Make logger template format safer to missing kwargs

Author: sl0thentr0py

.gitignore

@@ -28,6 +28,7 @@ relay
 pip-wheel-metadata
 .mypy_cache
 .vscode/
+.claude/
 
 # for running AWS Lambda tests using AWS SAM
 sam.template.yaml

sentry_sdk/logger.py

@@ -1,10 +1,10 @@
 # NOTE: this is the logger sentry exposes to users, not some generic logger.
 import functools
 import time
-from typing import Any
+from typing import Any, Dict
 
 from sentry_sdk import get_client
-from sentry_sdk.utils import safe_repr
+from sentry_sdk.utils import safe_repr, capture_internal_exceptions
 
 OTEL_RANGES = [
     # ((severity level range), severity text)
@@ -18,10 +18,19 @@
 ]
 
 
+class _dict_default_key(dict):  # type: ignore[type-arg]
+    """dict that returns the key if missing."""
+
+    def __missing__(self, key):
+        # type: (str) -> str
+        return "{" + key + "}"
+
+
 def _capture_log(severity_text, severity_number, template, **kwargs):
     # type: (str, int, str, **Any) -> None
     client = get_client()
 
+    body = template
     attrs = {}  # type: dict[str, str | bool | float | int]
     if "attributes" in kwargs:
         attrs.update(kwargs.pop("attributes"))
@@ -31,6 +40,9 @@ def _capture_log(severity_text, severity_number, template, **kwargs):
         # only attach template if there are parameters
         attrs["sentry.message.template"] = template
 
+        with capture_internal_exceptions():
+            body = template.format_map(_dict_default_key(kwargs))
+
     attrs = {
         k: (
             v
@@ -51,7 +63,7 @@ def _capture_log(severity_text, severity_number, template, **kwargs):
             "severity_text": severity_text,
             "severity_number": severity_number,
             "attributes": attrs,
-            "body": template.format(**kwargs),
+            "body": body,
             "time_unix_nano": time.time_ns(),
             "trace_id": None,
         },

tests/test_logs.py

@@ -397,3 +397,52 @@ def test_auto_flush_logs_after_5s(sentry_init, capture_envelopes):
             return
 
     raise AssertionError("1 logs was never flushed after 10 seconds")
+
+
+@minimum_python_37
+@pytest.mark.parametrize(
+    "message,expected_body,params",
+    [
+        ("any text with {braces} in it", "any text with {braces} in it", None),
+        (
+            'JSON data: {"key": "value", "number": 42}',
+            'JSON data: {"key": "value", "number": 42}',
+            None,
+        ),
+        ("Multiple {braces} {in} {message}", "Multiple {braces} {in} {message}", None),
+        ("Nested {{braces}}", "Nested {{braces}}", None),
+        ("Empty braces: {}", "Empty braces: {}", None),
+        ("Braces with params: {user}", "Braces with params: alice", {"user": "alice"}),
+        (
+            "Braces with partial params: {user1} {user2}",
+            "Braces with partial params: alice {user2}",
+            {"user1": "alice"},
+        ),
+    ],
+)
+def test_logs_with_literal_braces(
+    sentry_init, capture_envelopes, message, expected_body, params
+):
+    """
+    Test that log messages with literal braces (like JSON) work without crashing.
+    This is a regression test for issue #4975.
+    """
+    sentry_init(enable_logs=True)
+    envelopes = capture_envelopes()
+
+    if params:
+        sentry_sdk.logger.info(message, **params)
+    else:
+        sentry_sdk.logger.info(message)
+
+    get_client().flush()
+    logs = envelopes_to_logs(envelopes)
+
+    assert len(logs) == 1
+    assert logs[0]["body"] == expected_body
+
+    # Verify template is only stored when there are parameters
+    if params:
+        assert logs[0]["attributes"]["sentry.message.template"] == message
+    else:
+        assert "sentry.message.template" not in logs[0]["attributes"]