From 7f0b53c3ebc5bd63f293874f3488b72d101dcf4a Mon Sep 17 00:00:00 2001
From: Sasa Junuzovic <44276455+microsasa@users.noreply.github.com>
Date: Sun, 19 Apr 2026 00:42:49 -0700
Subject: [PATCH] fix: guard parse_token_int against IEEE 754 special floats
 (#875)

Add explicit math.isfinite() check in parse_token_int so float('inf'),
float('-inf'), and float('nan') are rejected before reaching Pydantic
int coercion. Previously these values were only handled incidentally via
float.is_integer() returning False.

- Add math.isfinite guard in parse_token_int (models.py)
- Update parse_token_int docstring to document IEEE special float rule
- Add parametrized test for _extract_output_tokens with special floats
- Extend _EQUIVALENCE_CASES cross-check with inf, -inf, and nan

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 src/copilot_usage/models.py        | 4 ++++
 tests/copilot_usage/test_parser.py | 8 ++++++++
 2 files changed, 12 insertions(+)

diff --git a/src/copilot_usage/models.py b/src/copilot_usage/models.py
index 8ff71044..d8d20f9d 100644
--- a/src/copilot_usage/models.py
+++ b/src/copilot_usage/models.py
@@ -6,6 +6,7 @@
 """
 
 import builtins
+import math
 from datetime import UTC, datetime
 from enum import StrEnum
 from pathlib import Path
@@ -220,6 +221,7 @@ def parse_token_int(raw: object) -> int | None:
     Rules:
 
     - ``bool`` / ``str`` → ``None`` (invalid, not coerced)
+    - IEEE 754 special ``float`` (``inf``, ``-inf``, ``nan``) → ``None``
     - non-whole ``float`` → ``None``
     - zero or negative ``int`` / ``float`` → ``None``
     - positive whole-number ``float`` → coerced to ``int``
@@ -229,6 +231,8 @@ def parse_token_int(raw: object) -> int | None:
     if isinstance(raw, (bool, str)):
         return None
     if isinstance(raw, float):
+        if not math.isfinite(raw):
+            return None
         if not raw.is_integer():
             return None
         tokens = int(raw)
diff --git a/tests/copilot_usage/test_parser.py b/tests/copilot_usage/test_parser.py
index 95a3a91f..76568f72 100644
--- a/tests/copilot_usage/test_parser.py
+++ b/tests/copilot_usage/test_parser.py
@@ -4948,6 +4948,11 @@ def test_returns_none_for_missing_key(self) -> None:
         )
         assert _extract_output_tokens(ev) is None
 
+    @pytest.mark.parametrize("special", [float("inf"), float("nan"), float("-inf")])
+    def test_returns_none_for_ieee_special_floats(self, special: float) -> None:
+        """IEEE 754 special floats (inf, nan, -inf) are not valid token counts."""
+        assert _extract_output_tokens(_make_assistant_event(special)) is None
+
 
 _EXTRACT_TOKENS_CASES: list[tuple[str, object, int | None]] = [
     ("valid_int", 42, 42),
@@ -5021,6 +5026,9 @@ def test_missing_key_no_pydantic(self) -> None:
     ("large_positive_int", 1234),
     ("whole_float", 1234.0),
     ("fractional_float", 3.14),
+    ("float_inf", float("inf")),
+    ("float_neg_inf", float("-inf")),
+    ("float_nan", float("nan")),
 ]