}

			// If metadata says encrypted, ask for it in quorum.
			if etyp, ok := crypto.IsEncrypted(meta.Metadata); ok {
				fmt.Fprint(h, etyp)
			}

			// If compressed, look for compressed FileInfo only
			if meta.IsCompressed() {
				fmt.Fprint(h, meta.Metadata[ReservedMetadataPrefix+"compression"])
			}

			metaHashes[i] = hex.EncodeToString(h.Sum(nil))
			h.Reset()
		}
	}

### 4. Excluded Types

- Already compressed objects are not fit for compression since they do not have compressible patterns.
Such objects do not produce efficient [`LZ compression`](https://en.wikipedia.org/wiki/LZ77_and_LZ78)
which is a fitness factor for a lossless data compression.

Pre-compressed input typically compresses in excess of 2GiB/s per core,

	// Read compression metadata preserved in the init multipart for the decision.
	_, isCompressed := mi.UserDefined[ReservedMetadataPrefix+"compression"]
	// Compress only if the compression is enabled during initial multipart.
	var idxCb func() []byte
	if isCompressed {
		wantEncryption := crypto.Requested(r.Header) || isEncrypted
		s2c, cb := newS2CompressReader(reader, actualPartSize, wantEncryption)

		index = opts.IndexCB()
	}

	actualSize := data.ActualSize()
	if actualSize < 0 {
		_, encrypted := crypto.IsEncrypted(fi.Metadata)
		compressed := fi.IsCompressed()
		switch {
		case compressed:
			// ... nothing changes for compressed stream.
			// if actualSize is -1 we have no known way to
			// determine what is the actualSize.
		case encrypted:
			decSize, err := sio.DecryptedSize(uint64(n))

Interceptors can be chained. Suppose you have both a compressing interceptor and a checksumming interceptor: you'll need to decide whether data is compressed and then checksummed, or checksummed and then compressed. OkHttp uses lists to track interceptors, and interceptors are called in order.

![Interceptors Diagram](../assets/images/******@****.***)

### Application Interceptors

    server.webSocket!!.send(message)
    taskFaker.runTasks()
    assertThat(client.clientSourceBufferSize())
      .isGreaterThan(message.length.toLong()) // Not compressed.
    assertThat(client.processNextFrame()).isTrue()
    client.listener.assertTextMessage(message)
  }

  @Test
  fun messagesCompressedWhenConfigured() {

#      batch: 100 # upto this many objects per archive
#      inmemory: true # indicates if the archive must be staged locally or in-memory
#      compress: false # S2/Snappy compressed archive
#      smallerThan: 5MiB # create archive for all objects smaller than 5MiB
#      skipErrs: false # skips any source side read() errors

  # target where the objects must be replicated
  target:

@SuppressWarnings("serial") // uses writeReplace(), not default serialization
final class SingletonImmutableSet<E> extends ImmutableSet<E> {
  // We deliberately avoid caching the asList and hashCode here, to ensure that with
  // compressed oops, a SingletonImmutableSet packs all the way down to the optimal 16 bytes.

  final transient E element;

  SingletonImmutableSet(E element) {
    this.element = Preconditions.checkNotNull(element);
  }

	// predicted date/time of transition
	MinIOTransition            = "X-Minio-Transition"
	MinIOLifecycleCfgUpdatedAt = "X-Minio-LifecycleConfig-UpdatedAt"
	// MinIOCompressed is returned when object is compressed
	MinIOCompressed = "X-Minio-Compressed"

	// SUBNET related
	SubnetAPIKey = "x-subnet-api-key"
)

// Common http query params S3 API
const (
	VersionID = "versionId"

	PartNumber = "partNumber"

	Spectre    = flag.String("spectre", "", "enable spectre mitigations in `list` (all, ret)")
)

var DebugFlags struct {
	CompressInstructions int    `help:"use compressed instructions when possible (if supported by architecture)"`
	MayMoreStack         string `help:"call named function before all stack growth checks"`