fix: exporting a large figure hangs

src/py/CHANGELOG.txt → CHANGELOG.md

@@ -1,15 +1,20 @@
-v1.3.0rc0
+## Unreleased
+
+### Fixed
+- Fix issue where exporting large figures could cause hang [[#442](https://github.com/plotly/Kaleido/pull/442)], with thanks to @EliasTalcott for the contribution!
+
+## v1.3.0rc0
 - Significant refactor, better organization
 - `write_fig` and `_from_object` now take an additional argument:
   `cancel_on_error: bool, default False`. See docs.
 - Unused `path` argument for `calc_fig` was deprecated.
 - Fixed race condition where two render tasks would choose the same filename
 
 
-v1.2.0
+## v1.2.0
 - Try to use plotly JSON encoder instead of default
 
-v1.1.0
+## v1.1.0
 - Add testing
 - Fix a variety of type bugs
 - Change order of browser closer to fix hang
@@ -20,51 +25,51 @@ v1.1.0
 - Add option to silence warnings in start/stop_sync_server
 - Fix bug where attribute was inconsistently named
 
-v1.1.0rc0
+## v1.1.0rc0
 - Improve verbosity of errors when starting kaleido improperly
 - Add new api functions start/stop_sync_server
 
-v1.0.0
+## v1.0.0
 - Add warning if using incompatible Plotly version
 
-v1.0.0rc15
+## v1.0.0rc15
 - BUG: Add regex sanitization for auto-filename generation
 - Further santiize title to filename conversion
 
-v1.0.0rc14
+## v1.0.0rc14
 - Pass `plotlyjs` option through from Kaleido() to PageGenerator()
 
-v1.0.0rc13
+## v1.0.0rc13
 - Pass mathjax option through when using default plotly.js template
 
-v1.0.0rc12
+## v1.0.0rc12
 - Add `kopts` args to top-level shortcuts to pass args to `Kaleido(**kopts)`
 
-v1.0.0rc11
+## v1.0.0rc11
 - Write mocker tool to parameterize opts in tests
 - Crop page to pdf size
 - Add type checks to user input for improved error messages
 - Fix latex strings in PDF bolding
 - Add some choreographer errors to kaleido.errors
 
-v1.0.0rc10
+## v1.0.0rc10
 - Allow user to pass Figure-like dicts
 - Fix bug by which calc fig rejected plotly figures
 - Improve testing
 
-v1.0.0rc9
+## v1.0.0rc9
 - Fix v1.0.0rc7 for logic reversal (was conditional error)
 
-v1.0.0rc8
+## v1.0.0rc8
 - Add kaleido.calc_fig to return bytes, not write file automatically
 - Add calc_fig[_sync], write_fig_sync, and write_fig_from_object_sync to kaleido API
 
-v1.0.0rc7
+## v1.0.0rc7
 - Use new choreo is_isolated() to improve platform support (snap /tmp sandboxing)
 
-v1.0.0rc6
+## v1.0.0rc6
 - Allow PageGenerator(force_cdn=True) to not use plotly.py's installed js
 
-v1.0.0rc5
+## ## v1.0.0rc5
 - Fix bug by which plotly.py's internal js was always ignored
 - Adds testing for PageGenerator

src/py/kaleido/_kaleido_tab/_tab.py

@@ -4,6 +4,7 @@
 from typing import TYPE_CHECKING
 
 import logistro
+import orjson
 
 from . import _devtools_utils as _dtools
 from . import _js_logger
@@ -19,10 +20,18 @@
 
 
 _TEXT_FORMATS = ("svg", "json")  # eps
+_CHUNK_SIZE = 10 * 1024 * 1024  # 10 MB
 
 _logger = logistro.getLogger(__name__)
 
