cmd/loop: return error in readMacaroon

As we only use the readMacaroon function inside getClientConn where we
have an error return value anyway, we might as well pass the error along
correctly instead of failing hard directly.

Author: guggero

cmd/loop/main.go

@@ -380,12 +380,16 @@ func getClientConn(address, tlsCertPath, macaroonPath string) (*grpc.ClientConn,
 	// TLS cannot be disabled, we'll always have a cert file to read.
 	creds, err := credentials.NewClientTLSFromFile(tlsCertPath, "")
 	if err != nil {
-		fatal(err)
+		return nil, err
 	}
 
 	// Macaroons are not yet enabled by default.
 	if macaroonPath != "" {
-		opts = append(opts, readMacaroon(macaroonPath))
+		macOption, err := readMacaroon(macaroonPath)
+		if err != nil {
+			return nil, err
+		}
+		opts = append(opts, macOption)
 	}
 
 	opts = append(opts, grpc.WithTransportCredentials(creds))
@@ -401,16 +405,16 @@ func getClientConn(address, tlsCertPath, macaroonPath string) (*grpc.ClientConn,
 
 // readMacaroon tries to read the macaroon file at the specified path and create
 // gRPC dial options from it.
-func readMacaroon(macPath string) grpc.DialOption {
+func readMacaroon(macPath string) (grpc.DialOption, error) {
 	// Load the specified macaroon file.
 	macBytes, err := ioutil.ReadFile(macPath)
 	if err != nil {
-		fatal(fmt.Errorf("unable to read macaroon path : %v", err))
+		return nil, fmt.Errorf("unable to read macaroon path : %v", err)
 	}
 
 	mac := &macaroon.Macaroon{}
 	if err = mac.UnmarshalBinary(macBytes); err != nil {
-		fatal(fmt.Errorf("unable to decode macaroon: %v", err))
+		return nil, fmt.Errorf("unable to decode macaroon: %v", err)
 	}
 
 	macConstraints := []macaroons.Constraint{
@@ -430,10 +434,10 @@ func readMacaroon(macPath string) grpc.DialOption {
 	// Apply constraints to the macaroon.
 	constrainedMac, err := macaroons.AddConstraints(mac, macConstraints...)
 	if err != nil {
-		fatal(err)
+		return nil, err
 	}
 
 	// Now we append the macaroon credentials to the dial options.
 	cred := macaroons.NewMacaroonCredential(constrainedMac)
-	return grpc.WithPerRPCCredentials(cred)
+	return grpc.WithPerRPCCredentials(cred), nil
 }