[WIP] Add TraceState.

api/include/opentelemetry/trace/span_context.h

@@ -0,0 +1,63 @@
+// Copyright 2020, OpenTelemetry 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.
+
+#pragma once
+
+//#include <cstdint>
+//#include <cstring>
+
+#include "opentelemetry/nostd/unique_ptr.h"
+#include "opentelemetry/trace/span_id.h"
+#include "opentelemetry/trace/trace_flags.h"
+#include "opentelemetry/trace/trace_id.h"
+#include "opentelemetry/trace/trace_state.h"
+
+namespace opentelemetry
+{
+namespace trace
+{
+
+// SpanContext contains the state that must propagate to child Spans and across
+// process boundaries. It contains the identifiers TraceId and SpanId,
+// TraceFlags, TraceState, and whether it has a remote parent.
+class SpanContext final
+{
+public:
+  // An invalid SpanContext.
+  SpanContext() noexcept : trace_state_(new TraceState) {}
+
+  // TODO
+  //
+  // static SpanContext Create(TraceId traceId, SpanId spanId, TraceFlags traceFlags, TraceState
+  // traceState); static SpanContext CreateFromRemoteParent(...);
+
+  const TraceId &trace_id() const noexcept { return trace_id_; }
+  const SpanId &span_id() const noexcept { return span_id_; }
+  const TraceFlags &trace_flags() const noexcept { return trace_flags_; }
+  const TraceState &trace_state() const noexcept { return *trace_state_; }
+
+  bool IsValid() const noexcept { return trace_id_.IsValid() && span_id_.IsValid(); }
+
+  bool HasRemoteParent() const noexcept { return remote_parent_; }
+
+private:
+  const TraceId trace_id_;
+  const SpanId span_id_;
+  const TraceFlags trace_flags_;
+  const nostd::unique_ptr<TraceState> trace_state_;  // Never nullptr.
+  const bool remote_parent_ = false;
+};
+
+}  // namespace trace
+}  // namespace opentelemetry

api/include/opentelemetry/trace/trace_state.h

@@ -0,0 +1,107 @@
+// Copyright 2020, OpenTelemetry 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.
+
+#pragma once
+
+#include <cstdint>
+#include <cstring>
+
+#include "opentelemetry/nostd/span.h"
+#include "opentelemetry/nostd/string_view.h"
+
+namespace opentelemetry
+{
+namespace trace
+{
+
+// TraceState carries tracing-system specific context in a list of key-value pairs. TraceState
+// allows different vendors to propagate additional information and inter-operate with their legacy
+// Id formats.
+//
+// Implementation is optimized for a small list of key-value pairs.
+//
+// Key is opaque string up to 256 characters printable. It MUST begin with a lowercase letter,
+// and can only contain lowercase letters a-z, digits 0-9, underscores _, dashes -, asterisks *, and
+// forward slashes /.
+//
+// Value is opaque string up to 256 characters, of printable ASCII RFC0020 characters (i.e. the
+// range 0x20 to 0x7E) except comma , and equals =.
+class TraceState
+{
+public:
+  static constexpr int kKeyMaxSize       = 256;
+  static constexpr int kValueMaxSize     = 256;
+  static constexpr int kMaxKeyValuePairs = 32;
+
+  class Entry
+  {
+  public:
+    virtual ~Entry() {}
+
+    virtual nostd::string_view key()   = 0;
+    virtual nostd::string_view value() = 0;
+  };
+
+  // An empty TraceState.
+  TraceState() noexcept = default;
+
+  virtual ~TraceState() = default;
+
+  // Returns false if no such key, otherwise returns true and populates value.
+  virtual bool Get(nostd::string_view key, nostd::string_view *value) const noexcept
+  {
+    return false;
+  }
+
+  // Returns true if there are no keys.
+  virtual bool empty() const noexcept { return true; }
+
+  // Returns a span of all the entries. The TraceState object must outlive the span.
+  virtual nostd::span<Entry *> entries() const noexcept { return {}; }
+
+  // Key is opaque string up to 256 characters printable. It MUST begin with a lowercase letter, and
+  // can only contain lowercase letters a-z, digits 0-9, underscores _, dashes -, asterisks *, and
+  // forward slashes /.  For multi-tenant vendor scenarios, an at sign (@) can be used to prefix the
+  // vendor name.
+  static bool IsValidKey(nostd::string_view key)
+  {
+    if (key.empty() || key.length() > kKeyMaxSize || !IsNumberOrDigit(key[0]))
+    {
+      return false;
+    }
+    int ats     = 0;
+    const int n = key.length();
+    for (int i = 0; i < n; ++i)
+    {
+      char c = key[i];
+      if (!IsNumberOrDigit(c) && c != '_' && c != '-' && c != '@' && c != '*' && c != '/')
+      {
+        return false;
+      }
+      if ((c == '@') && (++ats > 1))
+      {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  // TODO: IsValidValue
+
+private:
+  static bool IsNumberOrDigit(char c) { return (c >= 'a' && c <= 'z') || (c >= '0' && c <= '9'); }
+};
+
+}  // namespace trace
+}  // namespace opentelemetry

api/test/trace/BUILD

@@ -17,6 +17,17 @@ otel_cc_benchmark(
     deps = ["//api"],
 )
 
+cc_test(
+    name = "span_context_test",
+    srcs = [
+        "span_context_test.cc",
+    ],
+    deps = [
+        "//api",
+        "@com_google_googletest//:gtest_main",
+    ],
+)
+
 cc_test(
     name = "span_id_test",
     srcs = [
@@ -49,3 +60,14 @@ cc_test(
         "@com_google_googletest//:gtest_main",
     ],
 )
+
+cc_test(
+    name = "trace_state_test",
+    srcs = [
+        "trace_state_test.cc",
+    ],
+    deps = [
+        "//api",
+        "@com_google_googletest//:gtest_main",
+    ],
+)

api/test/trace/span_context_test.cc

@@ -0,0 +1,15 @@
+#include "opentelemetry/trace/span_context.h"
+
+#include <gtest/gtest.h>
+
+namespace
+{
+
+using opentelemetry::trace::SpanContext;
+
+TEST(SpanContextTest, DefaultConstruction)
+{
+  SpanContext ctx;
+}
+
+}  // namespace

api/test/trace/trace_state_test.cc

@@ -0,0 +1,17 @@
+#include "opentelemetry/trace/trace_state.h"
+
+#include <gtest/gtest.h>
+
+namespace
+{
+
+using opentelemetry::trace::TraceState;
+
+TEST(TraceStateTest, DefaultConstruction)
+{
+  TraceState s;
+  EXPECT_FALSE(s.Get("key", nullptr));
+  EXPECT_TRUE(s.empty());
+  EXPECT_EQ(0, s.entries().size());
+}
+}  // namespace