Implement viewing of the scrollback buffer in a separate window

README.asciidoc

@@ -32,6 +32,7 @@
 :sc_scroll_page_up: pass:quotes[`ctrl+shift+page_up`]
 :sc_second_window: pass:quotes[`ctrl+shift+2`]
 :sc_seventh_window: pass:quotes[`ctrl+shift+7`]
+:sc_show_scrollback: pass:quotes[`ctrl+shift+h`]
 :sc_sixth_window: pass:quotes[`ctrl+shift+6`]
 :sc_tenth_window: pass:quotes[`ctrl+shift+0`]
 :sc_third_window: pass:quotes[`ctrl+shift+3`]
@@ -49,6 +50,9 @@ layouts without needing to use an extra program like tmux
 * Supports all modern terminal features: unicode, true-color, mouse
 protocol, focus tracking, bracketed paste and so on.
 
+* Allows you to view the scrollback buffer in a separate window
+using your favorite pager program such as less
+
 * Easily hackable (UI layer written in python, inner loops in C for
 speed). Less than ten thousand lines of code.
 
@@ -121,6 +125,7 @@ different layouts, like windows are organized in a tiling window
 manager. The keyboard controls (which are all customizable) for tabs and
 windows are:
 
+[[scrolling-shortcuts]]
 [options="header"]
 .Scrolling
 |===
@@ -168,6 +173,20 @@ windows are:
 |===
 
 
+== The scrollback buffer
+
+kitty supports scrolling back to view history, just like most terminals. You
+can use either the <<scrolling-shortcuts,keyboard shortcuts>> or the mouse
+scroll wheel to do so.  However, kitty has an extra, neat feature. Sometime you
+need to explore the scrollback buffer in more detail, maybe search for some
+text or refer to it side-by-side while typing in a follow-up command. kitty
+allows you to do this by pressing the {sc_show_scrollback} key-combination,
+which will open the scrollback buffer in a new window, using your favorite
+pager program (which is less by default). You can then explore the scrollback
+buffer using whatever program you normally use. Colors and text formatting are
+preserved.
+
+
 == Configuration
 
 kitty is highly customizable, everything from keyboard shortcuts, to

kitty/boss.py

@@ -12,6 +12,7 @@ from functools import wraps
 from threading import Thread, current_thread
 from time import monotonic
 from queue import Queue, Empty
+from gettext import gettext as _
 
 from .constants import (
     viewport_size, set_boss, wakeup, cell_size, MODIFIER_KEYS,
@@ -29,7 +30,7 @@ from .constants import is_key_pressed
 from .keys import interpret_text_event, interpret_key_event, get_shortcut
 from .session import create_session
 from .shaders import Sprites, ShaderProgram
-from .tabs import TabManager
+from .tabs import TabManager, SpecialWindow
 from .timers import Timers
 from .utils import handle_unix_signals
 
@@ -291,6 +292,14 @@ class Boss(Thread):
             yield w
             w.focus_changed(focused)
 
+    def display_scrollback(self, data):
+        if self.opts.scrollback_in_new_tab:
+            self.queue_ui_action(self.display_scrollback_in_new_tab, data)
+        else:
+            tab = self.active_tab
+            if tab is not None:
+                tab.new_special_window(SpecialWindow(self.opts.scrollback_pager, data, _('History')))
+
     def window_for_pos(self, x, y):
         tab = self.active_tab
         if tab is not None:
@@ -454,4 +463,7 @@ class Boss(Thread):
 
     def move_tab_backward(self):
         self.queue_action(self.tab_manager.move_tab, -1)
+
+    def display_scrollback_in_new_tab(self, data):
+        self.tab_manager.new_tab(special_window=SpecialWindow(self.opts.scrollback_pager, data, _('History')))
     # }}}

kitty/char_grid.py

@@ -412,6 +412,12 @@ class CharGrid:
             if ps:
                 set_primary_selection(ps)
 
