"-conf stdin" required to pipe in Caddyfile

Some programs (Node.js, supervisor, etc.) open a stdin pipe by default and don't use it, causing Caddy to block. It is their error, but we have to try to accommodate unfortunately. To fix this more universally, parent must explicitly set -conf to "stdin" to read from pipe.

main.go

@@ -117,25 +117,17 @@ func mustLogFatal(args ...interface{}) {
 }
 
 func loadCaddyfile() (caddy.Input, error) {
-	// First try stdin pipe
-	cdyfile, err := caddy.CaddyfileFromPipe(os.Stdin)
-	if err != nil {
-		return nil, err
-	}
-	if cdyfile != nil {
-		// it is an error if -conf is also specified because, which to use?
-		if conf != "" {
-			return nil, errors.New("load: can't choose between stdin pipe and -conf flag")
-		}
-		return cdyfile, err
-	}
-
-	// -conf flag
+	// Try -conf flag
 	if conf != "" {
+		if conf == "stdin" {
+			return caddy.CaddyfileFromPipe(os.Stdin)
+		}
+
 		contents, err := ioutil.ReadFile(conf)
 		if err != nil {
 			return nil, err
 		}
+
 		return caddy.CaddyfileInput{
 			Contents: contents,
 			Filepath: conf,