api: adding trace.get_current_span (open-telemetry#552)

The span context is no longer coupled with the tracer itself.
As such, providing a get_current_span method bound to the
trace api module rather than a specific tracer is semantically
correct, and removes a hurdle where someone who wants to retrieve
the current trace would have to create a tracer to do so.

renaming and exporting get_span_in_context to get_current_span,
as the intention of the API is similar, and reduces unneeded
aliasing and duplication.

set_span_in_context is not renamed, as set_current_span would have
implied that the span would then be active in the default context,
which is only true after attaching the resulting context returned
by set_span_in_context. Keeping that name at least implies some
asymmetric behavior from get_current_span.

After discussion in the SIG, we decided to remove the
legacy get_current_span APIs from Tracer and TracerProvider
to reduce long-term confusion of how to idiomatically retrieve
the span.

Co-authored-by: alrex <aboten@lightstep.com>
Co-authored-by: Hector Hernandez <39923391+hectorhdzg@users.noreply.github.com>
Co-authored-by: Leighton Chen <lechen@microsoft.com>
Co-authored-by: Diego Hurtado <ocelotl@users.noreply.github.com>
Co-authored-by: Mauricio Vásquez <mauricio@kinvolk.io>
Co-authored-by: Andrew Xue <aaxue@google.com>
Co-authored-by: Cheng-Lung Sung <clsung@gmail.com>

docs/api/trace.rst

@@ -8,8 +8,9 @@ Submodules
 
    trace.sampling
    trace.status
+   trace.span
 
 Module contents
 ---------------
 
-.. automodule:: opentelemetry.trace
+.. automodule:: opentelemetry.trace

docs/api/trace.span.rst

@@ -0,0 +1,7 @@
+opentelemetry.trace.span
+========================
+
+.. automodule:: opentelemetry.trace.span
+    :members:
+    :undoc-members:
+    :show-inheritance:

ext/opentelemetry-ext-aiohttp-client/src/opentelemetry/ext/aiohttp_client/__init__.py

@@ -145,7 +145,7 @@ async def on_request_start(
         )
 
         trace_config_ctx.token = context_api.attach(
-            trace.propagation.set_span_in_context(trace_config_ctx.span)
+            trace.set_span_in_context(trace_config_ctx.span)
         )
 
         propagators.inject(type(params.headers).__setitem__, params.headers)

ext/opentelemetry-ext-datadog/src/opentelemetry/ext/datadog/propagator.py

@@ -16,10 +16,7 @@
 
 from opentelemetry import trace
 from opentelemetry.context import Context
-from opentelemetry.trace.propagation import (
-    get_span_from_context,
-    set_span_in_context,
-)
+from opentelemetry.trace import get_current_span, set_span_in_context
 from opentelemetry.trace.propagation.httptextformat import (
     Getter,
     HTTPTextFormat,
@@ -88,7 +85,7 @@ def inject(
         carrier: HTTPTextFormatT,
         context: typing.Optional[Context] = None,
     ) -> None:
-        span = get_span_from_context(context=context)
+        span = get_current_span(context)
         sampled = (trace.TraceFlags.SAMPLED & span.context.trace_flags) != 0
         set_in_carrier(
             carrier, self.TRACE_ID_KEY, format_trace_id(span.context.trace_id),

ext/opentelemetry-ext-datadog/tests/test_datadog_format.py

@@ -17,10 +17,7 @@
 from opentelemetry import trace as trace_api
 from opentelemetry.ext.datadog import constants, propagator
 from opentelemetry.sdk import trace
-from opentelemetry.trace.propagation import (
-    get_span_from_context,
-    set_span_in_context,
-)
+from opentelemetry.trace import get_current_span, set_span_in_context
 
 FORMAT = propagator.DatadogFormat()
 
