Add GetCurrentTagMap() and GetTagMapFromContext(). (#218)

Author: g-easy

opencensus/context/context.h

@@ -23,6 +23,7 @@
 
 namespace opencensus {
 namespace tags {
+class ContextPeer;
 class WithTagMap;
 }  // namespace tags
 namespace trace {
@@ -66,6 +67,7 @@ class Context {
 
   friend class ContextTestPeer;
   friend class WithContext;
+  friend class ::opencensus::tags::ContextPeer;
   friend class ::opencensus::tags::WithTagMap;
   friend class ::opencensus::trace::ContextPeer;
   friend class ::opencensus::trace::WithSpan;

opencensus/tags/BUILD

@@ -41,6 +41,18 @@ cc_library(
     ],
 )
 
+cc_library(
+    name = "context_util",
+    srcs = ["internal/context_util.cc"],
+    hdrs = ["context_util.h"],
+    copts = DEFAULT_COPTS,
+    visibility = ["//visibility:public"],
+    deps = [
+        ":tags",
+        "//opencensus/context",
+    ],
+)
+
 cc_library(
     name = "with_tag_map",
     srcs = ["internal/with_tag_map.cc"],
@@ -56,6 +68,19 @@ cc_library(
 # Tests
 # ========================================================================= #
 
+cc_test(
+    name = "context_util_test",
+    srcs = ["internal/context_util_test.cc"],
+    copts = TEST_COPTS,
+    deps = [
+        ":context_util",
+        ":tags",
+        ":with_tag_map",
+        "//opencensus/context",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "tag_key_test",
     srcs = ["internal/tag_key_test.cc"],

opencensus/tags/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_TAGS_CONTEXT_UTIL_H_
+#define OPENCENSUS_TAGS_CONTEXT_UTIL_H_
+
+#include "opencensus/context/context.h"
+#include "opencensus/tags/tag_map.h"
+
+namespace opencensus {
+namespace tags {
+
+// Returns the TagMap from the current Context.
+const TagMap& GetCurrentTagMap();
+
+// Returns the TagMap from the given Context.
+const TagMap& GetTagMapFromContext(const opencensus::context::Context& ctx);
+
+}  // namespace tags
+}  // namespace opencensus
+
+#endif  // OPENCENSUS_TAGS_CONTEXT_UTIL_H_

opencensus/tags/internal/context_util.cc

@@ -0,0 +1,41 @@
+// 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/tags/context_util.h"
+
+#include "opencensus/context/context.h"
+#include "opencensus/tags/tag_map.h"
+
+using ::opencensus::context::Context;
+
+namespace opencensus {
+namespace tags {
+
+class ContextPeer {
+ public:
+  static const TagMap& GetTagMapFromContext(const Context& ctx) {
+    return ctx.tags_;
+  }
+};
+
+const TagMap& GetCurrentTagMap() {
+  return GetTagMapFromContext(Context::Current());
+}
+
+const TagMap& GetTagMapFromContext(const Context& ctx) {
+  return ContextPeer::GetTagMapFromContext(ctx);
+}
+
+}  // namespace tags
+}  // namespace opencensus

opencensus/tags/internal/context_util_test.cc

@@ -0,0 +1,53 @@
+// 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/tags/context_util.h"
+
+#include "gtest/gtest.h"
+#include "opencensus/context/context.h"
+#include "opencensus/tags/tag_key.h"
+#include "opencensus/tags/tag_map.h"
+#include "opencensus/tags/with_tag_map.h"
+
+// Not in namespace ::opencensus::context in order to better reflect what user
+// code should look like.
+
+namespace {
+
+// Returns an example TagMap for testing.
+opencensus::tags::TagMap Tags1() {
+  static const auto k1 = opencensus::tags::TagKey::Register("key1");
+  static const auto k2 = opencensus::tags::TagKey::Register("key2");
+  return opencensus::tags::TagMap({{k1, "val1"}, {k2, "val2"}});
+}
+
+TEST(FromContextTest, GetCurrentTagMap) {
+  EXPECT_TRUE(opencensus::tags::GetCurrentTagMap().tags().empty());
+  {
+    opencensus::tags::WithTagMap wt(Tags1());
+    EXPECT_EQ(Tags1().tags(), opencensus::tags::GetCurrentTagMap().tags());
+  }
+}
+
+TEST(FromContextTest, GetTagMapFromContext) {
+  opencensus::context::Context ctx = opencensus::context::Context::Current();
+  EXPECT_TRUE(opencensus::tags::GetTagMapFromContext(ctx).tags().empty());
+  {
+    opencensus::tags::WithTagMap wt(Tags1());
+    ctx = opencensus::context::Context::Current();
+  }
+  EXPECT_EQ(Tags1().tags(), opencensus::tags::GetTagMapFromContext(ctx).tags());
+}
+
+}  // namespace