# Generator

This document contains information about GoVPP generator which is used for generating Go bindings for VPP binary API.

## Installation

### Prerequisites

- Go 1.13+ ([download](https://golang.org/dl))

### Install via Go toolchain

```shell
# Latest version (most recent tag)
go install git.fd.io/govpp.git/cmd/binapi-generator@latest

# Development version (master branch)
go install git.fd.io/govpp.git/cmd/binapi-generator@master
```

NOTE: Using `go install` to install programs is only supported in Go 1.16+ ([more info](https://go.dev/doc/go1.16#go-command)). For Go 1.15 or older, use `go get` instead of `go install`.

### Install from source

```sh
# Clone repository anywhere
git clone https://gerrit.fd.io/r/govpp.git
cd govpp

# Install binapi-generator
make install-generator
```

NOTE: There is no need to setup or clone inside `GOPATH` for Go 1.13+ ([more info](https://go.dev/doc/go1.13#modules))
and you can simply clone the repository _anywhere_ you want.

### Generating binapi

### Install vpp binary artifacts

Build locally, or download from packagecloud. Read more: https://fd.io/docs/vpp/master/gettingstarted/installing

### Generate binapi (Go bindings)

Generating Go bindings for VPP binary API from the JSON files
installed with the vpp binary artifacts - located in `/usr/share/vpp/api/`.

```sh
make generate-binapi
INFO[0000] found 110 files in API dir "/usr/share/vpp/api"
INFO[0000] Generating 203 files
```

The generated files will be generated under `binapi` directory.

### Generate VPP binary API code (Go bindings)

Once you have `binapi-generator` installed, you can use it to generate Go bindings for VPP binary API
using VPP APIs in JSON format. The JSON input can be specified as a single file (`input-file` argument), or
as a directory that will be scanned for all `.json` files (`input-dir`). The generated Go bindings will
be placed into `output-dir` (by default current working directory), where each Go package will be placed into
a separated directory, e.g.:

```sh
binapi-generator --input-file=acl.api.json --output-dir=binapi
binapi-generator --input-dir=/usr/share/vpp/api/core --output-dir=binapi
```

In Go, [go generate](https://blog.golang.org/generate) tool can be leveraged to ease the code generation
process. It allows specifying generator instructions in any one of the regular (non-generated) `.go` files
that are dependent on generated code using special comments:

```go
//go:generate binapi-generator --input-dir=bin_api --output-dir=bin_api
```

### Tracking down generated go code for a specific binary API

Golang uses capitalization to indicate exported names, so you'll have
to divide through by binapi-generator transformations. Example:

```
define create_loopback  -> type CreateLoopback struct ...
   vpp binapi definition      govpp exported type definition
```
The droids you're looking for will be in a file named
<something>.ba.go.  Suggest:

```
find git.fd.io/govpp/binapi -name "*.ba.go" | xargs grep -n GoTypeName
```

Look at the indicated <something>.ba.go file, deduce the package name
and import it. See the example above.