[PATCH v4 5/5] fix #5340: client: repository: add PBS_NAMESPACE environment variable

[Thomas Lamprecht <t.lamprecht@proxmox.com>]

Add PBS_NAMESPACE as a fallback when --ns is not given on the CLI,
addressing the request in bug #5340.

The env var is supported uniformly across all client tools
(proxmox-backup-client, proxmox-file-restore, proxmox-backup-debug).
Like the other PBS_* atom env vars, it provides a default that can be
overridden by the corresponding CLI option.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---

changes v3 -> v4:
- env var fallback now lives in the shared optional_ns_param() in
  pbs-client tools (moved in patch 3), so this patch only upgrades that
  single function instead of touching all three binaries
- made ENV_VAR_PBS_NAMESPACE private (consistent with other
  ENV_VAR_PBS_* constants, no external users after the move)

 docs/backup-client.rst      |  3 +++
 pbs-client/src/tools/mod.rs | 16 +++++++++++-----
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/docs/backup-client.rst b/docs/backup-client.rst
index 1d464a007..e2a05d4fc 100644
--- a/docs/backup-client.rst
+++ b/docs/backup-client.rst
@@ -131,6 +131,9 @@ Environment Variables
   Authentication identity (``user@realm`` or ``user@realm!tokenname``).
   Defaults to ``root@pam`` if unset.
 
+``PBS_NAMESPACE``
+  Backup namespace. Used as a fallback when ``--ns`` is not given.
+
 ``PBS_PASSWORD``
   When set, this value is used as the password for the backup server.
   You can also set this to an API token secret.
diff --git a/pbs-client/src/tools/mod.rs b/pbs-client/src/tools/mod.rs
index fa708a8b5..e034b9a31 100644
--- a/pbs-client/src/tools/mod.rs
+++ b/pbs-client/src/tools/mod.rs
@@ -36,6 +36,7 @@ const ENV_VAR_PBS_SERVER: &str = "PBS_SERVER";
 const ENV_VAR_PBS_PORT: &str = "PBS_PORT";
 const ENV_VAR_PBS_DATASTORE: &str = "PBS_DATASTORE";
 const ENV_VAR_PBS_AUTH_ID: &str = "PBS_AUTH_ID";
+const ENV_VAR_PBS_NAMESPACE: &str = "PBS_NAMESPACE";
 
 /// Directory with system [credential]s. See systemd-creds(1).
 ///
@@ -339,13 +340,17 @@ pub fn extract_repository_from_map(param: &HashMap<String, String>) -> Option<Ba
     resolve_repository(cli).ok()
 }
 
-/// Extract a [`BackupNamespace`] from CLI parameters.
+/// Extract a [`BackupNamespace`] from CLI parameters, falling back to PBS_NAMESPACE.
 pub fn optional_ns_param(param: &Value) -> Result<BackupNamespace, Error> {
-    Ok(match param.get("ns") {
-        Some(Value::String(ns)) => ns.parse()?,
+    match param.get("ns") {
+        Some(Value::String(ns)) => return ns.parse().map_err(Error::from),
         Some(_) => bail!("invalid namespace parameter"),
-        None => BackupNamespace::root(),
-    })
+        None => {}
+    }
+    if let Ok(ns) = std::env::var(ENV_VAR_PBS_NAMESPACE) {
+        return ns.parse().map_err(Error::from);
+    }
+    Ok(BackupNamespace::root())
 }
 
 pub fn connect(repo: &BackupRepository) -> Result<HttpClient, Error> {
@@ -849,6 +854,7 @@ mod tests {
         ENV_VAR_PBS_PORT,
         ENV_VAR_PBS_DATASTORE,
         ENV_VAR_PBS_AUTH_ID,
+        ENV_VAR_PBS_NAMESPACE,
         ENV_VAR_CREDENTIALS_DIRECTORY,
     ];
 
-- 
2.47.3