From 4b23482dd30b3f7bbc366714caea424c3b920bc3 Mon Sep 17 00:00:00 2001
From: Aling33 <152494711+Aling33@users.noreply.github.com>
Date: Tue, 3 Nov 2026 06:11:24 +0000
Subject: [PATCH] fix(dify-agent): validate plugin-declared blob size before
 allocating chunk buffer (#45209)

---
 .../layers/dify_plugin/tool_client.py         |  5 ++
 .../layers/dify_plugin/test_tool_client.py    | 77 +++++++++++++++++++
 2 files changed, 82 insertions(+)
 create mode 100644 dify-agent/tests/local/dify_agent/layers/dify_plugin/test_tool_client.py

diff --git a/dify-agent/src/dify_agent/layers/dify_plugin/tool_client.py b/dify-agent/src/dify_agent/layers/dify_plugin/tool_client.py
index fc5685b05d2..cff1ca78c29 100644
--- a/dify-agent/src/dify_agent/layers/dify_plugin/tool_client.py
+++ b/dify-agent/src/dify_agent/layers/dify_plugin/tool_client.py
@@ -294,6 +294,11 @@ def merge_blob_chunks(
             is_end = resp.message.end
 
             if chunk_id not in files:
+                # The declared length is plugin-controlled while the whole buffer is
+                # pre-allocated, so an oversized claim must be rejected before the
+                # allocation below rather than after it.
+                if total_length > max_file_size:
+                    raise ValueError(f"File is too large which reached the limit of {max_file_size / 1024 / 1024}MB")
                 files[chunk_id] = FileChunk(total_length)
 
             if files[chunk_id].bytes_written + len(blob_data) > max_file_size:
diff --git a/dify-agent/tests/local/dify_agent/layers/dify_plugin/test_tool_client.py b/dify-agent/tests/local/dify_agent/layers/dify_plugin/test_tool_client.py
new file mode 100644
index 00000000000..60471e00dac
--- /dev/null
+++ b/dify-agent/tests/local/dify_agent/layers/dify_plugin/test_tool_client.py
@@ -0,0 +1,77 @@
+"""Blob chunk merging validates the plugin-declared size before allocating."""
+
+import pytest
+
+from dify_agent.layers.dify_plugin.tool_client import (
+    DifyPluginToolInvokeMessage,
+    merge_blob_chunks,
+)
+
+
+def blob_chunk(
+    *, chunk_id: str, sequence: int, total_length: int, blob: bytes, end: bool
+) -> DifyPluginToolInvokeMessage:
+    return DifyPluginToolInvokeMessage(
+        type=DifyPluginToolInvokeMessage.MessageType.BLOB_CHUNK,
+        message=DifyPluginToolInvokeMessage.BlobChunkMessage(
+            id=chunk_id,
+            sequence=sequence,
+            total_length=total_length,
+            blob=blob,
+            end=end,
+        ),
+    )
+
+
+def test_merge_blob_chunks_rejects_declared_length_above_limit() -> None:
+    """A declared length above the limit fails before the buffer is allocated."""
+    chunks = [blob_chunk(chunk_id="file1", sequence=0, total_length=1025, blob=b"x", end=False)]
+
+    with pytest.raises(ValueError, match="File is too large"):
+        merge_blob_chunks(chunks, max_file_size=1024)
+
+
+def test_merge_blob_chunks_rejects_unallocatable_declared_length() -> None:
+    """An absurd declared length raises ValueError instead of MemoryError."""
+    chunks = [blob_chunk(chunk_id="file1", sequence=0, total_length=2**62, blob=b"x", end=False)]
+
+    with pytest.raises(ValueError, match="File is too large"):
+        merge_blob_chunks(chunks)
+
+
+def test_merge_blob_chunks_accepts_declared_length_at_the_limit() -> None:
+    """A declared length exactly at the limit is still accepted and merged."""
+    chunks = [
+        blob_chunk(chunk_id="file1", sequence=0, total_length=1024, blob=b"abc", end=False),
+        blob_chunk(chunk_id="file1", sequence=1, total_length=1024, blob=b"defg", end=True),
+    ]
+
+    merged = merge_blob_chunks(chunks, max_file_size=1024)
+
+    assert len(merged) == 1
+    assert merged[0].type is DifyPluginToolInvokeMessage.MessageType.BLOB
+    assert isinstance(merged[0].message, DifyPluginToolInvokeMessage.BlobMessage)
+    assert merged[0].message.blob == b"abcdefg"
+
+
+def test_merge_blob_chunks_keeps_non_chunk_messages_in_order() -> None:
+    """Text messages around blob chunks still pass through in stream order."""
+    chunks = [
+        DifyPluginToolInvokeMessage(
+            type=DifyPluginToolInvokeMessage.MessageType.TEXT,
+            message=DifyPluginToolInvokeMessage.TextMessage(text="before"),
+        ),
+        blob_chunk(chunk_id="file1", sequence=0, total_length=1, blob=b"x", end=True),
+        DifyPluginToolInvokeMessage(
+            type=DifyPluginToolInvokeMessage.MessageType.TEXT,
+            message=DifyPluginToolInvokeMessage.TextMessage(text="after"),
+        ),
+    ]
+
+    merged = merge_blob_chunks(chunks)
+
+    assert [message.type for message in merged] == [
+        DifyPluginToolInvokeMessage.MessageType.TEXT,
+        DifyPluginToolInvokeMessage.MessageType.BLOB,
+        DifyPluginToolInvokeMessage.MessageType.TEXT,
+    ]