@@ -45,7 +42,7 @@ def test_malformed_headers(self):
         """Test with no Datadog headers"""
         malformed_trace_id_key = FORMAT.TRACE_ID_KEY + "-x"
         malformed_parent_id_key = FORMAT.PARENT_ID_KEY + "-x"
-        context = get_span_from_context(
+        context = get_current_span(
             FORMAT.extract(
                 get_as_list,
                 {
@@ -66,7 +63,7 @@ def test_missing_trace_id(self):
         }
 
         ctx = FORMAT.extract(get_as_list, carrier)
-        span_context = get_span_from_context(ctx).get_context()
+        span_context = get_current_span(ctx).get_context()
         self.assertEqual(span_context.trace_id, trace_api.INVALID_TRACE_ID)
 
     def test_missing_parent_id(self):
@@ -76,12 +73,12 @@ def test_missing_parent_id(self):
         }
 
         ctx = FORMAT.extract(get_as_list, carrier)
-        span_context = get_span_from_context(ctx).get_context()
+        span_context = get_current_span(ctx).get_context()
         self.assertEqual(span_context.span_id, trace_api.INVALID_SPAN_ID)
 
     def test_context_propagation(self):
         """Test the propagation of Datadog headers."""
-        parent_context = get_span_from_context(
+        parent_context = get_current_span(
             FORMAT.extract(
                 get_as_list,
                 {
@@ -138,7 +135,7 @@ def test_context_propagation(self):
 
     def test_sampling_priority_auto_reject(self):
         """Test sampling priority rejected."""
-        parent_context = get_span_from_context(
+        parent_context = get_current_span(
             FORMAT.extract(
                 get_as_list,
                 {

ext/opentelemetry-ext-grpc/tests/test_server_interceptor.py

@@ -91,15 +91,13 @@ def test_span_lifetime(self):
         """Check that the span is active for the duration of the call."""
 
         interceptor = server_interceptor()
-        tracer = self.tracer_provider.get_tracer(__name__)
 
         # To capture the current span at the time the handler is called
         active_span_in_handler = None
 
         def handler(request, context):
             nonlocal active_span_in_handler
-            # The current span  is shared among all the tracers.
-            active_span_in_handler = tracer.get_current_span()
+            active_span_in_handler = trace.get_current_span()
             return b""
 
         server = grpc.server(
@@ -112,13 +110,13 @@ def handler(request, context):
         port = server.add_insecure_port("[::]:0")
         channel = grpc.insecure_channel("localhost:{:d}".format(port))
 
-        active_span_before_call = tracer.get_current_span()
+        active_span_before_call = trace.get_current_span()
         try:
             server.start()
             channel.unary_unary("")(b"")
         finally:
             server.stop(None)
-        active_span_after_call = tracer.get_current_span()
+        active_span_after_call = trace.get_current_span()
 
         self.assertIsNone(active_span_before_call)
         self.assertIsNone(active_span_after_call)
@@ -128,15 +126,13 @@ def handler(request, context):
     def test_sequential_server_spans(self):
         """Check that sequential RPCs get separate server spans."""
 
-        tracer = self.tracer_provider.get_tracer(__name__)
-
         interceptor = server_interceptor()
 
         # Capture the currently active span in each thread
         active_spans_in_handler = []
 
         def handler(request, context):
-            active_spans_in_handler.append(tracer.get_current_span())
+            active_spans_in_handler.append(trace.get_current_span())
             return b""
 
         server = grpc.server(
@@ -175,8 +171,6 @@ def test_concurrent_server_spans(self):
         context.
         """
 
-        tracer = self.tracer_provider.get_tracer(__name__)
-
         interceptor = server_interceptor()
 
         # Capture the currently active span in each thread
@@ -185,7 +179,7 @@ def test_concurrent_server_spans(self):
 
         def handler(request, context):
             latch()
-            active_spans_in_handler.append(tracer.get_current_span())
+            active_spans_in_handler.append(trace.get_current_span())
             return b""
 
         server = grpc.server(

ext/opentelemetry-ext-opentracing-shim/src/opentelemetry/ext/opentracing_shim/__init__.py

