YAMLDecoder Read function always returns n=0 bytes

[sel]

Is this a BUG REPORT or FEATURE REQUEST?:

Uncomment only one, leave it on its own line:

/kind bug

/kind feature

What happened:

In a go program, using the YAML utility package "k8s.io/apimachinery/pkg/util/yaml", the
YAMLDecoder Read function always returns n=0 bytes, indicating that nothing was read.

What you expected to happen:

The number of bytes read should be returned as specified in the Read contract

How to reproduce it (as minimally and precisely as possible):

func TestYAMLDecoder(t *testing.T) {
	d := `---
stuff: 1
	test-foo: 1
`
	s := NewDocumentDecoder(ioutil.NopCloser(bytes.NewReader([]byte(d))))
	b := make([]byte, len(d))
	n, err := s.Read(b)
	if err != nil || n != len(d) {
		t.Fatalf("unexpected body: %d / %v", n, err)
	}
}

See sel@86d02ac#diff-3b3ea800b8ebe625d0defd76c2e6f827

Anything else we need to know?:

Environment:

• Kubernetes version (use kubectl version): Client Version: version.Info{Major:"1", Minor:"8", GitVersion:"v1.8.4", GitCommit:"9befc2b8928a9426501d3bf62f72849d5cbcd5a3", GitTreeState:"clean", BuildDate:"2017-11-20T05:28:34Z", GoVersion:"go1.8.3", Compiler:"gc", Platform:"darwin/amd64"}
• Cloud provider or hardware configuration: minikube & AWS
• OS (e.g. from /etc/os-release): macOS 10.13.1 (17B1003)
• Kernel (e.g. uname -a): Darwin 17.2.0
• Install tools:
• Others: go version go1.9.2 darwin/amd64

[sel]

@kubernetes/sig-api-machinery-bugs

[k8s-ci-robot]

@sel: Reiterating the mentions to trigger a notification:
@kubernetes/sig-api-machinery-bugs

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@kubernetes/sig-api-machinery-bugs

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[roycaihw]

/cc @yliaog

[jennybuckley]

@jennybuckley