Refactor to split client from server

crates/musicfs-server/src/server/transport/mod.rs

@@ -0,0 +1,39 @@
+pub mod grpc;
+
+use std::net::SocketAddr;
+
+use anyhow::{Result, anyhow};
+use async_trait::async_trait;
+use tokio::sync::broadcast::Receiver;
+
+use crate::server::state::ServerState;
+use crate::server::watcher::ChangeEvent;
+
+/// Transport-agnostic musicfs server. A single implementation is wired in
+/// today (`grpc`); the factory in [`build`] is the seam where additional
+/// transports (HTTP/3, raw QUIC, in-process for tests, ...) get plugged in
+/// without touching the binary.
+///
+/// `run` consumes `self` — a transport serves exactly once. It receives the
+/// shared [`ServerState`] and a fresh broadcast receiver for change events.
+#[async_trait]
+pub trait MusicTransport: Send + Sync + 'static {
+    async fn run(self: Box<Self>, state: ServerState, events: Receiver<ChangeEvent>) -> Result<()>;
+}
+
+/// Arguments every transport understands. Transports may extend this with
+/// their own configuration via their constructors.
+#[derive(Debug, Clone, Copy)]
+pub struct TransportArgs {
+    pub listen: SocketAddr,
+}
+
+/// Construct the named transport. The list of accepted names is intentionally
+/// discoverable (a single match arm) so adding a transport means adding an
+/// arm here plus a module under `transport/`.
+pub fn build(name: &str, args: TransportArgs) -> Result<Box<dyn MusicTransport>> {
+    return match name {
+        "grpc" => Ok(Box::new(grpc::GrpcTransport::new(args))),
+        other => Err(anyhow!("unknown transport: {other}")),
+    };
+}