100 Words in 100 Days 7/100: An evolving API (7)

Gilbert Wat (屈振鵬) · November 16, 2019

In last article, Lucy had run a post mortem with the team and things went pretty well afterwards.

Until today, they faced an untraceable problem. Some of the ServiceRequest doesn’t get the right price.

class Api::ServiceRequestController
    # ... some other Concerns
    include ServiceRequestParamsSanitizer
    # ... some other Concerns
    # POST v10/service_request
    def place_request_of_service_v10
        begin
            sanitize(service_request_params)
            #...
            @service_request = ServiceRequest.new(service_request_params)
            @service_request.calculate_additional_requirement!
            @service_request.calculate_bonus_percentage!
            # ... some other update
            @service_request.save!
            render(json: { id: @service_request.id }, status: :created)
        rescue
            render_error
        end
    end
end

On the surface, the code of the whole API doesn’t give up any clue that where does it goes wrong. We must dig deep into each of the sub-routine to see what is going on.

After a while of reading through the code and going into the code for a long time, Lucy finally traced that there is only a specific input of API causing the bug. And here is the culprit.

def ServiceRequestParamsSanitizer < ActiveSupport::Concern
    def sanitize(&service_request_params)
        if (service_request_params.has_no_price?)
            service_request_params.price = 100
        end
    end
end
def ServiceRequest < ActiveRecord
    def calculate_breakdown
        if (has_no_price? && price == 0)
            #... generate breakdowns for no price
        end
    end
end

So only a service_request_params with has_no_price? will get a default price of 100, and this mutation of variable value will trigger another sub-routine in ANOTHER files! How can a developer be able to trace so many code across multiple files?

In our next article, Bob, a new developer who is always eager to learn new techniques, introduce a way to avoid the problem of abstraction leak.

Twitter, Facebook