Keep network status & ring in a tokio::sync::watch

advantages
- reads don't prevent preparing writes
- can be followed from other parts of the system by cloning the receiver

src/block.rs

@@ -1,15 +1,14 @@
 use std::path::PathBuf;
 
+use futures_util::future::*;
 use tokio::fs;
 use tokio::prelude::*;
 use tokio::sync::Mutex;
-use futures_util::future::*;
 
+use crate::background::*;
 use crate::data::*;
 use crate::error::Error;
 use crate::proto::*;
-use crate::background::*;
-
 
 pub struct BlockManager {
 	pub data_dir: PathBuf,
@@ -19,10 +18,11 @@ pub struct BlockManager {
 
 impl BlockManager {
 	pub fn new(db: &sled::Db, data_dir: PathBuf) -> Self {
-		let rc = db.open_tree("block_local_rc")
+		let rc = db
+			.open_tree("block_local_rc")
 			.expect("Unable to open block_local_rc tree");
 		rc.set_merge_operator(rc_merge);
-		Self{
+		Self {
 			rc,
 			data_dir,
 			lock: Mutex::new(()),
@@ -81,18 +81,20 @@ impl BlockManager {
 				background.spawn(tokio::fs::remove_file(path).map_err(Into::into));
 				Ok(())
 			}
-			Some(_) => Ok(())
+			Some(_) => Ok(()),
 		}
 	}
 }
 
 fn rc_merge(_key: &[u8], old: Option<&[u8]>, new: &[u8]) -> Option<Vec<u8>> {
-	let old = old.map(|x| {
-		assert!(x.len() == 8);
-		let mut x8 = [0u8; 8];
-		x8.copy_from_slice(x);
-		u64::from_be_bytes(x8)
-	}).unwrap_or(0);
+	let old = old
+		.map(|x| {
+			assert!(x.len() == 8);
+			let mut x8 = [0u8; 8];
+			x8.copy_from_slice(x);
+			u64::from_be_bytes(x8)
+		})
+		.unwrap_or(0);
 	assert!(new.len() == 1);
 	let new = match new[0] {
 		0 => {