return
				}
			}
		case "IfUnModifiedSince":
			if dc.IsNil() {
				err = dc.ReadNil()
				if err != nil {
					err = msgp.WrapError(err, "IfUnModifiedSince")
					return
				}
				z.IfUnModifiedSince = nil
			} else {
				if z.IfUnModifiedSince == nil {
					z.IfUnModifiedSince = new(time.Time)
				}
				*z.IfUnModifiedSince, err = dc.ReadTime()
				if err != nil {

			r.IfModifiedSince = &givenTime
		}
	}
	ifUnmodifiedSinceHeader := header.Get(xhttp.IfUnmodifiedSince)
	if ifUnmodifiedSinceHeader != "" {
		if givenTime, err := amztime.ParseHeader(ifUnmodifiedSinceHeader); err == nil {
			r.IfUnModifiedSince = &givenTime
		}
	}
	r.IfMatch = canonicalizeETag(header.Get(xhttp.IfMatch))
	r.IfNoneMatch = canonicalizeETag(header.Get(xhttp.IfNoneMatch))

// Non standard S3 HTTP response constants
const (
	XCache       = "X-Cache"
	XCacheLookup = "X-Cache-Lookup"
)

// Standard S3 HTTP request constants
const (
	IfModifiedSince   = "If-Modified-Since"
	IfUnmodifiedSince = "If-Unmodified-Since"
	IfMatch           = "If-Match"
	IfNoneMatch       = "If-None-Match"

	// Request tags used in GetObjectAttributes
	Checksum     = "Checksum"
	StorageClass = "StorageClass"

		}
	}

	// If-Unmodified-Since : Return the object only if it has not been modified since the specified
	// time, otherwise return a 412 (precondition failed).
	ifUnmodifiedSinceHeader := r.Header.Get(xhttp.IfUnmodifiedSince)
	if ifUnmodifiedSinceHeader != "" {
		if givenTime, err := amztime.ParseHeader(ifUnmodifiedSinceHeader); err == nil {
			if ifModifiedSince(objInfo.ModTime, givenTime) {