This example demonstrates how to interact with Metadata on RPCs: how to set and read it on unary and streaming requests, as well as how to set and read both initial and trailing metadata on unary and streaming responses. This is done using a simple 'echo' server and client and the SwiftNIO based HTTP/2 transport.

An echo-metadata command line tool that uses generated stubs for an 'echo-metadata' service which allows you to start a server and to make requests against it.

You can use any of the client's subcommands (get, collect, expand and update) to send the provided message as both the request's message, and as the value for the echo-message key in the request's metadata.

The server will then echo back the message and the metadata's echo-message key-value pair sent by the client. The request's metadata will be echoed both in the initial and the trailing metadata.

The tool uses the SwiftNIO HTTP/2 transport.

You must have the Protocol Buffers compiler (protoc) installed. You can find the instructions for doing this in the gRPC Swift Protobuf documentation. The swift commands below are all prefixed with PROTOC_PATH=$(which protoc), this is to let the build system know where protoc is located so that it can generate stubs for you. You can read more about it in the gRPC Swift Protobuf documentation.

Build and run the server using the CLI:

$ PROTOC_PATH=$(which protoc) swift run echo-metadata serve
Echo-Metadata listening on [ipv4]127.0.0.1:1234

Use the CLI to run the client and make a get (unary) request:

$ PROTOC_PATH=$(which protoc) swift run echo-metadata get --message "hello"
get → metadata: [("echo-message", "hello")]
get → message: hello
get ← initial metadata: [("echo-message", "hello")]
get ← message: hello
get ← trailing metadata: [("echo-message", "hello")]

Get help with the CLI by running:

$ PROTOC_PATH=$(which protoc) swift run echo-metadata --help