Network Working Group                                         Stone, Ed.

Internet-Draft                                           Six Apart, Ltd.

Intended status: Informational                               Norbye, Ed.

Expires: March 1, 2009                             Sun Microsystems, INC

                                                         August 28, 2008

                        Memcache Binary Protocol

                     draft-stone-memcache-binary-01

Abstract

   This memo explains the memcache binary protocol for informational

   purposes.

   Memcache is a high performance key-value cache.  It is intentionally

   a dumb cache, optimized for speed only.  Applications using memcache

   do not rely on it for data -- a persistent database with guaranteed

   reliability is strongly recommended -- but applications can run much

   faster when cached data is available in memcache.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the

   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering

   Task Force (IETF).  Note that other groups may also distribute

   working documents as Internet-Drafts.  The list of current Internet-

   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months

   and may be updated, replaced, or obsoleted by other documents at any

   time.  It is inappropriate to use Internet-Drafts as reference

   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 1, 2009.

Copyright Notice

   Copyright (c) 2008 IETF Trust and the persons identified as the

   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal

   Provisions Relating to IETF Documents

   (http://trustee.ietf.org/license-info) in effect on the date of

   publication of this document.  Please review these documents

   carefully, as they describe your rights and restrictions with respect

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   to this document.  Code Components extracted from this document must

   include Simplified BSD License text as described in Section 4.e of

   the Trust Legal Provisions and are provided without warranty as

   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2

     1.1.  Conventions Used In This Document . . . . . . . . . . . .   3

   2.  Packet Structure  . . . . . . . . . . . . . . . . . . . . . .   3

   3.  Defined Values  . . . . . . . . . . . . . . . . . . . . . . .   5

     3.1.  Magic Byte  . . . . . . . . . . . . . . . . . . . . . . .   5

     3.2.  Response Status . . . . . . . . . . . . . . . . . . . . .   5

     3.3.  Command Opcodes . . . . . . . . . . . . . . . . . . . . .   6

     3.4.  Data Types  . . . . . . . . . . . . . . . . . . . . . . .   6

   4.  Commands  . . . . . . . . . . . . . . . . . . . . . . . . . .   7

     4.1.  Introduction  . . . . . . . . . . . . . . . . . . . . . .   7

       4.1.1.  Example . . . . . . . . . . . . . . . . . . . . . . .   7

     4.2.  Get, Get Quietly, Get Key, Get Key Quietly  . . . . . . .   8

       4.2.1.  Example . . . . . . . . . . . . . . . . . . . . . . .   9

     4.3.  Set, Add, Replace . . . . . . . . . . . . . . . . . . . .  13

       4.3.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  13

     4.4.  Delete  . . . . . . . . . . . . . . . . . . . . . . . . .  15

       4.4.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  16

     4.5.  Increment, Decrement  . . . . . . . . . . . . . . . . . .  17

       4.5.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  18

     4.6.  quit  . . . . . . . . . . . . . . . . . . . . . . . . . .  20

       4.6.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  21

     4.7.  Flush . . . . . . . . . . . . . . . . . . . . . . . . . .  21

       4.7.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  22

     4.8.  noop  . . . . . . . . . . . . . . . . . . . . . . . . . .  23

       4.8.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  24

     4.9.  version . . . . . . . . . . . . . . . . . . . . . . . . .  24

       4.9.1.  Example . . . . . . . . . . . . . . . . . . . . . . .  25

     4.10. Append, Prepend . . . . . . . . . . . . . . . . . . . . .  26

       4.10.1.  Example  . . . . . . . . . . . . . . . . . . . . . .  27

     4.11. Stat  . . . . . . . . . . . . . . . . . . . . . . . . . .  28

       4.11.1.  Example  . . . . . . . . . . . . . . . . . . . . . .  28

   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  30

   6.  Normative References  . . . . . . . . . . . . . . . . . . . .  31

   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  31

   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  31

1.  Introduction

   Memcache is a high performance key-value cache.  It is intentionally

   a dumb cache, optimized for speed only.  Applications using memcache

   should not rely on it for data -- a persistent database with

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   guaranteed reliability is strongly recommended -- but applications

   can run much faster when cached data is available in memcache.

   Memcache was originally written to make LiveJournal [LJ] faster.  It

   now powers all of the fastest web sites that you love.

1.1.  Conventions Used In This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this

   document are to be interpreted as described in [KEYWORDS].

