View Source Protobuf.JSON (protobuf v0.13.0)

JSON encoding and decoding utilities for Protobuf structs.

It follows Google's specs and reference implementation. Some features such as well-known types are not fully supported yet.

Proto3 is supported as per the specification. Proto2 is supported in practice, but some of its features might not work correctly, such as extensions.

Types

Protobuf	JSON	Supported
`bool`	`true`/`false`	Yes
`int32`, `fixed32`, `uint32`	Number	Yes
`int64`, `fixed64`, `uint64`	String	Yes
`float`, `double`	Number	Yes
`bytes`	Base64 string	Yes
`string`	String	Yes
`message`	Object (`{…}`)	Yes
`enum`	String	Yes
`map<K,V>`	Object (`{…}`)	Yes
`repeated V`	Array of `[v, …]`	Yes
`Any`	Object (`{…}`)	Yes
`Timestamp`	RFC3339 datetime	Yes
`Duration`	String (`seconds.fraction`)	Yes
`Struct`	Object (`{…}`)	Yes
`Wrapper types`	Various types	Yes
`FieldMask`	String	Yes
`ListValue`	Array	Yes
`Value`	Any JSON value	Yes
`NullValue`	`null`	Yes
`Empty`	Object (`{…}`)	Yes

Usage

Protobuf.JSON requires a JSON library to work, so first make sure you have :jason added to your dependencies:

defp deps do
  [
    {:jason, "~> 1.2"},
    # ...
  ]
end

With encode/1 you can turn any Protobuf message struct into a JSON string:

iex> message = %Car{color: :RED, top_speed: 125.3}
iex> Protobuf.JSON.encode(message)
{:ok, "{\"color\":\"RED\",\"topSpeed\":125.3}"}

And go the other way around with decode/1:

iex> json = ~S|{"color":"RED","topSpeed":125.3}|
iex> Protobuf.JSON.decode(json, Car)
{:ok, %Car{color: :RED, top_speed: 125.3}}

JSON keys are encoded as camelCase strings by default, specified by the json_name field option. So make sure to recompile the .proto files in your project before working with JSON encoding, the compiler will generate all the required json_name options. You can set your own json_name for a particular field too:

message GeoCoordinate {
  double latitude = 1 [ json_name = "lat" ];
  double longitude = 2 [ json_name = "long" ];
}

Known Issues and Limitations

Currently, the protoc compiler won't check for field name collisions. This library won't check that either. Make sure your field names will be unique when serialized to JSON. For instance, this message definition will not encode correctly since it will emit just one of the two fields and the problem might go unnoticed:

message CollidingFields {
  int32 f1 = 1 [json_name = "sameName"];
  float f2 = 2 [json_name = "sameName"];
}

According to the specification, when duplicated JSON keys are found in maps, the library should raise a decoding error. It currently ignores duplicates and keeps the last occurrence.

`google.protobuf.Any`

The google.protobuf.Any type is supported. It can be used to encode and decode arbitrary messages. When decoding, the "type URL" is used to determine the message type to decode to. The type URL is expected to be in the format of type.googleapis.com/<package>.<message>. For example, the type URL for the google.protobuf.Duration message would be type.googleapis.com/google.protobuf.Duration. To determine the Elixir module from the type URL, the package and message names are split on . and transformed into a module name. In the previous example, we'd end up with Google.Protobuf.Duration. Due to arbitrary atom construction, we're forced to use Module.safe_concat/1 to construct the module name. This means that the module must exist before decoding. If the module doesn't exist, decoding will raise an error.

Summary

Types

encode_opt()

json_data()

Functions

decode(iodata, module)

Decodes a JSON iodata into a module Protobuf struct.

decode!(iodata, module)

Decodes a JSON iodata into a module Protobuf struct.

encode(struct, opts \\ [])

Generates a JSON representation of the given protobuf struct.

encode!(struct, opts \\ [])

Generates a JSON representation of the given protobuf struct.

from_decoded(json_data, module)

Decodes a json_data map into a module Protobuf struct.

to_encodable(struct, opts \\ [])

Generates a JSON-encodable map for the given Protobuf struct.

Types

encode_opt()

@type encode_opt() ::
  {:use_proto_names, boolean()}
  | {:use_enum_numbers, boolean()}
  | {:emit_unpopulated, boolean()}

json_data()

@type json_data() :: %{optional(binary()) => any()}

Functions

decode(iodata, module)

@spec decode(iodata(), module()) ::
  {:ok, struct()} | {:error, Protobuf.JSON.DecodeError.t() | Exception.t()}

Decodes a JSON iodata into a module Protobuf struct.

