Avrora

Getting Started

This Elixir library supports convenient encoding and decoding of Avro messages.

It can read the Avro schema from local files or the Confluent® Schema Registry, caching data in memory for performance.

It supports reading and writing data Kafka wire format prefix and from Object Container Files formats. Along with Confluent® Schema References it has Inter-Schema references feature for older Schema Registry versions.

Many thanks to the AvroTurf Ruby gem for the initial inspiration :blue_heart:

If you like the project and want to support me on my sleepless nights, you can

Add Avrora to your project

Add Avrora to mix.exs as a dependency

def deps do
  [
    {:avrora, "~> 0.27"}
  ]
end

Configuration

:beginner: It's recommended to configure private Avrora client^v0.17 to avoid risk of conflicts with other dependencies which might use shared Avrora client.

Don't worry if you already using the shared client because migration to the private is a matter of copy-paste.

Private client

Create your private Avrora client module

defmodule MyClient do
  use Avrora.Client,
    otp_app: :my_application,
    schemas_path: "./priv/schemas",
    registry_url: "http://localhost:8081",
    registry_auth: {:basic, ["username", "password"]},
    registry_user_agent: "Avrora/0.25.0 Elixir",
    registry_ssl_cacerts: File.read!("./priv/trusted.der"),
    registry_ssl_cacert_path: "./priv/trusted.crt",
    registry_schemas_autoreg: false,
    convert_null_values: false,
    convert_map_to_proplist: false,
    names_cache_ttl: :timer.minutes(5),
    decoder_hook: &MyClient.decoder_hook/4
end

please check the section below :point_down: for detailed explanation of each configuration option.

Shared client

Configure the Avrora shared client in config/config.exs

config :avrora,
  otp_app: :my_application, # optional, if you want to use it as a root folder for `schemas_path`
  schemas_path: "./priv/schemas",
  registry_url: "http://localhost:8081",
  registry_auth: {:basic, ["username", "password"]}, # optional
  registry_user_agent: "Avrora/0.24.2 Elixir", # optional: if you want to return previous behaviour, set it to `nil`
  registry_ssl_cacerts: File.read!("./priv/trusted.der"), # optional: if you have DER-encoded certificate
  registry_ssl_cacert_path: "./priv/trusted.crt", # optional: if you have PEM-encoded certificate file
  registry_schemas_autoreg: false, # optional: if you want manually register schemas
  convert_null_values: false, # optional: if you want to keep decoded `:null` values as is
  convert_map_to_proplist: false, # optional: if you want to restore the old behavior for decoding map-type
  names_cache_ttl: :timer.minutes(5), # optional: if you want periodic disk reads
  decoder_hook: &MyClient.decoder_hook/4 # optional: if you want to amend the data/result

• otp_app^v0.22 - Name of the OTP application to use for runtime configuration via env, default nil
• schemas_path - Base path for locally stored schema files, default ./priv/schemas
• registry_url - URL for the Schema Registry, default nil
• registry_auth – Credentials to authenticate in the Schema Registry, default nil
• registry_user_agent^v0.25 - HTTP User-Agent header for Schema Registry requests, default Avrora/<version> Elixir
• registry_ssl_cacerts^v0.28 - DER-encoded certificates, but without combined support, default nil
• registry_ssl_cacert_path^v0.28 - Path to a file containing PEM-encoded CA certificates, default nil
• registry_schemas_autoreg^v0.13 - Flag for automatic schemas registration in the Schema Registry, default true
• convert_null_values^v0.14 - Flag for automatic conversion of decoded :null values into nil, default true
• convert_map_to_proplist^v0.15 restore old behaviour and confiugre decoding map-type to proplist, default false
• names_cache_ttl^v0.10 - Time in ms to cache schemas by name in memory, default :infinity
• decoder_hook^v0.24 - Function with arity 4 to amend data or result, default fn _, _, data, fun -> fun.(data) end

Set names_cache_ttl to :infinity will cache forever (no more disk reads will happen). This is safe when schemas resolved in the Schema Registry by numeric id or versioned name, as it is unique. If you need to reload schema from the disk periodically, TTL different from :infinity ensures that.

If the schema resolved by name it will be always overwritten with the latest schema received from Schema Registry.^v0.10

Custom decoder hook will be first in the call-chain, after it's done Avrora will use the result in its own decoder hook.^v0.24

:bulb: Disable schemas auto-registration if you want to avoid storing schemas and manually control registration process. Also it's recommended to turn off auto-registration when schemas containing Confluent Schema References.^v0.14

:bulb: When you use releases and especially Umbrella apps with different clients it's recommended to set otp_app which will point to your OTP applications. This will allow you to have a per-client runtime resolution for all configuration options (i.e. schemas_path) with a fallback to staticly defined in a client itself.^v0.23

:bulb: If both registry_ssl_cacerts and registry_ssl_cacert_path given, then registry_ssl_cacerts has a priority.