2.  Packet Structure

   General format of a packet:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0/ HEADER                                                        /

       /                                                               /

       /                                                               /

       /                                                               /

       +---------------+---------------+---------------+---------------+

     24/ COMMAND-SPECIFIC EXTRAS (as needed)                           /

      +/  (note length in the extras length header field)              /

       +---------------+---------------+---------------+---------------+

      m/ Key (as needed)                                               /

      +/  (note length in key length header field)                     /

       +---------------+---------------+---------------+---------------+

      n/ Value (as needed)                                             /

      +/  (note length is total body length header field, minus        /

      +/   sum of the extras and key length body fields)               /

       +---------------+---------------+---------------+---------------+

       Total 24 bytes

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   Request header:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| Magic         | Opcode        | Key length                    |

       +---------------+---------------+---------------+---------------+

      4| Extras length | Data type     | Reserved                      |

       +---------------+---------------+---------------+---------------+

      8| Total body length                                             |

       +---------------+---------------+---------------+---------------+

     12| Opaque                                                        |

       +---------------+---------------+---------------+---------------+

     16| CAS                                                           |

       |                                                               |

       +---------------+---------------+---------------+---------------+

       Total 24 bytes

   Response header:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| Magic         | Opcode        | Key Length                    |

       +---------------+---------------+---------------+---------------+

      4| Extras length | Data type     | Status                        |

       +---------------+---------------+---------------+---------------+

      8| Total body length                                             |

       +---------------+---------------+---------------+---------------+

     12| Opaque                                                        |

       +---------------+---------------+---------------+---------------+

     16| CAS                                                           |

       |                                                               |

       +---------------+---------------+---------------+---------------+

       Total 24 bytes

   Header fields:

   Magic               Magic number.

   Opcode              Command code.

   Key length          Length in bytes of the text key that follows the

                       command extras.

   Status              Status of the response (non-zero on error).

   Extras length       Length in bytes of the command extras.

   Data type           Reserved for future use (Sean is using this

                       soon).

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   Reserved            Really reserved for future use (up for grabs).

   Total body length   Length in bytes of extra + key + value.

   Opaque              Will be copied back to you in the response.

   CAS                 Data version check.

3.  Defined Values

3.1.  Magic Byte

   0x80    Request packet for this protocol version

   0x81    Response packet for this protocol version

   Magic byte / version.  For each version of the protocol, we'll use a

   different request/response value pair.  This is useful for protocol

   analyzers to distinguish the nature of the packet from the direction

   which it is moving.  Note, it is common to run a memcached instance

   on a host that also runs an application server.  Such a host will

   both send and receive memcache packets.

   The version should hopefully correspond only to different meanings of

   the command byte.  In an ideal world, we will not change the header

   format.  As reserved bytes are given defined meaning, the protocol

   version / magic byte values should be incremented.

   Traffic analysis tools are encouraged to identify memcache packets

   and provide detailed interpretation if the magic bytes are recognized

   and otherwise to provide a generic breakdown of the packet.  Note,

   that the key and value positions can always be identified even if the

   magic byte or command opcode are not recognized.

3.2.  Response Status

   Possible values of this two-byte field:

   0x0000  No error

   0x0001  Key not found

   0x0002  Key exists

   0x0003  Value too large

   0x0004  Invalid arguments

   0x0005  Item not stored

   0x0006  Incr/Decr on non-numeric value.

   0x0081  Unknown command

   0x0082  Out of memory

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3.3.  Command Opcodes

   Possible values of the one-byte field:

   0x00    Get

   0x01    Set

   0x02    Add

   0x03    Replace

   0x04    Delete

   0x05    Increment

   0x06    Decrement

   0x07    Quit

   0x08    Flush

   0x09    GetQ

   0x0A    No-op

   0x0B    Version

   0x0C    GetK

   0x0D    GetKQ

   0x0E    Append

   0x0F    Prepend

   0x10    Stat

   0x11    SetQ

   0x12    AddQ

   0x13    ReplaceQ

   0x14    DeleteQ

   0x15    IncrementQ

   0x16    DecrementQ

   0x17    QuitQ

   0x18    FlushQ

   0x19    AppendQ

   0x1A    PrependQ

   As a convention all of the commands ending with "Q" for Quiet.  A

   quiet version of a command will omit responses that are considered

   uninteresting.  Whether a given response is interesting is dependent

   upon the command.  See the descriptions of the set commands

   (Section 4.2) and set commands (Section 4.3) for examples of commands

   that include quiet variants.

