95 lines
3.8 KiB
Markdown
95 lines
3.8 KiB
Markdown
# Making API Changes
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This document describes the process of how btcwallet developers must make
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changes to the RPC API and server. Due to the use of gRPC and Protocol Buffers
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for the RPC implementation, changes to this API require extra dependencies and
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steps before changes to the server can be implemented.
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## Requirements
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- The Protocol Buffer compiler `protoc` installed with support for the `proto3`
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language
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The `protoc` tool is part of the Protocol Buffers project. This can be
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installed [from source](https://github.com/google/protobuf/blob/master/INSTALL.txt),
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from an [official binary release](https://github.com/google/protobuf/releases),
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or through an operating system's package manager.
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- The gRPC `protoc` plugin for Go
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This plugin is written in Go and can be installed using `go get`:
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```
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go get github.com/golang/protobuf/protoc-gen-go
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```
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- Knowledge of Protocol Buffers version 3 (proto3)
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Note that a full installation of gRPC Core is not required, and only the
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`protoc` compiler and Go plugins are necessary. This is due to the project
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using a pure Go gRPC implementation instead of wrapping the C library from gRPC
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Core.
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## Step 1: Modify the `.proto`
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Once the developer dependencies have been met, changes can be made to the API by
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modifying the Protocol Buffers descriptor file [`api.proto`](../api.proto).
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The API is versioned according to the rules of [Semantic Versioning
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2.0](http://semver.org/). After any changes, bump the API version in the [API
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specification](./api.md) and add the changes to the spec.
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Unless backwards compatibility is broken (and the version is bumped to represent
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this change), message fields must never be removed or changed, and new fields
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must always be appended.
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It is forbidden to use the `required` attribute on a message field as this can
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cause errors during parsing when the new API is used by an older client.
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Instead, the (implicit) optional attribute is used, and the server
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implementation must return an appropriate error if the new request field is not
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set to a valid value.
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## Step 2: Compile the `.proto`
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Once changes to the descriptor file and API specification have been made, the
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`protoc` compiler must be used to compile the descriptor into a Go package.
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This code contains interfaces (stubs) for each service (to be implemented by the
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wallet) and message types used for each RPC. This same code can also be
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imported by a Go client that then calls same interface methods to perform RPC
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with the wallet.
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By committing the autogenerated package to the project repo, the `proto3`
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compiler and plugin are not needed by users installing the project by source or
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by other developers not making changes to the RPC API.
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A `sh` shell script is included to compile the Protocol Buffers descriptor. It
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must be run from the `rpc` directory.
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```bash
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$ sh regen.sh
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```
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If a `sh` shell is unavailable, the command can be run manually instead (again
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from the `rpc` directory).
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```
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protoc -I. api.proto --go_out=plugins=grpc:walletrpc
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```
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TODO(jrick): This step could be simplified and be more portable by putting the
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commands in a Go source file and executing them with `go generate`. It should,
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however, only be run when API changes are performed (not with `go generate
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./...` in the project root) since not all developers are expected to have
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`protoc` installed.
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## Step 3: Implement the API change in the RPC server
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After the Go code for the API has been regenated, the necessary changes can be
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implemented in the [`rpcserver`](../rpcserver/) package.
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## Additional Resources
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- [Protocol Buffers Language Guide (proto3)](https://developers.google.com/protocol-buffers/docs/proto3)
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- [Protocol Buffers Basics: Go](https://developers.google.com/protocol-buffers/docs/gotutorial)
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- [gRPC Basics: Go](http://www.grpc.io/docs/tutorials/basic/go.html)
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