Module: Toys::Middleware

Included in:
StandardMiddleware::AddVerbosityFlags, StandardMiddleware::HandleUsageErrors, StandardMiddleware::SetDefaultDescriptions, StandardMiddleware::ShowHelp, StandardMiddleware::ShowRootVersion
Defined in:
lib/toys/middleware.rb

Overview

A middleware is an object that has the opportunity to alter the configuration and runtime behavior of each tool in a Toys CLI. A CLI contains an ordered list of middleware, known as the middleware stack, that together define the CLI's default behavior.

Specifically, a middleware can perform two functions.

First, it can modify the configuration of a tool. After tools are defined from configuration, the middleware stack can make modifications to each tool. A middleware can add flags and arguments to the tool, modify the description, or make any other changes to how the tool is set up.

Second, a middleware can intercept and change tool execution. Like a Rack middleware, a Toys middleware can wrap execution with its own code, replace it outright, or leave it unmodified.

Generally, a middleware is a class that implements the two methods defined in this module: #config and #run. A middleware can include this module to get default implementations that do nothing, but this is not required.

Instance Method Summary collapse

Instance Method Details

#config(tool, loader) ⇒ void

This method returns an undefined value.

This method is called after a tool has been defined, and gives this middleware the opportunity to modify the tool definition. It is passed the tool definition object and the loader, and can make any changes to the tool definition. In most cases, this method should also call yield, which passes control to the next middleware in the stack. A middleware can disable modifications done by subsequent middleware by omitting the yield call, but this is uncommon.

This basic implementation does nothing and simply yields to the next middleware.

Parameters:

  • tool (Toys::Tool) —

    The tool definition to modify.

  • loader (Toys::Loader) —

    The loader that loaded this tool.



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# File 'lib/toys/middleware.rb', line 64

def config(tool, loader) # rubocop:disable Lint/UnusedMethodArgument
  yield
end

#run(context) ⇒ void

This method returns an undefined value.

This method is called when the tool is run. It gives the middleware an opportunity to modify the runtime behavior of the tool. It is passed the tool instance (i.e. the object that hosts a tool's run method), and you can use this object to access the tool's options and other context data. In most cases, this method should also call yield, which passes control to the next middleware in the stack. A middleware can "wrap" normal execution by calling yield somewhere in its implementation of this method, or it can completely replace the execution behavior by not calling yield at all.

Like a tool's run method, this method's return value is unused. If you want to output from a tool, write to stdout or stderr. If you want to set the exit status code, call Context#exit on the context.

This basic implementation does nothing and simply yields to the next middleware.

Parameters:



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# File 'lib/toys/middleware.rb', line 89

def run(context) # rubocop:disable Lint/UnusedMethodArgument
  yield
end