allow for empty X-Parent (#820)

The `X-Parent` header could be empty, and will be for the root span. This PR allows for that.

baseplate/__init__.py

@@ -130,9 +130,9 @@ def new(cls) -> "TraceInfo":
     @classmethod
     def from_upstream(
         cls,
-        trace_id: Optional[str],
+        trace_id: str,
         parent_id: Optional[str],
-        span_id: Optional[str],
+        span_id: str,
         sampled: Optional[bool],
         flags: Optional[int],
     ) -> "TraceInfo":
@@ -153,9 +153,6 @@ def from_upstream(
         if span_id is None:
             raise ValueError("invalid span_id")
 
-        if parent_id is None:
-            raise ValueError("invalid parent_id")
-
         if sampled is not None and not isinstance(sampled, bool):
             raise ValueError("invalid sampled value")
 

baseplate/frameworks/pyramid/__init__.py

@@ -402,7 +402,7 @@ def _get_trace_info(self, headers: Mapping[str, str]) -> TraceInfo:
         flags = headers.get("X-Flags", None)
         return TraceInfo.from_upstream(
             headers["X-Trace"],
-            headers["X-Parent"],
+            headers.get("X-Parent", None),
             headers["X-Span"],
             sampled,
             int(flags) if flags is not None else None,

baseplate/frameworks/thrift/__init__.py

@@ -205,7 +205,7 @@ def call_processor_with_span_context(
                 flags = headers.get(b"Flags", None)
                 trace_info = TraceInfo.from_upstream(
                     headers[b"Trace"].decode(),
-                    headers[b"Parent"].decode(),
+                    headers.get(b"Parent", b"").decode(),
                     headers[b"Span"].decode(),
                     sampled,
                     int(flags) if flags is not None else None,

tests/unit/core_tests.py

@@ -319,6 +319,11 @@ def test_new_does_not_have_parent_id(self):
         new_trace_info = TraceInfo.new()
         self.assertIsNone(new_trace_info.parent_id)
 
+    def test_new_sets_trace_and_span_ids(self):
+        new_trace_info = TraceInfo.new()
+        self.assertIsNotNone(new_trace_info.trace_id)
+        self.assertIsNotNone(new_trace_info.span_id)
+
     def test_new_does_not_set_flags(self):
         new_trace_info = TraceInfo.new()
         self.assertIsNone(new_trace_info.flags)
@@ -341,3 +346,10 @@ def test_from_upstream_handles_no_sampled_or_flags(self):
         span = TraceInfo.from_upstream(1, 2, 3, None, None)
         self.assertIsNone(span.sampled)
         self.assertIsNone(span.flags)
+
+    def test_from_upstream_handles_no_parent(self):
+        """Verify that `parent_id` can be left out without raising an exception."""
+        span = TraceInfo.from_upstream(1, None, 3, None, None)
+        self.assertIsNone(span.parent_id)
+        self.assertIsNotNone(span.trace_id)
+        self.assertIsNotNone(span.span_id)