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AvroEx

An Avro encoding/decoding library written in pure Elixir.

Documentation

The docs can be found on hex.pm

Installation

def deps do
  [{:avro_ex, "~> 2.0"}]
end

Usage

Schema Decoding

Avro uses schemas to define the shape and contract for data. The schemas that your application uses may be defined locally, or may come from a Schema Registry.

In either case, the first step is to decode a schema defined as JSON or Elixir terms into a t:AvroEx.Schema.t/0

iex> AvroEx.decode_schema!(["int", "string"])
%AvroEx.Schema{
  context: %AvroEx.Schema.Context{names: %{}},
  schema: %AvroEx.Schema.Union{
    possibilities: [
      %AvroEx.Schema.Primitive{metadata: %{}, type: :int},
      %AvroEx.Schema.Primitive{metadata: %{}, type: :string}
    ]
  }
}

AvroEx will automatically detect Elixir terms or JSON, so you can decode JSON schemas directly

iex> AvroEx.decode_schema!("[\"int\",\"string\"]")
%AvroEx.Schema{
  context: %AvroEx.Schema.Context{names: %{}},
  schema: %AvroEx.Schema.Union{
    possibilities: [
      %AvroEx.Schema.Primitive{metadata: %{}, type: :int},
      %AvroEx.Schema.Primitive{metadata: %{}, type: :string}
    ]
  }
}

Strict Schema Decoding

When writing an Avro schema, it is helpful to get feedback on unrecognized fields. For this purpose, it is recommended to use the :strict option to provide additional checks. Note that it is not recommended to use this option in production when pulling externally defined schemas, as they may have published a schema with looser validations.

iex> AvroEx.decode_schema!(%{"type" => "map", "values" => "int", "bogus" => "value"}, strict: true)
** (AvroEx.Schema.DecodeError) Unrecognized schema key `bogus` for AvroEx.Schema.Map in %{"bogus" => "value", "type" => "map", "values" => "int"}
    (avro_ex 1.2.0) lib/avro_ex/schema/parser.ex:43: AvroEx.Schema.Parser.parse!/2

Encoding

When publishing Avro data, it first must be encoded using the schema.

iex> schema = AvroEx.decode_schema!(%{
                "type" => "record",
                "name" => "MyRecord",
                "fields" => [
                  %{"name" => "a", "type" => "int"},
                  %{"name" => "b", "type" => "string"},
                ]
              })
iex> AvroEx.encode!(schema, %{a: 1, b: "two"})
<<2, 6, 116, 119, 111>

Decoding

When receiving Avro data, decode it using the schema

iex> AvroEx.decode!(schema, <<2, 6, 116, 119, 111>>)
%{"a" => 1, "b" => "two"}

Schema Encoding

AvroEx also supports encoding schemas back to JSON. This may be needed when registering schemas or serializing them to disk.

iex> AvroEx.encode_schema(schema)
"{\"fields\":[{\"name\":\"a\",\"type\":{\"type\":\"int\"}},{\"name\":\"b\",\"type\":{\"type\":\"string\"}}],\"name\":\"MyRecord\",\"type\":\"record\"}"

Additionally, schemas can be encoded to Parsing Canonical Form using the :canonical option.

iex> AvroEx.encode_schema(schema, canonical: true)
"{\"name\":\"MyRecord\",\"type\":\"record\",\"fields\":[{\"name\":\"a\",\"type\":\"int\"},{\"name\":\"b\",\"type\":\"string\"}]}"

Testing

For testing convenience, AvroEx.encodable?/2 is exported to check if data can be encoded against the given schema. Note that in production scenarios, it is not recommended to use this function.

defmodule MyModule.Test do
  use ExUnit.Case

  setup do
    data = ...
    schema = ...
    {:ok, %{data: data, schema: schema}}
  end

  describe "my_function/1" do
    test "builds a structure that can be encoded with our avro schema", context do
      result = MyModule.my_function(context.data)

      assert AvroEx.encodable?(context.schema, result)
    end
  end
end