feat(coap): auto-start CoAP server as needed

examples/coap-client/src/main.rs

@@ -5,15 +5,6 @@
 
 use ariel_os::debug::log::info;
 
-/// Run a CoAP stack without serving any actual resources.
-#[ariel_os::task(autostart)]
-async fn coap_run() {
-    use coap_handler_implementations::new_dispatcher;
-
-    let handler = new_dispatcher();
-    ariel_os::coap::coap_run(handler).await;
-}
-
 #[ariel_os::task(autostart)]
 async fn run_client_operations() {
     use coap_request::Stack;

laze-project.yml

@@ -785,6 +785,10 @@ modules:
     # will have their own entry point when they exist.
     depends:
       - coap
+    env:
+      global:
+        FEATURES:
+          - ariel-os/coap-server
 
   - name: coap-client
     help: Support for CoAP client functionality.

src/ariel-os-coap/Cargo.toml

@@ -29,6 +29,7 @@ lakers = { version = "0.7.2", default-features = false }
 ariel-os-debug.workspace = true
 ariel-os-embassy = { workspace = true, features = ["net"] }
 ariel-os-random = { workspace = true, features = ["csprng"] }
+ariel-os-macros = { path = "../ariel-os-macros" }
 static_cell = "2.1.0"
 
 # FIXME: Should go out eventually
@@ -43,9 +44,19 @@ embedded-io-async = "0.6.1"
 workspace = true
 
 [features]
+# Enables the coap_run function through which an own server is passed in. The
+# crate setting this must call `ariel_os{_,::}coap::coap_run()`; if not set,
+# that function is run with a default minimal server automatically (as is
+# required by the implementation to have client functionality).
+#
+# At the feature level, this is a bit of a misnomer, could also be
+# called "manual-server-start"; the name is chosen to align with
+# laze's name for this (where coap-server makes more sense).
+coap-server = []
+
 ## Enables an arbitrary set of features in dependencies where dependencies fail
 ## if no features are configured at all.
-doc = ["embassy-net/proto-ipv6", "embassy-net/medium-ip"]
+doc = ["embassy-net/proto-ipv6", "embassy-net/medium-ip", "coap-server"]
 
 ## Enables defmt logging of coapcore
 defmt = ["coapcore/defmt"]

src/ariel-os-coap/src/lib.rs

@@ -8,6 +8,8 @@
 #![no_std]
 #![deny(missing_docs)]
 #![deny(clippy::pedantic)]
+// for #[ariel_os_macros::task(autostart)]
+#![feature(impl_trait_in_assoc_type, used_with_arg)]
 
 // Moving work from https://github.com/embassy-rs/embassy/pull/2519 in here for the time being
 mod udp_nal;
@@ -63,7 +65,12 @@ mod demo_setup {
 /// # Panics
 ///
 /// This can only be run once, as it sets up a system wide CoAP handler.
+#[cfg(feature = "coap-server")]
 pub async fn coap_run(handler: impl coap_handler::Handler + coap_handler::Reporting) -> ! {
+    coap_run_impl(handler).await
+}
+
+async fn coap_run_impl(handler: impl coap_handler::Handler + coap_handler::Reporting) -> ! {
     static COAP: StaticCell<embedded_nal_coap::CoAPShared<CONCURRENT_REQUESTS>> = StaticCell::new();
 
     let stack = ariel_os_embassy::net::network_stack().await.unwrap();
@@ -155,3 +162,18 @@ pub async fn coap_client(
         .await // Not an actual await, just a convenient way to see which executor is running
         .expect("CoAP client can currently only be used from the thread the network is bound to")
 }
+
+/// Auto-started CoAP server that serves two purposes:
+///
+/// * It provides the backend for the CoAP client operation (which leaves message sending to that
+///   task).
+/// * It runs any CoAP server components provided by the OS (none yet).
+#[cfg(not(feature = "coap-server"))]
+#[ariel_os_macros::task(autostart)]
+async fn coap_run() {
+    use coap_handler_implementations::new_dispatcher;
+
+    // FIXME: Provide an "all system components" constructor in this crate.
+    let handler = new_dispatcher();
+    coap_run_impl(handler).await;
+}

src/ariel-os/Cargo.toml

@@ -59,6 +59,13 @@ dns = ["ariel-os-embassy/dns"]
 mdns = ["ariel-os-embassy/mdns"]
 ## Enables support for [CoAP](https://ariel-os.github.io/ariel-os/dev/docs/book/tooling/coap.html).
 coap = ["dep:ariel-os-coap", "random"]
+## Support for applications to set up own CoAP server handlers.
+##
+## When an application selects this, it needs to run `ariel_os::coap_run()`
+## in a task; otherwise, other components (eg. system components that also
+## run on the CoAP server, or the CoAP client that depends on the server
+## loop to run) get stalled.
+coap-server = ["coap", "ariel-os-coap/coap-server"]
 ## Selects static IP configuration.
 network-config-static = ["ariel-os-embassy/network-config-static"]