Handle B3 trace_id and span_id correctly

Fixes open-telemetry#933

These fields are not being handled correctly when one or both of them
receive invalid values.

opentelemetry-sdk/src/opentelemetry/sdk/trace/propagation/b3_format.py

@@ -13,8 +13,10 @@
 # limitations under the License.
 
 import typing
+from re import fullmatch
 
 import opentelemetry.trace as trace
+from opentelemetry.sdk.trace import generate_trace_id, generate_span_id
 from opentelemetry.context import Context
 from opentelemetry.trace.propagation.httptextformat import (
     Getter,
@@ -95,19 +97,33 @@ def extract(
                 or flags
             )
 
+        if (
+            fullmatch(r"[\da-fA-F]{16}|[\da-fA-F]{32}", trace_id) is None or
+            fullmatch(r"[\da-fA-F]{16}", span_id) is None
+        ):
+            trace_id = generate_trace_id()
+            span_id = generate_span_id()
+
         options = 0
         # The b3 spec provides no defined behavior for both sample and
         # flag values set. Since the setting of at least one implies
         # the desire for some form of sampling, propagate if either
         # header is set to allow.
         if sampled in self._SAMPLE_PROPAGATE_VALUES or flags == "1":
             options |= trace.TraceFlags.SAMPLED
+
+        if isinstance(trace_id, str):
+            trace_id = int(trace_id, 16)
+
+        if isinstance(span_id, str):
+            span_id = int(span_id, 16)
+
         return trace.set_span_in_context(
             trace.DefaultSpan(
                 trace.SpanContext(
                     # trace an span ids are encoded in hex, so must be converted
-                    trace_id=int(trace_id, 16),
-                    span_id=int(span_id, 16),
+                    trace_id=trace_id,
+                    span_id=span_id,
                     is_remote=True,
                     trace_flags=trace.TraceFlags(options),
                     trace_state=trace.TraceState(),
@@ -123,7 +139,7 @@ def inject(
     ) -> None:
         span = trace.get_current_span(context=context)
 
-        if span.get_context() == trace.INVALID_SPAN_CONTEXT:
+        if span is None:
             return
 
         sampled = (trace.TraceFlags.SAMPLED & span.context.trace_flags) != 0