Refactor to use a common template runtime package (#725)

Signed-off-by: David Chung <david.chung@docker.com>

Author: David Chung

docs/plugin/metadata/vars/README.md

@@ -1,8 +1,7 @@
 Vars Plugin
 ===========
 
-Design
-======
+## Design
 
 The `vars` plugin implements the [`metadata.Updatable`](../pkg/spi/metadata) SPI.  It supports
 
@@ -131,7 +130,7 @@ Usage:
 Available Commands:
   cat         Get metadata entry by path
   change      Update metadata where args are key=value pairs and keys are within namespace of the plugin.
-  ls          List metadata
+  vars        List metadata
 ```
 
 ### Listing, Reading
@@ -325,6 +324,123 @@ $ infrakit vars cat this/is/a/new/struct/message
 i am here
 ```
 
+## Template integration
+
+As mentioned earlier, metadata operations are integrated with templates so you
+can write templates that also access the variables stored in the vars plugin.
+
+As an example:
+
+```shell
+$infrakit plugin start vars  # starts up only the vars 
+```
+
+In another shell:
+
+```shell
+$ infrakit vars change
+Proposing 0 changes, hash=c53f4ebe9b2a50bc2b52fd88a5d503e1
+{}
+```
+
+Currently there's no data stored.
+
+Adding some values:
+
+```shell
+$ infrakit vars change cluster/name=foo cluster/workers/size=10 -c
+Committing 2 changes, hash=ad861ded7a0742f9662c2b78354c89f6
+{
+  "cluster": {
+    "name": "foo",
+    "workers": {
+      "size": 10
+    }
+  }
+}
+```
+
+Now querying:
+
+```shell
+$ infrakit vars vars -al
+total 2:
+cluster/name
+cluster/workers/size
+$ infrakit vars cat cluster/workers/size
+10
+```
+Or use template to read.
+
+```shell
+$ infrakit template -f 'str://{{ metadata `vars/cluster/workers/size`}}'
+10
+```
+
+Using template to update:
+
+```shell
+$ infrakit template -f 'str://{{ metadata `vars/cluster/workers/size` 1000 }}'
+~/project3/src/github.com/docker/infrakit$ infrakit vars change
+Proposing 0 changes, hash=8aff842d0f19e571e5c1e5810d562bb1
+{
+  "cluster": {
+    "name": "foo",
+    "workers": {
+      "size": 1000
+    }
+  }
+}
+$ infrakit vars cat cluster/workers/size
+1000
+```
+
+Sometimes, you want to have a single namespace between metadata and template
+variables to simplify writing templates.  The `var` template function, in
+correct contexts, can attempt to retrieve the value at the given path via accessing
+the path as though it's hosted in a metadata plugin, if the path cannot be resolved
+to an in-scope template variable:
+
+```shell
+$ infrakit template 'str://{{ var `vars/cluster/workers/size`}}'
+1000
+```
+which is the same as
+
+```shell
+$ infrakit template 'str://{{ metadata `vars/cluster/workers/size`}}'
+1000
+```
+
+This works even when a template is multi-pass: if a path cannot be resolved
+from in-scope template variables, then metadata plugins are tested.  Of course,
+the path has to also make sense in that the path can resolve to a running metadata
+plugin.
+
+If somewhere else in your template, a `var` function is used to set a value and
+that value comes into scope of the template, that value will takes precedence:
+
+```shell
+$ infrakit template 'str://{{ var `vars/cluster/workers/size` 4000 }}{{ var `vars/cluster/workers/size`}}'
+4000
+```
+This should not be surprising, as we are setting the `vars/cluster/workers/size`
+template variable to `4000`.  The next read will return that value and not the
+metadata stored in vars:
+
+```shell
+$ infrakit template 'str://{{ var `vars/cluster/workers/size`}}'
+1000
+```
+
+The value is back to 1000 because the second command line invocation is a
+totally different template context (ie a different shell process altogether).
+This makes it possible to implement a user override, while the backing
+metadata can be loaded from a JSON serving as default values.
+This also means that mutation of the value at a given path must be performed
+explicitly via the `metadata` template function (or via the `change -c` CLI) to
+affect durability across multiple template evaluations.
+
 ## TODO - Durability of Changes
 
 The metadata / updatable plugin is one of the key patterns provided by Infrakit. The base implementation

pkg/cli/context.go

@@ -10,6 +10,7 @@ import (
 	"strings"
 
