Feature: Configurable scroll buffer (#936)

* Configurable scroll buffer

* Fix unit test failures

* Add scroll_buffer_size description in the default config file

* Fix config file

zellij-server/src/lib.rs

@@ -37,6 +37,7 @@ use route::route_thread_main;
 use zellij_utils::{
     channels::{self, ChannelWithContext, SenderWithContext},
     cli::CliArgs,
+    consts::{DEFAULT_SCROLL_BUFFER_SIZE, SCROLL_BUFFER_SIZE},
     errors::{ContextType, ErrorInstruction, ServerContext},
     input::{
         command::{RunCommand, TerminalAction},
@@ -541,6 +542,15 @@ fn init_session(
         layout,
         plugins,
     } = options;
+
+    SCROLL_BUFFER_SIZE
+        .set(
+            config_options
+                .scroll_buffer_size
+                .unwrap_or(DEFAULT_SCROLL_BUFFER_SIZE),
+        )
+        .unwrap();
+
     let (to_screen, screen_receiver): ChannelWithContext<ScreenInstruction> = channels::unbounded();
     let to_screen = SenderWithContext::new(to_screen);
 

zellij-server/src/panes/grid.rs

@@ -7,10 +7,13 @@ use std::{
     str,
 };
 
-use zellij_utils::{position::Position, vte, zellij_tile};
+use zellij_utils::{
+    consts::{DEFAULT_SCROLL_BUFFER_SIZE, SCROLL_BUFFER_SIZE},
+    position::Position,
+    vte, zellij_tile,
+};
 
 const TABSTOP_WIDTH: usize = 8; // TODO: is this always right?
-pub const SCROLL_BACK: usize = 10_000;
 pub const MAX_TITLE_STACK_SIZE: usize = 1000;
 
 use vte::{Params, Perform};
@@ -226,7 +229,7 @@ fn transfer_rows_from_lines_below_to_viewport(
 
 fn bounded_push(vec: &mut VecDeque<Row>, value: Row) -> Option<usize> {
     let mut dropped_line_width = None;
-    if vec.len() >= SCROLL_BACK {
+    if vec.len() >= *SCROLL_BUFFER_SIZE.get().unwrap() {
         let line = vec.pop_front();
         if let Some(line) = line {
             dropped_line_width = Some(line.width());
@@ -419,7 +422,11 @@ impl Debug for Grid {
 impl Grid {
     pub fn new(rows: usize, columns: usize, colors: Palette) -> Self {
         Grid {
-            lines_above: VecDeque::with_capacity(SCROLL_BACK),
+            lines_above: VecDeque::with_capacity(
+                // .get_or_init() is used instead of .get().unwrap() to prevent
+                // unit tests from panicking where SCROLL_BUFFER_SIZE is uninitialized.
+                *SCROLL_BUFFER_SIZE.get_or_init(|| DEFAULT_SCROLL_BUFFER_SIZE),
+            ),
             viewport: vec![Row::new(columns).canonical()],
             lines_below: vec![],
             horizontal_tabstops: create_horizontal_tabstops(columns),
@@ -1350,7 +1357,7 @@ impl Grid {
         self.should_render = true;
     }
     fn reset_terminal_state(&mut self) {
-        self.lines_above = VecDeque::with_capacity(SCROLL_BACK);
+        self.lines_above = VecDeque::with_capacity(*SCROLL_BUFFER_SIZE.get().unwrap());
         self.lines_below = vec![];
         self.viewport = vec![Row::new(self.width).canonical()];
         self.alternative_lines_above_viewport_and_cursor = None;
@@ -1849,7 +1856,7 @@ impl Perform for Grid {
                     Some(1049) => {
                         let current_lines_above = std::mem::replace(
                             &mut self.lines_above,
-                            VecDeque::with_capacity(SCROLL_BACK),
+                            VecDeque::with_capacity(*SCROLL_BUFFER_SIZE.get().unwrap()),
                         );
                         let current_viewport = std::mem::replace(
                             &mut self.viewport,