3.4.  Data Types

   Possible values of the one-byte field:

   0x00    Raw bytes

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4.  Commands

4.1.  Introduction

   All communication is initiated by a request from the client, and the

   server will respond to each request with zero or multiple packets for

   each request.  If the status code of a response packet is non-nil,

   the body of the packet will contain a textual error message.  If the

   status code is nil, the command opcode will define the layout of the

   body of the message.

4.1.1.  Example

   The following figure illustrates the packet layout for a packet with

   an error message.

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   Packet layout:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x81          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      4| 0x00          | 0x00          | 0x00          | 0x01          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x09          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     24| 0x4e ('N')    | 0x6f ('o')    | 0x74 ('t')    | 0x20 (' ')    |

       +---------------+---------------+---------------+---------------+

     28| 0x66 ('f')    | 0x6f ('o')    | 0x75 ('u')    | 0x6e ('n')    |

       +---------------+---------------+---------------+---------------+

     32| 0x64 ('d')    |

       +---------------+

       Total 33 bytes (24 byte header, and 9 bytes value)

   Field        (offset) (value)

   Magic        (0)    : 0x81

   Opcode       (1)    : 0x00

   Key length   (2,3)  : 0x0000

   Extra length (4)    : 0x00

   Data type    (5)    : 0x00

   Status       (6,7)  : 0x0001

   Total body   (8-11) : 0x00000009

   Opaque       (12-15): 0x00000000

   CAS          (16-23): 0x0000000000000000

   Extras              : None

   Key                 : None

   Value        (24-32): The textual string "Not found"

4.2.  Get, Get Quietly, Get Key, Get Key Quietly

   Request:

      MUST NOT have extras.

      MUST have key.

      MUST NOT have value.

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   Response (if found):

      MUST have extras.

      MAY have key.

      MAY have value.

   o  4 byte flags

   Extra data for the get commands:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| Flags                                                         |

       +---------------+---------------+---------------+---------------+

       Total 4 bytes

   The get command gets a single key.  The getq command is both mum on

   cache miss and quiet, holding its response until a non-quiet command

   is issued.  Getk and getkq differs from get and getq by adding the

   key into the response packet.

   You're not guaranteed a response to a getq/getkq cache hit until you

   send a non-getq/getkq command later, which uncorks the server and

   bundles up IOs to send to the client in one go.

   Clients should implement multi-get (still important for reducing

   network roundtrips!) as n pipelined requests, the first n-1 being

   getq/getkq, the last being a regular get/getk.  That way you're

   guaranteed to get a response, and you know when the server's done.

   You can also do the naive thing and send n pipelined get/getks, but

   then you could potentially get back a lot of "NOT_FOUND" error code

   packets.  Alternatively, you can send 'n' getq/getkqs, followed by a

   'noop' command.

4.2.1.  Example

   To request the data associated with the key "Hello" the following

   fields must be specified in the packet.

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   get request:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x80          | 0x00          | 0x00          | 0x05          |

       +---------------+---------------+---------------+---------------+

      4| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x05          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     24| 0x48 ('H')    | 0x65 ('e')    | 0x6c ('l')    | 0x6c ('l')    |

       +---------------+---------------+---------------+---------------+

     28| 0x6f ('o')    |

       +---------------+

       Total 29 bytes (24 byte header, and 5 bytes key)

   Field        (offset) (value)

   Magic        (0)    : 0x80

   Opcode       (1)    : 0x00

   Key length   (2,3)  : 0x0005

   Extra length (4)    : 0x00

   Data type    (5)    : 0x00

   Reserved     (6,7)  : 0x0000

   Total body   (8-11) : 0x00000005

   Opaque       (12-15): 0x00000000

   CAS          (16-23): 0x0000000000000000

   Extras              : None

   Key          (24-29): The textual string: "Hello"

   Value               : None

   If the item exist on the server the following packet is returned,

   otherwise a packet with status code != 0 will be returned (see

   Introduction (Section 4.1))

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   get/getq response:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x81          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      4| 0x04          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x09          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x01          |

       +---------------+---------------+---------------+---------------+

     24| 0xde          | 0xad          | 0xbe          | 0xef          |

       +---------------+---------------+---------------+---------------+

     28| 0x57 ('W')    | 0x6f ('o')    | 0x72 ('r')    | 0x6c ('l')    |

       +---------------+---------------+---------------+---------------+

     32| 0x64 ('d')    |

       +---------------+

       Total 33 bytes (24 byte header, 4 byte extras and 5 byte value)

