reverse_proxy: Allow dynamic backends (closes #990 and #1539)

This PR enables the use of placeholders in an upstream's Dial address.

A Dial address must represent precisely one socket after replacements.

See also #998 and #1639.

1 files changed, 4 insertions, 3 deletions

diff --git a/listeners.go b/listeners.go
index 04ec788f0..8c2792c26 100644
--- a/listeners.go
+++ b/listeners.go
@@ -286,9 +286,10 @@ func JoinNetworkAddress(network, host, port string) string {
 	if network != "" {
 		a = network + "/"
 	}
-	a += host
-	if port != "" {
-		a += ":" + port
+	if host != "" && port == "" {
+		a += host
+	} else if port != "" {
+		a += net.JoinHostPort(host, port)
 	}
 	return a
 }