docker-cli/cli-plugins/manager/plugin.go

package manager

import (
	"encoding/json"
	"os"
	"os/exec"
	"path/filepath"
	"regexp"
	"strings"

	"github.com/pkg/errors"
	"github.com/spf13/cobra"
)

var pluginNameRe = regexp.MustCompile("^[a-z][a-z0-9]*$")

// Plugin represents a potential plugin with all it's metadata.
type Plugin struct {
	Metadata

	Name string `json:",omitempty"`
	Path string `json:",omitempty"`

	// Err is non-nil if the plugin failed one of the candidate tests.
	Err error `json:",omitempty"`

	// ShadowedPaths contains the paths of any other plugins which this plugin takes precedence over.
	ShadowedPaths []string `json:",omitempty"`
}

// newPlugin determines if the given candidate is valid and returns a
// Plugin.  If the candidate fails one of the tests then `Plugin.Err`
// is set, and is always a `pluginError`, but the `Plugin` is still
// returned with no error. An error is only returned due to a
// non-recoverable error.
func newPlugin(c Candidate, cmds []*cobra.Command) (Plugin, error) {
	path := c.Path()
	if path == "" {
		return Plugin{}, errors.New("plugin candidate path cannot be empty")
	}

	// The candidate listing process should have skipped anything
	// which would fail here, so there are all real errors.
	fullname := filepath.Base(path)
	if fullname == "." {
		return Plugin{}, errors.Errorf("unable to determine basename of plugin candidate %q", path)
	}
	var err error
	if fullname, err = trimExeSuffix(fullname); err != nil {
		return Plugin{}, errors.Wrapf(err, "plugin candidate %q", path)
	}
	if !strings.HasPrefix(fullname, NamePrefix) {
		return Plugin{}, errors.Errorf("plugin candidate %q: does not have %q prefix", path, NamePrefix)
	}

	p := Plugin{
		Name: strings.TrimPrefix(fullname, NamePrefix),
		Path: path,
	}

	// Now apply the candidate tests, so these update p.Err.
	if !pluginNameRe.MatchString(p.Name) {
		p.Err = NewPluginError("plugin candidate %q did not match %q", p.Name, pluginNameRe.String())
		return p, nil
	}

	for _, cmd := range cmds {
		// Ignore conflicts with commands which are
		// just plugin stubs (i.e. from a previous
		// call to AddPluginCommandStubs).
		if IsPluginCommand(cmd) {
			continue
		}
		if cmd.Name() == p.Name {
			p.Err = NewPluginError("plugin %q duplicates builtin command", p.Name)
			return p, nil
		}
		if cmd.HasAlias(p.Name) {
			p.Err = NewPluginError("plugin %q duplicates an alias of builtin command %q", p.Name, cmd.Name())
			return p, nil
		}
	}

	// We are supposed to check for relevant execute permissions here. Instead we rely on an attempt to execute.
	meta, err := c.Metadata()
	if err != nil {
		p.Err = wrapAsPluginError(err, "failed to fetch metadata")
		return p, nil
	}

	if err := json.Unmarshal(meta, &p.Metadata); err != nil {
		p.Err = wrapAsPluginError(err, "invalid metadata")
		return p, nil
	}
	if p.Metadata.SchemaVersion != "0.1.0" {
		p.Err = NewPluginError("plugin SchemaVersion %q is not valid, must be 0.1.0", p.Metadata.SchemaVersion)
		return p, nil
	}
	if p.Metadata.Vendor == "" {
		p.Err = NewPluginError("plugin metadata does not define a vendor")
		return p, nil
	}
	return p, nil
}

// RunHook executes the plugin's hooks command
// and returns its unprocessed output.
func (p *Plugin) RunHook(cmdName string, flags map[string]string) ([]byte, error) {
	hDataBytes, err := json.Marshal(HookPluginData{
		RootCmd: cmdName,
		Flags:   flags,
	})
	if err != nil {
		return nil, wrapAsPluginError(err, "failed to marshall hook data")
	}

	pCmd := exec.Command(p.Path, p.Name, HookSubcommandName, string(hDataBytes))
	pCmd.Env = os.Environ()
	pCmd.Env = append(pCmd.Env, ReexecEnvvar+"="+os.Args[0])
	hookCmdOutput, err := pCmd.Output()
	if err != nil {
		return nil, wrapAsPluginError(err, "failed to execute plugin hook subcommand")
	}

	return hookCmdOutput, nil
}