 	"github.com/docker/infrakit/pkg/discovery"
+	runtime "github.com/docker/infrakit/pkg/run/template"
 	"github.com/docker/infrakit/pkg/template"
 	"github.com/spf13/cobra"
 )
@@ -461,7 +462,7 @@ func (c *Context) BuildFlags() (err error) {
 		return
 	}
 	t.SetOptions(c.options)
-	_, err = configureTemplate(t, c.plugins).Render(c)
+	_, err = runtime.StdFunctions(t, c.plugins).Render(c)
 	return
 }
 
@@ -484,7 +485,7 @@ func (c *Context) Execute() (err error) {
 	// Process the input, render the template
 	t.SetOptions(opt)
 
-	script, err := configureTemplate(t, c.plugins).Render(c)
+	script, err := runtime.StdFunctions(t, c.plugins).Render(c)
 	if err != nil {
 		return err
 	}

pkg/cli/services.go

@@ -9,6 +9,7 @@ import (
 	"strings"
 
 	"github.com/docker/infrakit/pkg/discovery"
+	runtime "github.com/docker/infrakit/pkg/run/template"
 	"github.com/docker/infrakit/pkg/template"
 	"github.com/ghodss/yaml"
 	"github.com/spf13/pflag"
@@ -197,7 +198,7 @@ func templateProcessor(plugins func() discovery.Plugins) (*pflag.FlagSet, ToJSON
 				}
 			}
 
-			configureTemplate(engine, plugins)
+			runtime.StdFunctions(engine, plugins)
 
 			contextObject := (interface{})(nil)
 			if len(ctx) == 1 {

pkg/cli/template.go

@@ -1,13 +1,10 @@
 package group
 
 import (
-	"fmt"
-	"io"
 	"os"
-	"sort"
-	"strings"
 
 	"github.com/docker/infrakit/pkg/cli"
+	"github.com/docker/infrakit/pkg/cli/v0/instance"
 	"github.com/docker/infrakit/pkg/plugin"
 	"github.com/docker/infrakit/pkg/spi/group"
 	"github.com/spf13/cobra"
@@ -21,7 +18,10 @@ func Describe(name string, services *cli.Services) *cobra.Command {
 		Short: "Describe a group. Returns a list of members",
 	}
 
-	quiet := describe.Flags().BoolP("quiet", "q", false, "Print rows without column headers")
+	view := instance.View{}
+	describe.Flags().AddFlagSet(services.OutputFlags)
+	describe.Flags().AddFlagSet(view.FlagSet())
+
 	describe.RunE = func(cmd *cobra.Command, args []string) error {
 
 		pluginName := plugin.Name(name)
@@ -30,9 +30,15 @@ func Describe(name string, services *cli.Services) *cobra.Command {
 			if len(args) < 1 {
 				cmd.Usage()
 				os.Exit(1)
-			} else {
-				gid = args[0]
 			}
+			gid = args[0]
+			args = args[1:]
+		}
+
+		// get renderers first before costly rpc
+		renderer, err := view.Renderer(view.DefaultMatcher(args))
+		if err != nil {
+			return err
 		}
 
 		groupPlugin, err := LoadPlugin(services.Plugins(), name)
@@ -43,33 +49,17 @@ func Describe(name string, services *cli.Services) *cobra.Command {
 
 		groupID := group.ID(gid)
 
+		// TODO - here we are getting the properties back because
+		// in pkg/plugin/group/scaledGroup.List we are calling the instance
+		// plugin.Describe with 'true'.  We need to change the group SPI
+		// to allow control of this and taking in view filter, selectors
+		// to execute on the server side.
 		desc, err := groupPlugin.DescribeGroup(groupID)
 		if err != nil {
 			return err
 		}
 
-		return services.Output(os.Stdout, desc,
-			func(io.Writer, interface{}) error {
-				if !*quiet {
-					fmt.Printf("%-30s\t%-30s\t%-s\n", "ID", "LOGICAL", "TAGS")
-				}
-				for _, d := range desc.Instances {
-					logical := "  -   "
-					if d.LogicalID != nil {
-						logical = string(*d.LogicalID)
-					}
-
-					printTags := []string{}
-					for k, v := range d.Tags {
-						printTags = append(printTags, fmt.Sprintf("%s=%s", k, v))
-					}
-					sort.Strings(printTags)
-
-					fmt.Printf("%-30s\t%-30s\t%-s\n", d.ID, logical, strings.Join(printTags, ","))
-				}
-				return nil
-			})
+		return services.Output(os.Stdout, desc.Instances, renderer)
 	}
-	describe.Flags().AddFlagSet(services.OutputFlags)
 	return describe
 }