[ANCHOR-388] SEP-6: Implement RPC actions (#1166)

### Description

This updates the RPC actions for SEP-6 and updates the reference server
implementation to use them. This PR is quite large as it updates the
unit tests for most of the RPC actions but, implementation-wise, not
much has changed. It might helpful to start by reviewing the
`Sep6End2EndTest` to get a sense of what changed with this PR.

### Context

SEP-6 should support RPC API.

### Testing

- `./gradlew test`

### Known limitations

- Platform API integration tests do not test the new flow but are
covered by the SEP-6 e2e tests.
- Refunds and custody service integration have not been implemented.

Both of these will be addressed by ANCHOR-508

api-schema/src/main/java/org/stellar/anchor/api/rpc/method/RequestCustomerInfoUpdateRequest.java

@@ -1,5 +1,7 @@
 package org.stellar.anchor.api.rpc.method;
 
+import com.google.gson.annotations.SerializedName;
+import java.util.List;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.EqualsAndHashCode;
@@ -9,4 +11,11 @@
 @SuperBuilder
 @AllArgsConstructor
 @EqualsAndHashCode(callSuper = false)
-public class RequestCustomerInfoUpdateRequest extends RpcMethodParamsRequest {}
+public class RequestCustomerInfoUpdateRequest extends RpcMethodParamsRequest {
+
+  @SerializedName("required_customer_info_message")
+  private String requiredCustomerInfoMessage;
+
+  @SerializedName("required_customer_info_updates")
+  private List<String> requiredCustomerInfoUpdates;
+}

api-schema/src/main/java/org/stellar/anchor/api/rpc/method/RequestOffchainFundsRequest.java

@@ -1,10 +1,12 @@
 package org.stellar.anchor.api.rpc.method;
 
 import com.google.gson.annotations.SerializedName;
+import java.util.Map;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.EqualsAndHashCode;
 import lombok.experimental.SuperBuilder;
+import org.stellar.anchor.api.shared.InstructionField;
 
 @Data
 @SuperBuilder
@@ -23,4 +25,7 @@ public class RequestOffchainFundsRequest extends RpcMethodParamsRequest {
 
   @SerializedName("amount_expected")
   private AmountRequest amountExpected;
+
+  @SerializedName("instructions")
+  Map<String, InstructionField> instructions;
 }

core/src/main/java/org/stellar/anchor/sep6/Sep6Service.java

@@ -90,6 +90,14 @@ public StartDepositResponse deposit(Sep10Jwt token, StartDepositRequest request)
             .type(request.getType())
             .assetCode(request.getAssetCode())
             .assetIssuer(asset.getIssuer())
+            // NB: these are purposely set to incorrect values.
+            // amount_out and amount_fee assets cannot be determined when the
+            // platform creates the transaction, but the RPC API requires
+            // these to be set during a notify_amounts_updated call.
+            .amountOut(request.getAmount())
+            .amountOutAsset(asset.getSep38AssetName())
+            .amountFee("0")
+            .amountFeeAsset(asset.getSep38AssetName())
             .amountExpected(request.getAmount())
             .startedAt(Instant.now())
             .sep10Account(token.getAccount())
@@ -248,6 +256,16 @@ public StartWithdrawResponse withdraw(Sep10Jwt token, StartWithdrawRequest reque
             .type(request.getType())
             .assetCode(request.getAssetCode())
             .assetIssuer(asset.getIssuer())
+            .amountIn(request.getAmount())
+            .amountInAsset(asset.getSep38AssetName())
+            // NB: these are purposely set to incorrect values.
+            // amount_out and amount_fee assets cannot be determined when the
+            // platform creates the transaction, but the RPC API requires
+            // these to be set during a notify_amounts_updated call.
+            .amountOut(request.getAmount())
+            .amountOutAsset(asset.getSep38AssetName())
+            .amountFee("0")
+            .amountFeeAsset(asset.getSep38AssetName())
             .amountExpected(request.getAmount())
             .startedAt(Instant.now())
             .sep10Account(token.getAccount())

core/src/main/java/org/stellar/anchor/sep6/Sep6Transaction.java

@@ -103,6 +103,15 @@ public interface Sep6Transaction extends SepTransaction {
 
   void setCompletedAt(Instant completedAt);
 
+  /**
+   * The date and time the user funds were received.
+   *
+   * @return the transfer received at timestamp.
+   */
+  Instant getTransferReceivedAt();
+
+  void setTransferReceivedAt(Instant transferReceivedAt);
+
   /**
    * The deposit or withdrawal method used. E.g. <code>bank_account</code>, <code>cash</code>
    *

core/src/main/java/org/stellar/anchor/util/TransactionHelper.java

@@ -110,6 +110,7 @@ public static GetTransactionResponse toGetTransactionResponse(
         .startedAt(txn.getStartedAt())
         .updatedAt(txn.getUpdatedAt())
         .completedAt(txn.getCompletedAt())
+        .transferReceivedAt(txn.getTransferReceivedAt())
         .message(txn.getMessage())
         .refunds(txn.getRefunds())
         .stellarTransactions(txn.getStellarTransactions())

core/src/test/java/org/stellar/anchor/sep6/PojoSep6Transaction.java

@@ -22,6 +22,7 @@ public class PojoSep6Transaction implements Sep6Transaction {
   Instant startedAt;
   Instant completedAt;
   Instant updatedAt;
+  Instant transferReceivedAt;
   String type;
   String requestAssetCode;
   String requestAssetIssuer;