKey(parameter.getEd25519().getUint256());
-      this.muxedId = parameter.getId().getUint64().getNumber();
+      this.accountId = StrKey.encodeEd25519PublicKey(parameter.getEd25519());
+      this.muxedId = parameter.getId();
     } else {
       throw new IllegalArgumentException("Invalid address");
     }
@@ -87,10 +87,10 @@ public String getAddress() {
     if (muxedId == null) {
       return accountId;
     }
-    org.stellar.sdk.xdr.MuxedAccount.MuxedAccountMed25519 med25519 = toXdr().getMed25519();
     return StrKey.encodeMed25519PublicKey(
         StrKey.toRawMuxedAccountStrKey(
-            new StrKey.RawMuxedAccountStrKeyParameter(med25519.getEd25519(), med25519.getId())));
+            new StrKey.RawMuxedAccountStrKeyParameter(
+                StrKey.decodeEd25519PublicKey(accountId), muxedId)));
   }
 
   /**

src/main/java/org/stellar/sdk/StrKey.java

@@ -10,16 +10,14 @@
 import lombok.NonNull;
 import lombok.Value;
 import org.stellar.sdk.exception.UnexpectedException;
-import org.stellar.sdk.xdr.Uint256;
-import org.stellar.sdk.xdr.Uint64;
-import org.stellar.sdk.xdr.XdrUnsignedHyperInteger;
 
 /**
  * StrKey is a helper class that allows encoding and decoding Stellar keys to/from strings, i.e.
  * between their binary and string (i.e. "GABCD...", etc.) representations.
  */
 public class StrKey {
 
+  private static final BigInteger UINT64_MAX = new BigInteger("18446744073709551615");
   private static final byte[] b32Table = decodingTable();
   private static final Base32 base32Codec = Base32Factory.getInstance();
 
@@ -584,11 +582,22 @@ private static boolean isInAlphabet(final byte[] arrayOctet) {
 
   @Value
   static class RawMuxedAccountStrKeyParameter {
-    @NonNull Uint256 ed25519;
-    @NonNull Uint64 id;
+    byte @NonNull [] ed25519;
+    @NonNull BigInteger id;
   }
 
   static byte[] toRawMuxedAccountStrKey(RawMuxedAccountStrKeyParameter parameter) {
+    byte[] ed25519Bytes = parameter.getEd25519();
+    if (ed25519Bytes.length != 32) {
+      throw new IllegalArgumentException(
+          "Muxed account ed25519 bytes must be 32 bytes long, got " + ed25519Bytes.length);
+    }
+    if (parameter.getId().compareTo(BigInteger.ZERO) < 0
+        || parameter.getId().compareTo(UINT64_MAX) > 0) {
+      throw new IllegalArgumentException(
+          "Muxed account ID must be between 0 and 2^64 - 1 inclusive");
+    }
+
     // Get the 64-bit ID. This is the critical part of the explanation.
     //
     // THE KEY INSIGHT: Why using .longValue() is safe for a uint64
@@ -633,8 +642,7 @@ static byte[] toRawMuxedAccountStrKey(RawMuxedAccountStrKeyParameter parameter)
     // buffer,
     // it correctly serializes the original uint64 value into 8 bytes, regardless of whether Java
     // interpreted the intermediate `long` as positive or negative.
-    long idLong = parameter.getId().getUint64().getNumber().longValue();
-    byte[] ed25519Bytes = parameter.getEd25519().getUint256();
+    long idLong = parameter.getId().longValue();
     return ByteBuffer.allocate(ed25519Bytes.length + 8).put(ed25519Bytes).putLong(idLong).array();
   }
 
@@ -648,9 +656,7 @@ static RawMuxedAccountStrKeyParameter fromRawMuxedAccountStrKey(byte @NonNull []
     buffer.get(ed25519Bytes);
     byte[] idBytes = new byte[8];
     buffer.get(idBytes);
-    Uint256 ed25519 = new Uint256(ed25519Bytes);
-    Uint64 id = new Uint64(new XdrUnsignedHyperInteger(new BigInteger(1, idBytes)));
-    return new RawMuxedAccountStrKeyParameter(ed25519, id);
+    return new RawMuxedAccountStrKeyParameter(ed25519Bytes, new BigInteger(1, idBytes));
   }
 
   enum VersionByte {

src/test/kotlin/org/stellar/sdk/StrKeyTest.kt

@@ -461,17 +461,14 @@ class StrKeyTest :
           ),
         ) { testCase ->
           val ed25519Bytes = Util.hexToBytes(testCase.ed25519Hex)
-          val ed25519 = org.stellar.sdk.xdr.Uint256(ed25519Bytes)
-          val id =
-            org.stellar.sdk.xdr.Uint64(org.stellar.sdk.xdr.XdrUnsignedHyperInteger(testCase.id))
-          val param = StrKey.RawMuxedAccountStrKeyParameter(ed25519, id)
+          val param = StrKey.RawMuxedAccountStrKeyParameter(ed25519Bytes, testCase.id)
 
           val bytes = StrKey.toRawMuxedAccountStrKey(param)
           bytes.size shouldBe 40
 
           val decoded = StrKey.fromRawMuxedAccountStrKey(bytes)
-          decoded.ed25519.uint256 shouldBe ed25519Bytes
-          decoded.id.uint64.number shouldBe testCase.id
+          decoded.ed25519 shouldBe ed25519Bytes
+          decoded.id shouldBe testCase.id
         }
       }