cln_plugin: Example package subscribing to "*"

Creates an example package that subscribes to all notifications and logs
them. This is useful for testing the behavior of subscribing to "*".

I've also edited the Makefile to ensure that `make` builds the example
and that `make clean` removes the example

plugins/Makefile

@@ -254,10 +254,14 @@ PLUGIN_BASES := $(PLUGINS:plugins/%=%) $(PY_PLUGINS:plugins/%=%)
 plugins/list_of_builtin_plugins_gen.h: plugins/Makefile Makefile config.vars
 	@$(call VERBOSE,GEN $@,echo "static const char *list_of_builtin_plugins[] = { $(PLUGIN_BASES:%=\"%\",) NULL };" > $@)
 
+target/${RUST_PROFILE}/examples/cln-subscribe-wildcard: ${CLN_PLUGIN_SRC} plugins/examples/cln-subscribe-wildcard.rs
+	cargo build ${CARGO_OPTS} --example cln-subscribe-wildcard
+
 CLN_PLUGIN_EXAMPLES := \
 	target/${RUST_PROFILE}/examples/cln-plugin-startup \
 	target/${RUST_PROFILE}/examples/cln-plugin-reentrant \
-	target/${RUST_PROFILE}/examples/cln-rpc-getinfo
+	target/${RUST_PROFILE}/examples/cln-rpc-getinfo \
+	target/${RUST_PROFILE}/examples/cln-subscribe-wildcard
 
 CLN_PLUGIN_SRC = $(shell find plugins/src -name "*.rs")
 

plugins/examples/cln-subscribe-wildcard.rs

@@ -0,0 +1,35 @@
+/// This plug-in subscribes to the wildcard-notifications
+/// and creates a corresponding log-entry
+
+use anyhow::Result;
+use cln_plugin::{Builder, Plugin};
+
+#[tokio::main]
+async fn main() -> Result<()> {
+    let state = ();
+
+    let configured = Builder::new(tokio::io::stdin(), tokio::io::stdout())
+        .subscribe("*", handle_wildcard_notification)
+        .start(state)
+        .await?;
+
+    match configured {
+	Some(p) => p.join().await?,
+	None => return Ok(()) // cln was started with --help
+    };
+
+    Ok(())
+}
+
+async fn handle_wildcard_notification(_plugin: Plugin<()>, value : serde_json::Value) -> Result<()> {
+    let notification_type : String = value
+	.as_object()
+	.unwrap()
+	.keys()
+	.next()
+	.unwrap()
+	.into();
+
+    log::info!("Received notification {}", notification_type);
+    Ok(())
+}