make file creation lazy so that there are no more 0-byte files

src/main.rs

@@ -60,13 +60,9 @@ impl server::Server for Server {
         );
         let path = Path::new(path);
         create_dir_all(path.parent().unwrap()).unwrap();
-        let file = OpenOptions::new()
-            .create(true)
-            .append(true)
-            .open(path)
-            .unwrap();
         Handler {
-            file,
+            filename: path.display().to_string(),
+            lazy_file: None,
             buffer: vec![],
             user: "root".into(),
         }
@@ -79,12 +75,25 @@ fn send_str(session: &mut Session, channel: ChannelId, s: String) {
 }
 
 struct Handler {
-    file: File,
+    filename: String,
+    lazy_file: Option<File>,
     buffer: Vec<u8>,
     user: String,
 }
 
 impl Handler {
+    fn file(&mut self) -> &mut File {
+        if self.lazy_file.is_none() {
+            let file = OpenOptions::new()
+                .create(true)
+                .append(true)
+                .open(&self.filename)
+                .unwrap();
+            self.lazy_file = Some(file);
+        }
+        self.lazy_file.as_mut().unwrap()
+    }
+
     fn send_prompt(&self, session: &mut Session, channel: ChannelId) {
         send_str(session, channel, format!("{}@fnordister:~$ ", self.user));
     }
@@ -145,7 +154,7 @@ impl server::Handler for Handler {
 
     fn exec_request(mut self, channel: ChannelId, data: &[u8], mut session: Session) -> Self::FutureUnit {
         info!("exec_request");
-        writeln!(self.file, "Execute: {}\n", String::from_utf8_lossy(data))
+        writeln!(self.file(), "Execute: {}\n", String::from_utf8_lossy(data))
             .unwrap();
 
         let line = String::from_utf8_lossy(data).into();
@@ -166,21 +175,21 @@ impl server::Handler for Handler {
         session: Session
     ) -> Self::FutureUnit {
         info!("subsystem_request");
-        writeln!(self.file, "Subsystem requested: {}\n", name)
+        writeln!(self.file(), "Subsystem requested: {}\n", name)
             .unwrap();
 
         self.finished(session)
     }
 
     fn auth_password(mut self, user: &str, password: &str) -> Self::FutureAuth {
-        writeln!(self.file, "Authenticated as {} with {}\n", user, password)
+        writeln!(self.file(), "Authenticated as {} with {}\n", user, password)
             .unwrap();
         self.user = user.into();
         self.finished_auth(server::Auth::Accept)
     }
 
     fn data(mut self, channel: ChannelId, data: &[u8], mut session: Session) -> Self::FutureUnit {
-        self.file.write(data)
+        self.file().write(data)
             .unwrap();
         // echo input back
         session.data(channel, data.to_vec().into());