Allow selecting ssh user dynamically

...by setting `deployment.targetUser = null`.

This allows sharing a deployment file (hive.nix/flake.nix) between
multiple admins, without having to use a shared root account.

Cargo.lock

@@ -133,6 +133,7 @@ dependencies = [
  "tempfile",
  "tokio",
  "tokio-test",
+ "users",
  "validator",
 ]
 
@@ -890,6 +891,16 @@ dependencies = [
  "percent-encoding",
 ]
 
+[[package]]
+name = "users"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "24cc0f6d6f267b73e5a2cadf007ba8f9bc39c6a6f9666f8cf25ea809a153b032"
+dependencies = [
+ "libc",
+ "log",
+]
+
 [[package]]
 name = "validator"
 version = "0.12.0"

Cargo.toml

@@ -27,6 +27,7 @@ sys-info = "0.7.0"
 snafu = "0.6.10"
 tempfile = "3.1.0"
 tokio-test = "0.4.0"
+users = "0.11.0"
 validator = { version = "0.12", features = ["derive"] }
 
 [dependencies.tokio]

src/nix/eval.nix

@@ -113,9 +113,10 @@ let
         };
         targetUser = lib.mkOption {
           description = ''
-            The user to use to log into the remote node.
+            The user to use to log into the remote node. If null, login as the
+            current user.
           '';
-          type = types.str;
+          type = types.nullOr types.str;
           default = "root";
         };
         allowLocalDeployment = lib.mkOption {

src/nix/mod.rs

@@ -9,6 +9,7 @@ use serde::de::DeserializeOwned;
 use serde::Deserialize;
 use snafu::Snafu;
 use tokio::process::Command;
+use users::get_current_username;
 use validator::{Validate, ValidationErrors, ValidationError as ValidationErrorType};
 
 use crate::util::CommandExecution;
@@ -115,7 +116,7 @@ pub struct NodeConfig {
     target_host: Option<String>,
 
     #[serde(rename = "targetUser")]
-    target_user: String,
+    target_user: Option<String>,
 
     #[serde(rename = "targetPort")]
     target_port: Option<u16>,
@@ -140,7 +141,12 @@ impl NodeConfig {
 
     pub fn to_ssh_host(&self) -> Option<Ssh> {
         self.target_host.as_ref().map(|target_host| {
-            let mut host = Ssh::new(self.target_user.clone(), target_host.clone());
+            let username =
+                match &self.target_user {
+                    Some(uname) => uname.clone(),
+                    None => get_current_username().unwrap().into_string().ok().unwrap(),
+                };
+            let mut host = Ssh::new(username.clone(), target_host.clone());
             host.set_privilege_escalation_command(self.privilege_escalation_command.clone());
 
             if let Some(target_port) = self.target_port {

src/nix/tests/mod.rs

@@ -134,7 +134,7 @@ fn test_parse_simple() {
     ));
     assert_eq!(Some("host-a"), nodes["host-a"].target_host.as_deref());
     assert_eq!(None, nodes["host-a"].target_port);
-    assert_eq!("root", &nodes["host-a"].target_user);
+    assert_eq!(Some("root"), nodes["host-a"].target_user.as_deref());
 
     // host-b
     assert!(set_eq(
@@ -143,7 +143,7 @@ fn test_parse_simple() {
     ));
     assert_eq!(Some("somehost.tld"), nodes["host-b"].target_host.as_deref());
     assert_eq!(Some(1234), nodes["host-b"].target_port);
-    assert_eq!("luser", &nodes["host-b"].target_user);
+    assert_eq!(Some("luser"), nodes["host-b"].target_user.as_deref());
 }
 
 #[test]