+    def get_scrollback_as_ansi(self):
+        ans = []
+        self.screen.historybuf.as_ansi(ans.append)
+        self.screen.linebuf.as_ansi(ans.append)
+        return ''.join(ans).encode('utf-8')
+
     def text_for_selection(self, sel=None):
         s = sel or self.current_selection
         return s.text(self.screen.linebuf, self.screen.historybuf)

kitty/child.py

@@ -7,27 +7,37 @@ import termios
 import struct
 import fcntl
 import signal
+from threading import Thread
 
 from .constants import terminfo_dir
 
 
+def remove_cloexec(fd):
+    fcntl.fcntl(fd, fcntl.F_SETFD, fcntl.fcntl(fd, fcntl.F_GETFD) & ~fcntl.FD_CLOEXEC)
+
+
 class Child:
 
     child_fd = pid = None
     forked = False
 
-    def __init__(self, argv, cwd, opts):
+    def __init__(self, argv, cwd, opts, stdin=None):
         self.argv = argv
         self.cwd = os.path.abspath(os.path.expandvars(os.path.expanduser(cwd or os.getcwd())))
         self.opts = opts
+        self.stdin = stdin
 
     def fork(self):
         if self.forked:
             return
         self.forked = True
-        master, slave = os.openpty()
+        master, slave = os.openpty()  # Note that master and slave are in blocking mode
-        fcntl.fcntl(slave, fcntl.F_SETFD, fcntl.fcntl(slave, fcntl.F_GETFD) & ~fcntl.FD_CLOEXEC)
+        remove_cloexec(slave)
-        # Note that master and slave are in blocking mode
+        stdin, self.stdin = self.stdin, None
+        if stdin is not None:
+            stdin_read_fd, stdin_write_fd = os.pipe()
+            remove_cloexec(stdin_read_fd)
+            stdin_file = os.fdopen(stdin_write_fd, 'wb')
         pid = os.fork()
         if pid == 0:  # child
             try:
@@ -36,6 +46,10 @@ class Child:
                 os.chdir('/')
             os.setsid()
             for i in range(3):
+                if stdin is not None and i == 0:
+                    os.dup2(stdin_read_fd, i)
+                    os.close(stdin_read_fd), os.close(stdin_write_fd)
+                else:
                     os.dup2(slave, i)
             os.close(slave), os.close(master)
             os.closerange(3, 200)
@@ -55,6 +69,10 @@ class Child:
             os.close(slave)
             self.pid = pid
             self.child_fd = master
+            if stdin is not None:
+                t = Thread(name='WriteStdin', target=stdin_file.write, args=(stdin,))
+                t.daemon = True
+                t.start()
             return pid
 
     def resize_pty(self, w, h):

kitty/config.py

@@ -5,6 +5,7 @@
 import re
 import sys
 import os
+import shlex
 from collections import namedtuple
 
 from .fast_data_types import (
@@ -91,6 +92,8 @@ def to_layout_names(raw):
 
 type_map = {
     'scrollback_lines': int,
+    'scrollback_pager': shlex.split,
+    'scrollback_in_new_tab': to_bool,
     'font_size': to_font_size,
     'cursor_shape': to_cursor_shape,
     'cursor_opacity': to_opacity,

kitty/kitty.conf

@@ -38,6 +38,14 @@ cursor_stop_blinking_after 15.0
 # Number of lines of history to keep in memory for scrolling back
 scrollback_lines 2000
 
+# Program with which to view scrollback in a new window. The scrollback buffer is passed as
+# STDIN to this program. If you change it, make sure the program you use can
+# handle ANSI escape sequences for colors and text formatting.
+scrollback_pager less +G -R
+
+# When viewing scrollback in a new window, put it in a new tab as well
+scrollback_in_new_tab no
+
 # Wheel scroll multiplier (modify the amount scrolled by the mouse wheel)
 wheel_scroll_multiplier 5.0
 
