Updates based on review.

client/asset/eth/eth.go

@@ -354,14 +354,22 @@ func (c *coin) Value() uint64 {
 
 var _ asset.Coin = (*coin)(nil)
 
+// decodeCoinID decodes a coin id into a coin object. The coin id
+// must contain an AmountCoinID.
 func decodeCoinID(coinID []byte) (*coin, error) {
-	id, err := dexeth.DecodeAmountCoinID(coinID)
+	id, err := dexeth.DecodeCoinID(coinID)
 	if err != nil {
 		return nil, err
 	}
 
+	amountCoinID, ok := id.(*dexeth.AmountCoinID)
+	if !ok {
+		return nil,
+			fmt.Errorf("coinID is expected to be an amount coin id")
+	}
+
 	return &coin{
-		id: *id,
+		id: *amountCoinID,
 	}, nil
 }
 

server/asset/eth/common.go

@@ -188,8 +188,8 @@ func (c *AmountCoinID) Encode() []byte {
 
 var _ CoinID = (*AmountCoinID)(nil)
 
-// DecodeAmountCoinID decodes a byte slice into an AmountCoinID struct.
-func DecodeAmountCoinID(coinID []byte) (*AmountCoinID, error) {
+// decodeAmountCoinID decodes a byte slice into an AmountCoinID struct.
+func decodeAmountCoinID(coinID []byte) (*AmountCoinID, error) {
 	if len(coinID) != amountCoinIDSize {
 		return nil, fmt.Errorf("DecodeAmountCoinID: length expected %v, got %v",
 			txCoinIDSize, len(coinID))
@@ -215,13 +215,18 @@ func DecodeAmountCoinID(coinID []byte) (*AmountCoinID, error) {
 // DecodeCoinID decodes the coin id byte slice into an object implementing the
 // CoinID interface.
 func DecodeCoinID(coinID []byte) (CoinID, error) {
+	if len(coinID) < 2 {
+		return nil,
+			fmt.Errorf("DecodeCoinID: coinID length must be > 2, but got %v",
+				len(coinID))
+	}
 	flag := CoinIDFlag(binary.BigEndian.Uint16(coinID[:2]))
 	if flag == CIDTxID {
 		return decodeTxCoinID(coinID)
 	} else if flag == CIDSwap {
 		return decodeSwapCoinID(coinID)
 	} else if flag == CIDAmount {
-		return DecodeAmountCoinID(coinID)
+		return decodeAmountCoinID(coinID)
 	} else {
 		return nil, fmt.Errorf("DecodeCoinID: invalid coin id flag: %v", flag)
 	}