Configure rabbitmq via the sys-map server.

.gitignore

@@ -0,0 +1 @@
+/target/

Cargo.toml

@@ -0,0 +1,19 @@
+[package]
+name = "slingshot-microservice"
+version = "0.1.0"
+edition = "2021"
+description = "Opinionated Rust framework for queue-driven microservices"
+license = "MIT"
+
+[dependencies]
+futures-util = "0.3"
+lapin = "2"
+reqwest = { version = "0.12", features = ["blocking", "json", "rustls-tls"], default-features = false }
+serde = { version = "1", features = ["derive"] }
+serde_json = "1"
+tokio = { version = "1", features = ["rt-multi-thread", "macros"] }
+tracing = "0.1"
+tracing-subscriber = { version = "0.3", features = ["env-filter", "fmt"] }
+
+[dev-dependencies]
+anyhow = "1"

README.md

@@ -4,18 +4,20 @@
 framework for building microservices.  The framework makes the following
 assumptions about a microservice:
 
-1. Microservices listens to incoming requests on a RabbitMQ queue.
+1. Microservices listens to incoming requests on a single queue (RabbitMQ).
 2. Incoming requests are in the form of a 64-bit unsigned integer (enough
    granularity to work as a resource identifier or ID).
-2. Microservices process incoming requests via a `process` function, which
-   takes one argument: the incoming request (`u64`).
+2. Microservices process requests via a `process` function, which takes one
+   argument: the incoming request (`u64`).
 3. The `process` function returns a set of IDs (also `u64`) that are the result
    of processing the incoming request.  Each of these IDs is also associated
    with a "case variable" that is used for routing the result to the
    appropriate outbound queues.
 4. Rather than hard-coding the inbound and outbound RabbitMQ queues, the
-   microservice communicates with a configuration service which provides the
+   microservice communicates with a configuration service, which provides the
    inbound queue name, as well as any outbound queues and their corresponding case variables.
+5. RabbitMQ is also configured automatically via the configuration service
+   (i.e. host, port, username, password are all provided by the configuration service).
 