 
+def _orjson_default(obj):
+    """Fallback for types orjson can't handle natively (e.g. NumPy string arrays)."""
+    if hasattr(obj, "tolist"):
+        return obj.tolist()
+    raise TypeError(f"Type is not JSON serializable: {type(obj).__name__}")
+
+
 def _subscribe_new(tab: choreo.Tab, event: str) -> asyncio.Future:
     """Create subscription to tab clearing old ones first: helper function."""
     new_future = tab.subscribe_once(event)
@@ -117,22 +126,38 @@ async def _calc_fig(
         render_prof,
         stepper,
     ) -> bytes:
-        # js script
-        kaleido_js_fn = (
-            r"function(spec, ...args)"
-            r"{"
-            r"return kaleido_scopes.plotly(spec, ...args).then(JSON.stringify);"
-            r"}"
-        )
-        render_prof.profile_log.tick("sending javascript")
-        result = await _dtools.exec_js_fn(
-            self.tab,
-            self._current_js_id,
-            kaleido_js_fn,
+        render_prof.profile_log.tick("serializing spec")
+        spec_str = orjson.dumps(
             spec,
-            topojson,
-            stepper,
-        )
+            default=_orjson_default,
+            option=orjson.OPT_SERIALIZE_NUMPY,
+        ).decode()
+        render_prof.profile_log.tick("spec serialized")
+
+        render_prof.profile_log.tick("sending javascript")
+        if len(spec_str) <= _CHUNK_SIZE:
+            kaleido_js_fn = (
+                r"function(specStr, ...args)"
+                r"{"
+                r"return kaleido_scopes"
+                r".plotly(JSON.parse(specStr), ...args)"
+                r".then(JSON.stringify);"
+                r"}"
+            )
+            result = await _dtools.exec_js_fn(
+                self.tab,
+                self._current_js_id,
+                kaleido_js_fn,
+                spec_str,
+                topojson,
+                stepper,
+            )
+        else:
+            result = await self._calc_fig_chunked(
+                spec_str,
+                topojson=topojson,
+                stepper=stepper,
+            )
         _raise_error(result)
         render_prof.profile_log.tick("javascript sent")
 
@@ -154,3 +179,45 @@ async def _calc_fig(
         render_prof.data_out_size = len(res)
         render_prof.js_log = self.js_logger.log
         return res
+
+    async def _calc_fig_chunked(
+        self,
+        spec_str: str,
+        *,
+        topojson: str | None,
+        stepper,
+    ):
+        _raise_error(
+            await _dtools.exec_js_fn(
+                self.tab,
+                self._current_js_id,
+                r"function() { window.__kaleido_chunks = []; }",
+            )
+        )
+
+        for i in range(0, len(spec_str), _CHUNK_SIZE):
+            chunk = spec_str[i : i + _CHUNK_SIZE]
+            _raise_error(
+                await _dtools.exec_js_fn(
+                    self.tab,
+                    self._current_js_id,
+                    r"function(c) { window.__kaleido_chunks.push(c); }",
+                    chunk,
+                )
+            )
+
+        kaleido_js_fn = (
+            r"function(...args)"
+            r"{"
+            r"var spec = JSON.parse(window.__kaleido_chunks.join(''));"
+            r"delete window.__kaleido_chunks;"
+            r"return kaleido_scopes.plotly(spec, ...args).then(JSON.stringify);"
+            r"}"
+        )
+        return await _dtools.exec_js_fn(
+            self.tab,
+            self._current_js_id,
+            kaleido_js_fn,
+            topojson,
+            stepper,
+        )

src/py/tests/test_large_fig.py

@@ -0,0 +1,26 @@
+import numpy as np
+import plotly.graph_objects as go
+import pytest
+
+import kaleido
+
+TOTAL_POINTS = 5_000_000
+
+
+@pytest.mark.parametrize(
+    ("num_traces", "num_points"),
+    [
+        (1, TOTAL_POINTS),
+        (1_000, TOTAL_POINTS / 1_000),
+    ],
+)
+async def test_large_fig(num_traces, num_points):
+    fig = go.Figure()
+    for _ in range(num_traces):
+        fig.add_trace(
+            go.Scatter(
+                x=np.arange(num_points, dtype=float),
+                y=np.arange(num_points, dtype=float),
+            )
+        )
+    assert isinstance(await kaleido.calc_fig(fig), bytes)