ConfigurationSource: Move "usual" logic for construction

Cargo.lock

@@ -166,6 +166,7 @@ dependencies = [
  "arti-client",
  "config",
  "derive_builder_fork_arti",
+ "fs-mistrust",
  "once_cell",
  "regex",
  "serde",

crates/arti-config/Cargo.toml

@@ -17,6 +17,7 @@ tor-circmgr = { package = "tor-circmgr", path = "../tor-circmgr", version = "0.3
 tor-config = { package = "tor-config", path = "../tor-config", version = "0.3.0", features = [
     "expand-paths",
 ] }
+fs-mistrust = { path = "../fs-mistrust", version = "0.1.0" }
 config = { version = "0.13", default-features = false, features = ["toml"] }
 once_cell = "1"
 serde = { version = "1.0.103", features = ["derive"] }

crates/arti-config/src/lib.rs

@@ -90,6 +90,52 @@ impl ConfigurationSources {
         Self::default()
     }
 
+    /// Establish a [`ConfigurationSources`] the usual way from a command line and defaults
+    ///
+    /// The caller should have parsed the program's command line, and extracted (inter alia)
+    ///
+    ///  * `config_files_options`: Paths of config file(s)
+    ///  * `cmdline_toml_override_options`: Overrides ("key=value")
+    ///
+    /// The caller should also provide `default_config_file`, the default location of the
+    /// configuration file.  This is used if no file(s) are specified on the command line.
+    ///
+    /// `mistrust` is used to check whether the configuration files have appropriate permissions.
+    pub fn from_cmdline<'o, F>(
+        default_config_file: impl Into<PathBuf>,
+        config_files_options: impl IntoIterator<Item = F>,
+        cmdline_toml_override_options: impl IntoIterator<Item = &'o str>,
+        mistrust: &fs_mistrust::Mistrust,
+    ) -> Result<Self, fs_mistrust::Error>
+    where
+        F: AsRef<Path>,
+    {
+        let mut cfg_sources = ConfigurationSources::new_empty();
+
+        let mut any_files = false;
+        for f in config_files_options {
+            let f = f.as_ref();
+            mistrust.verifier().require_file().check(f)?;
+            cfg_sources.push_file(f);
+            any_files = true;
+        }
+        if !any_files {
+            let default = default_config_file.into();
+            match mistrust.verifier().require_file().check(&default) {
+                Ok(()) => {}
+                Err(fs_mistrust::Error::NotFound(_)) => {}
+                Err(e) => return Err(e),
+            }
+            cfg_sources.push_optional_file(default);
+        }
+
+        for s in cmdline_toml_override_options {
+            cfg_sources.push_option(s);
+        }
+
+        Ok(cfg_sources)
+    }
+
     /// Add `p` to the list of files that we want to read configuration from.
     ///
     /// Configuration files are loaded and applied in the order that they are

crates/arti/src/lib.rs

@@ -371,32 +371,12 @@ pub fn main_main() -> Result<()> {
         mistrust
     };
 
-    let cfg_sources = {
-        let mut cfg_sources = arti_config::ConfigurationSources::new_empty();
-
-        let config_files = matches.values_of_os("config-files").unwrap_or_default();
-        if config_files.len() == 0 {
-            let default = default_config_file()?;
-            match mistrust.verifier().require_file().check(&default) {
-                Ok(()) => {}
-                Err(fs_mistrust::Error::NotFound(_)) => {}
-                Err(e) => return Err(e.into()),
-            }
-            cfg_sources.push_optional_file(default);
-        } else {
-            for f in config_files {
-                mistrust.verifier().require_file().check(f)?;
-                cfg_sources.push_file(f);
-            }
-        }
-
-        matches
-            .values_of("option")
-            .unwrap_or_default()
-            .for_each(|s| cfg_sources.push_option(s));
-
-        cfg_sources
-    };
+    let cfg_sources = arti_config::ConfigurationSources::from_cmdline(
+        default_config_file()?,
+        matches.values_of_os("config-files").unwrap_or_default(),
+        matches.values_of("option").unwrap_or_default(),
+        &mistrust,
+    )?;
 
     let cfg = cfg_sources.load()?;