Add format to the docker system df command

Signed-off-by: Boaz Shuster <ripcurld.github@gmail.com>

cli/command/formatter/disk_usage.go

@@ -45,15 +45,33 @@ func (ctx *DiskUsageContext) startSubsection(format string) (*template.Template,
 	return ctx.parseFormat()
 }
 
-func (ctx *DiskUsageContext) Write() {
+//
+// NewDiskUsageFormat returns a format for rendering an DiskUsageContext
+func NewDiskUsageFormat(source string) Format {
+	switch source {
+	case TableFormatKey:
+		format := defaultDiskUsageTableFormat
+		return Format(format)
+	case RawFormatKey:
+		format := `type: {{.Type}}
+total: {{.TotalCount}}
+active: {{.Active}}
+size: {{.Size}}
+reclaimable: {{.Reclaimable}}
+`
+		return Format(format)
+	}
+	return Format(source)
+}
+
+func (ctx *DiskUsageContext) Write() (err error) {
 	if ctx.Verbose == false {
 		ctx.buffer = bytes.NewBufferString("")
-		ctx.Format = defaultDiskUsageTableFormat
 		ctx.preFormat()
 
 		tmpl, err := ctx.parseFormat()
 		if err != nil {
-			return
+			return err
 		}
 
 		err = ctx.contextFormat(tmpl, &diskUsageImagesContext{
@@ -61,20 +79,20 @@ func (ctx *DiskUsageContext) Write() {
 			images:    ctx.Images,
 		})
 		if err != nil {
-			return
+			return err
 		}
 		err = ctx.contextFormat(tmpl, &diskUsageContainersContext{
 			containers: ctx.Containers,
 		})
 		if err != nil {
-			return
+			return err
 		}
 
 		err = ctx.contextFormat(tmpl, &diskUsageVolumesContext{
 			volumes: ctx.Volumes,
 		})
 		if err != nil {
-			return
+			return err
 		}
 
 		diskUsageContainersCtx := diskUsageContainersContext{containers: []*types.Container{}}
@@ -87,7 +105,7 @@ func (ctx *DiskUsageContext) Write() {
 		}
 		ctx.postFormat(tmpl, &diskUsageContainersCtx)
 
-		return
+		return err
 	}
 
 	// First images
@@ -158,6 +176,7 @@ func (ctx *DiskUsageContext) Write() {
 		}
 	}
 	ctx.postFormat(tmpl, newVolumeContext())
+	return
 }
 
 type diskUsageImagesContext struct {

cli/command/formatter/disk_usage_test.go

@@ -8,13 +8,17 @@ import (
 )
 
 func TestDiskUsageContextFormatWrite(t *testing.T) {
-	// Check default output format (verbose and non-verbose mode) for table headers
 	cases := []struct {
 		context  DiskUsageContext
 		expected string
 	}{
+		// Check default output format (verbose and non-verbose mode) for table headers
 		{
-			DiskUsageContext{Verbose: false},
+			DiskUsageContext{
+				Context: Context{
+					Format: NewDiskUsageFormat("table"),
+				},
+				Verbose: false},
 			`TYPE                TOTAL               ACTIVE              SIZE                RECLAIMABLE
 Images              0                   0                   0B                  0B
 Containers          0                   0                   0B                  0B
@@ -34,6 +38,77 @@ CONTAINER ID        IMAGE               COMMAND             LOCAL VOLUMES
 Local Volumes space usage:
 
 VOLUME NAME         LINKS               SIZE
+`,
+		},
+		// Errors
+		{
+			DiskUsageContext{
+				Context: Context{
+					Format: "{{InvalidFunction}}",
+				},
+			},
+			`Template parsing error: template: :1: function "InvalidFunction" not defined
+`,
+		},
+		{
+			DiskUsageContext{
+				Context: Context{
+					Format: "{{nil}}",
+				},
+			},
+			`Template parsing error: template: :1:2: executing "" at <nil>: nil is not a command
+`,
+		},
+		// Table Format
+		{
+			DiskUsageContext{
+				Context: Context{
+					Format: NewDiskUsageFormat("table"),
+				},
+			},
+			`TYPE                TOTAL               ACTIVE              SIZE                RECLAIMABLE
+Images              0                   0                   0B                  0B
+Containers          0                   0                   0B                  0B
+Local Volumes       0                   0                   0B                  0B
+`,
+		},
+		{
+			DiskUsageContext{
+				Context: Context{
+					Format: NewDiskUsageFormat("table {{.Type}}\t{{.Active}}"),
+				},
+			},
+			`TYPE                ACTIVE
+Images              0
+Containers          0
+Local Volumes       0
+`,
+		},
+		// Raw Format
+		{
+			DiskUsageContext{
+				Context: Context{
+					Format: NewDiskUsageFormat("raw"),
+				},
+			},
+			`type: Images
+total: 0
+active: 0
+size: 0B
+reclaimable: 0B
+
+type: Containers
+total: 0
+active: 0
+size: 0B
+reclaimable: 0B
+
+type: Local Volumes
+total: 0
+active: 0
+size: 0B
+reclaimable: 0B
+
 `,
 		},
 	}
@@ -41,7 +116,10 @@ VOLUME NAME         LINKS               SIZE
 	for _, testcase := range cases {
 		out := bytes.NewBufferString("")
 		testcase.context.Output = out
-		testcase.context.Write()
+		if err := testcase.context.Write(); err != nil {
-		assert.Equal(t, out.String(), testcase.expected)
+			assert.Equal(t, err.Error(), testcase.expected)
+		} else {
+			assert.Equal(t, out.String(), testcase.expected)
+		}
 	}
 }

