Class: AvroTurf::Messaging

Inherits:
Object
  • Object
show all
Defined in:
lib/avro_turf/messaging.rb

Overview

Provides a way to encode and decode messages without having to embed schemas in the encoded data. Confluent's Schema Registry is used to register a schema when encoding a message – the registry will issue a schema id that will be included in the encoded data alongside the actual message. When decoding the data, the schema id will be used to look up the writer's schema from the registry.

1: github.com/confluentinc/schema-registry

Constant Summary collapse

MAGIC_BYTE =
[0].pack("C").freeze

Instance Method Summary collapse

Constructor Details

#initialize(registry: nil, registry_url: nil, schema_store: nil, schemas_path: nil, namespace: nil, logger: nil, proxy: nil, user: nil, password: nil, client_cert: nil, client_key: nil, client_key_pass: nil, client_cert_data: nil, client_key_data: nil) ⇒ Messaging

Instantiate a new Messaging instance with the given configuration.

registry - A schema registry object that responds to all methods in the

AvroTurf::ConfluentSchemaRegistry interface.

registry_url - The String URL of the schema registry that should be used. schema_store - A schema store object that responds to #find(schema_name, namespace). schemas_path - The String file system path where local schemas are stored. namespace - The String default schema namespace. logger - The Logger that should be used to log information (optional).  proxy - Forward the request via proxy (optional). user - User for basic auth (optional). password - Password for basic auth (optional). client_cert - Name of file containing client certificate (optional). client_key - Name of file containing client private key to go with client_cert (optional). client_key_pass - Password to go with client_key (optional). client_cert_data - In-memory client certificate (optional). client_key_data - In-memory client private key to go with client_cert_data (optional).


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# File 'lib/avro_turf/messaging.rb', line 44

def initialize(
  registry: nil,
  registry_url: nil,
  schema_store: nil,
  schemas_path: nil,
  namespace: nil,
  logger: nil,
  proxy: nil,
  user: nil,
  password: nil,
  client_cert: nil,
  client_key: nil,
  client_key_pass: nil,
  client_cert_data: nil,
  client_key_data: nil
)
  @logger = logger || Logger.new($stderr)
  @namespace = namespace
  @schema_store = schema_store || SchemaStore.new(path: schemas_path || DEFAULT_SCHEMAS_PATH)
  @registry = registry || CachedConfluentSchemaRegistry.new(
    ConfluentSchemaRegistry.new(
      registry_url,
      logger: @logger,
      proxy: proxy,
      user: user,
      password: password,
      client_cert: client_cert,
      client_key: client_key,
      client_key_pass: client_key_pass,
      client_cert_data: client_cert_data,
      client_key_data: client_key_data
    )
  )
  @schemas_by_id = {}
end

Instance Method Details

#decode(data, schema_name: nil, namespace: @namespace) ⇒ Object

Decodes data into the original message.

data - A String containing encoded data. schema_name - The String name of the schema that should be used to decode

the data. Must match the schema used when encoding (optional).

namespace - The namespace of the schema (optional).

Returns the decoded message.


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# File 'lib/avro_turf/messaging.rb', line 143

def decode(data, schema_name: nil, namespace: @namespace)
  decode_message(data, schema_name: schema_name, namespace: namespace).message
end

#decode_message(data, schema_name: nil, namespace: @namespace) ⇒ Object

Decodes data into the original message.

data - A String containing encoded data. schema_name - The String name of the schema that should be used to decode

the data. Must match the schema used when encoding (optional).

namespace - The namespace of the schema (optional).

Returns Struct with the next attributes:

schema_id  - The integer id of schema used to encode the message
message    - The decoded message

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# File 'lib/avro_turf/messaging.rb', line 157

def decode_message(data, schema_name: nil, namespace: @namespace)
  readers_schema = schema_name && @schema_store.find(schema_name, namespace)
  stream = StringIO.new(data)
  decoder = Avro::IO::BinaryDecoder.new(stream)

  # The first byte is MAGIC!!!
  magic_byte = decoder.read(1)

  if magic_byte != MAGIC_BYTE
    raise "Expected data to begin with a magic byte, got `#{magic_byte.inspect}`"
  end

