Add framework for separate printer control thread

6 files changed, 116 insertions, 8 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 91e2a64..b1aee2b 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -18,9 +18,19 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe"
 
 [[package]]
+name = "argonaut-control"
+version = "0.1.0"
+dependencies = [
+ "tokio",
+ "tracing",
+ "tracing-subscriber",
+]
+
+[[package]]
 name = "argonaut-web"
 version = "0.1.0"
 dependencies = [
+ "argonaut-control",
  "axum",
  "serde",
  "tokio",
diff --git a/Cargo.toml b/Cargo.toml
index b90f2bb..e7c3e21 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,7 +1,8 @@
 [workspace]
 resolver = "2"
 members = [
-        "crates/web"
+    "crates/control",
+    "crates/web"
 ]
 
 [workspace.dependencies]
diff --git a/crates/control/Cargo.toml b/crates/control/Cargo.toml
new file mode 100644
index 0000000..6934db5
--- /dev/null
+++ b/crates/control/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "argonaut-control"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+tokio = { workspace = true }
+tracing = { workspace = true }
+tracing-subscriber = { workspace = true }
diff --git a/crates/control/src/lib.rs b/crates/control/src/lib.rs
new file mode 100644
index 0000000..5691cf2
--- /dev/null
+++ b/crates/control/src/lib.rs
@@ -0,0 +1,81 @@
+//! Printer control related code
+//!
+//! To ensure the volume of web requests doesn't mess with printing, communication with the printer is done
+//! in a separate thread, on its own async executor.
+//!
+//! The main server spawns this thread by creating a [`Handle`] and communicates by sending [messages](crate::Message) over an MPSC channel.
+
+use std::{
+    mem::ManuallyDrop,
+    thread::{self, JoinHandle},
+};
+use tokio::{
+    runtime,
+    sync::mpsc::{self, Receiver, Sender},
+};
+use tracing::info;
+
+/// The maximum number of messages to buffer before 'blocking' new ones
+/// This provides a form of backpressure
+const CHANNEL_CAPACITY: usize = 100;
+
+/// A control message sent from the API to the printer control thread
+pub enum Message {
+    Quit,
+}
+
+/// A handle to the printer control thread, allowing for communication.
+pub struct Handle {
+    cmd_send: Sender<Message>,
+    thread_handle: ManuallyDrop<JoinHandle<()>>,
+}
+
+impl Handle {
+    /// Spawn a printer control thread, returning a handle
+    pub fn spawn() -> Self {
+        let (send, recv) = mpsc::channel(CHANNEL_CAPACITY);
+
+        let state = State { cmd_recv: recv };
+        let thread_handle = thread::spawn(move || {
+            let rt = runtime::Builder::new_current_thread()
+                .build()
+                .expect("error spawning printer control thread");
+
+            rt.block_on(async move { state.entrypoint().await });
+        });
+
+        Self {
+            cmd_send: send,
+            thread_handle: ManuallyDrop::new(thread_handle),
+        }
+    }
+}
+
+impl Drop for Handle {
+    fn drop(&mut self) {
+        let _ = self.cmd_send.blocking_send(Message::Quit);
+        unsafe {
+            info!("waiting for printer thread to exit...");
+            ManuallyDrop::take(&mut self.thread_handle)
+                .join()
+                .expect("error joining printer thread")
+        };
+    }
+}
+
+/// The state held by the printer control thread
+pub struct State {
+    cmd_recv: Receiver<Message>,
+}
+
+impl State {
+    /// The entrypoint of the printer control thread
+    pub async fn entrypoint(mut self) {
+        info!("listening for events");
+        while let Some(msg) = self.cmd_recv.recv().await {
+            match msg {
+                Message::Quit => break,
+            }
+        }
+    }
+}
diff --git a/crates/web/Cargo.toml b/crates/web/Cargo.toml
index 62a3504..2528a0a 100644
--- a/crates/web/Cargo.toml
+++ b/crates/web/Cargo.toml
@@ -4,6 +4,7 @@ version = "0.1.0"
 edition = "2021"
 
 [dependencies]
+argonaut-control = { path = "../control" }
 axum = "0.7.5"
 tracing = { workspace = true }
 tracing-subscriber = { workspace = true }
diff --git a/crates/web/src/main.rs b/crates/web/src/main.rs
index f641ce0..d80b232 100644
--- a/crates/web/src/main.rs
+++ b/crates/web/src/main.rs
@@ -1,17 +1,23 @@
-use axum::{
-    http::StatusCode,
-    routing::{get, post},
-    Json, Router,
-};
-use serde::{Deserialize, Serialize};
+use std::sync::Arc;
+
+use axum::{routing::get, Router};
+
+pub use argonaut_control::Handle as PrinterThread;
+use tracing::info;
 
 #[tokio::main(flavor = "current_thread")]
 async fn main() {
     tracing_subscriber::fmt::init();
 
-    let app = Router::new().route("/", get(root));
+    let printer_thread = PrinterThread::spawn();
+    let printer_thread = Arc::new(printer_thread);
 
+    let app = Router::new()
+        .route("/", get(root))
+        .with_state(printer_thread);
     let listener = tokio::net::TcpListener::bind("0.0.0.0:3000").await.unwrap();
+
+    info!("init completed, listening");
     axum::serve(listener, app).await.unwrap();
 }