Interview Assignment

Overview

You assignment is to create a Protocol Buffers (Protobuf) plugin, which is executed with the protoc compiler. In this exercise, we expect you to use v3.13.0, so please install it from the the releases.

We expect this assignment to take between 2-3 hours to complete. A significant portion of this assignment is to test your ability to research and learn how to interact with a foreign tool. The implementation itself is not intended to be overly complex - the real challenge is getting a program that can run correctly with protoc.

What is a plugin, and how do I write one?

A protoc plugin allows users to generate custom code according to the structured representation of Protobuf files. In simpler terms, plugins are programs that take Protobuf files as input, and produce code as output.

As you'll notice in some of the additional plugin documentation, the plugin must either be discoverable by your machine's PATH, or be manually targeted with the --plugin flag. In this case, we recommend placing the plugin on your PATH so that you can quickly go install between test invocations, but this is up to you.

For references, there are many examples of plugins you can find on the web.

What does the plugin need to do?

The plugin must be implemented in Go.

The plugin must output one YAML file for each of the input files specified in the protoc invocation.

The YAML file must conform to the following constraints:

• The plugin is named protoc-gen-yaml.
• The plugin outputs one YAML file for every input file.
• Each of the files should be named by adding the .yaml suffix to their filename.
  • For example, an input file named proto/echo.proto will create proto/echo.proto.yaml.
• The YAML output will represent a subset of the Protobuf file's content. Specifically, the plugin will create two maps in each file: one for messages and another for services. Each map key have a list of messages and services, respectively.
• For each message, a list of fields will be represented under the fields key.
• For each method, a list of methods will be represented under the methods key.

A template representation of the expected output is shown below. Pay close attention to the names of the map keys, as well as the required values associated with them.

If your are confused at all by any of these definitions, such as a field number, please refer to the Language Guide. The Testing section below gives an example that will make it easier to understand.

messages:
# For each message in this file, sorted by name...
- name: <$message_name>
  fields:
  # For each field in this message, sorted by number...
  - name: <$field_name>
    number: <$field_number>
services:
# For each service in this file, sorted by name...
- name: <$service_name>
  # For each method in this service, sorted by name...
  methods:
  - name: <$method_name>
    input_type: <$input_type>
    output_type: <$output_type>

Hint: Use Marshal from gopkg.in/yaml.v2 instead of using gopkg.in/yaml.v3 to get the correct indentation.

Testing

The following file located in test/input/proto/echo.proto.

syntax = "proto3";

package echo.v1;

message EchoRequest {
  string value = 1;
}

message EchoResponse {
  Foo foo = 1;
}

message Foo {
  message Bar {
    string value = 1;
  }
  string two = 2;
  string one = 1;
}

service EchoService {
  rpc Echo(EchoRequest) returns (EchoResponse);
}

Assuming that your plugin is installed in PATH, we should be able to execute the plugin like so:

$ protoc -I test/input test/input/proto/echo.proto --yaml_out=./output

The expected output for the test/input/proto/echo.proto file is shown below:

messages:
- name: echo.v1.EchoRequest
  fields:
  - name: value
    number: 1
- name: echo.v1.EchoResponse
  fields:
  - name: foo
    number: 1
- name: echo.v1.Foo
  fields:
  - name: one
    number: 1
  - name: two
    number: 2
- name: echo.v1.Foo.Bar
  fields:
  - name: value
    number: 1
services:
- name: echo.v1.EchoService
  methods:
  - name: Echo
    input_type: echo.v1.EchoRequest
    output_type: echo.v1.EchoResponse

You can verify if you've implemented the correct solution with diff:

$ protoc -I test/input test/input/proto/echo.proto --yaml_out=./output
$ diff ./output/proto/echo.proto.yaml ./test/output/proto/echo.proto.yaml

Note that the ouptut is sanitized, such that any . prefixes are trimmed in the relevant places. A proper solution will need to handle these cases, so pay special attention!

Submitting

Send a tar ball containing your solution and, optionally, any additional test cases you've created. We should be able to build the plugin with go build.