grpc: optional interface to provide channel authority

clientconn.go

@@ -1980,28 +1980,15 @@ func (cc *ClientConn) determineAuthority() error {
 		return fmt.Errorf("ClientConn's authority from transport creds %q and dial option %q don't match", authorityFromCreds, authorityFromDialOption)
 	}
 
-	endpoint := cc.parsedTarget.Endpoint()
-	target := cc.target
-	switch {
-	case authorityFromDialOption != "":
+	if authorityFromDialOption != "" {
 		cc.authority = authorityFromDialOption
-	case authorityFromCreds != "":
+	} else if authorityFromCreds != "" {
 		cc.authority = authorityFromCreds
-	case strings.HasPrefix(target, "unix:") || strings.HasPrefix(target, "unix-abstract:"):
-		// TODO: remove when the unix resolver implements optional interface to
-		// return channel authority.
-		cc.authority = "localhost"
-	case strings.HasPrefix(endpoint, ":"):
+	} else if auth, isAuthOverrider := cc.resolverBuilder.(resolver.AuthorityOverrider); isAuthOverrider {
+		cc.authority = auth.OverrideAuthority(cc.parsedTarget)
+	} else if endpoint := cc.parsedTarget.Endpoint(); strings.HasPrefix(endpoint, ":") {
 		cc.authority = "localhost" + endpoint
-	default:
-		// TODO: Define an optional interface on the resolver builder to return
-		// the channel authority given the user's dial target. For resolvers
-		// which don't implement this interface, we will use the endpoint from
-		// "scheme://authority/endpoint" as the default authority.
-		// Escape the endpoint to handle use cases where the endpoint
-		// might not be a valid authority by default.
-		// For example an endpoint which has multiple paths like
-		// 'a/b/c', which is not a valid authority by default.
+	} else {
 		cc.authority = encodeAuthority(endpoint)
 	}
 	channelz.Infof(logger, cc.channelzID, "Channel authority set to %q", cc.authority)

internal/resolver/unix/unix.go

@@ -61,6 +61,10 @@ func (b *builder) Scheme() string {
 	return b.scheme
 }
 
+func (b *builder) OverrideAuthority(t resolver.Target) string {
+	return "localhost"
+}
+
 type nopResolver struct {
 }
 

resolver/resolver.go

@@ -319,3 +319,12 @@ type Resolver interface {
 	// Close closes the resolver.
 	Close()
 }
+
+// AuthorityOverrider is implemented by Builders that wish to override the
+// default authority for the ClientConn.
+// By default, the authority used is target.Endpoint()
+type AuthorityOverrider interface {
+	// OverrideAuthority returns the authority to use for a ClientConn with the
+	// given target. It must not perform I/O or any other blocking operations.
+	OverrideAuthority(Target) string
+}