cli/command/system/df.go

@@ -1,6 +1,8 @@
 package system
 
 import (
+	"errors"
+
 	"github.com/docker/docker/cli"
 	"github.com/docker/docker/cli/command"
 	"github.com/docker/docker/cli/command/formatter"
@@ -10,6 +12,7 @@ import (
 
 type diskUsageOptions struct {
 	verbose bool
+	format  string
 }
 
 // NewDiskUsageCommand creates a new cobra.Command for `docker df`
@@ -29,19 +32,30 @@ func NewDiskUsageCommand(dockerCli *command.DockerCli) *cobra.Command {
 	flags := cmd.Flags()
 
 	flags.BoolVarP(&opts.verbose, "verbose", "v", false, "Show detailed information on space usage")
+	flags.StringVar(&opts.format, "format", "", "Pretty-print images using a Go template")
 
 	return cmd
 }
 
 func runDiskUsage(dockerCli *command.DockerCli, opts diskUsageOptions) error {
+	if opts.verbose && len(opts.format) != 0 {
+		return errors.New("the verbose and the format options conflict")
+	}
+
 	du, err := dockerCli.Client().DiskUsage(context.Background())
 	if err != nil {
 		return err
 	}
 
+	format := opts.format
+	if len(format) == 0 {
+		format = formatter.TableFormatKey
+	}
+
 	duCtx := formatter.DiskUsageContext{
 		Context: formatter.Context{
 			Output: dockerCli.Out(),
+			Format: formatter.NewDiskUsageFormat(format),
 		},
 		LayersSize: du.LayersSize,
 		Images:     du.Images,
@@ -50,7 +64,5 @@ func runDiskUsage(dockerCli *command.DockerCli, opts diskUsageOptions) error {
 		Verbose:    opts.verbose,
 	}
 
-	duCtx.Write()
+	return duCtx.Write()
-
-	return nil
 }

docs/reference/commandline/system_df.md

@@ -86,6 +86,51 @@ volumes or in systems where some images, containers, or volumes have very large
 filesystems with many files. You should also be careful not to run this command
 in systems where performance is critical.
 
+## Format the output
+
+The formatting option (`--format`) pretty prints the disk usage output
+using a Go template.
+
+Valid placeholders for the Go template are listed below:
+
+| Placeholder    | Description                                |
+| -------------- | ------------------------------------------ |
+| `.Type`        | `Images`, `Containers` and `Local Volumes` |
+| `.TotalCount`  | Total number of items                      |
+| `.Active`      | Number of active items                     |
+| `.Size`        | Available size                             |
+| `.Reclaimable` | Reclaimable size                           |
+
+When using the `--format` option, the `system df` command outputs
+the data exactly as the template declares or, when using the
+`table` directive, will include column headers as well.
+
+The following example uses a template without headers and outputs the
+`Type` and `TotalCount` entries separated by a colon:
+
+```bash
+$ docker system df --format "{{.Type}}: {{.TotalCount}}"
+
+Images: 2
+Containers: 4
+Local Volumes: 1
+```
+
+To list the disk usage with size and reclaimable size in a table format you
+can use:
+
+```bash
+$ docker system df --format "table {{.Type}}\t{{.Size}}\t{{.Reclaimable}}"
+
+TYPE                SIZE                RECLAIMABLE
+Images              2.547 GB            2.342 GB (91%)
+Containers          0 B                 0 B
+Local Volumes       150.3 MB            150.3 MB (100%)
+<Paste>
+```
+
+**Note** the format option is meaningless when verbose is true.
+
 ## Related commands
 * [system prune](system_prune.md)
 * [container prune](container_prune.md)