more xdg cleanup and encryption parameter improvements

Have a single common function to get the BaseDirectories
instance and a wrapper for `find()` and `place()` which
wrap the error with some context.

Signed-off-by: Wolfgang Bumiller <w.bumiller@proxmox.com>

src/bin/proxmox_backup_client/mod.rs

@@ -1,3 +1,5 @@
+use anyhow::{Context, Error};
+
 mod benchmark;
 pub use benchmark::*;
 mod mount;
@@ -8,3 +10,30 @@ mod catalog;
 pub use catalog::*;
 
 pub mod key;
+
+pub fn base_directories() -> Result<xdg::BaseDirectories, Error> {
+    xdg::BaseDirectories::with_prefix("proxmox-backup").map_err(Error::from)
+}
+
+/// Convenience helper for better error messages:
+pub fn find_xdg_file(
+    file_name: impl AsRef<std::path::Path>,
+    description: &'static str,
+) -> Result<Option<std::path::PathBuf>, Error> {
+    let file_name = file_name.as_ref();
+    base_directories()
+        .map(|base| base.find_config_file(file_name))
+        .with_context(|| format!("error searching for {}", description))
+}
+
+pub fn place_xdg_file(
+    file_name: impl AsRef<std::path::Path>,
+    description: &'static str,
+) -> Result<std::path::PathBuf, Error> {
+    let file_name = file_name.as_ref();
+    base_directories()
+        .and_then(|base| {
+            base.place_config_file(file_name).map_err(Error::from)
+        })
+        .with_context(|| format!("failed to place {} in xdg home", description))
+}