Implement configuration handling

This patch implements basic configuration handling that reads a
configuration file and stores the parsed data in the ExecCtx and RunCtx
structs.  It supports three configuration items:
- model (previously only --model)
- no_cache (previously only NITROCLI_NO_CACHE)
- verbosity (previously only --verbose)

1 files changed, 70 insertions, 0 deletions

diff --git a/src/config.rs b/src/config.rs
new file mode 100644
index 0000000..850d217
--- /dev/null
+++ b/src/config.rs
@@ -0,0 +1,70 @@
+// config.rs
+
+// *************************************************************************
+// * Copyright (C) 2020 Daniel Mueller (deso@posteo.net)                   *
+// *                                                                       *
+// * This program is free software: you can redistribute it and/or modify  *
+// * it under the terms of the GNU General Public License as published by  *
+// * the Free Software Foundation, either version 3 of the License, or     *
+// * (at your option) any later version.                                   *
+// *                                                                       *
+// * This program is distributed in the hope that it will be useful,       *
+// * but WITHOUT ANY WARRANTY; without even the implied warranty of        *
+// * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the         *
+// * GNU General Public License for more details.                          *
+// *                                                                       *
+// * You should have received a copy of the GNU General Public License     *
+// * along with this program.  If not, see <http://www.gnu.org/licenses/>. *
+// *************************************************************************
+
+use std::fs;
+use std::path;
+
+use crate::args;
+
+use anyhow::Context as _;
+
+/// The configuration for nitrocli, usually read from configuration
+/// files and environment variables.
+#[derive(Clone, Copy, Debug, Default, PartialEq, serde::Deserialize)]
+pub struct Config {
+  /// The model to connect to.
+  pub model: Option<args::DeviceModel>,
+  /// Whether to bypass the cache for all secrets or not.
+  #[serde(default)]
+  pub no_cache: bool,
+  /// The log level.
+  #[serde(default)]
+  pub verbosity: u8,
+}
+
+impl Config {
+  pub fn load() -> anyhow::Result<Self> {
+    load_user_config().map(|o| o.unwrap_or_default())
+  }
+
+  pub fn update(&mut self, args: &args::Args) {
+    if args.model.is_some() {
+      self.model = args.model;
+    }
+    if args.verbose > 0 {
+      self.verbosity = args.verbose;
+    }
+  }
+}
+
+fn load_user_config() -> anyhow::Result<Option<Config>> {
+  let path = path::Path::new("config.toml");
+  if path.is_file() {
+    read_config_file(&path).map(Some)
+  } else {
+    Ok(None)
+  }
+}
+
+pub fn read_config_file(path: &path::Path) -> anyhow::Result<Config> {
+  let s = fs::read_to_string(path)
+    .with_context(|| format!("Failed to read configuration file '{}'", path.display()))?;
+  toml::from_str(&s)
+    .with_context(|| format!("Failed to parse configuration file '{}'", path.display()))
+}