Add support for the irc+insecure address scheme

Some servers do not support TLS, or have invalid, expired or self-signed
TLS certificates. While the right fix would be toi contact each server
owner to add support for valid TLS, supporting plaintext upstream
connections is sometimes necessary.

This adds support for the irc+insecure address scheme, which connects to
a network in plain-text over TCP.

doc/soju.1.scd

@@ -97,6 +97,7 @@ abbreviated form, for instance *network* can be abbreviated as *net* or just
 
 	_addr_ supports several connection types:
 	- _[ircs://]host[:port]_ connects with TLS over TCP
+	- _irc+insecure://host[:port]_ connects with plain-text TCP
 
 	Other options are:
 

service.go

@@ -206,9 +206,9 @@ func handleServiceCreateNetwork(dc *downstreamConn, params []string) error {
 	if addrParts := strings.SplitN(*addr, "://", 2); len(addrParts) == 2 {
 		scheme := addrParts[0]
 		switch scheme {
-		case "ircs":
+		case "ircs", "irc+insecure":
 		default:
-			return fmt.Errorf("unknown scheme %q (supported schemes: ircs)", scheme)
+			return fmt.Errorf("unknown scheme %q (supported schemes: ircs, irc+insecure)", scheme)
 		}
 	}
 

upstream.go

@@ -90,6 +90,13 @@ func connectToUpstream(network *network) (*upstreamConn, error) {
 
 		logger.Printf("connecting to TLS server at address %q", addr)
 		netConn, err = tls.DialWithDialer(&dialer, "tcp", addr, nil)
+	case "irc+insecure":
+		if !strings.ContainsRune(addr, ':') {
+			addr = addr + ":6667"
+		}
+
+		logger.Printf("connecting to plain-text server at address %q", addr)
+		netConn, err = dialer.Dial("tcp", addr)
 	default:
 		return nil, fmt.Errorf("failed to dial %q: unknown scheme: %v", addr, scheme)
 	}