httpcaddyfile: Fix bind when IPv6 is specified with network (#4950)

* fix listening on IPv6 addresses: use net.JoinHostPort

Commit 1e18afb5c8 broke my caddy setup.
This commit fixes it.

* Refactor solution; simplify, add descriptive comment

* Move network to host, not copy

Co-authored-by: Matthew Holt <mholt@users.noreply.github.com>

caddyconfig/httpcaddyfile/addresses.go

@@ -36,12 +36,12 @@ import (
 // server block that share the same address stay grouped together so the config
 // isn't repeated unnecessarily. For example, this Caddyfile:
 //
-// 	example.com {
-// 		bind 127.0.0.1
-// 	}
-// 	www.example.com, example.net/path, localhost:9999 {
-// 		bind 127.0.0.1 1.2.3.4
-// 	}
+//	example.com {
+//		bind 127.0.0.1
+//	}
+//	www.example.com, example.net/path, localhost:9999 {
+//		bind 127.0.0.1 1.2.3.4
+//	}
 //
 // has two server blocks to start with. But expressed in this Caddyfile are
 // actually 4 listener addresses: 127.0.0.1:443, 1.2.3.4:443, 127.0.0.1:9999,
@@ -219,7 +219,7 @@ func (st *ServerType) listenerAddrsForServerBlockKey(sblock serverBlock, key str
 		return nil, fmt.Errorf("[%s] scheme and port violate convention", key)
 	}
 
-	// the bind directive specifies hosts, but is optional
+	// the bind directive specifies hosts (and potentially network), but is optional
 	lnHosts := make([]string, 0, len(sblock.pile["bind"]))
 	for _, cfgVal := range sblock.pile["bind"] {
 		lnHosts = append(lnHosts, cfgVal.Value.([]string)...)
@@ -234,11 +234,23 @@ func (st *ServerType) listenerAddrsForServerBlockKey(sblock serverBlock, key str
 
 	// use a map to prevent duplication
 	listeners := make(map[string]struct{})
-	for _, host := range lnHosts {
-		// host can have network + host (e.g. "tcp6/localhost") but
-		// will/should not have port information because this usually
-		// comes from the bind directive, so we append the port
-		addr, err := caddy.ParseNetworkAddress(host + ":" + lnPort)
+	for _, lnHost := range lnHosts {
+		// normally we would simply append the port,
+		// but if lnHost is IPv6, we need to ensure it
+		// is enclosed in [ ]; net.JoinHostPort does
+		// this for us, but lnHost might also have a
+		// network type in front (e.g. "tcp/") leading
+		// to "[tcp/::1]" which causes parsing failures
+		// later; what we need is "tcp/[::1]", so we have
+		// to split the network and host, then re-combine
+		network, host, ok := strings.Cut(lnHost, "/")
+		if !ok {
+			host = network
+			network = ""
+		}
+		host = strings.Trim(host, "[]") // IPv6
+		networkAddr := caddy.JoinNetworkAddress(network, host, lnPort)
+		addr, err := caddy.ParseNetworkAddress(networkAddr)
 		if err != nil {
 			return nil, fmt.Errorf("parsing network address: %v", err)
 		}