Class: Grape::PrecompiledJson

Inherits:
Object
  • Object
show all
Defined in:
lib/grape/precompiled_json.rb

Overview

Marks a body as JSON that has already been rendered, so the JSON formatters serve it verbatim instead of encoding it a second time.

Grape::Formatter::Json calls to_json on whatever the endpoint returned, so a String holding pre-rendered JSON — a blob cached in Redis, a json_agg column read straight from Postgres, output from another serializer — comes back encoded twice:

'{"a":1}'  =>  "\"{\\\"a\\\":1}\""

Wrapping the body opts that one response out of encoding:

get '/cached' do
body Grape::PrecompiledJson.new(Rails.cache.read('payload'))
end

An Array is joined into a JSON array without its members being parsed, which is what makes a cached collection cheap — N rendered blobs are spliced together rather than round-tripped:

Grape::PrecompiledJson.new(['{"id":1}', '{"id":2}']).to_s # => '[{"id":1},{"id":2}]'

Array#join calls to_s on each member, so members may themselves be PrecompiledJson instances.

Wrap only the whole body. A wrapper nested inside a Hash or Array that is then handed to an encoder is serialized as an ordinary object — ActiveSupport::JSON renders it through as_json as {"value":"{\"a\":1}"} — because no encoder knows to unwrap it. Nothing checks that the String actually holds JSON; that is the caller's responsibility.

Instance Method Summary collapse

Constructor Details

#initialize(value) ⇒ PrecompiledJson

Returns a new instance of PrecompiledJson.

Parameters:

  • value (String, Array<String>) —

    pre-rendered JSON



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# File 'lib/grape/precompiled_json.rb', line 35

def initialize(value)
  @value = value
end

Instance Method Details

#to_s ⇒ String

Returns the JSON to serve.

Returns:

  • (String) —

    the JSON to serve

Raises:

  • (Grape::Exceptions::InvalidFormatter) —

    if the value is neither a String nor an Array; the formatter middleware turns this into a 500 rather than letting a body Rack cannot serve reach the SPEC check.



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# File 'lib/grape/precompiled_json.rb', line 43

def to_s
  return @value if @value.is_a?(String)
  return "[#{@value.join(',')}]" if @value.is_a?(Array)

  raise Grape::Exceptions::InvalidFormatter.new(@value.class, 'json')
end