 The `slingshot-microservice` framework handles setting up the RabbitMQ
 connection, listening to the inbound queue and routing results based on case variables.
@@ -60,7 +62,7 @@ For example:
         },
         {
             "case": "case_b",
-            "queue": ["case_b_outbound"]
+            "queues": ["case_b_outbound"]
         }
     ]
 }
@@ -80,12 +82,15 @@ to send results to based on a case variable that is either `false` or `true`:
         },
         {
             "case": true,
-            "queue": ["binary-classification-true-outbound"]
+            "queues": ["binary-classification-true-outbound"]
         }
     ]
 }
 ```
 
+The configuration service also provides the RabbitMQ connection details (host,
+port, etc.):
+
 When the microservice first starts up, it makes a request to the configuration
 service to get the queue metadata.  Then it starts to listen to the inbound
 queue.  Inbound requests are processed by the user-programmed `process`

examples/simple.rs

@@ -0,0 +1,12 @@
+use slingshot_microservice::Microservice;
+
+fn process(request: u64) -> Vec<(u64, String)> {
+    vec![(request, "case_a".to_string())]
+}
+
+fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
+    let microservice = Microservice::new("simple-microservice", "sys-map.slingshot.cv", process);
+
+    microservice.start()?;
+    Ok(())
+}

src/lib.rs

@@ -0,0 +1,287 @@
+use std::collections::HashMap;
+use std::error::Error;
+use std::process::Command;
+use std::sync::Arc;
+
+use futures_util::StreamExt;
+use lapin::options::{
+	BasicAckOptions, BasicConsumeOptions, BasicNackOptions, BasicPublishOptions,
+	QueueDeclareOptions,
+};
+use tracing::{error, info};
+use lapin::types::FieldTable;
+use lapin::{BasicProperties, Channel, Connection, ConnectionProperties};
+use serde::Deserialize;
+use serde::Serialize;
+use serde_json::Value;
+use tracing_subscriber::EnvFilter;
+
+type AnyError = Box<dyn Error + Send + Sync + 'static>;
+
+type ProcessFn = dyn Fn(u64) -> Vec<(u64, Value)> + Send + Sync + 'static;
+
+fn init_tracing() {
+	let filter = EnvFilter::try_from_default_env().unwrap_or_else(|_| EnvFilter::new("info"));
+	tracing_subscriber::fmt().with_env_filter(filter).init();
+}
+
+#[derive(Debug, Deserialize)]
+struct QueueConfig {
+	#[serde(rename = "in")]
+	inbound: String,
+	out: Vec<OutboundCase>,
+}
+
+#[derive(Debug, Deserialize)]
+struct OutboundCase {
+	#[serde(rename = "case")]
+	case_value: Value,
+	queues: Vec<String>,
+}
+
+/// A simple queue-driven microservice runtime.
+///
+/// The microservice:
+/// 1) Retrieves queue metadata from a configuration service,
+/// 2) Consumes u64 IDs from an inbound queue,
+/// 3) Runs the user-provided processing function,
+/// 4) Routes each output ID to outbound queue(s) based on case variables.
+pub struct Microservice {
+	name: String,
+	config_host: String,
+	process: Arc<ProcessFn>,
+}
+
+impl Microservice {
+	/// Create a new microservice runtime.
+	///
+	/// `process` accepts an inbound request ID and returns a list of
+	/// `(result_id, case_variable)` tuples. Case variables can be any
+	/// serializable primitive, such as `String`, `bool`, or integers.
+	pub fn new<F, C>(name: impl Into<String>, config_host: impl Into<String>, process: F) -> Self
+	where
+		F: Fn(u64) -> Vec<(u64, C)> + Send + Sync + 'static,
+		C: Serialize,
+	{
+		init_tracing();
+		let process_wrapper = move |request: u64| -> Vec<(u64, Value)> {
+			process(request)
+				.into_iter()
+				.map(|(id, case)| {
+					let value = serde_json::to_value(case)
+						.expect("case variable must be serializable to JSON");
+					(id, value)
+				})
+				.collect()
+		};
+
+		Self {
+			name: name.into(),
+			config_host: config_host.into(),
+			process: Arc::new(process_wrapper),
+		}
+	}
+
+	/// Start the microservice. This call blocks while the consumer loop runs.
+	pub fn start(&self) -> Result<(), AnyError> {
+		let config = self.fetch_config()?;
+		let route_map = build_route_map(&config.out);
+		let amqp_url = fetch_rabbitmq_url_from_sys_map()?;
+
+		let runtime = tokio::runtime::Builder::new_multi_thread()
+			.enable_all()
+			.build()?;
+
+		runtime.block_on(self.run_consumer(config.inbound, route_map, amqp_url))
+	}
+
+	fn fetch_config(&self) -> Result<QueueConfig, AnyError> {
+		let url = config_url(&self.config_host, &self.name);
+		let response = reqwest::blocking::get(url)?;
+		let response = response.error_for_status()?;
+		let config = response.json::<QueueConfig>()?;
+		Ok(config)
+	}
+
+	async fn run_consumer(
+		&self,
+		inbound_queue: String,
+		route_map: HashMap<String, Vec<String>>,
+		amqp_url: String,
+	) -> Result<(), AnyError> {
