Add reflection server example (#2149)

Motivation:

We've added back the reflection server; we should have an example of how
to use it.

Modifications:

- Add a reflection server example
- Split the echo service into a separate file in the echo example so
that it can be symlinked from the reflection server

Result:

More examples

.licenseignore

@@ -40,3 +40,4 @@ LICENSE
 **/*.swift
 dev/protos/**/*.proto
 Examples/hello-world/Protos/HelloWorld.proto
+**/*.pb

Examples/echo/Sources/Subcommands/EchoService.swift

@@ -0,0 +1,55 @@
+/*
+ * Copyright 2024, gRPC Authors All rights reserved.
+ *
+ * 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.
+ */
+
+import GRPCCore
+
+struct EchoService: Echo_Echo.SimpleServiceProtocol {
+  func get(
+    request: Echo_EchoRequest,
+    context: ServerContext
+  ) async throws -> Echo_EchoResponse {
+    return .with { $0.text = request.text }
+  }
+
+  func collect(
+    request: RPCAsyncSequence<Echo_EchoRequest, any Error>,
+    context: ServerContext
+  ) async throws -> Echo_EchoResponse {
+    let messages = try await request.reduce(into: []) { $0.append($1.text) }
+    let joined = messages.joined(separator: " ")
+    return .with { $0.text = joined }
+  }
+
+  func expand(
+    request: Echo_EchoRequest,
+    response: RPCWriter<Echo_EchoResponse>,
+    context: ServerContext
+  ) async throws {
+    let parts = request.text.split(separator: " ")
+    let messages = parts.map { part in Echo_EchoResponse.with { $0.text = String(part) } }
+    try await response.write(contentsOf: messages)
+  }
+
+  func update(
+    request: RPCAsyncSequence<Echo_EchoRequest, any Error>,
+    response: RPCWriter<Echo_EchoResponse>,
+    context: ServerContext
+  ) async throws {
+    for try await message in request {
+      try await response.write(.with { $0.text = message.text })
+    }
+  }
+}

Examples/echo/Sources/Subcommands/Serve.swift

@@ -41,41 +41,3 @@ struct Serve: AsyncParsableCommand {
     }
   }
 }
-
-struct EchoService: Echo_Echo.SimpleServiceProtocol {
-  func get(
-    request: Echo_EchoRequest,
-    context: ServerContext
-  ) async throws -> Echo_EchoResponse {
-    return .with { $0.text = request.text }
-  }
-
-  func collect(
-    request: RPCAsyncSequence<Echo_EchoRequest, any Error>,
-    context: ServerContext
-  ) async throws -> Echo_EchoResponse {
-    let messages = try await request.reduce(into: []) { $0.append($1.text) }
-    let joined = messages.joined(separator: " ")
-    return .with { $0.text = joined }
-  }
-
-  func expand(
-    request: Echo_EchoRequest,
-    response: RPCWriter<Echo_EchoResponse>,
-    context: ServerContext
-  ) async throws {
-    let parts = request.text.split(separator: " ")
-    let messages = parts.map { part in Echo_EchoResponse.with { $0.text = String(part) } }
-    try await response.write(contentsOf: messages)
-  }
-
-  func update(
-    request: RPCAsyncSequence<Echo_EchoRequest, any Error>,
-    response: RPCWriter<Echo_EchoResponse>,
-    context: ServerContext
-  ) async throws {
-    for try await message in request {
-      try await response.write(.with { $0.text = message.text })
-    }
-  }
-}

Examples/reflection-server/.gitignore

@@ -0,0 +1,8 @@
+.DS_Store
+/.build
+/Packages
+xcuserdata/
+DerivedData/
+.swiftpm/configuration/registries.json
+.swiftpm/xcode/package.xcworkspace/contents.xcworkspacedata
+.netrc

Examples/reflection-server/Package.swift

@@ -0,0 +1,45 @@
+// swift-tools-version:6.0
+/*
+ * Copyright 2024, gRPC Authors All rights reserved.
+ *
+ * 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.
+ */
+
+import PackageDescription
+
+let package = Package(
+  name: "reflection-server",
+  platforms: [.macOS(.v15)],
+  dependencies: [
+    .package(url: "https://github.com/grpc/grpc-swift.git", branch: "main"),
+    .package(url: "https://github.com/grpc/grpc-swift-protobuf.git", branch: "main"),
+    .package(url: "https://github.com/grpc/grpc-swift-nio-transport.git", branch: "main"),
+    .package(url: "https://github.com/grpc/grpc-swift-extras.git", branch: "main"),
+    .package(url: "https://github.com/apple/swift-argument-parser.git", from: "1.5.0"),
+  ],
+  targets: [
+    .executableTarget(
+      name: "reflection-server",
+      dependencies: [
+        .product(name: "GRPCCore", package: "grpc-swift"),
+        .product(name: "GRPCNIOTransportHTTP2", package: "grpc-swift-nio-transport"),
+        .product(name: "GRPCProtobuf", package: "grpc-swift-protobuf"),
+        .product(name: "GRPCReflectionService", package: "grpc-swift-extras"),
+        .product(name: "ArgumentParser", package: "swift-argument-parser"),
+      ],
+      resources: [
+        .copy("DescriptorSets")
+      ]
+    )
+  ]
+)

Examples/reflection-server/README.md

@@ -0,0 +1,61 @@
+# Reflection Server
+
+This example demonstrates the gRPC Reflection service which is described in more
+detail in the [gRPC documentation](https://github.com/grpc/grpc/blob/6fa8043bf9befb070b846993b59a3348248e6566/doc/server-reflection.md).
+
+## Overview
+
+A 'reflection-server' command line tool that uses the reflection service implementation
+from [grpc/grpc-swift-extras](https://github.com/grpc/grpc-swift-extras) and the
+Echo service (see the 'echo' example).
+
+The reflection service requires you to initialize it with a set of Protobuf file
+descriptors for the services you're offering. You can use `protoc` to create a
+descriptor set including dependencies and source information for each service.
+
+The following command will generate a descriptor set at `path/to/output.pb` from
+the `path/to/input.proto` file with source information and any imports used in
+`input.proto`:
+
+```console
+protoc --descriptor_set_out=path/to/output.pb path/to/input.proto \
+  --include_source_info \
+  --include_imports
+```
+
+## Usage
+
+Build and run the server using the CLI:
+
+```console
+$ swift run reflection-server
+Reflection server listening on [ipv4]127.0.0.1:31415
+```
+
+You can use 'grpcurl' to query the reflection service. If you don't already have
+it installed follow the instructions in the 'grpcurl' project's
+[README](https://github.com/fullstorydev/grpcurl).
+
+You can list all services with:
+
+```console
+$ grpcurl -plaintext 127.0.0.1:31415 list
+echo.Echo
+```
+
+And describe the 'Get' method in the 'echo.Echo' service:
+
+```console
+$ grpcurl -plaintext 127.0.0.1:31415 describe echo.Echo.Get
+echo.Echo.Get is a method:
+// Immediately returns an echo of a request.
+rpc Get ( .echo.EchoRequest ) returns ( .echo.EchoResponse );
+```
+
+You can also call the 'echo.Echo.Get' method:
+```console
+$ grpcurl -plaintext -d '{ "text": "Hello" }' 127.0.0.1:31415 echo.Echo.Get
+{
+  "text": "Hello"
+}
+```

Examples/reflection-server/Sources/Echo/EchoService.swift

@@ -0,0 +1 @@
+../../../echo/Sources/Subcommands/EchoService.swift