Class: ElastomerClient::Middleware::OpaqueId

Inherits:
Faraday::Middleware
  • Object
show all
Defined in:
lib/elastomer_client/middleware/opaque_id.rb

Overview

This Faraday middleware implements the “X-Opaque-Id” request / response headers for Elasticsearch. The X-Opaque-Id header, when provided on the request header, will be returned as a header in the response. This is useful in environments which reuse connections to ensure that cross-talk does not occur between two requests.

The SecureRandom lib is used to generate a UUID string for each request. This value is used as the content for the “X-Opaque-Id” header. If the value is different between the request and the response, then an ‘ElastomerClient::Client::OpaqueIdError` is raised. In this case no response will be returned.

See [Elasticsearch “X-Opaque-Id” header](github.com/elasticsearch/elasticsearch/issues/1202) for more details.

Constant Summary collapse

X_OPAQUE_ID = 
"X-Opaque-Id".freeze
COUNTER_MAX = 
2**32 - 1

Instance Method Summary collapse

Instance Method Details

#call(env) ⇒ Object

Faraday middleware implementation.

env - Faraday environment Hash

Returns the environment Hash



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# File 'lib/elastomer_client/middleware/opaque_id.rb', line 32

def call(env)
  uuid = generate_uuid.freeze
  env[:request_headers][X_OPAQUE_ID] = uuid

  @app.call(env).on_complete do |renv|
    response_uuid = renv[:response_headers][X_OPAQUE_ID]
    # Don't raise OpaqueIdError if the response is a 5xx
    if !response_uuid.nil? && uuid != response_uuid && renv.status < 500
      raise ::ElastomerClient::Client::OpaqueIdError,
            "Conflicting 'X-Opaque-Id' headers: request #{uuid.inspect}, response #{response_uuid.inspect}"
    end
  end
end

#generate_uuid ⇒ Object

Generate a UUID using the built-in SecureRandom class. This can be a little slow at times, so we will reuse the same UUID and append an incrementing counter.

Returns the UUID string.



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# File 'lib/elastomer_client/middleware/opaque_id.rb', line 51

def generate_uuid
  t = Thread.current

  unless t.key? :opaque_id_base
    t[:opaque_id_base]    = (SecureRandom.urlsafe_base64(12) + "%08x").freeze
    t[:opaque_id_counter] = -1
  end

  t[:opaque_id_counter] += 1
  t[:opaque_id_counter] = 0 if t[:opaque_id_counter] > COUNTER_MAX
  t[:opaque_id_base] % t[:opaque_id_counter]
end