+		let connection = Connection::connect(&amqp_url, ConnectionProperties::default()).await?;
+		let channel = connection.create_channel().await?;
+
+		declare_queues(&channel, &inbound_queue, &route_map).await?;
+
+		let mut consumer = channel
+			.basic_consume(
+				&inbound_queue,
+				&format!("{}-consumer", self.name),
+				BasicConsumeOptions::default(),
+				FieldTable::default(),
+			)
+			.await?;
+
+		info!("Microservice '{}' started, consuming from queue '{}'", self.name, inbound_queue);
+		while let Some(delivery_result) = consumer.next().await {
+			let delivery = match delivery_result {
+				Ok(delivery) => delivery,
+				Err(err) => {
+					error!("Error receiving message: {}", err);
+					return Err(Box::new(err));
+				}
+			};
+
+			let raw = std::str::from_utf8(&delivery.data)?;
+			let request_id: u64 = match raw.trim().parse() {
+				Ok(value) => value,
+				Err(_) => {
+					delivery.nack(BasicNackOptions::default()).await?;
+					continue;
+				}
+			};
+
+			let outputs = (self.process)(request_id);
+			publish_outputs(&channel, outputs, &route_map).await?;
+			delivery.ack(BasicAckOptions::default()).await?;
+		}
+
+		Ok(())
+	}
+}
+
+#[derive(Debug, Deserialize)]
+struct RabbitMqConfig {
+	port: Vec<u16>,
+	host: Vec<String>,
+	username: Vec<String>,
+	pass: Vec<String>,
+}
+
+fn fetch_rabbitmq_url_from_sys_map() -> Result<String, AnyError> {
+	let response = reqwest::blocking::get("https://sys-map.slingshot.cv/rabbitmq")?;
+	let response = response.error_for_status()?;
+	let config = response.json::<RabbitMqConfig>()?;
+
+	let port = single_value(&config.port, "port")?;
+	let host = single_value(&config.host, "host")?;
+	let username = single_value(&config.username, "username")?;
+	let pass_key = single_value(&config.pass, "pass")?;
+	let pass = resolve_password_from_pass(&pass_key)?;
+
+	info!("Fetched RabbitMQ config from sys-map: host={}, port={}, username={}",
+		host, port, username);
+
+	Ok(format!("amqp://{}:{}@{}:{}/%2f", username, pass, host, port))
+}
+
+fn resolve_password_from_pass(pass_key: &str) -> Result<String, AnyError> {
+	let output = Command::new("pass").arg("show").arg(pass_key).output()?;
+
+	if !output.status.success() {
+		let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
+		let message = if stderr.is_empty() {
+			format!("failed to resolve GNU pass entry '{}'", pass_key)
+		} else {
+			format!("failed to resolve GNU pass entry '{}': {}", pass_key, stderr)
+		};
+		return Err(message.into());
+	}
+
+	let stdout = String::from_utf8(output.stdout)?;
+	let password = stdout.lines().next().unwrap_or("").trim().to_string();
+
+	if password.is_empty() {
+		return Err(format!("GNU pass entry '{}' returned an empty secret", pass_key).into());
+	}
+
+	Ok(password)
+}
+
+fn single_value<T: Clone>(values: &[T], field_name: &str) -> Result<T, AnyError> {
+	if values.len() != 1 {
+		return Err(format!(
+			"sys-map.rabbitmq field '{}' must contain exactly one value, got {}",
+			field_name,
+			values.len()
+		)
+		.into());
+	}
+
+	Ok(values[0].clone())
+}
+
+fn config_url(host: &str, microservice_name: &str) -> String {
+	if host.starts_with("http://") || host.starts_with("https://") {
+		format!("{}/{}", host.trim_end_matches('/'), microservice_name)
+	} else {
+		format!("https://{}/{}", host.trim_end_matches('/'), microservice_name)
+	}
+}
+
+fn build_route_map(outbound: &[OutboundCase]) -> HashMap<String, Vec<String>> {
+	let mut map = HashMap::new();
+	for entry in outbound {
+		map.insert(case_key(&entry.case_value), entry.queues.clone());
+	}
+	map
+}
+
+fn case_key(case_value: &Value) -> String {
+	case_value.to_string()
+}
+
+async fn declare_queues(
+	channel: &Channel,
+	inbound_queue: &str,
+	route_map: &HashMap<String, Vec<String>>,
+) -> Result<(), AnyError> {
+	channel
+		.queue_declare(
+			inbound_queue,
+			QueueDeclareOptions::default(),
+			FieldTable::default(),
+		)
+		.await?;
+
+	for queues in route_map.values() {
+		for queue in queues {
+			channel
+				.queue_declare(
+					queue,
+					QueueDeclareOptions::default(),
+					FieldTable::default(),
+				)
+				.await?;
+		}
+	}
+
+	Ok(())
+}
+
+async fn publish_outputs(
+	channel: &Channel,
+	outputs: Vec<(u64, Value)>,
+	route_map: &HashMap<String, Vec<String>>,
+) -> Result<(), AnyError> {
+	for (result_id, case_var) in outputs {
+		if let Some(outbound_queues) = route_map.get(&case_key(&case_var)) {
+			for queue in outbound_queues {
+				let payload = result_id.to_string();
+				let confirm = channel
+					.basic_publish(
+						"",
+						queue,
+						BasicPublishOptions::default(),
+						payload.as_bytes(),
+						BasicProperties::default(),
+					)
+					.await?;
+				confirm.await?;
+			}
+		}
+	}
+
+	Ok(())
+}