cli/command/formatter: minor cleanups

no need to initialize with an empty string

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cli/command/formatter/container.go

@@ -68,16 +68,14 @@ ports: {{- pad .Ports 1 0}}
 
 // ContainerWrite renders the context for a list of containers
 func ContainerWrite(ctx Context, containers []container.Summary) error {
-	render := func(format func(subContext SubContext) error) error {
+	return ctx.Write(NewContainerContext(), func(format func(subContext SubContext) error) error {
 		for _, ctr := range containers {
-			err := format(&ContainerContext{trunc: ctx.Trunc, c: ctr})
+			if err := format(&ContainerContext{trunc: ctx.Trunc, c: ctr}); err != nil {
-			if err != nil {
 				return err
 			}
 		}
 		return nil
-	}
+	})
-	return ctx.Write(NewContainerContext(), render)
 }
 
 // ContainerContext is a struct used for rendering a list of containers in a Go template.

cli/command/formatter/container_test.go

@@ -371,9 +371,6 @@ size: 0B
 }
 
 func TestContainerContextWriteWithNoContainers(t *testing.T) {
-	out := bytes.NewBufferString("")
-	containers := []container.Summary{}
-
 	cases := []struct {
 		context  Context
 		expected string
@@ -381,40 +378,34 @@ func TestContainerContextWriteWithNoContainers(t *testing.T) {
 		{
 			context: Context{
 				Format: "{{.Image}}",
-				Output: out,
 			},
 		},
 		{
 			context: Context{
 				Format: "table {{.Image}}",
-				Output: out,
 			},
 			expected: "IMAGE\n",
 		},
 		{
 			context: Context{
 				Format: NewContainerFormat("{{.Image}}", false, true),
-				Output: out,
 			},
 		},
 		{
 			context: Context{
 				Format: NewContainerFormat("table {{.Image}}", false, true),
-				Output: out,
 			},
 			expected: "IMAGE\n",
 		},
 		{
 			context: Context{
 				Format: "table {{.Image}}\t{{.Size}}",
-				Output: out,
 			},
 			expected: "IMAGE     SIZE\n",
 		},
 		{
 			context: Context{
 				Format: NewContainerFormat("table {{.Image}}\t{{.Size}}", false, true),
-				Output: out,
 			},
 			expected: "IMAGE     SIZE\n",
 		},
@@ -422,11 +413,11 @@ func TestContainerContextWriteWithNoContainers(t *testing.T) {
 
 	for _, tc := range cases {
 		t.Run(string(tc.context.Format), func(t *testing.T) {
-			err := ContainerWrite(tc.context, containers)
+			out := new(bytes.Buffer)
+			tc.context.Output = out
+			err := ContainerWrite(tc.context, nil)
 			assert.NilError(t, err)
 			assert.Equal(t, out.String(), tc.expected)
-			// Clean buffer
-			out.Reset()
 		})
 	}
 }

cli/command/formatter/disk_usage.go

@@ -43,7 +43,7 @@ type DiskUsageContext struct {
 }
 
 func (ctx *DiskUsageContext) startSubsection(format string) (*template.Template, error) {
-	ctx.buffer = bytes.NewBufferString("")
+	ctx.buffer = &bytes.Buffer{}
 	ctx.header = ""
 	ctx.Format = Format(format)
 	ctx.preFormat()
@@ -87,7 +87,7 @@ func (ctx *DiskUsageContext) Write() (err error) {
 	if ctx.Verbose {
 		return ctx.verboseWrite()
 	}
-	ctx.buffer = bytes.NewBufferString("")
+	ctx.buffer = &bytes.Buffer{}
 	ctx.preFormat()
 
 	tmpl, err := ctx.parseFormat()

cli/command/formatter/formatter.go

@@ -82,6 +82,9 @@ func (c *Context) parseFormat() (*template.Template, error) {
 }
 
 func (c *Context) postFormat(tmpl *template.Template, subContext SubContext) {
+	if c.Output == nil {
+		c.Output = io.Discard
+	}
 	if c.Format.IsTable() {
 		t := tabwriter.NewWriter(c.Output, 10, 1, 3, ' ', 0)
 		buffer := bytes.NewBufferString("")
@@ -111,7 +114,7 @@ type SubFormat func(func(SubContext) error) error
 
 // Write the template to the buffer using this Context
 func (c *Context) Write(sub SubContext, f SubFormat) error {
-	c.buffer = bytes.NewBufferString("")
+	c.buffer = &bytes.Buffer{}
 	c.preFormat()
 
 	tmpl, err := c.parseFormat()