  # The schema id is a 4-byte big-endian integer.
  schema_id = decoder.read(4).unpack("N").first

  writers_schema = @schemas_by_id.fetch(schema_id) do
    schema_json = @registry.fetch(schema_id)
    @schemas_by_id[schema_id] = Avro::Schema.parse(schema_json)
  end

  reader = Avro::IO::DatumReader.new(writers_schema, readers_schema)
  message = reader.read(decoder)

  DecodedMessage.new(schema_id, writers_schema, readers_schema, message)
rescue Excon::Error::NotFound
  raise SchemaNotFoundError.new("Schema with id: #{schema_id} is not found on registry")
end

#encode(message, schema_name: nil, namespace: @namespace, subject: nil, version: nil, schema_id: nil, validate: false) ⇒ Object

Encodes a message using the specified schema.

message - The message that should be encoded. Must be compatible with

the schema.

schema_name - The String name of the schema that should be used to encode

the data.

namespace - The namespace of the schema (optional). subject - The subject name the schema should be registered under in

the schema registry (optional).

version - The integer version of the schema that should be used to decode

the data. Must match the schema used when encoding (optional).

schema_id - The integer id of the schema that should be used to encode

the data.

validate - The boolean for performing complete message validation before

encoding it, Avro::SchemaValidator::ValidationError with
a descriptive message will be raised in case of invalid message.

Returns the encoded data as a String.


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# File 'lib/avro_turf/messaging.rb', line 98

def encode(message, schema_name: nil, namespace: @namespace, subject: nil, version: nil, schema_id: nil, validate: false)
  schema, schema_id = if schema_id
    fetch_schema_by_id(schema_id)
  elsif subject && version
    fetch_schema(subject: subject, version: version)
  elsif schema_name
    register_schema(subject: subject, schema_name: schema_name, namespace: namespace)
  else
    raise ArgumentError.new('Neither schema_name nor schema_id nor subject + version provided to determine the schema.')
  end

  if validate
    Avro::SchemaValidator.validate!(schema, message, recursive: true, encoded: false, fail_on_extra_fields: true)
  end

  stream = StringIO.new
  writer = Avro::IO::DatumWriter.new(schema)
  encoder = Avro::IO::BinaryEncoder.new(stream)

  # Always start with the magic byte.
  encoder.write(MAGIC_BYTE)

  # The schema id is encoded as a 4-byte big-endian integer.
  encoder.write([schema_id].pack("N"))

  # The actual message comes last.
  writer.write(message, encoder)

  stream.string
rescue Excon::Errors::NotFound
  if schema_id
    raise SchemaNotFoundError.new("Schema with id: #{schema_id} is not found on registry")
  else
    raise SchemaNotFoundError.new("Schema with subject: `#{subject}` version: `#{version}` is not found on registry")
  end
end

#fetch_schema(subject:, version: 'latest') ⇒ Object

Providing subject and version to determine the schema, which skips the auto registeration of schema on the schema registry. Fetch the schema from registry with the provided subject name and version.


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# File 'lib/avro_turf/messaging.rb', line 188

def fetch_schema(subject:, version: 'latest')
  schema_data = @registry.subject_version(subject, version)
  schema_id = schema_data.fetch('id')
  schema = Avro::Schema.parse(schema_data.fetch('schema'))
  [schema, schema_id]
end

#fetch_schema_by_id(schema_id) ⇒ Object

Fetch the schema from registry with the provided schema_id.


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# File 'lib/avro_turf/messaging.rb', line 196

def fetch_schema_by_id(schema_id)
  schema = @schemas_by_id.fetch(schema_id) do
    schema_json = @registry.fetch(schema_id)
    Avro::Schema.parse(schema_json)
  end
  [schema, schema_id]
end

#register_schema(schema_name:, subject: nil, namespace: nil) ⇒ Object

Schemas are registered under the full name of the top level Avro record type, or `subject` if it's provided.


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# File 'lib/avro_turf/messaging.rb', line 206

def register_schema(schema_name:, subject: nil, namespace: nil)
  schema = @schema_store.find(schema_name, namespace)
  schema_id = @registry.register(subject || schema.fullname, schema)
  [schema, schema_id]
end