class AvroTurf::Messaging

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

Constants

MAGIC_BYTE

Public Class Methods

new( registry: nil, registry_url: nil, schema_context: nil, schema_store: nil, schemas_path: nil, namespace: nil, registry_path_prefix: nil, logger: nil, proxy: nil, user: nil, password: nil, ssl_ca_file: nil, client_cert: nil, client_key: nil, client_key_pass: nil, client_cert_data: nil, client_key_data: nil, connect_timeout: nil, resolv_resolver: nil ) click to toggle source

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_context - Schema registry context name (optional) 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. registry_path_prefix - The String URL path prefix used to namespace schema registry requests (optional). 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). ssl_ca_file - Name of file containing CA certificate (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). connect_timeout - Timeout to use in the connection with the schema registry (optional). resolv_resolver - Custom domain name resolver (optional).

# File lib/avro_turf/messaging.rb, line 61
def initialize(
  registry: nil,
  registry_url: nil,
  schema_context: nil,
  schema_store: nil,
  schemas_path: nil,
  namespace: nil,
  registry_path_prefix: nil,
  logger: nil,
  proxy: nil,
  user: nil,
  password: nil,
  ssl_ca_file: nil,
  client_cert: nil,
  client_key: nil,
  client_key_pass: nil,
  client_cert_data: nil,
  client_key_data: nil,
  connect_timeout: nil,
  resolv_resolver: 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,
      schema_context: schema_context,
      logger: @logger,
      proxy: proxy,
      user: user,
      password: password,
      ssl_ca_file: ssl_ca_file,
      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,
      path_prefix: registry_path_prefix,
      connect_timeout: connect_timeout,
      resolv_resolver: resolv_resolver
    )
  )
  @schemas_by_id = {}
end

Public Instance Methods

decode(data, schema_name: nil, namespace: @namespace) click to toggle source

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.

# File lib/avro_turf/messaging.rb, line 176
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) click to toggle source

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
# File lib/avro_turf/messaging.rb, line 190
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, register_schemas: true) click to toggle source

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.

register_schemas - The boolean that indicates whether or not the schema should be

registered in case it does not exist, or if it should be fetched
from the registry without registering it (register_schemas: false).

Returns the encoded data as a String.

# File lib/avro_turf/messaging.rb, line 128
def encode(message, schema_name: nil, namespace: @namespace, subject: nil, version: nil, schema_id: nil, validate: false,
           register_schemas: true)
  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_schemas
    fetch_schema_by_body(subject: subject, schema_name: schema_name, namespace: namespace)
  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::Error::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') click to toggle source

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.

# File lib/avro_turf/messaging.rb, line 221
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_body(schema_name:, subject: nil, namespace: nil) click to toggle source
# File lib/avro_turf/messaging.rb, line 237
def fetch_schema_by_body(schema_name:, subject: nil, namespace: nil)
  schema = @schema_store.find(schema_name, namespace)
  schema_data = @registry.check(subject || schema.fullname, schema)
  raise SchemaNotFoundError.new("Schema with structure: #{schema} not found on registry") unless schema_data

  [schema, schema_data["id"]]
end
fetch_schema_by_id(schema_id) click to toggle source

Fetch the schema from registry with the provided schema_id.

# File lib/avro_turf/messaging.rb, line 229
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) click to toggle source

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

# File lib/avro_turf/messaging.rb, line 247
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