Add RPC semantic attributes

Author: slashmo

Sources/OpenTelemetryInstrumentationSupport/SpanAttribute+RPCSemantics.swift

@@ -0,0 +1,62 @@
+//===----------------------------------------------------------------------===//
+//
+// This source file is part of the Swift Distributed Tracing open source project
+//
+// Copyright (c) 2020 Moritz Lang and the Swift Tracing project authors
+// Licensed under Apache License v2.0
+//
+// See LICENSE.txt for license information
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+//===----------------------------------------------------------------------===//
+
+import TracingInstrumentation
+
+extension SpanAttributeName {
+    /// - See: RPCAttributes
+    public static let rpcSystem = "rpc.system"
+    /// - See: RPCAttributes
+    public static let rpcService = "rpc.service"
+    /// - See: RPCAttributes
+    public static let rpcMethod = "rpc.method"
+}
+
+#if swift(>=5.2)
+extension SpanAttributes {
+    /// Semantic conventions for RPC spans.
+    public var rpc: RPCAttributes {
+        get {
+            .init(attributes: self)
+        }
+        set {
+            self = newValue.attributes
+        }
+    }
+}
+
+/// Semantic conventions for RPC spans as defined in the OpenTelemetry spec.
+///
+/// - SeeAlso: [OpenTelemetry: Semantic conventions for RPC spans](https://github.com/open-telemetry/opentelemetry-specification/blob/b70565d5a8a13d26c91fb692879dc874d22c3ac8/specification/trace/semantic_conventions/rpc.md) (as of August 2020)
+@dynamicMemberLookup
+public struct RPCAttributes: SpanAttributeNamespace {
+    public var attributes: SpanAttributes
+
+    public init(attributes: SpanAttributes) {
+        self.attributes = attributes
+    }
+
+    public struct NestedAttributes: NestedSpanAttributesProtocol {
+        public init() {}
+
+        /// A string identifying the remoting system, e.g., "grpc", "java_rmi" or "wcf".
+        public var system: SpanAttributeKey<String> { .init(name: SpanAttributeName.rpcSystem) }
+
+        /// The full name of the service being called, including its package name, if applicable.
+        public var service: SpanAttributeKey<String> { .init(name: SpanAttributeName.rpcService) }
+
+        /// The name of the method being called, must be equal to the $method part in the span name.
+        public var method: SpanAttributeKey<String> { .init(name: SpanAttributeName.rpcMethod) }
+    }
+}
+#endif