@@ -94,11 +94,7 @@
 from opentelemetry import propagators
 from opentelemetry.ext.opentracing_shim import util
 from opentelemetry.ext.opentracing_shim.version import __version__
-from opentelemetry.trace import DefaultSpan
-from opentelemetry.trace.propagation import (
-    get_span_from_context,
-    set_span_in_context,
-)
+from opentelemetry.trace import DefaultSpan, set_span_in_context
 
 logger = logging.getLogger(__name__)
 
@@ -473,7 +469,7 @@ def active(self):
             shim and is likely to be handled in future versions.
         """
 
-        span = self._tracer.unwrap().get_current_span()
+        span = trace_api.get_current_span()
         if span is None:
             return None
 
@@ -703,6 +699,10 @@ def get_as_list(dict_object, key):
 
         propagator = propagators.get_global_httptextformat()
         ctx = propagator.extract(get_as_list, carrier)
-        otel_context = get_span_from_context(ctx).get_context()
+        span = trace_api.get_current_span(ctx)
+        if span is not None:
+            otel_context = span.get_context()
+        else:
+            otel_context = trace_api.INVALID_SPAN_CONTEXT
 
         return SpanContextShim(otel_context)

ext/opentelemetry-ext-opentracing-shim/tests/test_shim.py

@@ -24,7 +24,10 @@
 from opentelemetry import propagators, trace
 from opentelemetry.ext.opentracing_shim import util
 from opentelemetry.sdk.trace import TracerProvider
-from opentelemetry.test.mock_httptextformat import MockHTTPTextFormat
+from opentelemetry.test.mock_httptextformat import (
+    MockHTTPTextFormat,
+    NOOPHTTPTextFormat,
+)
 
 
 class TestShim(TestCase):
@@ -515,6 +518,20 @@ def test_extract_http_headers(self):
         self.assertEqual(ctx.unwrap().trace_id, 1220)
         self.assertEqual(ctx.unwrap().span_id, 7478)
 
+    def test_extract_empty_context_returns_invalid_context(self):
+        """In the case where the propagator cannot extract a
+        SpanContext, extract should return and invalid span context.
+        """
+        _old_propagator = propagators.get_global_httptextformat()
+        propagators.set_global_httptextformat(NOOPHTTPTextFormat())
+        try:
+            carrier = {}
+
+            ctx = self.shim.extract(opentracing.Format.HTTP_HEADERS, carrier)
+            self.assertEqual(ctx.unwrap(), trace.INVALID_SPAN_CONTEXT)
+        finally:
+            propagators.set_global_httptextformat(_old_propagator)
+
     def test_extract_text_map(self):
         """Test `extract()` method for Format.TEXT_MAP."""
 

ext/opentelemetry-ext-wsgi/src/opentelemetry/ext/wsgi/__init__.py

@@ -62,7 +62,6 @@ def hello():
 from opentelemetry import context, propagators, trace
 from opentelemetry.ext.wsgi.version import __version__
 from opentelemetry.instrumentation.utils import http_status_to_canonical_code
-from opentelemetry.trace.propagation import get_span_from_context
 from opentelemetry.trace.status import Status, StatusCanonicalCode
 
 _HTTP_VERSION_PREFIX = "HTTP/"

opentelemetry-api/CHANGELOG.md

@@ -6,6 +6,8 @@
   ([#751](https://github.com/open-telemetry/opentelemetry-python/pull/751))
 - Rename Measure to ValueRecorder in metrics
   ([#761](https://github.com/open-telemetry/opentelemetry-python/pull/761))
+- Adding trace.get_current_span, Removing Tracer.get_current_span
+  ([#552](https://github.com/open-telemetry/opentelemetry-python/pull/552))
 - Rename Observer to ValueObserver
   ([#764](https://github.com/open-telemetry/opentelemetry-python/pull/764))