Split the service in multiple crates

crates/config/src/util.rs

@@ -0,0 +1,72 @@
+// Copyright 2021 The Matrix.org Foundation C.I.C.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::path::Path;
+
+use anyhow::Context;
+use async_trait::async_trait;
+use figment::{
+    error::Error as FigmentError,
+    providers::{Env, Format, Serialized, Yaml},
+    Figment, Profile,
+};
+use serde::{Deserialize, Serialize};
+
+#[async_trait]
+/// Trait implemented by all configuration section to help loading specific part
+/// of the config and generate the sample config.
+pub trait ConfigurationSection<'a>: Sized + Deserialize<'a> + Serialize {
+    /// Specify where this section should live relative to the root.
+    fn path() -> &'static str;
+
+    /// Generate a sample configuration for this section.
+    async fn generate() -> anyhow::Result<Self>;
+
+    /// Generate a sample configuration and override it with environment
+    /// variables.
+    ///
+    /// This is what backs the `config generate` subcommand, allowing to
+    /// programatically generate a configuration file, e.g.
+    ///
+    /// ```sh
+    /// export MAS_OAUTH2_ISSUER=https://example.com/
+    /// export MAS_HTTP_ADDRESS=127.0.0.1:1234
+    /// matrix-authentication-service config generate
+    /// ```
+    async fn load_and_generate() -> anyhow::Result<Self> {
+        let base = Self::generate()
+            .await
+            .context("could not generate configuration")?;
+
+        Figment::new()
+            .merge(Serialized::from(&base, Profile::Default))
+            .merge(Env::prefixed("MAS_").split("_"))
+            .extract_inner(Self::path())
+            .context("could not load configuration")
+    }
+
+    /// Load configuration from a file and environment variables.
+    fn load_from_file<P>(path: P) -> Result<Self, FigmentError>
+    where
+        P: AsRef<Path>,
+    {
+        Figment::new()
+            .merge(Env::prefixed("MAS_").split("_"))
+            .merge(Yaml::file(path))
+            .extract_inner(Self::path())
+    }
+
+    /// Generate config used in unit tests
+    fn test() -> Self;
+}