w.Header()[xhttp.ETag] = []string{"\"" + objInfo.ETag + "\""}
		}
	}
	// x-amz-copy-source-if-modified-since: Return the object only if it has been modified
	// since the specified time otherwise return 412 (precondition failed).
	ifModifiedSinceHeader := r.Header.Get(xhttp.AmzCopySourceIfModifiedSince)
	if ifModifiedSinceHeader != "" {
		if givenTime, err := amztime.ParseHeader(ifModifiedSinceHeader); err == nil {

```

### Checking cluster health for maintenance

You may query the cluster probe endpoint to check if the node which received the request can be taken down for maintenance, if the server replies back '412 Precondition Failed' this means you will lose HA. '200 OK' means you are okay to proceed.

```
curl http://minio1:9001/minio/health/cluster?maintenance=true
HTTP/1.1 412 Precondition Failed
Accept-Ranges: bytes

	if c.TraceOutput != nil && resp.StatusCode != http.StatusOK {
		c.dumpHTTP(req, resp)
	}

	if resp.StatusCode != http.StatusOK {
		// If server returns 412 pre-condition failed, it would
		// mean that authentication succeeded, but another
		// side-channel check has failed, we shall take
		// the client offline in such situations.

func stack404()  { var buf [404]byte; use(buf[:]); C.callGoStackCheck() }
func stack408()  { var buf [408]byte; use(buf[:]); C.callGoStackCheck() }
func stack412()  { var buf [412]byte; use(buf[:]); C.callGoStackCheck() }
func stack416()  { var buf [416]byte; use(buf[:]); C.callGoStackCheck() }
func stack420()  { var buf [420]byte; use(buf[:]); C.callGoStackCheck() }

    assertCached(false, 408)
    assertCached(false, 409)
    // the HTTP spec permits caching 410s, but the RI doesn't.
    assertCached(true, 410)
    assertCached(false, 411)
    assertCached(false, 412)
    assertCached(false, 413)
    assertCached(true, 414)
    assertCached(false, 415)
    assertCached(false, 416)
    assertCached(false, 417)
    assertCached(false, 418)
    assertCached(false, 500)

// If-Unmodified-Since - Return the object only if it has not been modified since the specified time, else return a 412 (precondition failed).
func (s *TestSuiteCommon) TestHeadOnObjectLastModified(c *check) {
	// generate a random bucket name.
	bucketName := getRandomBucketName()
	// HTTP request to create the bucket.