Add constants for predefined tags.

BUILD.bazel

@@ -1,7 +1,7 @@
 cc_library(
     name = "opentracing",
-    srcs = glob(["src/*.cpp"], exclude=["src/dynamic_load_unsupported.cpp"]),
-    hdrs = glob(["include/opentracing/*.h"]) + [
+    srcs = glob(["src/**/*.cpp"], exclude=["src/dynamic_load_unsupported.cpp"]),
+    hdrs = glob(["include/opentracing/**/*.h"]) + [
         ":include/opentracing/config.h",
         ":include/opentracing/version.h",
     ],

CMakeLists.txt

@@ -105,7 +105,8 @@ set(SRCS src/propagation.cpp
          src/dynamic_load.cpp
          src/noop.cpp
          src/tracer.cpp
-         src/tracer_factory.cpp)
+         src/tracer_factory.cpp
+         src/ext/tags.cpp)
 
 if (BUILD_DYNAMIC_LOADING)
   list(APPEND SRCS src/dynamic_load_unix.cpp)

include/opentracing/ext/tags.h

@@ -0,0 +1,121 @@
+#ifndef OPENTRACING_EXT_TAGS_H
+#define OPENTRACING_EXT_TAGS_H
+
+#include <opentracing/string_view.h>
+#include <opentracing/version.h>
+
+namespace opentracing {
+BEGIN_OPENTRACING_ABI_NAMESPACE
+namespace ext {
+// The following tags are described in greater detail at the following url:
+// https://github.com/opentracing/specification/blob/master/semantic_conventions.md
+//
+// Here we define standard names for tags that can be added to spans by the
+// instrumentation code. The actual tracing systems are not required to
+// retain these as tags in the stored spans if they have other means of
+// representing the same data. For example, the SPAN_KIND='server' can be
+// inferred from a Zipkin span by the presence of ss/sr annotations.
+
+// ---------------------------------------------------------------------------
+// span_kind hints at relationship between spans, e.g. client/server
+// ---------------------------------------------------------------------------
+extern const opentracing::string_view span_kind;
+
+// Marks a span representing the client-side of an RPC or other remote call
+extern const opentracing::string_view span_kind_rpc_client;
+
+// Marks a span representing the server-side of an RPC or other remote call
+extern const opentracing::string_view span_kind_rpc_server;
+
+// ---------------------------------------------------------------------------
+// error indicates whether a Span ended in an error state.
+// ---------------------------------------------------------------------------
+extern const opentracing::string_view error;
+
+// ---------------------------------------------------------------------------
+// component (string) ia s low-cardinality identifier of the module, library,
+// or package that is generating a span.
+// ---------------------------------------------------------------------------
+extern const opentracing::string_view component;
+
+// ---------------------------------------------------------------------------
+// sampling_priority (uint16) determines the priority of sampling this Span.
+// ---------------------------------------------------------------------------
+extern const opentracing::string_view sampling_priority;
+
+// ---------------------------------------------------------------------------
+// peer_* tags can be emitted by either client-side of server-side to describe
+// the other side/service in a peer-to-peer communications, like an RPC call.
+// ---------------------------------------------------------------------------
+// peer_service (string) records the service name of the peer
+extern const opentracing::string_view peer_service;
+
+// peer_hostname (string) records the host name of the peer
+extern const opentracing::string_view peer_hostname;
+
+// peer_address (string) suitable for use in a networking client library.
+// This may be a "ip:port", a bare "hostname", a FQDN, or even a
+// JDBC substring like "mysql://prod-db:3306"
+extern const opentracing::string_view peer_address;
+
+// peer_host_ipv4 (uint32) records IP v4 host address of the peer
+extern const opentracing::string_view peer_host_ipv4;
+
+// peer_host_ipv6 (string) records IP v6 host address of the peer
+extern const opentracing::string_view peer_host_ipv6;
+
+// peer_port (uint16) records port number of the peer
+extern const opentracing::string_view peer_port;
+
+// ---------------------------------------------------------------------------
+// HTTP tags
+// ---------------------------------------------------------------------------
+
+// http_url (string) should be the URL of the request being handled in this
+// segment of the trace, in standard URI format. The protocol is optional.
+extern const opentracing::string_view http_url;
+
+// http_method (string) is the HTTP method of the request.
+// Both upper/lower case values are allowed.
+extern const opentracing::string_view http_method;
+
+// http_status_code (int) is the numeric HTTP status code (200, 404, etc)
+// of the HTTP response.
+extern const opentracing::string_view http_status_code;
+
+// ---------------------------------------------------------------------------
+// DATABASE tags
+// ---------------------------------------------------------------------------
+
+// database_instance (string) The database instance name. E.g., In java, if
+// the jdbc.url="jdbc:mysql://127.0.0.1:3306/customers", the instance
+// name is "customers"
+extern const opentracing::string_view database_instance;
+
+// database_statement (string) A database statement for the given database
+// type. E.g., for db.type="SQL", "SELECT * FROM user_table";
+// for db.type="redis", "SET mykey 'WuValue'".
+extern const opentracing::string_view database_statement;
+
+// database_type (string) For any SQL database, "sql". For others,
+// the lower-case database category, e.g. "cassandra", "hbase", or "redis".
+extern const opentracing::string_view database_type;
+
+// database_user (string) Username for accessing database. E.g.,
+// "readonly_user" or "reporting_user"
+extern const opentracing::string_view database_user;
+
+// ---------------------------------------------------------------------------
+// message_bus tags
+// ---------------------------------------------------------------------------
+
+// message_bus_destination (string) An address at which messages can be
+// exchanged. E.g. A Kafka record has an associated "topic name" that can
+// be extracted by the instrumented producer or consumer and stored
+// using this tag.
+extern const opentracing::string_view message_bus_destination;
+}  // namespace ext
+END_OPENTRACING_ABI_NAMESPACE
+}  // namespace opentracing
+
+#endif  // OPENTRACING_EXT_TAGS_H

