104 lines
5.1 KiB
Markdown
104 lines
5.1 KiB
Markdown
<!--
|
|
order: 6
|
|
synopsis: Amino and Protobuf are the primary binary wire encoding schemes in the Cosmos SDK.
|
|
-->
|
|
|
|
# Encoding
|
|
|
|
> NOTE: This document a WIP.
|
|
|
|
## Pre-requisite Readings {hide}
|
|
|
|
- [Anatomy of an SDK application](../basics/app-anatomy.md) {prereq}
|
|
|
|
## Encoding
|
|
|
|
The Cosmos SDK utilizes two binary wire encoding protocols, [Amino](https://github.com/tendermint/go-amino/)
|
|
and [Protocol Buffers](https://developers.google.com/protocol-buffers), where Amino
|
|
is an object encoding specification. It is a subset of Proto3 with an extension for
|
|
interface support. See the [Proto3 spec](https://developers.google.com/protocol-buffers/docs/proto3)
|
|
for more information on Proto3, which Amino is largely compatible with (but not with Proto2).
|
|
|
|
Due to Amino having significant performance drawbacks, being reflection-based, and
|
|
not having any meaningful cross-language/client support, Protocol Buffers, specifically
|
|
[gogoprotobuf](https://github.com/gogo/protobuf/), is being used in place of Amino.
|
|
Note, this process of using Protocol Buffers over Amino is still an ongoing process.
|
|
|
|
Binary wire encoding of types in the Cosmos SDK can be broken down into two main
|
|
categories, client encoding and store encoding. Client encoding mainly revolves
|
|
around transaction processing and signing, whereas store encoding revolves around
|
|
types used in state-machine transitions and what is ultimately stored in the Merkle
|
|
tree.
|
|
|
|
For store encoding, protobuf definitions can exist for any type and will typically
|
|
have an Amino-based "intermediary" type. Specifically, the protobuf-based type
|
|
definition is used for serialization and persistence, whereas the Amino-based type
|
|
is used for business logic in the state-machine where they may converted back-n-forth.
|
|
Note, the Amino-based types may slowly be phased-out in the future so developers
|
|
should take note to use the protobuf message definitions where possible.
|
|
|
|
In the `codec` package, there exists two core interfaces, `Marshaler` and `ProtoMarshaler`,
|
|
where the former encapsulates the current Amino interface except it operates on
|
|
types implementing the latter instead of generic `interface{}` types.
|
|
|
|
In addition, there exists three implementations of `Marshaler`. The first being
|
|
`AminoCodec`, where both binary and JSON serialization is handled via Amino. The
|
|
second being `ProtoCodec`, where both binary and JSON serialization is handled
|
|
via Protobuf. Finally, `HybridCodec`, a codec that utilizes Protobuf for binary
|
|
serialization and Amino for JSON serialization. The `HybridCodec` is typically
|
|
the codec that used in majority in situations as it's easier to use for client
|
|
and state serialization.
|
|
|
|
This means that modules may use Amino or Protobuf encoding but the types must
|
|
implement `ProtoMarshaler`. If modules wish to avoid implementing this interface
|
|
for their types, they may use an Amino codec directly.
|
|
|
|
### Amino
|
|
|
|
Every module uses an Amino codec to serialize types and interfaces. This codec typically
|
|
has types and interfaces registered in that module's domain only (e.g. messages),
|
|
but there are exceptions like `x/gov`. Each module exposes a `RegisterCodec` function
|
|
that allows a user to provide a codec and have all the types registered. An application
|
|
will call this method for each necessary module.
|
|
|
|
Where there is no protobuf-based type definition for a module (see below), Amino
|
|
is used to encode and decode raw wire bytes to the concrete type or interface:
|
|
|
|
```go
|
|
bz := keeper.cdc.MustMarshalBinaryBare(typeOrInterface)
|
|
keeper.cdc.MustUnmarshalBinaryBare(bz, &typeOrInterface)
|
|
```
|
|
|
|
Note, there are length-prefixed variants of the above functionality and this is
|
|
typically used for when the data needs to be streamed or grouped together
|
|
(e.g. `ResponseDeliverTx.Data`)
|
|
|
|
Another important use of the Amino is the encoding and decoding of
|
|
[transactions](./transactions.md). Transactions are defined by the application or
|
|
the SDK, but passed to the underlying consensus engine in order to be relayed to
|
|
other peers. Since the underlying consensus engine is agnostic to the application,
|
|
it only accepts transactions in the form of raw bytes. The encoding is done by an
|
|
object called `TxEncoder` and the decoding by an object called `TxDecoder`.
|
|
|
|
+++ https://github.com/cosmos/cosmos-sdk/blob/7d7821b9af132b0f6131640195326aa02b6751db/types/tx_msg.go#L45-L49
|
|
|
|
A standard implementation of both these objects can be found in the [`auth` module](https://github.com/cosmos/cosmos-sdk/blob/master/x/auth):
|
|
|
|
+++ https://github.com/cosmos/cosmos-sdk/blob/7d7821b9af132b0f6131640195326aa02b6751db/x/auth/types/stdtx.go#L241-L266
|
|
|
|
### Gogoproto
|
|
|
|
Modules are encouraged to utilize Protobuf encoding for their respective types.
|
|
If modules do not contain any interfaces (e.g. `Account` or `Content`), then they
|
|
may simply accept a `Marshaler` as the codec which is implemented via the `HybridCodec`
|
|
without any further customization.
|
|
|
|
However, if modules are to handle type interfaces, they should seek to extend the
|
|
`Marshaler` interface contract for these types (e.g. `MarshalAccount`). Note, they
|
|
should still use a `HybridCodec` internally. These extended contracts will typically
|
|
use concrete types with unique `oneof` messages.
|
|
|
|
## Next {hide}
|
|
|
|
Learn about [events](./events.md) {hide}
|