Add a dummy tacd standalone server

Even if the tacd server might be one of the last thing implemented using
ring, it should not block the compilation.

tacd/src/main.rs

@@ -1,3 +1,12 @@
+#[cfg(not(feature = "standalone"))]
+mod openssl_server;
+#[cfg(not(feature = "standalone"))]
+use openssl_server::start as server_start;
+#[cfg(feature = "standalone")]
+mod standalone_server;
+#[cfg(feature = "standalone")]
+use standalone_server::start as server_start;
+
 use acme_common::crypto::X509Certificate;
 use acme_common::error::Error;
 use clap::{App, Arg, ArgMatches};
@@ -5,8 +14,6 @@ use log::{debug, error, info};
 use std::fs::File;
 use std::io::{self, Read};
 
-mod server;
-
 const APP_NAME: &str = env!("CARGO_PKG_NAME");
 const APP_VERSION: &str = env!("CARGO_PKG_VERSION");
 const DEFAULT_PID_FILE: &str = "/var/run/admed.pid";
@@ -47,7 +54,7 @@ fn init(cnf: &ArgMatches) -> Result<(), Error> {
     let listen_addr = cnf.value_of("listen").unwrap_or(DEFAULT_LISTEN_ADDR);
     let (pk, cert) = X509Certificate::from_acme_ext(&domain, &ext)?;
     info!("Starting {} on {} for {}", APP_NAME, listen_addr, domain);
-    server::start(listen_addr, &cert, &pk)?;
+    server_start(listen_addr, &cert, &pk)?;
     Ok(())
 }
 

tacd/src/standalone_server.rs

@@ -0,0 +1,10 @@
+use acme_common::crypto::{PrivateKey, X509Certificate};
+use acme_common::error::Error;
+
+pub fn start(
+    listen_addr: &str,
+    certificate: &X509Certificate,
+    private_key: &PrivateKey,
+) -> Result<(), Error> {
+    Err("The standalone server is not implemented yet.".into())
+}