如何实现响应GET /time接口的极简Rack时间格式化应用？

Got it, let's walk through creating this Rack app step by step. I'll break down the logic and code so it's easy to follow and adapt.

Step 1: Recap the Core Requirements #

First, let's make sure we cover all your needs clearly:

• Respond only to GET /time requests
• Accept a format query parameter with comma-separated values (e.g., year,month,day, URL-encoded as year%2Cmonth%2Cday)
• Return plain-text time matching the requested format order
• Throw a clear error if any unknown format values are provided
• Set the correct Content-Type: text/plain header for all responses

Step 2: Write the Rack App Code #

We'll use a Ruby class for this (it's more organized than a lambda for handling validation and formatting logic). Save this as config.ru (Rack's default configuration file):

require 'rack'
require 'cgi'

class TimeFormatterApp
  # Map user-friendly format names to Ruby's strftime codes
  SUPPORTED_FORMATS = {
    'year' => '%Y',
    'month' => '%m',
    'day' => '%d',
    'hour' => '%H',
    'minute' => '%M',
    'second' => '%S'
  }.freeze

  def call(env)
    request = Rack::Request.new(env)

    # Handle non-matching routes/methods first
    unless request.path == '/time' && request.get?
      return [404, {'Content-Type' => 'text/plain'}, ['404 Not Found']]
    end

    # Check for missing format parameter
    format_param = request.params['format']
    unless format_param
      return [400, {'Content-Type' => 'text/plain'}, ['Error: Missing "format" query parameter']]
    end

    # Decode URL-encoded commas and split into individual format parts
    requested_formats = CGI.unescape(format_param).split(',')

    # Validate all requested formats
    invalid_formats = requested_formats.reject { |format| SUPPORTED_FORMATS.key?(format) }
    unless invalid_formats.empty?
      error_msg = "Error: Unsupported format(s): #{invalid_formats.join(', ')}"
      return [400, {'Content-Type' => 'text/plain'}, [error_msg]]
    end

    # Build the time format string and generate the output
    time_format = requested_formats.map { |f| SUPPORTED_FORMATS[f] }.join('-')
    # Use Time.at(0) if you want the epoch example (1970-01-01) instead of current time
    formatted_time = Time.now.strftime(time_format)

    # Return successful response
    [200, {'Content-Type' => 'text/plain'}, [formatted_time]]
  end
end

run TimeFormatterApp.new

Step 3: Break Down the Logic #

Let's unpack what each part does:

• SUPPORTED_FORMATS: A frozen hash that maps human-readable format names to Ruby's strftime codes—this makes it trivial to add/remove supported formats later.
• call method: The mandatory Rack interface; every Rack app must respond to call with an environment hash, returning a [status code, headers, body] array.
• Route/Method Validation: We first check if the request is for /time and uses GET. If not, we return a 404.
• Format Parameter Handling: We decode URL-encoded commas (since %2C is the URL escape for ,) and split the parameter into individual format parts.
• Invalid Format Check: We filter out any formats that aren't in our supported list. If there are invalid ones, we return a 400 error with a specific message.
• Time Formatting: We build the strftime string by mapping each requested format to its code, join with -, and format the current time (or epoch time, if you swap Time.now for Time.at(0)).

Step 4: Test the App #

First, install Rack if you haven't already:

gem install rack

Run the app with:

rackup config.ru

Now test these scenarios:

• Valid request: GET http://localhost:9292/time?format=year%2Cmonth%2Cday returns something like 2024-05-20
• Invalid format: GET http://localhost:9292/time?format=year%2Cfoo returns Error: Unsupported format(s): foo
• Missing parameter: GET http://localhost:9292/time returns Error: Missing "format" query parameter
• Wrong route: GET http://localhost:9292/foo returns 404 Not Found

内容的提问来源于stack exchange，提问作者Danil Panshin