include/opentracing/value.h

@@ -53,6 +53,7 @@ class Value : public variant_type {
 
   Value(const std::string& s) : variant_type(s) {}
   Value(std::string&& s) : variant_type(std::move(s)) {}
+  Value(opentracing::string_view s) : variant_type(std::string{s}) {}
 
   Value(const Values& values) : variant_type(values) {}
   Value(Values&& values) : variant_type(std::move(values)) {}

src/ext/tags.cpp

@@ -0,0 +1,37 @@
+#include <opentracing/ext/tags.h>
+
+namespace opentracing {
+BEGIN_OPENTRACING_ABI_NAMESPACE
+namespace ext {
+const opentracing::string_view span_kind = "span.kind";
+const opentracing::string_view span_kind_rpc_client = "client";
+const opentracing::string_view span_kind_rpc_server = "server";
+
+const opentracing::string_view error = "error";
+
+const opentracing::string_view component = "component";
+
+const opentracing::string_view sampling_priority = "sampling.priority";
+
+const opentracing::string_view peer_service = "peer.service";
+
+extern const opentracing::string_view peer_hostname = "peer.hostname";
+extern const opentracing::string_view peer_address = "peer.address";
+extern const opentracing::string_view peer_host_ipv4 = "peer.ipv4";
+extern const opentracing::string_view peer_host_ipv6 = "peer.ipv6";
+extern const opentracing::string_view peer_port = "peer.port";
+
+extern const opentracing::string_view http_url = "http.url";
+extern const opentracing::string_view http_method = "http.method";
+extern const opentracing::string_view http_status_code = "http.status_code";
+
+extern const opentracing::string_view database_instance = "db.instance";
+extern const opentracing::string_view database_statement = "db.statement";
+extern const opentracing::string_view database_type = "db.type";
+extern const opentracing::string_view database_user = "db.user";
+
+extern const opentracing::string_view message_bus_destination =
+    "message_bus.destination";
+}  // namespace ext
+END_OPENTRACING_ABI_NAMESPACE
+}  // namespace opentracing

test/tracer_test.cpp

@@ -1,3 +1,4 @@
+#include <opentracing/ext/tags.h>
 #include <opentracing/noop.h>
 #include <opentracing/tracer.h>
 using namespace opentracing;
@@ -20,6 +21,8 @@ TEST_CASE("tracer") {
     CHECK(span2);
     span2->SetOperationName("b1");
     span2->SetTag("x", true);
+    span2->SetTag(opentracing::ext::span_kind,
+                  opentracing::ext::span_kind_rpc_client);
     CHECK(span2->BaggageItem("y").empty());
     span2->Log({{"event", "xyz"}, {"abc", 123}});
     span2->Finish();