Make Instances of SpanContext Immutable (#1134)

Author: Jason Liu

opentelemetry-api/CHANGELOG.md

@@ -10,6 +10,8 @@
   ([#1153](https://github.com/open-telemetry/opentelemetry-python/pull/1153))
 - Update baggage propagation header
   ([#1194](https://github.com/open-telemetry/opentelemetry-python/pull/1194))
+- Make instances of SpanContext immutable
+  ([#1134](https://github.com/open-telemetry/opentelemetry-python/pull/1134))
 
 ## Version 0.13b0
 

opentelemetry-api/src/opentelemetry/trace/span.py

@@ -1,10 +1,13 @@
 import abc
+import logging
 import types as python_types
 import typing
 
 from opentelemetry.trace.status import Status
 from opentelemetry.util import types
 
+_logger = logging.getLogger(__name__)
+
 
 class Span(abc.ABC):
     """A span represents a single operation within a trace."""
@@ -143,7 +146,9 @@ def get_default(cls) -> "TraceState":
 DEFAULT_TRACE_STATE = TraceState.get_default()
 
 
-class SpanContext:
+class SpanContext(
+    typing.Tuple[int, int, bool, "TraceFlags", "TraceState", bool]
+):
     """The state of a Span to propagate between processes.
 
     This class includes the immutable attributes of a :class:`.Span` that must
@@ -157,26 +162,58 @@ class SpanContext:
         is_remote: True if propagated from a remote parent.
     """
 
-    def __init__(
-        self,
+    def __new__(
+        cls,
         trace_id: int,
         span_id: int,
         is_remote: bool,
         trace_flags: "TraceFlags" = DEFAULT_TRACE_OPTIONS,
         trace_state: "TraceState" = DEFAULT_TRACE_STATE,
-    ) -> None:
+    ) -> "SpanContext":
         if trace_flags is None:
             trace_flags = DEFAULT_TRACE_OPTIONS
         if trace_state is None:
             trace_state = DEFAULT_TRACE_STATE
-        self.trace_id = trace_id
-        self.span_id = span_id
-        self.trace_flags = trace_flags
-        self.trace_state = trace_state
-        self.is_remote = is_remote
-        self.is_valid = (
-            self.trace_id != INVALID_TRACE_ID
-            and self.span_id != INVALID_SPAN_ID
+
+        is_valid = trace_id != INVALID_TRACE_ID and span_id != INVALID_SPAN_ID
+
+        return tuple.__new__(
+            cls,
+            (trace_id, span_id, is_remote, trace_flags, trace_state, is_valid),
+        )
+
+    @property
+    def trace_id(self) -> int:
+        return self[0]  # pylint: disable=unsubscriptable-object
+
+    @property
+    def span_id(self) -> int:
+        return self[1]  # pylint: disable=unsubscriptable-object
+
+    @property
+    def is_remote(self) -> bool:
+        return self[2]  # pylint: disable=unsubscriptable-object
+
+    @property
+    def trace_flags(self) -> "TraceFlags":
+        return self[3]  # pylint: disable=unsubscriptable-object
+
+    @property
+    def trace_state(self) -> "TraceState":
+        return self[4]  # pylint: disable=unsubscriptable-object
+
+    @property
+    def is_valid(self) -> bool:
+        return self[5]  # pylint: disable=unsubscriptable-object
+
+    def __setattr__(self, *args: str) -> None:
+        _logger.debug(
+            "Immutable type, ignoring call to set attribute", stack_info=True
+        )
+
+    def __delattr__(self, *args: str) -> None:
+        _logger.debug(
+            "Immutable type, ignoring call to set attribute", stack_info=True
         )
 
     def __repr__(self) -> str:

opentelemetry-api/tests/trace/test_immutablespancontext.py

@@ -0,0 +1,58 @@
+# Copyright The OpenTelemetry Authors
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import unittest
+
+from opentelemetry import trace
+from opentelemetry.trace import TraceFlags, TraceState
+
+
+class TestImmutableSpanContext(unittest.TestCase):
+    def test_ctor(self):
+        context = trace.SpanContext(
+            1,
+            1,
+            is_remote=False,
+            trace_flags=trace.DEFAULT_TRACE_OPTIONS,
+            trace_state=trace.DEFAULT_TRACE_STATE,
+        )
+
+        self.assertEqual(context.trace_id, 1)
+        self.assertEqual(context.span_id, 1)
+        self.assertEqual(context.is_remote, False)
+        self.assertEqual(context.trace_flags, trace.DEFAULT_TRACE_OPTIONS)
+        self.assertEqual(context.trace_state, trace.DEFAULT_TRACE_STATE)
+
+    def test_attempt_change_attributes(self):
+        context = trace.SpanContext(
+            1,
+            2,
+            is_remote=False,
+            trace_flags=trace.DEFAULT_TRACE_OPTIONS,
+            trace_state=trace.DEFAULT_TRACE_STATE,
+        )
+
+        # attempt to change the attribute values
+        context.trace_id = 2  # type: ignore
+        context.span_id = 3  # type: ignore
+        context.is_remote = True  # type: ignore
+        context.trace_flags = TraceFlags(3)  # type: ignore
+        context.trace_state = TraceState([("test", "test")])  # type: ignore
+
+        # check if attributes changed
+        self.assertEqual(context.trace_id, 1)
+        self.assertEqual(context.span_id, 2)
+        self.assertEqual(context.is_remote, False)
+        self.assertEqual(context.trace_flags, trace.DEFAULT_TRACE_OPTIONS)
+        self.assertEqual(context.trace_state, trace.DEFAULT_TRACE_STATE)