helm/pkg/plugin/plugin.go

/*
Copyright The Helm Authors.
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package plugin // import "helm.sh/helm/v3/pkg/plugin"

import (
	"fmt"
	"io/ioutil"
	"os"
	"path/filepath"
	"runtime"
	"strings"

	"sigs.k8s.io/yaml"

	"helm.sh/helm/v3/pkg/cli"
)

const PluginFileName = "plugin.yaml"

// Downloaders represents the plugins capability if it can retrieve
// charts from special sources
type Downloaders struct {
	// Protocols are the list of schemes from the charts URL.
	Protocols []string `json:"protocols"`
	// Command is the executable path with which the plugin performs
	// the actual download for the corresponding Protocols
	Command string `json:"command"`
}

// PlatformCommand represents a command for a particular operating system and architecture
type PlatformCommand struct {
	OperatingSystem string `json:"os"`
	Architecture    string `json:"arch"`
	Command         string `json:"command"`
}

// Metadata describes a plugin.
//
// This is the plugin equivalent of a chart.Metadata.
type Metadata struct {
	// Name is the name of the plugin
	Name string `json:"name"`

	// Version is a SemVer 2 version of the plugin.
	Version string `json:"version"`

	// Usage is the single-line usage text shown in help
	Usage string `json:"usage"`

	// Description is a long description shown in places like `helm help`
	Description string `json:"description"`

	// Command is the command, as a single string.
	//
	// The command will be passed through environment expansion, so env vars can
	// be present in this command. Unless IgnoreFlags is set, this will
	// also merge the flags passed from Helm.
	//
	// Note that command is not executed in a shell. To do so, we suggest
	// pointing the command to a shell script.
	//
	// The following rules will apply to processing commands:
	// - If platformCommand is present, it will be searched first
	// - If both OS and Arch match the current platform, search will stop and the command will be executed
	// - If OS matches and there is no more specific match, the command will be executed
	// - If no OS/Arch match is found, the default command will be executed
	// - If no command is present and no matches are found in platformCommand, Helm will exit with an error
	PlatformCommand []PlatformCommand `json:"platformCommand"`
	Command         string            `json:"command"`

	// IgnoreFlags ignores any flags passed in from Helm
	//
	// For example, if the plugin is invoked as `helm --debug myplugin`, if this
	// is false, `--debug` will be appended to `--command`. If this is true,
	// the `--debug` flag will be discarded.
	IgnoreFlags bool `json:"ignoreFlags"`

	// Hooks are commands that will run on events.
	Hooks Hooks

	// Downloaders field is used if the plugin supply downloader mechanism
	// for special protocols.
	Downloaders []Downloaders `json:"downloaders"`
}

// Plugin represents a plugin.
type Plugin struct {
	// Metadata is a parsed representation of a plugin.yaml
	Metadata *Metadata
	// Dir is the string path to the directory that holds the plugin.
	Dir string
}

// The following rules will apply to processing the Plugin.PlatformCommand.Command:
// - If both OS and Arch match the current platform, search will stop and the command will be prepared for execution
// - If OS matches and there is no more specific match, the command will be prepared for execution
// - If no OS/Arch match is found, return nil
func getPlatformCommand(cmds []PlatformCommand) []string {
	var command []string
	eq := strings.EqualFold
	for _, c := range cmds {
		if eq(c.OperatingSystem, runtime.GOOS) {
			command = strings.Split(os.ExpandEnv(c.Command), " ")
		}
		if eq(c.OperatingSystem, runtime.GOOS) && eq(c.Architecture, runtime.GOARCH) {
			return strings.Split(os.ExpandEnv(c.Command), " ")
		}
	}
	return command
}

// PrepareCommand takes a Plugin.PlatformCommand.Command, a Plugin.Command and will applying the following processing:
// - If platformCommand is present, it will be searched first
// - If both OS and Arch match the current platform, search will stop and the command will be prepared for execution
// - If OS matches and there is no more specific match, the command will be prepared for execution
// - If no OS/Arch match is found, the default command will be prepared for execution
// - If no command is present and no matches are found in platformCommand, will exit with an error
//
// It merges extraArgs into any arguments supplied in the plugin. It
// returns the name of the command and an args array.
//
// The result is suitable to pass to exec.Command.
func (p *Plugin) PrepareCommand(extraArgs []string) (string, []string, error) {
	var parts []string
	platCmdLen := len(p.Metadata.PlatformCommand)
	if platCmdLen > 0 {
		parts = getPlatformCommand(p.Metadata.PlatformCommand)
	}
	if platCmdLen == 0 || parts == nil {
		parts = strings.Split(os.ExpandEnv(p.Metadata.Command), " ")
	}
	if len(parts) == 0 || parts[0] == "" {
		return "", nil, fmt.Errorf("No plugin command is applicable")
	}

	main := parts[0]
	baseArgs := []string{}
	if len(parts) > 1 {
		baseArgs = parts[1:]
	}
	if !p.Metadata.IgnoreFlags {
		baseArgs = append(baseArgs, extraArgs...)
	}
	return main, baseArgs, nil
}

// LoadDir loads a plugin from the given directory.
func LoadDir(dirname string) (*Plugin, error) {
	data, err := ioutil.ReadFile(filepath.Join(dirname, PluginFileName))
	if err != nil {
		return nil, err
	}

	plug := &Plugin{Dir: dirname}
	if err := yaml.Unmarshal(data, &plug.Metadata); err != nil {
		return nil, err
	}
	return plug, nil
}

// LoadAll loads all plugins found beneath the base directory.
//
// This scans only one directory level.
func LoadAll(basedir string) ([]*Plugin, error) {
	plugins := []*Plugin{}
	// We want basedir/*/plugin.yaml
	scanpath := filepath.Join(basedir, "*", PluginFileName)
	matches, err := filepath.Glob(scanpath)
	if err != nil {
		return plugins, err
	}

	if matches == nil {
		return plugins, nil
	}

	for _, yaml := range matches {
		dir := filepath.Dir(yaml)
		p, err := LoadDir(dir)
		if err != nil {
			return plugins, err
		}
		plugins = append(plugins, p)
	}
	return plugins, nil
}

// FindPlugins returns a list of YAML files that describe plugins.
func FindPlugins(plugdirs string) ([]*Plugin, error) {
	found := []*Plugin{}
	// Let's get all UNIXy and allow path separators
	for _, p := range filepath.SplitList(plugdirs) {
		matches, err := LoadAll(p)
		if err != nil {
			return matches, err
		}
		found = append(found, matches...)
	}
	return found, nil
}

// SetupPluginEnv prepares os.Env for plugins. It operates on os.Env because
// the plugin subsystem itself needs access to the environment variables
// created here.
func SetupPluginEnv(settings *cli.EnvSettings, name, base string) {
	env := settings.EnvVars()
	env["HELM_PLUGIN_NAME"] = name
	env["HELM_PLUGIN_DIR"] = base
	for key, val := range env {
		os.Setenv(key, val)
	}
}