httpcaddyfile: Fix incorrect handling of IPv6 bind addresses (#4532)

The `net.JoinHostPort()` function has some naiive logic for handling IPv6, it just checks if the host part has a `:` and if so it wraps the host part with `[ ]` but this causes our network type prefix to get wrapped as well, which is invalid for `caddy.NetworkAddress`. Instead, we can just concatenate the host and port manually here to avoid this side-effect.

caddyconfig/httpcaddyfile/addresses.go

@@ -223,7 +223,7 @@ func (st *ServerType) listenerAddrsForServerBlockKey(sblock serverBlock, key str
 		if err == nil && addr.IsUnixNetwork() {
 			listeners[host] = struct{}{}
 		} else {
-			listeners[net.JoinHostPort(host, lnPort)] = struct{}{}
+			listeners[host+":"+lnPort] = struct{}{}
 		}
 	}
 

caddytest/integration/caddyfile_adapt/bind_ipv6.txt

@@ -0,0 +1,29 @@
+example.com {
+	bind tcp6/[::]
+}
+----------
+{
+	"apps": {
+		"http": {
+			"servers": {
+				"srv0": {
+					"listen": [
+						"tcp6/[::]:443"
+					],
+					"routes": [
+						{
+							"match": [
+								{
+									"host": [
+										"example.com"
+									]
+								}
+							],
+							"terminal": true
+						}
+					]
+				}
+			}
+		}
+	}
+}