Examples

Given this Protobuf message:

syntax = "proto3";

message Car {
  enum Color {
    GREEN = 0;
    RED = 1;
  }

  Color color = 1;
  float top_speed = 2;
}

You can build its structs from JSON like this:

iex> Protobuf.JSON.decode("{}", Car)
{:ok, %Car{color: :GREEN, top_speed: 0.0}}

iex> ~S|{"color":"RED"}| |> Protobuf.JSON.decode(Car)
{:ok, %Car{color: :RED, top_speed: 0.0}}

iex> ~S|{"color":"GREEN","topSpeed":80.0}| |> Protobuf.JSON.decode(Car)
{:ok, %Car{color: :GREEN, top_speed: 80.0}}

decode!(iodata, module)

@spec decode!(iodata(), module()) :: struct() | no_return()

Decodes a JSON iodata into a module Protobuf struct.

Similar to decode!/2 except it will unwrap the error tuple and raise in case of errors.

Examples

iex> Protobuf.JSON.decode!("{}", Car)
%Car{color: :GREEN, top_speed: 0.0}

iex> ~S|{"color":"RED"}| |> Protobuf.JSON.decode!(Car)
%Car{color: :RED, top_speed: 0.0}

iex> ~S|{"color":"GREEN","topSpeed":80.0}| |> Protobuf.JSON.decode!(Car)
%Car{color: :GREEN, top_speed: 80.0}

encode(struct, opts \\ [])

@spec encode(
  struct(),
  [encode_opt()]
) :: {:ok, String.t()} | {:error, Protobuf.JSON.EncodeError.t() | Exception.t()}

Generates a JSON representation of the given protobuf struct.

Options

:use_proto_names - use original field name instead of the camelCase json_name for JSON keys. Defaults to false.
:use_enum_numbers - encode enum field values as numbers instead of their labels. Defaults to false.
:emit_unpopulated - emit all fields, even when they are blank, empty, or set to their default value. Defaults to false.

Examples

Suppose that this is you Protobuf message:

syntax = "proto3";

message Car {
  enum Color {
    GREEN = 0;
    RED = 1;
  }

  Color color = 1;
  float top_speed = 2;
}

Encoding is as simple as:

iex> Protobuf.JSON.encode(%Car{color: :RED, top_speed: 125.3})
{:ok, ~S|{"color":"RED","topSpeed":125.3}|}

iex> Protobuf.JSON.encode(%Car{color: :GREEN})
{:ok, "{}"}

iex> Protobuf.JSON.encode(%Car{}, emit_unpopulated: true)
{:ok, ~S|{"color":"GREEN","topSpeed":0.0}|}

encode!(struct, opts \\ [])

@spec encode!(
  struct(),
  [encode_opt()]
) :: String.t() | no_return()

Generates a JSON representation of the given protobuf struct.

Similar to encode/2 except it will unwrap the error tuple and raise in case of errors.

Examples

iex> Protobuf.JSON.encode!(%Car{top_speed: 80.0})
~S|{"topSpeed":80.0}|

from_decoded(json_data, module)

@spec from_decoded(json_data(), module()) ::
  {:ok, struct()} | {:error, Protobuf.JSON.DecodeError.t()}

Decodes a json_data map into a module Protobuf struct.

Similar to decode/2 except it takes a JSON map representation of the data. This is especially useful if you want to use custom JSON encoding or a custom JSON library.

Examples

iex> Protobuf.JSON.from_decoded(%{}, Car)
{:ok, %Car{color: :GREEN, top_speed: 0.0}}

iex> Protobuf.JSON.from_decoded(%{"color" => "RED"}, Car)
{:ok, %Car{color: :RED, top_speed: 0.0}}

iex> Protobuf.JSON.from_decoded(%{"color" => "GREEN","topSpeed" => 80.0}, Car)
{:ok, %Car{color: :GREEN, top_speed: 80.0}}

to_encodable(struct, opts \\ [])

@spec to_encodable(
  struct(),
  [encode_opt()]
) :: {:ok, json_data()} | {:error, Protobuf.JSON.EncodeError.t()}

Generates a JSON-encodable map for the given Protobuf struct.

Similar to encode/2 except it will return an intermediate map representation. This is especially useful if you want to use custom JSON encoding or a custom JSON library.

Supports the same options as encode/2.

Examples

iex> Protobuf.JSON.to_encodable(%Car{color: :RED, top_speed: 125.3})
{:ok, %{"color" => :RED, "topSpeed" => 125.3}}

iex> Protobuf.JSON.to_encodable(%Car{color: :GREEN})
{:ok, %{}}

iex> Protobuf.JSON.to_encodable(%Car{}, emit_unpopulated: true)
{:ok, %{"color" => :GREEN, "topSpeed" => 0.0}}