@@ -139,6 +147,7 @@ map ctrl+shift+page_up   scroll_page_up
 map ctrl+shift+page_down scroll_page_down
 map ctrl+shift+home      scroll_home
 map ctrl+shift+end       scroll_end
+map ctrl+shift+h         show_scrollback
 
 # Window management
 map ctrl+shift+enter    new_window

kitty/tabs.py

@@ -18,9 +18,13 @@ from .borders import Borders
 from .window import Window
 
 
+def SpecialWindow(cmd, stdin=None, override_title=None):
+    return (cmd, stdin, override_title)
+
+
 class Tab:
 
-    def __init__(self, opts, args, on_title_change, session_tab=None):
+    def __init__(self, opts, args, on_title_change, session_tab=None, special_window=None):
         self.opts, self.args = opts, args
         self.name = getattr(session_tab, 'name', '')
         self.on_title_change = on_title_change
@@ -31,7 +35,10 @@ class Tab:
         if session_tab is None:
             self.cwd = args.directory
             l = self.enabled_layouts[0]
+            if special_window is None:
                 queue_action(self.new_window)
+            else:
+                queue_action(self.new_special_window, special_window)
         else:
             self.cwd = session_tab.cwd or args.directory
             l = session_tab.layout
@@ -86,23 +93,29 @@ class Tab:
                 w.is_visible_in_layout = True
             self.relayout()
 
-    def launch_child(self, use_shell=False, cmd=None):
+    def launch_child(self, use_shell=False, cmd=None, stdin=None):
         if cmd is None:
             if use_shell:
                 cmd = [shell_path]
             else:
                 cmd = self.args.args or [shell_path]
-        ans = Child(cmd, self.cwd, self.opts)
+        ans = Child(cmd, self.cwd, self.opts, stdin)
         ans.fork()
         return ans
 
-    def new_window(self, use_shell=True, cmd=None):
+    def new_window(self, use_shell=True, cmd=None, stdin=None, override_title=None):
-        child = self.launch_child(use_shell=use_shell, cmd=cmd)
+        child = self.launch_child(use_shell=use_shell, cmd=cmd, stdin=stdin)
         window = Window(self, child, self.opts, self.args)
+        if override_title is not None:
+            window.title = window.override_title = override_title
         get_boss().add_child_fd(child.child_fd, window.read_ready, window.write_ready)
         self.active_window_idx = self.current_layout.add_window(self.windows, window, self.active_window_idx)
         self.borders(self.windows, self.active_window, self.current_layout.needs_window_borders and len(self.windows) > 1)
         glfw_post_empty_event()
+        return window
+
+    def new_special_window(self, special_window):
+        self.new_window(False, *special_window)
 
     def close_window(self):
         if self.windows:
@@ -241,9 +254,9 @@ class TabManager:
     def __len__(self):
         return len(self.tabs)
 
-    def new_tab(self):
+    def new_tab(self, special_window=None):
         self.active_tab_idx = len(self.tabs)
-        self.tabs.append(Tab(self.opts, self.args, self.title_changed))
+        self.tabs.append(Tab(self.opts, self.args, self.title_changed, special_window=special_window))
 
     @property
     def active_tab(self):

kitty/window.py

@@ -27,6 +27,7 @@ class Window:
 
     def __init__(self, tab, child, opts, args):
         self.tabref = weakref.ref(tab)
+        self.override_title = None
         self.last_mouse_cursor_pos = 0, 0
         self.destroyed = False
         self.click_queue = deque(maxlen=3)
@@ -117,6 +118,7 @@ class Window:
                 self.write_to_child(b'\x1b[O')
 
     def title_changed(self, new_title):
+        if self.override_title is not None:
             self.title = sanitize_title(new_title or appname)
             t = self.tabref()
             if t is not None:
@@ -260,6 +262,10 @@ class Window:
 
     # actions {{{
 
+    def show_scrollback(self):
+        data = self.char_grid.get_scrollback_as_ansi()
+        get_boss().display_scrollback(data)
+
     def paste(self, text):
         if text and not self.destroyed:
             if isinstance(text, str):