Start cache process

Avrora uses an in-memory cache to speed up schema lookup.

Private client

After you've created your private Avrora client, add it to your supervision tree

children = [
  MyClient
]

Supervisor.start_link(children, strategy: :one_for_one)

or start the process manually

{:ok, pid} = MyClient.start_link()

Shared client

Add shared Avrora module to your supervision tree

children = [
  Avrora
]

Supervisor.start_link(children, strategy: :one_for_one)

or start the process manually

{:ok, pid} = Avrora.start_link()

Usage

:beginner: All the examples below (including Schemas registration) will use Avrora shared client, but if you are using private client, just replace Avrora with your client module name.

The primary way to use the library is via the Avrora.encode/2 and Avrora.decode/2 functions. These functions load the Avro schema for you.

If registry_url defined, it enables Schema Registry storage. If the schema file found locally but not in the registry, either fuction will register the schema.

These examples assume you have a Payment schema stored in the file priv/schemas/io/confluent/Payment.avsc

{
  "type": "record",
  "name": "Payment",
  "namespace": "io.confluent",
  "fields": [
    {
      "name": "id",
      "type": "string"
    },
    {
      "name": "amount",
      "type": "double"
    }
  ]
}

When running interactively, first make sure the cache started

{:ok, pid} = Avrora.start_link()

encode/2

To encode a Payment message:

{:ok, pid} = Avrora.start_link()
message = %{"id" => "tx-1", "amount" => 15.99}

{:ok, encoded} = Avrora.encode(message, schema_name: "io.confluent.Payment")
<<79, 98, 106, 1, 3, 204, 2, 20, 97, 118, 114, 111, 46, 99, 111, 100, 101, 99,
  8, 110, 117, 108, 108, 22, 97, 118, 114, 111, 46, 115, 99, 104, 101, 109, 97,
  144, 2, 123, 34, 110, 97, 109, 101, 115, 112, 97, 99, 101, 34, 58, 34, 105,
  111, 46, 99, 111, 110, 102, 108, 117, 101, 110, 116, 34, 44, 34, 110, 97, 109,
  101, 34, 58, 34, 80, 97, 121, 109, 101, 110, 116, 34, 44, 34, 116, 121, 112,
  101, 34, 58, 34, 114, 101, 99, 111, 114, 100, 34, 44, 34, 102, 105, 101, 108,
  100, 115, 34, 58, 91, 123, 34, 110, 97, 109, 101, 34, 58, 34, 105, 100, 34,
  44, 34, 116, 121, 112, 101, 34, 58, 34, 115, 116, 114, 105, 110, 103, 34, 125,
  44, 123, 34, 110, 97, 109, 101, 34, 58, 34, 97, 109, 111, 117, 110, 116, 34,
  44, 34, 116, 121, 112, 101, 34, 58, 34, 100, 111, 117, 98, 108, 101, 34, 125,
  93, 125, 0, 138, 124, 66, 49, 157, 51, 242, 3, 33, 52, 161, 147, 221, 174,
  114, 48, 2, 26, 8, 116, 120, 45, 49, 123, 20, 174, 71, 225, 250, 47, 64, 138,
  124, 66, 49, 157, 51, 242, 3, 33, 52, 161, 147, 221, 174, 114, 48>>

The :format argument controls output format:

• :plain^{deprecated v0.18} - Just return Avro binary data, with no header or embedded schema
• :ocf - Use Object Container File format, embedding the full schema with the data
• :registry - Write data with Confluent Schema Registry Wire Format, which prefixes the data with the schema id
• :guess - Use :registry if possible, otherwise use :ocf (default)

{:ok, pid} = Avrora.start_link()
message = %{"id" => "tx-1", "amount" => 15.99}

{:ok, encoded} = Avrora.encode(message, schema_name: "io.confluent.Payment", format: :registry)
<<0, 0, 42, 0, 8, 116, 120, 45, 49, 123, 20, 174, 71, 225, 250, 47, 64>>

decode/2

Decode Payment message using the specified schema

{:ok, pid} = Avrora.start_link()
message = <<0, 0, 42, 0, 8, 116, 120, 45, 49, 123, 20, 174, 71, 225, 250, 47, 64>>

{:ok, decoded} = Avrora.decode(message, schema_name: "io.confluent.Payment")
%{"id" => "tx-1", "amount" => 15.99}

decode/1

Decode a message, auto-detecting the schema using magic bytes. It first tries resolving the schema using the integer id in the wire format header.

