From 0cecc9ea9469ce1b1bbb26292bc4a054c4a799a6 Mon Sep 17 00:00:00 2001
From: mateo-berri <277851410+mateo-berri@users.noreply.github.com>
Date: Wed, 28 Oct 2026 22:38:17 -0700
Subject: [PATCH] perf(logging): skip the base64 data URI scan and thread hop
 for text without a data URI

---
 litellm/litellm_core_utils/logging_utils.py   | 17 ++++--
 .../litellm_core_utils/test_logging_utils.py  | 55 +++++++++++++++++++
 2 files changed, 67 insertions(+), 5 deletions(-)

diff --git a/litellm/litellm_core_utils/logging_utils.py b/litellm/litellm_core_utils/logging_utils.py
index 8f58e8b7051..8e9e23c5cb7 100644
--- a/litellm/litellm_core_utils/logging_utils.py
+++ b/litellm/litellm_core_utils/logging_utils.py
@@ -44,6 +44,7 @@ Helper utils used for logging callbacks
 # Regex matching data-URI base64 content: "data:<mime>;base64,<payload>"
 # Captures: group(1)=mime_type, group(2)=base64_payload
 _DATA_URI_RE: Final = re.compile(r"data:([^;,\s]{1,255});base64,([A-Za-z0-9+/=]+)")
+_DATA_URI_BASE64_MARKER: Final = ";base64,"
 
 # Maximum nesting depth for _truncate_base64_in_value to guard against
 # pathological payloads. OpenAI message format is typically 3-4 levels deep.
@@ -60,9 +61,13 @@ def _base64_data_uri_replacer(match: re.Match[str]) -> str:
     return f"data:{mime_type};base64,[base64_data truncated: {size_str}]"
 
 
+def _may_contain_base64_data_uri(value: str) -> bool:
+    return ";" in value and _DATA_URI_BASE64_MARKER in value
+
+
 def _truncate_base64_in_string(value: str) -> str:
     """Replace long base64 data-URI payloads in a string with a size placeholder."""
-    if MAX_BASE64_LENGTH_FOR_LOGGING <= 0:
+    if MAX_BASE64_LENGTH_FOR_LOGGING <= 0 or not _may_contain_base64_data_uri(value):
         return value
     return _DATA_URI_RE.sub(_base64_data_uri_replacer, value)
 
@@ -155,14 +160,16 @@ async def truncate_base64_in_messages_async(
     messages: str | list | dict | None,  # mutable-ok: same contract as truncate_base64_in_messages
 ) -> str | list | dict | None:  # mutable-ok: same contract as truncate_base64_in_messages
     """
-    Same result as truncate_base64_in_messages, but payloads whose string content
-    reaches BASE64_TRUNCATION_OFFLOAD_THRESHOLD_CHARS are scanned in a worker
+    Same result as truncate_base64_in_messages, but payloads whose data-URI-bearing
+    strings reach BASE64_TRUNCATION_OFFLOAD_THRESHOLD_CHARS are scanned in a worker
     thread so the regex pass over multi-MB base64 images does not block the event loop.
     """
     if messages is None or MAX_BASE64_LENGTH_FOR_LOGGING <= 0:
         return messages
-    total_chars: Final = sum(len(leaf) for leaf in _iter_string_leaves(messages))
-    if total_chars < BASE64_TRUNCATION_OFFLOAD_THRESHOLD_CHARS:
+    data_uri_chars: Final = sum(
+        len(leaf) for leaf in _iter_string_leaves(messages) if _may_contain_base64_data_uri(leaf)
+    )
+    if data_uri_chars < BASE64_TRUNCATION_OFFLOAD_THRESHOLD_CHARS:
         return truncate_base64_in_messages(messages)
     return await asyncio.to_thread(truncate_base64_in_messages, messages)
 
diff --git a/tests/unit/litellm_core_utils/test_logging_utils.py b/tests/unit/litellm_core_utils/test_logging_utils.py
index edf0dc7960b..5cfd470cb9a 100644
--- a/tests/unit/litellm_core_utils/test_logging_utils.py
+++ b/tests/unit/litellm_core_utils/test_logging_utils.py
@@ -241,6 +241,38 @@ def scan_threads(monkeypatch):
     return threads
 
 
+@pytest.fixture
+def regex_scans(monkeypatch):
+    """Record every string the data URI regex runs over."""
+    scanned: list[str] = []
+    original = logging_utils._DATA_URI_RE
+
+    class RecordingPattern:
+        def sub(self, repl, string: str) -> str:
+            scanned.append(string)
+            return original.sub(repl, string)
+
+    monkeypatch.setattr(logging_utils, "_DATA_URI_RE", RecordingPattern())
+    return scanned
+
+
+def _tool_result_messages(tool_output: str) -> list:
+    return [
+        {"role": "user", "content": "Summarize the rows the tool returned."},
+        {
+            "role": "assistant",
+            "content": None,
+            "tool_calls": [
+                {"id": "call_1", "type": "function", "function": {"name": "dump_rows", "arguments": "{}"}}
+            ],
+        },
+        {"role": "tool", "tool_call_id": "call_1", "content": tool_output},
+    ]
+
+
+_PLAIN_TOOL_OUTPUT_CHARS = 400 * 1024
+
+
 class TestTruncateBase64InMessagesAsync:
     @pytest.mark.asyncio
     async def test_large_payload_is_scanned_off_the_event_loop(self, monkeypatch, scan_threads):
@@ -268,6 +300,29 @@ class TestTruncateBase64InMessagesAsync:
         assert scan_threads
         assert set(scan_threads) == {threading.get_ident()}
 
+    @pytest.mark.asyncio
+    @pytest.mark.parametrize(
+        "row",
+        [
+            '{"id": 7, "name": "widget", "status": "ok"}\n',
+            "data: {\"choices\": [{\"delta\": {\"content\": \"hi\"}}]}\n\n",
+            "const total = rows.map((r) => r.price).reduce((a, b) => a + b, 0);\n",
+        ],
+        ids=["json_rows", "sse_lines", "code_with_semicolons"],
+    )
+    async def test_tool_message_without_data_uri_skips_the_regex_and_the_thread_hop(
+        self, scan_threads, regex_scans, row
+    ):
+        tool_output = (row * (_PLAIN_TOOL_OUTPUT_CHARS // len(row) + 1))[:_PLAIN_TOOL_OUTPUT_CHARS]
+        messages = _tool_result_messages(tool_output)
+
+        result = await truncate_base64_in_messages_async(messages)
+
+        assert result == messages
+        assert regex_scans == []
+        assert scan_threads
+        assert set(scan_threads) == {threading.get_ident()}
+
     @pytest.mark.asyncio
     async def test_none_and_disabled_truncation_short_circuit(self, monkeypatch, scan_threads):
         assert await truncate_base64_in_messages_async(None) is None