fix(celery): coerce non-string values in CeleryGetter.get()

Celery's Context copies all message properties as instance attributes
via __dict__.update(), including non-string values like timelimit
(tuple of ints) and priority (int). The TextMapPropagator contract
requires string values from Getter.get(), but CeleryGetter returned
these non-string values as-is, causing TraceState.from_header() to
crash with TypeError when calling re.split() on an int.

Coerce all non-string values to strings before returning them.

See #4359

Author: DrMeers

instrumentation/opentelemetry-instrumentation-celery/src/opentelemetry/instrumentation/celery/__init__.py

@@ -104,8 +104,16 @@ def get(self, carrier, key):
         value = getattr(carrier, key, None)
         if value is None:
             return None
-        if isinstance(value, str) or not isinstance(value, Iterable):
+        # Celery's Context copies all message properties as instance
+        # attributes, including non-string values like timelimit (tuple
+        # of ints).  The TextMapPropagator contract requires string
+        # values, so coerce anything that isn't already a string.
+        if isinstance(value, str):
             value = (value,)
+        elif isinstance(value, Iterable):
+            value = tuple(str(v) if not isinstance(v, str) else v for v in value)
+        else:
+            value = (str(value),)
         return value
 
     def keys(self, carrier):

instrumentation/opentelemetry-instrumentation-celery/tests/test_getter.py

@@ -36,7 +36,40 @@ def test_get_iter(self):
         getter = CeleryGetter()
         mock_obj.test = ["val"]
         val = getter.get(mock_obj, "test")
-        self.assertEqual(val, ["val"])
+        self.assertEqual(val, ("val",))
+
+    def test_get_int(self):
+        """Non-string scalar values should be coerced to strings.
+
+        Celery's Context stores some attributes as ints (e.g. priority).
+        The TextMapPropagator contract requires string values; passing
+        an int to re.split() in TraceState.from_header() causes a
+        TypeError.
+        """
+        mock_obj = mock.Mock()
+        getter = CeleryGetter()
+        mock_obj.test = 42
+        val = getter.get(mock_obj, "test")
+        self.assertEqual(val, ("42",))
+
+    def test_get_iter_with_non_string_elements(self):
+        """Iterable values containing non-strings should be coerced.
+
+        Celery's timelimit attribute is a tuple of ints, e.g. (300, 60).
+        """
+        mock_obj = mock.Mock()
+        getter = CeleryGetter()
+        mock_obj.test = (300, 60)
+        val = getter.get(mock_obj, "test")
+        self.assertEqual(val, ("300", "60"))
+
+    def test_get_iter_with_mixed_types(self):
+        """Iterables with a mix of strings and non-strings."""
+        mock_obj = mock.Mock()
+        getter = CeleryGetter()
+        mock_obj.test = ["val", 123]
+        val = getter.get(mock_obj, "test")
+        self.assertEqual(val, ("val", "123"))
 
     def test_keys(self):
         getter = CeleryGetter()