Add Span kind to the Span.

opencensus/proto/trace/trace.proto

@@ -31,6 +31,8 @@ option go_package = "traceproto";
 // its sub-operations. A trace can also contain multiple root spans,
 // or none at all. Spans do not need to be contiguous - there may be
 // gaps or overlaps between spans in a trace.
+//
+// The next id is 15.
 // TODO(bdrutu): Add an example.
 message Span {
   // A unique identifier for a trace. All spans from the same trace share
@@ -59,6 +61,26 @@ message Span {
   // This field is required.
   TruncatableString name = 4;
 
+  // Type of span. Can be used to specify additional relationships between spans
+  // in addition to a parent/child relationship.
+  enum SpanKind {
+    // Unspecified.
+    SPAN_KIND_UNSPECIFIED = 0;
+
+    // Indicates that the span covers server-side handling of an RPC or other
+    // remote network request.
+    SERVER = 1;
+
+    // Indicates that the span covers the client-side wrapper around an RPC or
+    // other remote request.
+    CLIENT = 2;
+  }
+
+  // Distinguishes between spans generated in a particular context. For example,
+  // two spans with the same name may be distinguished using `CLIENT`
+  // and `SERVER` to identify queueing latency associated with the span.
+  SpanKind kind = 14;
+
   // The start time of the span. On the client side, this is the time kept by
   // the local machine where the span execution starts. On the server side, this
   // is the time when the server's application handler starts running.