Add GetCurrentSpan() and GetSpanFromContext(). (#211)

Author: g-easy

opencensus/context/context.h

@@ -26,6 +26,7 @@ namespace tags {
 class WithTagMap;
 }  // namespace tags
 namespace trace {
+class ContextPeer;
 class WithSpan;
 }  // namespace trace
 namespace context {
@@ -66,6 +67,7 @@ class Context {
   friend class ContextTestPeer;
   friend class WithContext;
   friend class ::opencensus::tags::WithTagMap;
+  friend class ::opencensus::trace::ContextPeer;
   friend class ::opencensus::trace::WithSpan;
 
   opencensus::tags::TagMap tags_;

opencensus/trace/BUILD

@@ -92,6 +92,18 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "context_util",
+    srcs = ["internal/context_util.cc"],
+    hdrs = ["context_util.h"],
+    copts = DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+    deps = [
+        ":trace",
+        "//opencensus/context",
+    ],
+)
+
 cc_library(
     name = "with_span",
     srcs = ["internal/with_span.cc"],
@@ -140,6 +152,19 @@ cc_test(
     ],
 )
 
+cc_test(
+    name = "context_util_test",
+    srcs = ["internal/context_util_test.cc"],
+    copts = TEST_COPTS,
+    deps = [
+        ":context_util",
+        ":trace",
+        ":with_span",
+        "//opencensus/context",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "link_test",
     srcs = ["internal/link_test.cc"],

opencensus/trace/context_util.h

@@ -0,0 +1,33 @@
+// Copyright 2018, OpenCensus 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.
+
+#ifndef OPENCENSUS_TRACE_CONTEXT_UTIL_H_
+#define OPENCENSUS_TRACE_CONTEXT_UTIL_H_
+
+#include "opencensus/context/context.h"
+#include "opencensus/trace/span.h"
+
+namespace opencensus {
+namespace trace {
+
+// Returns the Span from the current Context.
+const Span& GetCurrentSpan();
+
+// Returns the Span from the given Context.
+const Span& GetSpanFromContext(const opencensus::context::Context& ctx);
+
+}  // namespace trace
+}  // namespace opencensus
+
+#endif  // OPENCENSUS_TRACE_CONTEXT_UTIL_H_

opencensus/trace/internal/context_util.cc

@@ -0,0 +1,39 @@
+// Copyright 2018, OpenCensus 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.
+
+#include "opencensus/trace/context_util.h"
+
+#include "opencensus/context/context.h"
+#include "opencensus/trace/span.h"
+
+using ::opencensus::context::Context;
+
+namespace opencensus {
+namespace trace {
+
+class ContextPeer {
+ public:
+  static const Span& GetSpanFromContext(const Context& ctx) {
+    return ctx.span_;
+  }
+};
+
+const Span& GetCurrentSpan() { return GetSpanFromContext(Context::Current()); }
+
+const Span& GetSpanFromContext(const Context& ctx) {
+  return ContextPeer::GetSpanFromContext(ctx);
+}
+
+}  // namespace trace
+}  // namespace opencensus

opencensus/trace/internal/context_util_test.cc

@@ -0,0 +1,55 @@
+// Copyright 2018, OpenCensus 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.
+
+#include "opencensus/trace/context_util.h"
+
+#include "gtest/gtest.h"
+#include "opencensus/context/context.h"
+#include "opencensus/trace/span.h"
+#include "opencensus/trace/span_context.h"
+#include "opencensus/trace/with_span.h"
+
+// Not in namespace ::opencensus::context in order to better reflect what user
+// code should look like.
+
+namespace {
+
+TEST(FromContextTest, GetCurrentSpan) {
+  opencensus::trace::SpanContext zeroed_span_context;
+  auto span = opencensus::trace::Span::StartSpan("MySpan");
+  EXPECT_EQ(zeroed_span_context, opencensus::trace::GetCurrentSpan().context());
+  {
+    opencensus::trace::WithSpan ws(span);
+    EXPECT_EQ(span.context(), opencensus::trace::GetCurrentSpan().context());
+  }
+  span.End();
+}
+
+TEST(FromContextTest, GetSpanFromContext) {
+  opencensus::trace::SpanContext zeroed_span_context;
+  auto span = opencensus::trace::Span::StartSpan("MySpan");
+  opencensus::context::Context ctx = opencensus::context::Context::Current();
+  EXPECT_EQ(zeroed_span_context,
+            opencensus::trace::GetSpanFromContext(ctx).context());
+  {
+    opencensus::trace::WithSpan ws(span);
+    ctx = opencensus::context::Context::Current();
+  }
+  EXPECT_EQ(zeroed_span_context, opencensus::trace::GetCurrentSpan().context());
+  EXPECT_EQ(span.context(),
+            opencensus::trace::GetSpanFromContext(ctx).context());
+  span.End();
+}
+
+}  // namespace