fix: fail gracefully when livecode_to_svg crashes

That seems to be happening in some cases and couldn't really figure out
the reason. Handling the error to gracefully to show an empty image in
those cases.

community/lms/doctype/lms_sketch/livecode.py

@@ -3,6 +3,7 @@
 import websocket
 import json
 from .svg import SVG
+import frappe
 
 # Files to pass to livecode server
 # The same code is part of livecode-canvas.js
@@ -62,26 +63,29 @@ clear()
 def livecode_to_svg(livecode_ws_url, code, *, timeout=3):
     """Renders the code as svg.
     """
-    ws = websocket.WebSocket()
-    ws.settimeout(timeout)
-    ws.connect(livecode_ws_url)
+    try:
+        ws = websocket.WebSocket()
+        ws.settimeout(timeout)
+        ws.connect(livecode_ws_url)
 
-    msg = {
-        "msgtype": "exec",
-        "runtime": "python",
-        "code": code,
-        "files": [
-            {"filename": "start.py", "contents": START},
-            {"filename": "sketch.py", "contents": SKETCH},
-        ],
-        "command": ["python", "start.py"]
-    }
-    ws.send(json.dumps(msg))
+        msg = {
+            "msgtype": "exec",
+            "runtime": "python",
+            "code": code,
+            "files": [
+                {"filename": "start.py", "contents": START},
+                {"filename": "sketch.py", "contents": SKETCH},
+            ],
+            "command": ["python", "start.py"]
+        }
+        ws.send(json.dumps(msg))
 
-    messages = _read_messages(ws)
-    commands = [m for m in messages if m['msgtype'] == 'draw']
-    img = draw_image(commands)
-    return img.tostring()
+        messages = _read_messages(ws)
+        commands = [m for m in messages if m['msgtype'] == 'draw']
+        img = draw_image(commands)
+        return img.tostring()
+    except websocket.WebSocketException as e:
+        frappe.log_error(frappe.get_traceback(), 'livecode_to_svg failed')
 
 def _read_messages(ws):
     messages = []

community/lms/doctype/lms_sketch/lms_sketch.py

@@ -9,6 +9,11 @@ import frappe
 from frappe.model.document import Document
 from . import livecode
 
+DEFAULT_IMAGE = """
+<svg viewBox="0 0 300 300" width="300" xmlns="http://www.w3.org/2000/svg">
+</svg>
+"""
+
 class LMSSketch(Document):
     @property
     def sketch_id(self):
@@ -48,8 +53,9 @@ class LMSSketch(Document):
         else:
             ws_url = self.get_livecode_ws_url()
             value = livecode.livecode_to_svg(ws_url, self.code)
-            cache.set(key, value)
-        return value
+            if value:
+                cache.set(key, value)
+        return value or DEFAULT_IMAGE
 
     @staticmethod
     def get_recent_sketches(limit=100, owner=None):