feat(core): Autogenerate filenames for when converting file content blocks to OpenAI format (#30984)

CC @ccurme

---------

Co-authored-by: Chester Curme <chester.curme@gmail.com>

libs/core/langchain_core/messages/utils.py

@@ -12,6 +12,7 @@ from __future__ import annotations
 import base64
 import inspect
 import json
+import logging
 import math
 from collections.abc import Iterable, Sequence
 from functools import partial
@@ -47,6 +48,8 @@ if TYPE_CHECKING:
     from langchain_core.prompt_values import PromptValue
     from langchain_core.runnables.base import Runnable
 
+logger = logging.getLogger(__name__)
+
 
 def _get_type(v: Any) -> str:
     """Get the type associated with the object for serialization purposes."""
@@ -1070,7 +1073,15 @@ def convert_to_openai_messages(
                     )
                 # Standard multi-modal content block
                 elif is_data_content_block(block):
-                    content.append(convert_to_openai_data_block(block))
+                    formatted_block = convert_to_openai_data_block(block)
+                    if (
+                        formatted_block.get("type") == "file"
+                        and "file" in formatted_block
+                        and "filename" not in formatted_block["file"]
+                    ):
+                        logger.info("Generating a fallback filename.")
+                        formatted_block["file"]["filename"] = "LC_AUTOGENERATED"
+                    content.append(formatted_block)
                 # Anthropic and Bedrock converse format
                 elif (block.get("type") == "image") or "image" in block:
                     # Anthropic

libs/core/tests/unit_tests/messages/test_utils.py

@@ -1202,12 +1202,6 @@ def test_convert_to_openai_messages_multimodal() -> None:
                     "data": "<base64 string>",
                     "mime_type": "image/png",
                 },
-                {
-                    "type": "file",
-                    "source_type": "base64",
-                    "data": "<base64 string>",
-                    "mime_type": "application/pdf",
-                },
                 {
                     "type": "file",
                     "source_type": "base64",
@@ -1232,7 +1226,34 @@ def test_convert_to_openai_messages_multimodal() -> None:
     result = convert_to_openai_messages(messages, text_format="block")
     assert len(result) == 1
     message = result[0]
-    assert len(message["content"]) == 7
+    assert len(message["content"]) == 6
+
+    # Test adding filename
+    messages = [
+        HumanMessage(
+            content=[
+                {
+                    "type": "file",
+                    "source_type": "base64",
+                    "data": "<base64 string>",
+                    "mime_type": "application/pdf",
+                },
+            ]
+        )
+    ]
+    with pytest.warns(match="filename"):
+        result = convert_to_openai_messages(messages, text_format="block")
+    assert len(result) == 1
+    message = result[0]
+    assert len(message["content"]) == 1
+    block = message["content"][0]
+    assert block == {
+        "type": "file",
+        "file": {
+            "file_data": "data:application/pdf;base64,<base64 string>",
+            "filename": "LC_AUTOGENERATED",
+        },
+    }
 
 
 def test_count_tokens_approximately_empty_messages() -> None: