Build API Endpoint Tutorial Part 2

This README is a continuation of Hello World Tutorial Part 1, creating a “Hello world!” endpoint from scratch. This tutorial assumes you have already executed all the steps in Part 1, and have all its code in place.

Hello World Part 2: “Hello {argument}!”

“World” is great and all, but it'd be nice to be able to say hello to other things. This continuation will walk through adding fields to requests, using them in the endpoints, and manually executing parameterized endpoints.

Step 1: Parameterizing the library.

First, let's upgrade our lib.


def hello(target):
    print(f'Hello, {target}!')

Now we can say hello to whatever we want!

Step 2: Parameterizing the proto.

Next, we need to add a field to our proto, so we can pass it in through the API. This time we‘ll just look at the HelloRequest message, as it’s the only part that needs changes. We'll add a new string field to pass our target.


// HelloService/Hello request and response messages.
message HelloRequest {
  string target = 1;

Since we‘ve updated the proto, we’ll need to regenerate the protobuf bindings again.

$> cd ~/chromiumos/chromite/infra/proto
$> ./
$> cd ~/chromiumos/chromite/api
$> ./compile_build_api_proto

Step 3: Passing arguments.

Finally, we update our controller. We just need to pull the field out of the proto and pass it through to our hello_lib.hello call. The input proto is the instance of the HelloRequest we provide, so we just need to grab the field from the message.


from chromite.lib import hello_lib

def Hello(input_proto, output_proto, config_proto):

Step 4: Calling the parameterized endpoint.

We can still use the gen_call_scripts workflow we used in Step 6, we just need to add the values to our request. As noted earlier, the gen_call_scripts workflow generates an input for each endpoint automatically. By default, it'll generate an empty input file, so we just need to add to the file we already have.

$> cat chromite/api/contrib/call_scripts/hello__hello_input.json

Let's say hello to the moon, instead.


{"target": "moon"}

And that's it! Now if we run the endpoint, we should see our updated greeting.

$> cd ~/chromiumos/chromite/api/contrib/call_scripts/
$> ./hello__hello
Running chromite.api.HelloService/Hello
14:39:27: DEBUG: Services registered successfully.
Hello, moon!
Completed chromite.api.HelloService/Hello
Return Code: 0


Up Next

Continue to Part 3, where we'll look at validating the input.