feat: Extract content encode/decode logic to a shared util and resolve issues with JSON serialization.

feat: Update key length for DB table to avoid key too long issue in mysql

PiperOrigin-RevId: 753614879

src/google/adk/sessions/_session_util.py

@@ -0,0 +1,29 @@
+"""Utility functions for session service."""
+
+import base64
+from typing import Any, Optional
+
+from google.genai import types
+
+
+def encode_content(content: types.Content):
+  """Encodes a content object to a JSON dictionary."""
+  encoded_content = content.model_dump(exclude_none=True)
+  for p in encoded_content["parts"]:
+    if "inline_data" in p:
+      p["inline_data"]["data"] = base64.b64encode(
+          p["inline_data"]["data"]
+      ).decode("utf-8")
+  return encoded_content
+
+
+def decode_content(
+    content: Optional[dict[str, Any]],
+) -> Optional[types.Content]:
+  """Decodes a content object from a JSON dictionary."""
+  if not content:
+    return None
+  for p in content["parts"]:
+    if "inline_data" in p:
+      p["inline_data"]["data"] = base64.b64decode(p["inline_data"]["data"])
+  return types.Content.model_validate(content)