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Optimize screenshot updates using pyte dirty tracking

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- get_screen_state() now returns has_changes flag indicating if screen changed
- pyte's dirty set tracks which rows have been modified since last read
- Screenshot handler returns cached SVG immediately when no changes detected
- Removed _screenshot_last_rendered_activity tracking (replaced by dirty flag)
- Added test for dirty flag behavior

Bump version to 0.1.16
This commit is contained in:
GitHub Copilot
2026-01-24 11:27:33 +00:00
parent 8ae3f77f23
commit ff8f5efabd
5 changed files with 54 additions and 34 deletions
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pyproject.toml
+1 -1
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@@ -1,6 +1,6 @@
[tool.poetry]
name = "textual-webterm"
version = "0.1.15"
version = "0.1.16"
description = "Serve terminal sessions over the web"
authors = ["Will McGugan <will@textualize.io>"]
license = "MIT"
src/textual_webterm/local_server.py
+8 -21
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@@ -211,7 +211,6 @@ class LocalServer:
self._screenshot_cache_etag: dict[str, str] = {}
self._screenshot_locks: dict[str, asyncio.Lock] = {}
self._route_last_activity: dict[str, float] = {}
self._screenshot_last_rendered_activity: dict[str, float] = {}
@property
def app_count(self) -> int:
@@ -516,30 +515,21 @@ class LocalServer:
if session_process is None or not hasattr(session_process, "get_screen_state"):
raise web.HTTPNotFound(text="Session not found")
# If nothing has changed since the last render, serve cached screenshot without
# touching the session replay buffer.
last_activity = self._route_last_activity.get(route_key, 0.0)
last_rendered_activity = self._screenshot_last_rendered_activity.get(route_key, -1.0)
if last_activity <= last_rendered_activity:
# Get the actual screen state from the terminal session's pyte screen
# This includes has_changes flag from pyte's dirty tracking
screen_width, screen_height, screen_buffer, has_changes = await session_process.get_screen_state() # type: ignore[union-attr]
# If screen hasn't changed, serve cached screenshot immediately
cached = self._screenshot_cache.get(route_key)
if cached is not None and not has_changes:
cached_response = self._get_cached_screenshot_response(request, route_key)
if cached_response is not None:
return cached_response
# Get the actual screen state from the terminal session's pyte screen
# This uses the correct dimensions that match what the terminal is rendering
screen_width, screen_height, screen_buffer = await session_process.get_screen_state() # type: ignore[union-attr]
now = asyncio.get_event_loop().time()
ttl = self._get_screenshot_cache_ttl(route_key, now)
cached = self._screenshot_cache.get(route_key)
# If we have a cached screenshot and the session is idle, keep serving it until
# new activity occurs (no periodic re-render).
if cached is not None and self._route_last_activity.get(route_key, 0.0) == 0.0:
cached_response = self._get_cached_screenshot_response(request, route_key)
if cached_response is not None:
return cached_response
# Also check time-based cache for recently rendered screenshots
if cached is not None and (now - cached[0]) < ttl:
cached_response = self._get_cached_screenshot_response(request, route_key)
if cached_response is not None:
@@ -620,9 +610,6 @@ class LocalServer:
etag = hashlib.sha1(svg.encode("utf-8"), usedforsecurity=False).hexdigest()
self._screenshot_cache[route_key] = (asyncio.get_event_loop().time(), svg)
self._screenshot_cache_etag[route_key] = etag
self._screenshot_last_rendered_activity[route_key] = self._route_last_activity.get(
route_key, 0.0
)
headers = {"Cache-Control": "no-cache", "ETag": etag}
return web.Response(text=svg, content_type="image/svg+xml", headers=headers)
src/textual_webterm/terminal_session.py
+11 -4
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@@ -140,16 +140,23 @@ class TerminalSession(Session):
async with self._screen_lock:
return [line.rstrip() for line in self._screen.display]
async def get_screen_state(self) -> tuple[int, int, list]:
async def get_screen_state(self) -> tuple[int, int, list, bool]:
"""Get the current screen state including dimensions and character buffer.
Returns:
Tuple of (width, height, buffer) where buffer is a list of rows,
each row containing character data with styling attributes.
