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.
Constants
- MAGIC_BYTE
Public Class Methods
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
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
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
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
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
# 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 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
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