github.com/makyo/juju@v0.0.0-20160425123129-2608902037e9/resource/context/cmd/get.go (about)

     1  // Copyright 2016 Canonical Ltd.
     2  // Licensed under the AGPLv3, see LICENCE file for details.
     3  
     4  package cmd
     5  
     6  import (
     7  	"fmt"
     8  
     9  	"github.com/juju/cmd"
    10  	"github.com/juju/errors"
    11  )
    12  
    13  // GetCmdName is the name of the resource-get command.
    14  const GetCmdName = "resource-get"
    15  
    16  // NewGetCmd creates a new GetCmd for the given hook context.
    17  func NewGetCmd(c HookContext) (*GetCmd, error) {
    18  	return &GetCmd{
    19  		hookContext: c,
    20  	}, nil
    21  }
    22  
    23  // GetCmd provides the functionality of the resource-get command.
    24  type GetCmd struct {
    25  	cmd.CommandBase
    26  
    27  	hookContext  HookContext
    28  	resourceName string
    29  }
    30  
    31  // TODO(ericsnow) Also provide an indicator of whether or not
    32  // the resource has changed (in addition to the file path)?
    33  
    34  // Info implements cmd.Command.
    35  func (c GetCmd) Info() *cmd.Info {
    36  	return &cmd.Info{
    37  		Name:    GetCmdName,
    38  		Args:    "<resource name>",
    39  		Purpose: "get the path to the locally cached resource file",
    40  		Doc: `
    41  "resource-get" is used while a hook is running to get the local path
    42  to the file for the identified resource. This file is an fs-local copy,
    43  unique to the unit for which the hook is running. It is downloaded from
    44  the controller, if necessary.
    45  
    46  If "resource-get" for a resource has not been run before (for the unit)
    47  then the resource is downloaded from the controller at the revision
    48  associated with the unit's service. That file is stored in the unit's
    49  local cache. If "resource-get" *has* been run before then each
    50  subsequent run syncs the resource with the controller. This ensures
    51  that the revision of the unit-local copy of the resource matches the
    52  revision of the resource associated with the unit's service.
    53  
    54  Either way, the path provided by "resource-get" references the
    55  up-to-date file for the resource. Note that the resource may get
    56  updated on the controller for the service at any time, meaning the
    57  cached copy *may* be out of date at any time after you call
    58  "resource-get". Consequently, the command should be run at every
    59  point where it is critical that the resource be up to date.
    60  
    61  The "upgrade-charm" hook is useful for keeping your charm's resources
    62  on a unit up to date.  Run "resource-get" there for each of your
    63  charm's resources to do so. The hook fires whenever the the file for
    64  one of the service's resources changes on the controller (in addition
    65  to when the charm itself changes). That means it happens in response
    66  to "juju upgrade-charm" as well as to "juju push-resource".
    67  
    68  Note that the "upgrade-charm" hook does not run when the unit is
    69  started up. So be sure to run "resource-get" for your resources in the
    70  "install" hook (or "config-changed", etc.).
    71  
    72  Note that "resource-get" only provides an FS path to the resource file.
    73  It does not provide any information about the resource (e.g. revision).
    74  `,
    75  	}
    76  }
    77  
    78  // Init implements cmd.Command.
    79  func (c *GetCmd) Init(args []string) error {
    80  	if len(args) < 1 {
    81  		return errors.Errorf("missing required resource name")
    82  	} else if err := cmd.CheckEmpty(args[1:]); err != nil {
    83  		return errors.Trace(err)
    84  	}
    85  	c.resourceName = args[0]
    86  	return nil
    87  }
    88  
    89  // Run implements cmd.Command.
    90  func (c GetCmd) Run(ctx *cmd.Context) error {
    91  	filePath, err := c.hookContext.Download(c.resourceName)
    92  	if err != nil {
    93  		return errors.Annotate(err, "could not download resource")
    94  	}
    95  
    96  	if _, err := fmt.Fprintf(ctx.Stdout, filePath); err != nil {
    97  		return errors.Annotate(err, "could not write resource path to stdout")
    98  	}
    99  	return nil
   100  }