Next it tries reading using the Object Container Files embedded schema.

NOTE: Messages encoded with OCF wrapped in a List.

{:ok, pid} = Avrora.start_link()
message =
  <<79, 98, 106, 1, 3, 204, 2, 20, 97, 118, 114, 111, 46, 99, 111, 100, 101, 99,
    8, 110, 117, 108, 108, 22, 97, 118, 114, 111, 46, 115, 99, 104, 101, 109, 97,
    144, 2, 123, 34, 110, 97, 109, 101, 115, 112, 97, 99, 101, 34, 58, 34, 105,
    111, 46, 99, 111, 110, 102, 108, 117, 101, 110, 116, 34, 44, 34, 110, 97, 109,
    101, 34, 58, 34, 80, 97, 121, 109, 101, 110, 116, 34, 44, 34, 116, 121, 112,
    101, 34, 58, 34, 114, 101, 99, 111, 114, 100, 34, 44, 34, 102, 105, 101, 108,
    100, 115, 34, 58, 91, 123, 34, 110, 97, 109, 101, 34, 58, 34, 105, 100, 34, 44,
    34, 116, 121, 112, 101, 34, 58, 34, 115, 116, 114, 105, 110, 103, 34, 125, 44,
    123, 34, 110, 97, 109, 101, 34, 58, 34, 97, 109, 111, 117, 110, 116, 34, 44,
    34, 116, 121, 112, 101, 34, 58, 34, 100, 111, 117, 98, 108, 101, 34, 125, 93,
    125, 0, 84, 229, 97, 195, 95, 74, 85, 204, 143, 132, 4, 241, 94, 197, 178, 106,
    2, 26, 8, 116, 120, 45, 49, 123, 20, 174, 71, 225, 250, 47, 64, 84, 229, 97,
    195, 95, 74, 85, 204, 143, 132, 4, 241, 94, 197, 178, 106>>

{:ok, decoded} = Avrora.decode(message)
[%{"id" => "tx-1", "amount" => 15.99}]

:bulb: Due to possible collision of the :plain format and :registry via magic-like byte sequence it's recommended^v0.18 to use Avrora.decode_plain/2 and Avrora.encode_plain/2 if you are working with :plain format (see in all available functions).

Schemas registration

There are two ways you can register AVRO schemas if you have disabled auto-registration.

If you want to make it a part of your code, but with better control, you can use Avrora.Utils.Registrar module and if you want to embed it in the deployment use a mix task avrora.reg.schema.

Avrora.Utils.Registrar^v0.16

This module is cache-aware and thus it can be used inside intensive loops if needed. It provides two ways to register schema:

• by name, then it will be resolved to a file with library conventions
• by schema, then a given schema will be used without any disk reads

But keep in mind that either way has a memory check to ensure that schema was not registered before and to bypass this check you have to use force: true flag

{:ok, schema} = Avrora.Utils.Registrar.register_schema_by_name("io.confluent.Payment", force: true)

In addition, any schema can be registered under different subject via as: "NewName" option

{:ok, schema} = Avrora.Storage.File.get("io.confluent.Payment")
{:ok, schema_with_id} = Avrora.Utils.Registrar.register_schema(schema, as: "NewName")

mix avrora.reg.schema^v0.12

A separate mix task to register a specific schema or all found schemas in schemas folder (see configuration section).

For instance, if you configure Avrora schemas folder to be at ./priv/schemas and you want to register a schema io/confluent/Payment.avsc then you can use this command

$ mix avrora.reg.schema --name io.confluent.Payment
schema `io.confluent.Payment' will be registered

In addition, any schema can be registered under different subject via --as option^v0.16

$ mix avrora.reg.schema --name io.confluent.Payment --as MyCustomName
schema `io.confluent.Payment' will be registered as `MyCustomName'

If you would like to register all schemas found under ./priv/schemas then you can simply execute this command

$ mix avrora.reg.schema --all
schema `io.confluent.Payment' will be registered
schema `io.confluent.Wrong' will be skipped due to an error `argument error'

Additional application config to load additional can be set via --appconfig option^v0.26

$ mix avrora.reg.schema --name io.confluent.Payment --appconfig runtime
schema `io.confluent.Payment' will be registered