zellij-utils/Cargo.toml

@@ -20,7 +20,7 @@ interprocess = "1.1.1"
 lazy_static = "1.4.0"
 libc = "0.2"
 nix = "0.19.1"
-once_cell = "1.7.2"
+once_cell = "1.8.0"
 serde = { version = "1.0", features = ["derive"] }
 serde_yaml = "0.8"
 serde_json = "1.0"

zellij-utils/assets/config/default.yaml

@@ -461,3 +461,10 @@ plugins:
 #   - true (default)
 #   - false
 #mouse_mode: false
+
+# Configure the scroll back buffer size
+# This is the number of lines zellij stores for each pane in the scroll back
+# buffer. Excess number of lines are discarded in a FIFO fashion.
+# Valid values: positive integers
+# Default value: 10000
+#scroll_buffer_size: 10000

zellij-utils/src/consts.rs

@@ -5,6 +5,7 @@ use crate::shared::set_permissions;
 use directories_next::ProjectDirs;
 use lazy_static::lazy_static;
 use nix::unistd::Uid;
+use once_cell::sync::OnceCell;
 use std::path::PathBuf;
 use std::{env, fs};
 
@@ -12,6 +13,8 @@ pub const ZELLIJ_CONFIG_FILE_ENV: &str = "ZELLIJ_CONFIG_FILE";
 pub const ZELLIJ_CONFIG_DIR_ENV: &str = "ZELLIJ_CONFIG_DIR";
 pub const ZELLIJ_LAYOUT_DIR_ENV: &str = "ZELLIJ_LAYOUT_DIR";
 pub const VERSION: &str = env!("CARGO_PKG_VERSION");
+pub const DEFAULT_SCROLL_BUFFER_SIZE: usize = 10_000;
+pub static SCROLL_BUFFER_SIZE: OnceCell<usize> = OnceCell::new();
 
 pub const SYSTEM_DEFAULT_CONFIG_DIR: &str = "/etc/zellij";
 pub const SYSTEM_DEFAULT_DATA_DIR_PREFIX: &str = system_default_data_dir();

zellij-utils/src/input/options.rs

@@ -72,6 +72,8 @@ pub struct Options {
     /// Set behaviour on force close (quit or detach)
     #[structopt(long)]
     pub on_force_close: Option<OnForceClose>,
+    #[structopt(long)]
+    pub scroll_buffer_size: Option<usize>,
 }
 
 impl Options {
@@ -96,6 +98,7 @@ impl Options {
         let layout_dir = other.layout_dir.or_else(|| self.layout_dir.clone());
         let theme = other.theme.or_else(|| self.theme.clone());
         let on_force_close = other.on_force_close.or(self.on_force_close);
+        let scroll_buffer_size = other.scroll_buffer_size.or(self.scroll_buffer_size);
 
         Options {
             simplified_ui,
@@ -107,6 +110,7 @@ impl Options {
             pane_frames,
             mirror_session,
             on_force_close,
+            scroll_buffer_size,
         }
     }
 
@@ -135,6 +139,7 @@ impl Options {
         let layout_dir = other.layout_dir.or_else(|| self.layout_dir.clone());
         let theme = other.theme.or_else(|| self.theme.clone());
         let on_force_close = other.on_force_close.or(self.on_force_close);
+        let scroll_buffer_size = other.scroll_buffer_size.or(self.scroll_buffer_size);
 
         Options {
             simplified_ui,
@@ -146,6 +151,7 @@ impl Options {
             pane_frames,
             mirror_session,
             on_force_close,
+            scroll_buffer_size,
         }
     }
 
@@ -193,6 +199,7 @@ impl From<CliOptions> for Options {
             pane_frames: opts.pane_frames,
             mirror_session: opts.mirror_session,
             on_force_close: opts.on_force_close,
+            scroll_buffer_size: opts.scroll_buffer_size,
         }
     }
 }