Recover the OT context header from the B3 headers if not propagated

source/common/tracing/zipkin/span_context.h

@@ -19,6 +19,17 @@ class SpanContext {
    */
   SpanContext() : trace_id_(0), id_(0), parent_id_(0), is_initialized_(false) {}
 
+  /**
+   * Constructor that creates a context object from the supplied trace, span
+   * and parent ids.
+   *
+   * @param trace_id The trace id.
+   * @param id The span id.
+   * @param parent_id The parent id.
+   */
+  SpanContext(const uint64_t trace_id, const uint64_t id, const uint64_t parent_id)
+      : trace_id_(trace_id), id_(id), parent_id_(parent_id), is_initialized_(true) {}
+
   /**
    * Constructor that creates a context object from the given Zipkin span object.
    *

source/common/tracing/zipkin/zipkin_tracer_impl.cc

@@ -107,6 +107,20 @@ Tracing::SpanPtr Driver::startSpan(const Tracing::Config& config, Http::HeaderMa
 
     new_zipkin_span =
         tracer.startSpan(config, request_headers.Host()->value().c_str(), start_time, context);
+
+  } else if (request_headers.XB3TraceId() && request_headers.XB3SpanId()) {
+    uint64_t parentId(0);
+    if (request_headers.XB3ParentSpanId()) {
+      parentId = std::stoull(request_headers.XB3ParentSpanId()->value().c_str(), nullptr, 16);
+    }
+
+    SpanContext context(std::stoull(request_headers.XB3TraceId()->value().c_str(), nullptr, 16),
+                        std::stoull(request_headers.XB3SpanId()->value().c_str(), nullptr, 16),
+                        parentId);
+
+    new_zipkin_span =
+        tracer.startSpan(config, request_headers.Host()->value().c_str(), start_time, context);
+
   } else {
     // Create a root Zipkin span. No context was found in the headers.
     new_zipkin_span = tracer.startSpan(config, request_headers.Host()->value().c_str(), start_time);

test/common/tracing/zipkin/zipkin_tracer_impl_test.cc

@@ -344,5 +344,51 @@ TEST_F(ZipkinDriverTest, ZipkinSpanTest) {
   EXPECT_EQ("key3", zipkin_zipkin_span3.binaryAnnotations()[0].key());
   EXPECT_EQ("value3", zipkin_zipkin_span3.binaryAnnotations()[0].value());
 }
+
+TEST_F(ZipkinDriverTest, ZipkinSpanContextFromOtSpanContextHeaderTest) {
+  setupValidDriver();
+
+  const std::string trace_id = Hex::uint64ToHex(Util::generateRandom64());
+  const std::string span_id = Hex::uint64ToHex(Util::generateRandom64());
+  const std::string parent_id = Hex::uint64ToHex(Util::generateRandom64());
+  const std::string context =
+      trace_id + ";" + span_id + ";" + parent_id + ";" + ZipkinCoreConstants::get().CLIENT_SEND;
+
+  request_headers_.insertOtSpanContext().value(context);
+
+  // New span will have an SR annotation - so its span and parent ids will be
+  // the same as the supplied span context (i.e. shared context)
+  Tracing::SpanPtr span =
+      driver_->startSpan(config_, request_headers_, operation_name_, start_time_);
+
+  ZipkinSpanPtr zipkin_span(dynamic_cast<ZipkinSpan*>(span.release()));
+
+  EXPECT_EQ(trace_id, zipkin_span->span().traceIdAsHexString());
+  EXPECT_EQ(span_id, zipkin_span->span().idAsHexString());
+  EXPECT_EQ(parent_id, zipkin_span->span().parentIdAsHexString());
+}
+
+TEST_F(ZipkinDriverTest, ZipkinSpanContextFromB3HeadersTest) {
+  setupValidDriver();
+
+  const std::string trace_id = Hex::uint64ToHex(Util::generateRandom64());
+  const std::string span_id = Hex::uint64ToHex(Util::generateRandom64());
+  const std::string parent_id = Hex::uint64ToHex(Util::generateRandom64());
+
+  request_headers_.insertXB3TraceId().value(trace_id);
+  request_headers_.insertXB3SpanId().value(span_id);
+  request_headers_.insertXB3ParentSpanId().value(parent_id);
+
+  // New span will have an SR annotation - so its span and parent ids will be
+  // the same as the supplied span context (i.e. shared context)
+  Tracing::SpanPtr span =
+      driver_->startSpan(config_, request_headers_, operation_name_, start_time_);
+
+  ZipkinSpanPtr zipkin_span(dynamic_cast<ZipkinSpan*>(span.release()));
+
+  EXPECT_EQ(trace_id, zipkin_span->span().traceIdAsHexString());
+  EXPECT_EQ(span_id, zipkin_span->span().idAsHexString());
+  EXPECT_EQ(parent_id, zipkin_span->span().parentIdAsHexString());
+}
 } // namespace Zipkin
 } // namespace Envoy