Limit order size to a minimum of 2 DOGE.

The "dust" threshold is around 1 DOGE - meaning orders below this size cannot be refunded or redeemed. The simplest solution is to prevent orders of this size being placed to begin with.

src/main/java/org/qortal/api/ApiError.java

@@ -129,7 +129,10 @@ public enum ApiError {
 	// Foreign blockchain
 	FOREIGN_BLOCKCHAIN_NETWORK_ISSUE(1201, 500),
 	FOREIGN_BLOCKCHAIN_BALANCE_ISSUE(1202, 402),
-	FOREIGN_BLOCKCHAIN_TOO_SOON(1203, 408);
+	FOREIGN_BLOCKCHAIN_TOO_SOON(1203, 408),
+
+	// Trade portal
+	ORDER_SIZE_TOO_SMALL(1300, 402);
 
 	private static final Map<Integer, ApiError> map = stream(ApiError.values()).collect(toMap(apiError -> apiError.code, apiError -> apiError));
 
@@ -157,4 +160,4 @@ public enum ApiError {
 		return this.status;
 	}
 
-}
+}

src/main/java/org/qortal/api/resource/CrossChainTradeBotResource.java

@@ -107,7 +107,7 @@ public class CrossChainTradeBotResource {
 			)
 		}
 	)
-	@ApiErrors({ApiError.INVALID_PUBLIC_KEY, ApiError.INVALID_ADDRESS, ApiError.INVALID_CRITERIA, ApiError.INSUFFICIENT_BALANCE, ApiError.REPOSITORY_ISSUE})
+	@ApiErrors({ApiError.INVALID_PUBLIC_KEY, ApiError.INVALID_ADDRESS, ApiError.INVALID_CRITERIA, ApiError.INSUFFICIENT_BALANCE, ApiError.REPOSITORY_ISSUE, ApiError.ORDER_SIZE_TOO_SMALL})
 	@SuppressWarnings("deprecation")
 	public String tradeBotCreator(TradeBotCreateRequest tradeBotCreateRequest) {
 		Security.checkApiCallAllowed(request);
@@ -128,10 +128,13 @@ public class CrossChainTradeBotResource {
 			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_CRITERIA);
 
 		if (tradeBotCreateRequest.foreignAmount == null || tradeBotCreateRequest.foreignAmount <= 0)
-			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_CRITERIA);
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.ORDER_SIZE_TOO_SMALL);
+
+		if (tradeBotCreateRequest.foreignAmount < foreignBlockchain.getMinimumOrderAmount())
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.ORDER_SIZE_TOO_SMALL);
 
 		if (tradeBotCreateRequest.qortAmount <= 0 || tradeBotCreateRequest.fundingQortAmount <= 0)
-			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.INVALID_CRITERIA);
+			throw ApiExceptionFactory.INSTANCE.createException(request, ApiError.ORDER_SIZE_TOO_SMALL);
 
 		try (final Repository repository = RepositoryManager.getRepository()) {
 			// Do some simple checking first
@@ -283,4 +286,4 @@ public class CrossChainTradeBotResource {
 		return atData;
 	}
 
-}
+}

src/main/java/org/qortal/crosschain/Bitcoiny.java

@@ -169,6 +169,11 @@ public abstract class Bitcoiny implements ForeignBlockchain {
 		return this.bitcoinjContext.getFeePerKb();
 	}
 
+	/** Returns minimum order size in sats. To be overridden for coins that need to restrict order size. */
+	public long getMinimumOrderAmount() {
+		return 0L;
+	}
+
 	/**
 	 * Returns fixed P2SH spending fee, in sats per 1000bytes, optionally for historic timestamp.
 	 *

src/main/java/org/qortal/crosschain/Dogecoin.java

@@ -21,6 +21,8 @@ public class Dogecoin extends Bitcoiny {
 
 	private static final Coin DEFAULT_FEE_PER_KB = Coin.valueOf(500000000); // 5 DOGE per 1000 bytes
 
+	private static final long MINIMUM_ORDER_AMOUNT = 200000000L; // 2 DOGE minimum order. The RPC dust threshold is around 1 DOGE
+
 	// Temporary values until a dynamic fee system is written.
 	private static final long MAINNET_FEE = 110000000L;
 	private static final long NON_MAINNET_FEE = 10000L; // TODO: calibrate this
@@ -150,6 +152,11 @@ public class Dogecoin extends Bitcoiny {
 		return DEFAULT_FEE_PER_KB;
 	}
 
+	@Override
+	public long getMinimumOrderAmount() {
+		return MINIMUM_ORDER_AMOUNT;
+	}
+
 	/**
 	 * Returns estimated DOGE fee, in sats per 1000bytes, optionally for historic timestamp.
 	 * 

src/main/java/org/qortal/crosschain/ForeignBlockchain.java

@@ -6,4 +6,6 @@ public interface ForeignBlockchain {
 
 	public boolean isValidWalletKey(String walletKey);
 
+	public long getMinimumOrderAmount();
+
 }

src/main/resources/i18n/ApiError_en.properties

@@ -64,3 +64,5 @@ TRANSACTION_UNKNOWN = transaction unknown
 TRANSFORMATION_ERROR = could not transform JSON into transaction
 
 UNAUTHORIZED = API call unauthorized
+
+ORDER_SIZE_TOO_SMALL = order size too small