protoc-gen-cobra

Cobra command line tool generator for Go gRPC.

What's this?

A plugin for the protobuf compiler protoc that generates Go code using cobra. It is capable of generating client code for command line tools consistent with your protobuf description.

This proto definition:

service Bank {
	rpc Deposit(DepositRequest) returns (DepositReply);
}

message DepositRequest {
	string account = 1;
	double amount = 2;
}

message DepositReply {
	string account = 1;
	double balance = 2;
}

produces a client that can do:

$ ./example bank deposit --account foobar --amount 10
$ echo '{"account":"foobar"}' | ./example bank deposit --amount 10 -f -
$ set BANK_DEPOSIT_ACCOUNT=foobar; ./example bank deposit --amount 10

It generates one cobra.Command per gRPC service (e.g. bank). The service's RPC methods are sub-commands and share the same command line semantics. They take flags, a request file, or stdin for input, and print the response to the terminal in the specified format. The client currently supports basic connectivity settings such as TLS on/off, TLS client authentication and so on.

$ ./example bank deposit -h
Deposit RPC client

Usage:
  example bank deposit [flags]

Flags:
      --account string   account number of recipient
      --amount float     amount to deposit
  -h, --help             help for deposit

Global Flags:
      --auth-access-token string   authorization access token
      --auth-token-type string     authorization token type (default "Bearer")
      --config string              config file (default is $HOME/.example.yaml)
      --jwt-key string             JWT key
      --jwt-key-file string        JWT key file
  -f, --request-file string        client request file; use "-" for stdin
  -i, --request-format string      request format (json, xml, yaml) (default "json")
  -o, --response-format string     response format (json, prettyjson, prettyxml, xml, yaml) (default "json")
  -s, --server-addr string         server address in the form host:port (default "localhost:8080")
      --timeout duration           client connection timeout (default 10s)
      --tls                        enable TLS
      --tls-ca-cert-file string    CA certificate file
      --tls-cert-file string       client certificate file
      --tls-insecure-skip-verify   INSECURE: skip TLS checks
      --tls-key-file string        client key file
      --tls-server-name string     TLS server name override

Streams

gRPC client and server streams are supported by concatenating multiple requests and responses. Client stream requests can be passed from a file or stdin with optional whitespace between each document (typically a new line). Server stream responses are printed one per line using the specified response format.

Example client stream:

$ cat req.json
{"key":"hello","value":"world"}
{"key":"foo","value":"bar"}

$ ./example cache multiset -f req.json

Example client and server streams:

$ echo '{"key":"hello"}{"key":"foo"}' | ./example cache multiget -f -
{"value":"world"}
{"value":"bar"}

Idle server streams hang until the server closes the stream or a timeout occurs.

Custom input/output formats

New input decoders and output encoders can be registered in the host program prior to executing the command.

client.RegisterOutputEncoder("fmtprint", func(w io.Writer) iocodec.Encoder {
	return func(v interface{}) error {
		_, err := fmt.Fprint(w, v)
		return err
	}
})

These formats can then be specified using the -o or --response-format flags or via a RESPONSE_FORMAT environment variable.

$ ./example bank deposit --account foobar --amount 10 -o fmtprint
$ set RESPONSE_FORMAT=fmtprint; ./example bank deposit --account foobar --amount 10

See the yaml format extension for a complete example.

Custom authentication schemes

Pre-dial hooks can be registered in the host program to support custom authentication schemes.

client.RegisterPreDialer(func(ctx context.Context, opts *[]grpc.DialOption) error {
	if creds, ok := ctx.Value(CredsContextKey).(*Creds); ok {
		*opts = append(*opts, grpc.WithPerRPCCredentials(creds))
	}
	return nil
})

See the jwt authentication extension for a complete example.