relation-get.go

// Copyright 2012, 2013 Canonical Ltd.
// Licensed under the AGPLv3, see LICENCE file for details.

package jujuc

import (
	"fmt"

	"github.com/juju/cmd/v3"
	"github.com/juju/errors"
	"github.com/juju/gnuflag"
	"github.com/juju/names/v4"

	jujucmd "github.com/juju/juju/cmd"
	"github.com/juju/juju/rpc/params"
)

// RelationGetCommand implements the relation-get command.
type RelationGetCommand struct {
	cmd.CommandBase
	ctx Context

	RelationId      int
	relationIdProxy gnuflag.Value
	Application     bool

	Key           string
	UnitOrAppName string
	out           cmd.Output
}

func NewRelationGetCommand(ctx Context) (cmd.Command, error) {
	var err error
	cmd := &RelationGetCommand{ctx: ctx}
	cmd.relationIdProxy, err = NewRelationIdValue(ctx, &cmd.RelationId)
	if err != nil {
		return nil, errors.Trace(err)
	}

	return cmd, nil
}

// Info is part of the cmd.Command interface.
func (c *RelationGetCommand) Info() *cmd.Info {
	args := "<key> <unit id>"
	doc := `
relation-get prints the value of a unit's relation setting, specified by key.
If no key is given, or if the key is "-", all keys and values will be printed.

A unit can see its own settings by calling "relation-get - MYUNIT", this will include
any changes that have been made with "relation-set".

When reading remote relation data, a charm can call relation-get --app - to get
the data for the application data bag that is set by the remote applications
leader.
`
	// There's nothing we can really do about the error here.
	if name, err := c.ctx.RemoteUnitName(); err == nil {
		args = "[<key> [<unit id>]]"
		doc += fmt.Sprintf("Current default unit id is %q.", name)
	} else if !errors.IsNotFound(err) {
		logger.Errorf("Failed to retrieve remote unit name: %v", err)
	}
	return jujucmd.Info(&cmd.Info{
		Name:    "relation-get",
		Args:    args,
		Purpose: "get relation settings",
		Doc:     doc,
	})
}

// SetFlags is part of the cmd.Command interface.
func (c *RelationGetCommand) SetFlags(f *gnuflag.FlagSet) {
	c.out.AddFlags(f, "smart", cmd.DefaultFormatters.Formatters())
	f.Var(c.relationIdProxy, "r", "Specify a relation by id")
	f.Var(c.relationIdProxy, "relation", "")

	f.BoolVar(&c.Application, "app", false,
		`Get the relation data for the overall application, not just a unit`)
}

func (c *RelationGetCommand) determineUnitOrAppName(args *[]string) error {
	// The logic is as follows:
	// 1) If a user supplies a unit or app name, that overrides any default
	//  a) If they supply --app and a unit name, we turn that back into an application name
	//  b) note, if they *don't* supply --app, and they specify an app name, that should be an error
	// 2) If no unit/app is supplied then we look at our context
	//  a) If --app is specified, then we use the context app
	//  b) If --app is not specified, but we don't have a context unit but do have a context app
	//     then we set --app, and set the target as the app
	//  c) If we have a context unit, then that is used
	if len(*args) > 0 {
		userSupplied := (*args)[0]
		*args = (*args)[1:]
		if c.Application {
			if names.IsValidApplication(userSupplied) {
				c.UnitOrAppName = userSupplied
			} else if names.IsValidUnit(userSupplied) {
				appName, err := names.UnitApplication(userSupplied)
				if err != nil {
					// Shouldn't happen, as we just validated it is a valid unit name
					return errors.Trace(err)
				}
				c.UnitOrAppName = appName
			}
		} else {
			c.UnitOrAppName = userSupplied
		}
		return nil
	}
	if c.Application {
		name, err := c.ctx.RemoteApplicationName()
		if errors.IsNotFound(err) {
			return fmt.Errorf("no unit or application specified")
		} else if err != nil {
			return errors.Trace(err)
		}
		c.UnitOrAppName = name
		return nil
	}
	// No args, no flags, check if there is a Unit context, or an App context
	if name, err := c.ctx.RemoteUnitName(); err == nil {
		c.UnitOrAppName = name
		return nil
	} else if !errors.IsNotFound(err) {
		return errors.Trace(err)
	}
	// Unit name not found, look for app context

	if name, err := c.ctx.RemoteApplicationName(); err == nil {
		c.UnitOrAppName = name
		c.Application = true
		return nil
	} else if !errors.IsNotFound(err) {
		return errors.Trace(err)
	}
	// If we got this far, there is no default value to give and nothing was
	// supplied, so it is an error
	return errors.New("no unit or application specified")
}

// Init is part of the cmd.Command interface.
func (c *RelationGetCommand) Init(args []string) error {
	if c.RelationId == -1 {
		return fmt.Errorf("no relation id specified")
	}
	c.Key = ""
	if len(args) > 0 {
		if c.Key = args[0]; c.Key == "-" {
			c.Key = ""
		}
		args = args[1:]
	}

	if err := c.determineUnitOrAppName(&args); err != nil {
		return errors.Trace(err)
	}
	return cmd.CheckEmpty(args)
}

func (c *RelationGetCommand) Run(ctx *cmd.Context) error {
	r, err := c.ctx.Relation(c.RelationId)
	if err != nil {
		return errors.Trace(err)
	}

	settingsReaderFn := c.readLocalUnitOrAppSettings

	getFromController, err := c.mustReadSettingsFromController()
	if err != nil {
		return errors.Trace(err)
	}
	if getFromController {
		settingsReaderFn = c.readRemoteUnitOrAppSettings
	}

	settings, err := settingsReaderFn(r)
	if err != nil {
		return err
	}

	if c.Key == "" {
		return c.out.Write(ctx, settings)
	}
	if value, ok := settings[c.Key]; ok {
		return c.out.Write(ctx, value)
	}
	return c.out.Write(ctx, nil)
}

func (c *RelationGetCommand) mustReadSettingsFromController() (bool, error) {
	localUnitName := c.ctx.UnitName()
	if c.UnitOrAppName == localUnitName {
		return false, nil
	}

	localAppName, _ := names.UnitApplication(c.ctx.UnitName())
	if c.UnitOrAppName == localAppName {
		isLeader, err := c.ctx.IsLeader()
		if err != nil {
			return false, errors.Annotate(err, "cannot determine leadership status")
		}

		// If we are the leader for the requested app, read from local
		// uniter context
		if isLeader {
			return false, nil
		}
	}

	// Delegate the read to the controller
	return true, nil
}

func (c *RelationGetCommand) readLocalUnitOrAppSettings(r ContextRelation) (params.Settings, error) {
	var (
		node Settings
		err  error
	)

	if c.Application {
		node, err = r.ApplicationSettings()
	} else {
		node, err = r.Settings()
	}
	if err != nil {
		return nil, err
	}

	return node.Map(), nil
}

func (c *RelationGetCommand) readRemoteUnitOrAppSettings(r ContextRelation) (params.Settings, error) {
	if !c.Application {
		return r.ReadSettings(c.UnitOrAppName)
	}

	return r.ReadApplicationSettings(c.UnitOrAppName)
}