Fix handling of IO WouldBlock error in Stratum server

If WouldBlock error happens Stratum server drops part of a message to
read or write. This PR inroduces a worker's buffer to store partially
read message which will be completed next time. For write the existing
util function is used.
Fixes mimblewimble#2524

servers/src/mining/stratumserver.rs

@@ -152,6 +152,7 @@ pub struct Worker {
 	stream: BufStream<TcpStream>,
 	error: bool,
 	authenticated: bool,
+	buffer: String,
 }
 
 impl Worker {
@@ -164,15 +165,18 @@ impl Worker {
 			stream: stream,
 			error: false,
 			authenticated: false,
+			buffer: String::with_capacity(4096),
 		}
 	}
 
 	// Get Message from the worker
-	fn read_message(&mut self, line: &mut String) -> Option<usize> {
+	fn read_message(&mut self) -> Option<String> {
 		// Read and return a single message or None
-		match self.stream.read_line(line) {
-			Ok(n) => {
-				return Some(n);
+		match self.stream.read_line(&mut self.buffer) {
+			Ok(_) => {
+				let res = self.buffer.clone();
+				self.buffer.clear();
+				return Some(res);
 			}
 			Err(ref e) if e.kind() == ErrorKind::WouldBlock => {
 				// Not an error, just no messages ready
@@ -183,6 +187,7 @@ impl Worker {
 					"(Server ID: {}) Error in connection with stratum client: {}",
 					self.id, e
 				);
+				self.buffer.clear();
 				self.error = true;
 				return None;
 			}
@@ -195,7 +200,11 @@ impl Worker {
 		if !message.ends_with("\n") {
 			message += "\n";
 		}
-		match self.stream.write(message.as_bytes()) {
+		match util::read_write::write_all(
+			&mut self.stream,
+			message.as_bytes(),
+			Duration::from_secs(1),
+		) {
 			Ok(_) => match self.stream.flush() {
 				Ok(_) => {}
 				Err(e) => {
@@ -281,10 +290,9 @@ impl StratumServer {
 	// Handle an RPC request message from the worker(s)
 	fn handle_rpc_requests(&mut self, stratum_stats: &mut Arc<RwLock<StratumStats>>) {
 		let mut workers_l = self.workers.lock();
-		let mut the_message = String::with_capacity(4096);
 		for num in 0..workers_l.len() {
-			match workers_l[num].read_message(&mut the_message) {
-				Some(_) => {
+			match workers_l[num].read_message() {
+				Some(the_message) => {
 					// Decompose the request from the JSONRpc wrapper
 					let request: RpcRequest = match serde_json::from_str(&the_message) {
 						Ok(request) => request,
@@ -297,13 +305,10 @@ impl StratumServer {
 								the_message.as_bytes(),
 							);
 							workers_l[num].error = true;
-							the_message.clear();
 							continue;
 						}
 					};
 
-					the_message.clear();
-
 					let mut stratum_stats = stratum_stats.write();
 					let worker_stats_id = match stratum_stats
 						.worker_stats