Reload Tributaries

add_active_tributary writes the spec to disk before it returns, so even if the
VecDeque it pushes to isn't popped, the tributary will still be loaded on boot.

coordinator/src/db.rs

@@ -0,0 +1,44 @@
+pub use serai_db::*;
+
+use crate::tributary::TributarySpec;
+
+#[derive(Debug)]
+pub struct MainDb<D: Db>(pub D);
+impl<D: Db> MainDb<D> {
+  pub fn new(db: D) -> Self {
+    Self(db)
+  }
+
+  fn main_key(dst: &'static [u8], key: impl AsRef<[u8]>) -> Vec<u8> {
+    D::key(b"MAIN", dst, key)
+  }
+
+  fn acive_tributaries_key() -> Vec<u8> {
+    Self::main_key(b"active_tributaries", [])
+  }
+  pub fn active_tributaries(&self) -> (Vec<u8>, Vec<TributarySpec>) {
+    let bytes = self.0.get(Self::acive_tributaries_key()).unwrap_or(vec![]);
+    let mut bytes_ref: &[u8] = bytes.as_ref();
+
+    let mut tributaries = vec![];
+    while !bytes_ref.is_empty() {
+      tributaries.push(TributarySpec::read(&mut bytes_ref).unwrap());
+    }
+
+    (bytes, tributaries)
+  }
+  pub fn add_active_tributary(&mut self, spec: &TributarySpec) {
+    let key = Self::acive_tributaries_key();
+    let (mut existing_bytes, existing) = self.active_tributaries();
+    for tributary in &existing {
+      if tributary == spec {
+        return;
+      }
+    }
+
+    spec.write(&mut existing_bytes).unwrap();
+    let mut txn = self.0.txn();
+    txn.put(key, existing_bytes);
+    txn.commit();
+  }
+}