GripMock

GripMock is a mock server for GRPC services. It's using a .proto file to generate implementation of gRPC service for you. You can use gripmock for setting up end-to-end testing or as a dummy server in a software development phase. The server implementation is in GoLang but the client can be any programming language that support gRPC.

---

Announcement:

The latest version (v1.10) of gripmock is requiring go_package declaration in the .proto file. This is due to the latest update of protoc plugin that being used by gripmock is making the go_package declaration mandatory.

Update Feb 2022:

Version 1.11-beta release is available. It supports NO declaration of go_package, please download and test before it can be tagged as stable.

you can get the docker image using docker pull tkpd/gripmock:v1.11-beta.

---

Quick Usage

First, prepare your .proto file. Or you can use hello.proto in example/simple/ folder. Suppose you put it in /mypath/hello.proto. We are gonna use Docker image for easier example test. basic syntax to run GripMock is gripmock <protofile>

• Install Docker
• Run docker pull tkpd/gripmock to pull the image
• We are gonna mount /mypath/hello.proto (it must be a fullpath) into a container and also we expose ports needed. Run docker run -p 4770:4770 -p 4771:4771 -v /mypath:/proto tkpd/gripmock /proto/hello.proto
• On a separate terminal we are gonna add a stub into the stub service. Run curl -X POST -d '{"service":"Gripmock","method":"SayHello","input":{"equals":{"name":"gripmock"}},"output":{"data":{"message":"Hello GripMock"}}}' localhost:4771/add
• Now we are ready to test it with our client. You can find a client example file under example/simple/client/. Execute one of your preferred language. Example for go: go run example/simple/client/*.go

Check example folder for various usecase of gripmock.

---

How It Works

From client perspective, GripMock has 2 main components:

1. GRPC server that serves on tcp://localhost:4770. Its main job is to serve incoming rpc call from client and then parse the input so that it can be posted to Stub service to find the perfect stub match.
2. Stub server that serves on http://localhost:4771. Its main job is to store all the stub mapping. We can add a new stub or list existing stub using http request.

Matched stub will be returned to GRPC service then further parse it to response the rpc call.

From technical perspective, GripMock consists of 2 binaries. The first binary is the gripmock itself, when it will generate the gRPC server using the plugin installed in the system (see Dockerfile). When the server sucessfully generated, it will be invoked in parallel with stub server which ends up opening 2 ports for client to use.

The second binary is the protoc plugin which located in folder protoc-gen-gripmock. This plugin is the one who translates protobuf declaration into a gRPC server in Go programming language.

---

Stubbing

Stubbing is the essential mocking of GripMock. It will match and return the expected result into GRPC service. This is where you put all your request expectation and response

Dynamic stubbing

You could add stubbing on the fly with a simple REST API. HTTP stub server is running on port :4771

• GET / Will list all stubs mapping.
• POST /add Will add stub with provided stub data
• POST /find Find matching stub with provided input. see Input Matching below.
• GET /clear Clear stub mappings.

Stub Format is JSON text format. It has a skeleton as follows:

{
  "service":"<servicename>", // name of service defined in proto
  "method":"<methodname>", // name of method that we want to mock
  "input":{ // input matching rule. see Input Matching Rule section below
    // put rule here
  },
  "output":{ // output json if input were matched
    "data":{
      // put result fields here
    },
    "error":"<error message>" // Optional. if you want to return error instead.
    "code":"<response code>" // Optional. Grpc response code. if code !=0  return error instead.
  }
}

For our hello service example we put a stub with the text below:

  {
    "service":"Greeter",
    "method":"SayHello",
    "input":{
      "equals":{
        "name":"gripmock"
      }
    },
    "output":{
      "data":{
        "message":"Hello GripMock"
      }
    }
  }

Static stubbing

You could initialize gripmock with stub json files and provide the path using --stub argument. For example you may mount your stub file in /mystubs folder then mount it to docker like

docker run -p 4770:4770 -p 4771:4771 -v /mypath:/proto -v /mystubs:/stub tkpd/gripmock --stub=/stub /proto/hello.proto

Please note that Gripmock still serves http stubbing to modify stored stubs on the fly.

Input Matching

Stub will respond with the expected response only if the request matches any rule. Stub service will serve /find endpoint with format:

{
  "service":"<service name>",
  "method":"<method name>",
  "data":{
    // input that suppose to match with stored stubs
  }
}

So if you do a curl -X POST -d '{"service":"Greeter","method":"SayHello","data":{"name":"gripmock"}}' localhost:4771/find stub service will find a match from listed stubs stored there.

Input Matching Rule

Input matching has 4 rules to match an input: equals, equals_unordered, contains and regex
Nested fields are allowed for input matching too for all JSON data types. (string, bool, array, etc.)
Gripmock recursively goes over the fields and tries to match with given input.
equals will match the exact field name and value of input into expected stub. example stub JSON:

{
  .
  .
  "input":{
    "equals":{
      "name":"gripmock",
      "greetings": {
            "english": "Hello World!",
            "indonesian": "Halo Dunia!",
            "turkish": "Merhaba Dünya!"
      },
      "ok": true,
      "numbers": [4, 8, 15, 16, 23, 42]
      "null": null
    }
  }
  .
  .
}

equals_unordered will match the exact field name and value of input into expected stub, except lists (which are compared as sets). example stub JSON:

{
  .
  .
  "input":{
    "equals_unordered":{
      "name":"gripmock",
      "greetings": {
            "english": "Hello World!",
            "indonesian": "Halo Dunia!",
            "turkish": "Merhaba Dünya!"
      },
      "ok": true,
      "numbers": [4, 8, 15, 16, 23, 42]
      "null": null
    }
  }
  .
  .
}

contains will match input that has the value declared expected fields. example stub JSON:

{
  .
  .
  "input":{
    "contains":{
      "field2":"hello",
      "field4":{
        "field5": "value5"
      } 
    }
  }
  .
  .
}

matches using regex for matching fields expectation. example:

{
  .
  .
  "input":{
    "matches":{
      "name":"^grip.*$",
      "cities": ["Jakarta", "Istanbul", ".*grad$"]
    }
  }
  .
  .
}