docs: add support for asset group key in price oracle

Extend the price oracle to support requests using an asset group key.

Refactor by renaming two functions and extracting constants to make
supported asset IDs and asset group keys easier to locate and modify.

Author: ffranr

docs/examples/basic-price-oracle/main.go

@@ -34,6 +34,16 @@ import (
 const (
 	// serviceListenAddress is the listening address of the service.
 	serviceListenAddress = "localhost:8095"
+
+	// supportedAssetIdStr is the hex-encoded asset ID for which this price
+	// oracle provides exchange rates.
+	supportedAssetIdStr = "7b4336d33b019df9438e586f83c587ca00fa6560249" +
+		"7b93ace193e9ce53b1a67"
+
+	// supportedGroupKeyStr is the hex-encoded asset group key for which
+	// this price oracle provides exchange rates.
+	supportedGroupKeyStr = "02875ce409b587a6656357639d099ad9eb08396d0d" +
+		"fea8930a45e742c81d6fc782"
 )
 
 // setupLogger sets up the logger to write logs to a file.
@@ -65,42 +75,86 @@ type RpcPriceOracleServer struct {
 	oraclerpc.UnimplementedPriceOracleServer
 }
 
-// isSupportedSubjectAsset returns true if the given subject asset is supported
-// by the price oracle, and false otherwise.
-func isSupportedSubjectAsset(subjectAsset *oraclerpc.AssetSpecifier) bool {
+// isSupportedAssetID returns true if the given asset ID is supported by the
+// price oracle, and false otherwise.
+func isSupportedAssetID(rpcAssetSpec *oraclerpc.AssetSpecifier) bool {
 	// Ensure that the subject asset is set.
-	if subjectAsset == nil {
+	if rpcAssetSpec == nil {
 		logrus.Info("Subject asset is not set (nil)")
 		return false
 	}
 
-	supportedAssetIdStr := "7b4336d33b019df9438e586f83c587ca00fa65602497b9" +
-		"3ace193e9ce53b1a67"
 	supportedAssetIdBytes, err := hex.DecodeString(supportedAssetIdStr)
 	if err != nil {
 		fmt.Println("Error decoding supported asset hex string:", err)
 		return false
 	}
 
 	// Check the subject asset bytes if set.
-	subjectAssetIdBytes := subjectAsset.GetAssetId()
+	subjectAssetIdBytes := rpcAssetSpec.GetAssetId()
 	if len(subjectAssetIdBytes) > 0 {
 		logrus.Infof("Subject asset ID bytes populated: %x",
 			supportedAssetIdBytes)
 		return bytes.Equal(supportedAssetIdBytes, subjectAssetIdBytes)
 	}
 
-	subjectAssetIdStr := subjectAsset.GetAssetIdStr()
+	subjectAssetIdStr := rpcAssetSpec.GetAssetIdStr()
 	if len(subjectAssetIdStr) > 0 {
 		logrus.Infof("Subject asset ID str populated: %s",
 			supportedAssetIdStr)
 		return subjectAssetIdStr == supportedAssetIdStr
 	}
 
 	logrus.Infof("Subject asset ID not set")
+
+	return false
+}
+
+// isSupportedAssetGroupKey returns true if the given asset group key is
+// supported by the price oracle, and false otherwise.
+func isSupportedAssetGroupKey(
+	rpcAssetSpec *oraclerpc.AssetSpecifier) bool {
+
+	// Ensure that the subject asset is not nil.
+	if rpcAssetSpec == nil {
+		logrus.Info("Subject asset is not set (nil)")
+		return false
+	}
+
+	supportedGroupKeyBytes, err := hex.DecodeString(supportedGroupKeyStr)
+	if err != nil {
+		fmt.Println("Error decoding supported asset group key hex "+
+			"string:", err)
+		return false
+	}
+
+	// Check the subject asset group key bytes if set.
+	subjectGroupKeyBytes := rpcAssetSpec.GetGroupKey()
+	if len(subjectGroupKeyBytes) > 0 {
+		logrus.Infof("Subject asset group key bytes populated: %x",
+			supportedGroupKeyBytes)
+		return bytes.Equal(supportedGroupKeyBytes, subjectGroupKeyBytes)
+	}
+
+	subjectGroupKeyStr := rpcAssetSpec.GetGroupKeyStr()
+	if len(subjectGroupKeyStr) > 0 {
+		logrus.Infof("Subject asset group key str populated: %s",
+			supportedGroupKeyStr)
+		return subjectGroupKeyStr == supportedGroupKeyStr
+	}
+
+	logrus.Infof("Subject asset group key not set")
+
 	return false
 }
 
+// isSupportedAssetID returns true if the given subject asset is
+// supported by the price oracle, and false otherwise.
+func isSupportedSubjectAsset(subjectAsset *oraclerpc.AssetSpecifier) bool {
+	return isSupportedAssetID(subjectAsset) ||
+		isSupportedAssetGroupKey(subjectAsset)
+}
+
 // getPurchaseRate returns the buy (purchase) rate for the asset. The unit of
 // the rate is the number of TAP asset units per BTC.
 //
@@ -265,7 +319,7 @@ func (p *RpcPriceOracleServer) QueryAssetRates(_ context.Context,
 
 	// Ensure that the subject asset is supported.
 	if !isSupportedSubjectAsset(req.SubjectAsset) {
-		logrus.Infof("Unsupported subject asset ID str: %v\n",
+		logrus.Infof("Unsupported subject asset: %v\n",
 			req.SubjectAsset)
 
 		return &oraclerpc.QueryAssetRatesResponse{