Tuple of (width, height, buffer, has_changes) where:
- width: screen width in columns
- height: screen height in rows
- buffer: list of rows, each containing character data with styling
- has_changes: True if screen has changed since last call
"""
async with self._screen_lock:
width = self._screen.columns
height = self._screen.lines
# Check if any rows are dirty (changed since last clear)
has_changes = len(self._screen.dirty) > 0
# Clear dirty set after checking
self._screen.dirty.clear()
# Copy the buffer data to avoid holding the lock
buffer = []
for row in range(height):
@@ -166,7 +173,7 @@ class TerminalSession(Session):
"reverse": char.reverse,
})
buffer.append(row_data)
return (width, height, buffer)
return (width, height, buffer, has_changes)
def update_connector(self, connector: SessionConnector) -> None:
"""Update the connector for reconnection without restarting the session."""
tests/test_local_server_unit.py
+8 -8
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@@ -199,7 +199,7 @@ class TestLocalServerHelpers:
[{"data": " ", "fg": "default", "bg": "default", "bold": False, "italics": False, "underscore": False, "reverse": False}] * 80,
]
session = MagicMock()
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer))
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer, True))
monkeypatch.setattr(server.session_manager, "get_session_by_route_key", lambda _rk: session)
@@ -222,7 +222,7 @@ class TestLocalServerHelpers:
[{"data": " ", "fg": "default", "bg": "default", "bold": False, "italics": False, "underscore": False, "reverse": False}] * 80,
]
session = MagicMock()
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer))
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer, True))
# Pretend app exists for slug "known"
server.session_manager.apps_by_slug["known"] = App(
@@ -548,23 +548,23 @@ class TestLocalServerMoreCoverage:
assert server_with_no_apps._get_screenshot_cache_ttl("rk", now=1000.0) == 60.0
@pytest.mark.asyncio
async def test_handle_screenshot_uses_cache_when_no_new_activity(self, server_with_no_apps, monkeypatch):
async def test_handle_screenshot_uses_cache_when_no_changes(self, server_with_no_apps, monkeypatch):
"""Test that cached screenshot is returned when pyte reports no changes."""
request = MagicMock()
request.query = {"route_key": "rk"}
request.headers = {}
# has_changes=False indicates no screen changes since last call
session = MagicMock()
session.get_screen_state = AsyncMock(return_value=(80, 2, []))
session.get_screen_state = AsyncMock(return_value=(80, 2, [], False))
monkeypatch.setattr(server_with_no_apps.session_manager, "get_session_by_route_key", lambda _rk: session)
server_with_no_apps._screenshot_cache["rk"] = (0.0, "<svg>cached</svg>")
server_with_no_apps._screenshot_cache_etag["rk"] = "etag"
server_with_no_apps._route_last_activity["rk"] = 5.0
server_with_no_apps._screenshot_last_rendered_activity["rk"] = 5.0
resp = await server_with_no_apps._handle_screenshot(request)
assert "cached" in resp.text
session.get_screen_state.assert_not_awaited()
@pytest.mark.asyncio
async def test_handle_screenshot_renders_screen_state(self, server_with_no_apps, monkeypatch):
@@ -578,7 +578,7 @@ class TestLocalServerMoreCoverage:
[{"data": " ", "fg": "default", "bg": "default", "bold": False, "italics": False, "underscore": False, "reverse": False}] * 80,
]
session = MagicMock()
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer))
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer, True))
monkeypatch.setattr(server_with_no_apps.session_manager, "get_session_by_route_key", lambda _rk: session)
resp = await server_with_no_apps._handle_screenshot(request)
@@ -760,7 +760,7 @@ class TestLocalServerMoreCoverage:
[{"data": c, "fg": "default", "bg": "default", "bold": False, "italics": False, "underscore": False, "reverse": False} for c in "line2" + " " * 75],
]
session = MagicMock()
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer))
session.get_screen_state = AsyncMock(return_value=(80, 2, screen_buffer, True))
monkeypatch.setattr(server_with_no_apps.session_manager, "get_session_by_route_key", lambda _rk: session)
server_with_no_apps._route_last_activity["rk"] = 1.0
tests/test_terminal_session.py
+26
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@@ -130,6 +130,32 @@ class TestTerminalSession:
assert lines[1] == "Updated Line 2"
assert lines[2] == "Line 3"
@pytest.mark.asyncio
async def test_get_screen_state_returns_dirty_flag(self):
"""Test that get_screen_state returns has_changes flag based on pyte dirty tracking."""
from textual_webterm.terminal_session import TerminalSession
mock_poller = MagicMock()
session = TerminalSession(mock_poller, "test-session", "bash")
# After creation, all rows are dirty (initialized)
_w, _h, _buf, has_changes = await session.get_screen_state()
assert has_changes is True # Initial state marks all rows dirty
# After getting state, dirty set is cleared
# Without new data, has_changes should be False
_, _, _, has_changes = await session.get_screen_state()
assert has_changes is False # No changes since last call
# Feed new data
await session._update_screen(b"New content\r\n")
_, _, _, has_changes = await session.get_screen_state()
assert has_changes is True # Screen was updated
# Check again without new data
_, _, _, has_changes = await session.get_screen_state()
assert has_changes is False # No changes
def test_update_connector(self):
"""Test updating connector."""
from textual_webterm.terminal_session import TerminalSession