Add example implementation using async source

Signed-off-by: Matthias Beyer <[email protected]>
Reviewed-by: Matthias Beyer <[email protected]>

Author: szarykott

Cargo.toml

@@ -40,3 +40,7 @@ json5_rs = { version = "0.3", optional = true, package = "json5" }
 serde_derive = "1.0.8"
 float-cmp = "0.8"
 chrono = { version = "0.4", features = ["serde"] }
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "fs", "io-util", "time"]}
+warp = "0.3.1"
+futures = "0.3.15"
+reqwest = "0.11.3"

examples/async_source/main.rs

@@ -0,0 +1,75 @@
+use std::{collections::HashMap, error::Error};
+
+use config::{builder::AsyncState, AsyncSource, ConfigBuilder, ConfigError, FileFormat};
+
+use async_trait::async_trait;
+use futures::{select, FutureExt};
+use warp::Filter;
+
+// Example below presents sample configuration server and client.
+//
+// Server serves simple configuration on HTTP endpoint.
+// Client consumes it using custom HTTP AsyncSource built on top of reqwest.
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn Error>> {
+    select! {
+        r = run_server().fuse() => r,
+        r = run_client().fuse() => r
+    }
+}
+
+async fn run_server() -> Result<(), Box<dyn Error>> {
+    let service = warp::path("configuration").map(|| r#"{ "value" : 123 }"#);
+
+    println!("Running server on localhost:5001");
+
+    warp::serve(service).bind(([127, 0, 0, 1], 5001)).await;
+
+    Ok(())
+}
+
+async fn run_client() -> Result<(), Box<dyn Error>> {
+    // Good enough for an example to allow server to start
+    tokio::time::sleep(tokio::time::Duration::from_secs(3)).await;
+
+    let config = ConfigBuilder::<AsyncState>::default()
+        .add_async_source(HttpSource {
+            uri: "http://localhost:5001/configuration".into(),
+            format: FileFormat::Json,
+        })
+        .build()
+        .await?;
+
+    println!("Config value is {}", config.get::<String>("value")?);
+
+    Ok(())
+}
+
+// Actual implementation of AsyncSource can be found below
+
+#[derive(Debug)]
+struct HttpSource {
+    uri: String,
+    format: FileFormat,
+}
+
+impl HttpSource {
+    async fn call(&self) -> Result<String, reqwest::Error> {
+        reqwest::get(&self.uri).await?.text().await
+    }
+}
+
+#[async_trait]
+impl AsyncSource for HttpSource {
+    async fn collect(&self) -> Result<HashMap<String, config::Value>, ConfigError> {
+        self.call()
+            .await
+            .map_err(|e| ConfigError::Foreign(Box::new(e)))
+            .and_then(|text| {
+                self.format
+                    .parse(Some(&self.uri), &text)
+                    .map_err(|e| ConfigError::Foreign(e))
+            })
+    }
+}