Use envy to parse environment variables for Config

This patch uses the envy crate to parse the environment.  A variable
NITROCLI_KEY can be used to overwrite the configuration for *key*.  This
has the side effect that the NITROCLI_NO_CACHE variable is evaluated as
a boolean variable (instead of only checking whether it is set).  We
also accept two new variables, NITROCLI_MODEL and NITROCLI_VERBOSITY.

5 files changed, 80 insertions, 8 deletions

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5c22351..17c176c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@ Unreleased
 - Added support for configuration files
   - Added `toml` dependency in version `0.5.6`
   - Added `serde` dependency in version `1.0.114`
+  - Added `envy` dependency in version `0.4.1`
+  - Added `merge` dependency in version `0.1.0`
 
 
 0.3.4
@@ -10,6 +12,11 @@ Unreleased
 - Changed default OTP format from `hex` to `base32`
 - Improved error reporting format and fidelity
   - Added `anyhow` dependency in version `1.0.32`
+- Reworked environment variables:
+  - Added the `NITROCLI_MODEL` and `NITROCLI_VERBOSITY` variables that
+    set the defaults for the `--model` and `--verbose` options
+  - Changed the handling of the `NITROCLI_NO_CACHE` variable to check
+    the value of the variable instead of only the presence
 - Updated minimum required Rust version to `1.42.0`
 - Bumped `nitrokey` dependency to `0.7.1`
 - Bumped `proc-macro2` dependency to `1.0.19`
diff --git a/Cargo.lock b/Cargo.lock
index 6893b95..3eff078 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -16,6 +16,12 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "6b602bfe940d21c130f3895acd65221e8a61270debe89d628b9cb4e3ccb8569b"
 
 [[package]]
+name = "autocfg"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cdb031dd78e28731d87d56cc8ffef4a8f36ca26c38fe2de700543e627f8a464a"
+
+[[package]]
 name = "base32"
 version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -51,6 +57,15 @@ dependencies = [
 ]
 
 [[package]]
+name = "envy"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f938a4abd5b75fe3737902dbc2e79ca142cc1526827a9e40b829a086758531a9"
+dependencies = [
+ "serde",
+]
+
+[[package]]
 name = "getrandom"
 version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -89,12 +104,36 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3728d817d99e5ac407411fa471ff9800a778d88a24685968b36824eaf4bee400"
 
 [[package]]
+name = "merge"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "10bbef93abb1da61525bbc45eeaff6473a41907d19f8f9aa5168d214e10693e9"
+dependencies = [
+ "merge_derive",
+ "num-traits",
+]
+
+[[package]]
+name = "merge_derive"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "209d075476da2e63b4b29e72a2ef627b840589588e71400a25e3565c4f849d07"
+dependencies = [
+ "proc-macro-error",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
 name = "nitrocli"
 version = "0.3.4"
 dependencies = [
  "anyhow",
  "base32",
+ "envy",
  "libc",
+ "merge",
  "nitrokey",
  "nitrokey-test",
  "nitrokey-test-state",
@@ -143,6 +182,15 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "a59b732ed6d5212424ed31ec9649f05652bcbc38f45f2292b27a6044e7098803"
 
 [[package]]
+name = "num-traits"
+version = "0.2.12"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac267bcc07f48ee5f8935ab0d24f316fb722d7a1292e2913f0cc196b29ffd611"
+dependencies = [
+ "autocfg",
+]
+
+[[package]]
 name = "proc-macro-error"
 version = "1.0.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
diff --git a/Cargo.toml b/Cargo.toml
index 23602ec..2e2e47f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -52,9 +52,15 @@ version = "1.0"
 [dependencies.base32]
 version = "0.4.0"
 
+[dependencies.envy]
+version = "0.4.1"
+
 [dependencies.libc]
 version = "0.2"
 
+[dependencies.merge]
+version = "0.1"
+
 [dependencies.nitrokey]
 version = "0.7.1"
 
diff --git a/src/config.rs b/src/config.rs
index 850d217..2e8f3ba 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -26,21 +26,31 @@ use anyhow::Context as _;
 
 /// The configuration for nitrocli, usually read from configuration
 /// files and environment variables.
-#[derive(Clone, Copy, Debug, Default, PartialEq, serde::Deserialize)]
+#[derive(Clone, Copy, Debug, Default, PartialEq, merge::Merge, 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.
+  #[merge(strategy = merge::bool::overwrite_false)]
   #[serde(default)]
   pub no_cache: bool,
   /// The log level.
+  #[merge(strategy = merge::num::overwrite_zero)]
   #[serde(default)]
   pub verbosity: u8,
 }
 
 impl Config {
   pub fn load() -> anyhow::Result<Self> {
-    load_user_config().map(|o| o.unwrap_or_default())
+    use merge::Merge as _;
+
+    let mut config = Config::default();
+    if let Some(user_config) = load_user_config()? {
+      config.merge(user_config);
+    }
+    config.merge(load_env_config()?);
+
+    Ok(config)
   }
 
   pub fn update(&mut self, args: &args::Args) {
@@ -62,6 +72,12 @@ fn load_user_config() -> anyhow::Result<Option<Config>> {
   }
 }
 
+fn load_env_config() -> anyhow::Result<Config> {
+  envy::prefixed("NITROCLI_")
+    .from_env()
+    .context("Failed to parse environment variables")
+}
+
 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()))?;
diff --git a/src/main.rs b/src/main.rs
index 3535a91..b53358e 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -84,7 +84,6 @@ const NITROCLI_USER_PIN: &str = "NITROCLI_USER_PIN";
 const NITROCLI_NEW_ADMIN_PIN: &str = "NITROCLI_NEW_ADMIN_PIN";
 const NITROCLI_NEW_USER_PIN: &str = "NITROCLI_NEW_USER_PIN";
 const NITROCLI_PASSWORD: &str = "NITROCLI_PASSWORD";
-const NITROCLI_NO_CACHE: &str = "NITROCLI_NO_CACHE";
 
 trait Stdio {
   fn stdio(&mut self) -> (&mut dyn io::Write, &mut dyn io::Write);
@@ -206,11 +205,7 @@ fn main() {
   let mut stderr = io::stderr();
 
   let rc = match config::Config::load() {
-    Ok(mut config) => {
-      if env::var_os(NITROCLI_NO_CACHE).is_some() {
-        config.no_cache = true;
-      }
-
+    Ok(config) => {
       let args = env::args().collect::<Vec<_>>();
       let ctx = &mut RunCtx {
         stdout: &mut stdout,