chore: import upstream snapshot with attribution

contributing/samples/workflows/message/agent.py

@@ -0,0 +1,104 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import asyncio
+import base64
+import os
+from typing import Any
+
+from google.adk import Event
+from google.adk import Workflow
+from google.genai import types
+
+
+async def sleep_if_not_pytest(seconds: float):
+  if "PYTEST_CURRENT_TEST" not in os.environ:
+    await asyncio.sleep(seconds)
+
+
+def send_string(node_input: Any = None):
+  """Sends a single string message."""
+  yield Event(message="#1 This is a simple string message.")
+
+
+def send_multimodal(node_input: Any = None):
+  """Sends a multi-modal message containing a string and an inline image."""
+  # A 16x16 solid red PNG base64 encoded
+  red_square_png = base64.b64decode(
+      "iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAAXElEQVR4nO2TSQ7AIAwD"
+      "7fz/z+ZQtapwmrJc8QklmjBIgZJgIZMiAIl9KYbhjx4fgwosbNxgMrF0+4uhgHnYDM6"
+      "AzQHJeg5HYtyHFfgy2AztN/5tZWfrBtVzkl4DzfQkEPd+cEkAAAAASUVORK5CYII="
+  )
+  yield Event(
+      message=[
+          types.Part.from_text(
+              text=(
+                  "#2 Here is a multi-modal message with an inline image (red"
+                  " circle):"
+              )
+          ),
+          types.Part.from_bytes(data=red_square_png, mime_type="image/png"),
+      ]
+  )
+
+
+async def multiple_messages(node_input: Any = None):
+  """Sends multiple complete messages from the same node with an interval."""
+  yield Event(message="#3 Multiple messages")
+  await sleep_if_not_pytest(1.0)
+
+  yield Event(message="Processing step 1...")
+  await sleep_if_not_pytest(1.0)
+
+  yield Event(message="Processing step 2...")
+  await sleep_if_not_pytest(1.0)
+
+  yield Event(message="Done processing.")
+
+
+async def stream_sentence(node_input: Any = None):
+  """
+  Demonstrates streaming by sending a sentence in chunks.
+  The `partial=True` flag tells the UI that this is part of an ongoing message.
+  """
+  yield Event(message="#4 Starting to stream...")
+  sentence = """\
+This is a streaming message sent in chunks.
+
+You can stream in markdown as well. For example, the table below:
+
+| Header 1 | Header 2 |
+|----------|----------|
+| Cell 1   | Cell 2   |
+| Cell 3   | Cell 4   |
+"""
+
+  for i in range(0, len(sentence), 5):
+    chunk = sentence[i : i + 5]
+    yield Event(message=chunk, partial=True)
+    await sleep_if_not_pytest(0.2)
+
+
+root_agent = Workflow(
+    name="message",
+    edges=[
+        (
+            "START",
+            send_string,
+            send_multimodal,
+            multiple_messages,
+            stream_sentence,
+        ),
+    ],
+)