View Source Protobuf behaviour (protobuf v0.12.0)
protoc should always be used to generate code instead of writing the code by hand.
usage
Usage
By use'ing this module, macros defined in Protobuf.DSL will be injected. Most of these
macros are equal to definition in .proto schemas.
defmodule Foo do
use Protobuf, syntax: :proto3
field :a, 1, type: :int32
field :b, 2, type: :string
endYour Protobuf message (module) is just a normal Elixir struct. The default values in the struct match the correct ones for the Protobuf schema definition. You can construct new messages by hand:
foo = %Foo{a: 1}
Protobuf.encode(foo)
#=> <<...>>Except functions in "Callbacks", some other functions may be defined:
- Extension functions when your Protobuf message use extensions. See
Protobuf.Extensionfor details.put_extension(struct, extension_mod, field, value)get_extension(struct, extension_mod, field, default \ nil)
options
Options
These are the options that you can pass to use Protobuf:
:syntax- The syntax of the schema. Can be:proto2or:proto3. Defaults to:proto2.:enum- A boolean that tells whether this message is an enum. Defaults tofalse.:map- A boolean that tells whether this message is a map. Defaults tofalse.
Link to this section Summary
Callbacks
Decodes a Protobuf binary into a struct.
Encodes the given struct into to a Protobuf binary.
Builds a blank struct with default values.
Builds and updates the struct with passed fields.
Returns nil or a transformer module that implements the Protobuf.TransformModule
behaviour.
Functions
Decodes the given binary data interpreting it as the Protobuf message module.
Encodes the given Protobuf struct into a binary.
Encodes the given Protobuf struct into iodata.
Returns the unknown fields that were decoded but were not understood from the schema.
Loads extensions modules.
Link to this section Callbacks
Decodes a Protobuf binary into a struct.
Errors may be raised if there's something wrong in the binary.
Encodes the given struct into to a Protobuf binary.
Errors may be raised if there's something wrong in the struct.
If you want to encode to iodata instead of to a binary, use encode_to_iodata/1.
@callback new() :: struct()
Builds a blank struct with default values.
Deprecated
This is deprecated in favor of building the struct with
%MyMessage{...}or usingstruct/1.
Builds and updates the struct with passed fields.
This function will:
- Recursively call
new/1for embedded fields - Create structs using
struct/2for keyword lists and maps - Create the correct struct if passed the wrong struct
- Call
new/1for each element in the list for repeated fields
Deprecated
This is deprecated in favor of building the struct with
%MyMessage{...}or usingstruct/2.
examples
Examples
MyMessage.new(field1: "foo")
#=> %MyMessage{field1: "foo", ...}
MyMessage.new(field1: [field2: "foo"])
#=> %MyMessage{field1: %MySubMessage{field2: "foo"}}
MyMessage.new(field1: %WrongStruct{field2: "foo"})
#=> %MyMessage{field1: %MySubMessage{field2: "foo"}}
MyMessage.new(repeated: [%{field1: "foo"}, %{field1: "bar"}])
#=> %MyMessage{repeated: [%MyRepeated{field1: "foo"}, %MyRepeated{field1: "bar"}]}Similar to new/1, but use struct!/2 to build the struct, so
errors will be raised if unknown keys are passed.
Deprecated
This is deprecated in favor of building the struct with
%MyMessage{...}or usingstruct!/2directly.
@callback transform_module() :: module() | nil
Returns nil or a transformer module that implements the Protobuf.TransformModule
behaviour.
This function is overridable in your module.
Link to this section Functions
Decodes the given binary data interpreting it as the Protobuf message module.
This function raises an error if anything goes wrong with decoding.
examples
Examples
Protobuf.decode(<<...>>, MyMessage)
#=> %MyMessage{...}
Protobuf.decode(<<"bad data">>, MyMessage)
#=> ** (Protobuf.DecodeError) ...Encodes the given Protobuf struct into a binary.
If you want to encode to iodata instead, see encode_to_iodata/1.
examples
Examples
Protobuf.encode(%MyMessage{...})
#=> <<...>>Encodes the given Protobuf struct into iodata.
examples
Examples
Protobuf.encode_to_iodata(%MyMessage{...})
#=> [...]@spec get_unknown_fields(struct()) :: [unknown_field] when unknown_field: {field_number :: integer(), Protobuf.Wire.Types.wire_type(), value :: any()}
Returns the unknown fields that were decoded but were not understood from the schema.
In Protobuf, you can decode a payload (for the same message) encoded with a different version of the schema for that message. This can result in, for example, the payload containing fields that cannot be decoded correctly because they're not present in the schema used for decoding. These fields are skipped, but in some cases you might wish to preserve them in order to re-encode them, log them, or other. A common case is having to do "round-trips" with messages: you decode a payload, update the resulting message somehow, and re-encode it for future use. In these cases, you would probably want to re-encode the unknown fields to maintain symmetry.
The returned value of this function is a list of {field_number, field_value} tuples where
field_number is the number of the unknown field in the schema used for its encoding and
field_value is its value. The library does not make any assumptions on the value of the
field since it can't know for sure. This means that, for example, it can't properly decode
an integer as signed or unsigned. The only guarantee is that the unknown fields are re-encoded
correctly.
The reason why these fields need to be accessed through this function is that the way they are stored in the struct is private.
examples
Examples
Imagine you have this Protobuf schema:
message User {
string email = 1;
}You encode this:
payload = Protobuf.encode(User.new!(email: "user@example.com))
#=> <<...>>Now, you try to decode this payload using this schema instead:
message User {
string full_name = 2;
}In this case, this function will return the decoded unknown field:
message = User.decode(<<...>>)
Protobuf.get_unknown_fields(message)
#=> [{_field_number = 1, _wire_type = 3, "user@example.com}]@spec load_extensions() :: :ok
Loads extensions modules.
This function should be called in your application's Application.start/2 callback,
as seen in the example below, if you wish to use extensions.
example
Example
@impl Application
def start(_type, _args) do
Protobuf.load_extensions()
Supervisor.start_link([], strategy: :one_for_one)
end