# [WIP] Plugin Develop Guide

All compiled plugins need to place in `/usr/local/dragonfly/plugins/`.

## Plugin Design

Dragonfly2 use golang plugin to build its plugins, refer: [https://pkg.go.dev/plugin#section-documentation](https://pkg.go.dev/plugin#section-documentation).

## Resource Plugin for CDN and Dfget

The resource plugin is used to download custom resource like `dfget -u d7yfs://host:56001/path/to/resource`.

All resource plugins need to implement `d7y.io/dragonfly/v2/pkg/source.ResourceClient`
and a function

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`func DragonflyPluginInit(option map[string]string) (interface{}, map[string]string, error)`.

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```golang
// ResourceClient defines the API interface to interact with source.
type ResourceClient interface {
    // GetContentLength get length of resource content
    // return source.UnknownSourceFileLen if response status is not StatusOK and StatusPartialContent
    GetContentLength(request *Request) (int64, error)

    // IsSupportRange checks if resource supports breakpoint continuation
    // return false if response status is not StatusPartialContent
    IsSupportRange(request *Request) (bool, error)

    // IsExpired checks if a resource received or stored is the same.
    // return false and non-nil err to prevent the source from exploding if
    // fails to get the result, it is considered that the source has not expired
    IsExpired(request *Request, info *ExpireInfo) (bool, error)

    // Download downloads from source
    Download(request *Request) (*Response, error)

    // GetLastModified gets last modified timestamp milliseconds of resource
    GetLastModified(request *Request) (int64, error)
}
```

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### Example Code

#### 1. main.go

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```golang
package main

import (
	"bytes"
	"io"

	"d7y.io/dragonfly/v2/pkg/source"
)

var data = "hello world"

var _ source.ResourceClient = (*client)(nil)

var (
	buildCommit = "unknown"
	buildTime   = "unknown"
	vendor      = "d7y"
)

type client struct {
}

func (c *client) GetContentLength(request *source.Request) (int64, error) {
	return int64(len(data)), nil
}

func (c *client) IsSupportRange(request *source.Request) (bool, error) {
	return false, nil
}

func (c *client) IsExpired(request *source.Request, info *source.ExpireInfo) (bool, error) {
	panic("implement me")
}

func (c *client) Download(request *source.Request) (*source.Response, error) {
	return source.NewResponse(io.NopCloser(bytes.NewBufferString(data))), nil
}

func (c *client) DownloadWithExpireInfo(request *source.Request) (io.ReadCloser, *source.ExpireInfo, error) {
	return io.NopCloser(bytes.NewBufferString(data)), nil, nil
}

func (c *client) GetLastModified(request *source.Request) (int64, error) {
	panic("implement me")
}

func DragonflyPluginInit(option map[string]string) (interface{}, map[string]string, error) {
	return &client{}, map[string]string{
		"schema":      "d7yfs",
		"type":        "resource",
		"name":        "d7yfs",
		"buildCommit": buildCommit,
		"buildTime":   buildTime,
		"vendor":      vendor,
	}, nil
}


```

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#### 2. go.mod

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```
module example.com/d7yfs

go 1.17

require d7y.io/dragonfly/v2 v2.0.1

require (
        github.com/go-http-utils/headers v0.0.0-20181008091004-fed159eddc2a // indirect
        github.com/pkg/errors v0.9.1 // indirect
        go.uber.org/atomic v1.9.0 // indirect
        go.uber.org/multierr v1.5.0 // indirect
        go.uber.org/zap v1.16.0 // indirect
        google.golang.org/grpc v1.39.0 // indirect
        gopkg.in/yaml.v3 v3.0.0-20210107192922-496545a6307b // indirect
)

// fix golang build error: `plugin was built with a different version of package d7y.io/dragonfly/v2/internal/dflog`
replace d7y.io/dragonfly/v2 => /Dragonfly2
```

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### Build

> We have created a plugin builder in docker, follow [this document](./plugin-builder.md).
> With the plugin builder, `go.mod` will be ignored.

#### 1. Build plugin with target Dragonfly2 commit

> Update `D7Y_COMMIT` in the following script.

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```shell
# golang plugin need cgo
# original Dragonfly2 image is built with CGO_ENABLED=0 for alpine linux
# "dfdaemon" and "cdn" need to re-compile with CGO_ENABLED=1
export CGO_ENABLED="1"

# ensure same commit of code base
D7Y_COMMIT=01798aa08a6b4510210dd0a901e9f89318405440
git clone https://github.com/dragonflyoss/Dragonfly2.git /Dragonfly2 && git reset --hard ${D7Y_COMMIT}
(cd /Dragonfly2 && make build-dfget build-cdn)

# build plugin
BUILD_TIME=$(date -u '+%Y-%m-%dT%H:%M:%SZ')
BUILD_COMMIT=$(git rev-parse --short HEAD)
go mod tidy -compat=1.17
go build -ldflags="-X main.buildTime=${BUILD_TIME} -X main.buildCommit=${BUILD_COMMIT}" \
    -buildmode=plugin -o=/usr/local/dragonfly/plugins/d7y-resource-plugin-d7yfs.so ./main.go
```

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#### 2. Validate plugin

```shell
/Dragonfly2/bin/linux_amd64/dfget plugin
```

Example output:

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```text
search plugin in /usr/local/dragonfly/plugins
resource plugin d7yfs, location: d7y-resource-plugin-d7yfs.so, attribute: {"buildCommit":"bb65f13","buildTime":"2021-12-13T08:53:04Z","name":"d7yfs","schema":"d7yfs","type":"resource","vendor":"d7y"}
```

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## Evaluator Plugin for Scheduler

TODO

## Searcher Plugin for Manager

TODO