Merge pull request #11 from ttak0422/fix/snapshot-output-duplicate-rendering

fix: prevent duplicate rendering when attaching via :Pterm

Author: ttak0422

README.md

@@ -90,7 +90,8 @@ require("pterm").setup({
   binary = nil,
   -- Default shell command
   shell = vim.env.SHELL or "/bin/sh",
-  -- Fallback terminal size (Neovim window size takes priority)
+  -- Default terminal size for `pterm new` when created outside Neovim
+  -- (the bridge reads the actual PTY size via TIOCGWINSZ at attach time)
   cols = 80,
   rows = 24,
   -- Socket directory (nil = let daemon decide)

docs/DESIGN.md

@@ -78,7 +78,7 @@ Notable behavior:
 - session socket path: `<socket_root>/<session>/socket`
 - if socket file is removed externally, daemon treats session as deleted and exits
 - output delivery uses per-client send queues and writable polling to avoid disconnecting on backpressure (`WouldBlock`)
-- **snapshot delivery**: no timer-based deferral; snapshot is sent either when the client sends RESIZE (correct dimensions) or when the first PTY OUTPUT arrives (current dimensions as fallback)
+- **snapshot delivery**: no timer-based deferral; snapshot is sent either when the client sends RESIZE (correct dimensions) or when the first PTY OUTPUT arrives (current dimensions as fallback). Clients that receive a snapshot are excluded from the same flush cycle's OUTPUT broadcast to prevent duplicate rendering (the snapshot already reflects the effect of those bytes)
 - **drain-and-flush**: PTY output uses non-blocking drain (reads until `WouldBlock`) followed by immediate flush — no timer-based micro-batching, minimizing latency while naturally coalescing bytes available at each poll cycle
 - EXIT message is queued into `send_buf` (not written directly) to preserve OUTPUT→EXIT ordering under backpressure, and is sent exactly once via an `exit_sent` guard
 

lua/pterm/init.lua

@@ -174,17 +174,17 @@ function M.open(session_name, args)
 			end
 		end
 
-		local win_cols = vim.api.nvim_win_get_width(0)
-		local win_rows = vim.api.nvim_win_get_height(0)
-
+		-- Do NOT pass --cols/--rows to `pterm new` here.  The bridge
+		-- (started by M.attach) will send an accurate RESIZE based on
+		-- the actual PTY size after terminal-friendly window options
+		-- (number=false, signcolumn=no, …) have been applied.  Passing
+		-- dimensions at this point would use the pre-option window size,
+		-- which may differ and trigger an unnecessary resize + snapshot
+		-- race on the daemon side.
 		local create_cmd = {
 			bin,
 			"new",
 			session_name,
-			"--cols",
-			tostring(win_cols),
-			"--rows",
-			tostring(win_rows),
 		}
 
 		if #cmd_parts > 0 then
@@ -249,15 +249,13 @@ function M.attach(session_name)
 	vim.api.nvim_set_option_value("foldcolumn", "0", { win = win })
 	vim.api.nvim_set_option_value("statuscolumn", "", { win = win })
 
-	-- Pass the current window size so the bridge sends an accurate initial
-	-- RESIZE before the daemon generates the snapshot.
-	local win_cols = vim.api.nvim_win_get_width(win)
-	local win_rows = vim.api.nvim_win_get_height(win)
-
+	-- Let the bridge read the actual PTY size via TIOCGWINSZ instead of
+	-- passing --cols/--rows from Lua.  jobstart({term=true}) creates a PTY
+	-- sized to the current window, and the bridge's get_winsize(stdout)
+	-- will return exactly that size.  This avoids any mismatch between the
+	-- Lua-reported dimensions and the real PTY geometry.
 	local job_id = vim.fn.jobstart({
 		bin, "attach", session_name,
-		"--cols", tostring(win_cols),
-		"--rows", tostring(win_rows),
 	}, {
 		term = true,
 		on_exit = function(_, exit_code, _)

src/server.rs

@@ -253,17 +253,22 @@ impl Server {
 
         // Clients awaiting snapshot: the arrival of OUTPUT means the VT state
         // is populated, so send their snapshot now (no timer needed).
+        // These clients must NOT also receive the raw OUTPUT bytes below,
+        // because the snapshot already reflects the effect of those bytes
+        // (read_pty feeds data to the VT parser before this method runs).
+        // Sending both would cause Neovim's libvterm to process the same
+        // content twice, resulting in duplicated rendering.
         let snapshot_ids: Vec<usize> = self
             .clients
             .iter()
             .filter_map(|(&id, c)| if c.pending_snapshot { Some(id) } else { None })
             .collect();
-        for id in snapshot_ids {
+        for id in &snapshot_ids {
             log::info!(
                 "Client {} snapshot triggered by PTY output arrival",
-                id
+                *id
             );
-            self.send_snapshot_to_client(id);
+            self.send_snapshot_to_client(*id);
         }
 
         let msg = proto::encode(proto::server::OUTPUT, &self.pending_pty_output);
@@ -272,6 +277,11 @@ impl Server {
         let mut disconnected = Vec::new();
         let mut flush_ids = Vec::new();
         for (&id, client) in self.clients.iter_mut() {
+            // Skip clients that just received a snapshot — they already have
+            // the up-to-date screen state and must not get the raw bytes again.
+            if snapshot_ids.contains(&id) {
+                continue;
+            }
             client.send_buf.extend_from_slice(&msg);
             flush_ids.push(id);
         }