   Field        (offset) (value)

   Magic        (0)    : 0x81

   Opcode       (1)    : 0x00

   Key length   (2,3)  : 0x0000

   Extra length (4)    : 0x04

   Data type    (5)    : 0x00

   Status       (6,7)  : 0x0000

   Total body   (8-11) : 0x00000009

   Opaque       (12-15): 0x00000000

   CAS          (16-23): 0x0000000000000001

   Extras              :

     Flags      (24-27): 0xdeadbeef

   Key                 : None

   Value        (28-32): The textual string "World"

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   getk/getkq response:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x81          | 0x00          | 0x00          | 0x05          |

       +---------------+---------------+---------------+---------------+

      4| 0x04          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x09          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x01          |

       +---------------+---------------+---------------+---------------+

     24| 0xde          | 0xad          | 0xbe          | 0xef          |

       +---------------+---------------+---------------+---------------+

     28| 0x48 ('H')    | 0x65 ('e')    | 0x6c ('l')    | 0x6c ('l')    |

       +---------------+---------------+---------------+---------------+

     32| 0x6f ('o')    | 0x57 ('W')    | 0x6f ('o')    | 0x72 ('r')    |

       +---------------+---------------+---------------+---------------+

     36| 0x6c ('l')    | 0x64 ('d')    |

       +---------------+---------------+

       Total 38 bytes (24 byte header, 4 byte extras, 5 byte key

                       and 5 byte value)

   Field        (offset) (value)

   Magic        (0)    : 0x81

   Opcode       (1)    : 0x00

   Key length   (2,3)  : 0x0005

   Extra length (4)    : 0x04

   Data type    (5)    : 0x00

   Status       (6,7)  : 0x0000

   Total body   (8-11) : 0x0000000E

   Opaque       (12-15): 0x00000000

   CAS          (16-23): 0x0000000000000001

   Extras              :

     Flags      (24-27): 0xdeadbeef

   Key          (28-32): The textual string: "Hello"

   Value        (33-37): The textual string: "World"

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4.3.  Set, Add, Replace

      MUST have extras.

      MUST have key.

      MUST have value.

   o  4 byte flags

   o  4 byte expiration time

   Extra data for set/add/replace:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| Flags                                                         |

       +---------------+---------------+---------------+---------------+

      4| Expiration                                                    |

       +---------------+---------------+---------------+---------------+

       Total 8 bytes

   If the Data Version Check (CAS) is nonzero, the requested operation

   MUST only succeed if the item exists and has a CAS value identical to

   the provided value.

   Add MUST fail if the item already exist.

   Replace MUST fail if the item doesn't exist.

   Set should store the data unconditionally if the item exists or not.

   Quiet mutations only return responses on failure.  Success is

   considered the general case and is suppressed when in quiet mode, but

   errors should not be allowed to go unnoticed.

4.3.1.  Example

   The following figure shows an add-command for

      Key: "Hello"

      Value: "World"

      Flags: 0xdeadbeef

      Expiry: in two hours

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   Add request:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x80          | 0x02          | 0x00          | 0x05          |

       +---------------+---------------+---------------+---------------+

      4| 0x08          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x12          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     24| 0xde          | 0xad          | 0xbe          | 0xef          |

       +---------------+---------------+---------------+---------------+

     28| 0x00          | 0x00          | 0x1c          | 0x20          |

       +---------------+---------------+---------------+---------------+

     32| 0x48 ('H')    | 0x65 ('e')    | 0x6c ('l')    | 0x6c ('l')    |

       +---------------+---------------+---------------+---------------+

     36| 0x6f ('o')    | 0x57 ('W')    | 0x6f ('o')    | 0x72 ('r')    |

       +---------------+---------------+---------------+---------------+

     40| 0x6c ('l')    | 0x64 ('d')    |

       +---------------+---------------+

       Total 42 bytes (24 byte header, 8 byte extras, 5 byte key and

                       5 byte value)

   Field        (offset) (value)

   Magic        (0)    : 0x80

   Opcode       (1)    : 0x02

   Key length   (2,3)  : 0x0005

   Extra length (4)    : 0x08

   Data type    (5)    : 0x00

   Reserved     (6,7)  : 0x0000

   Total body   (8-11) : 0x00000012

   Opaque       (12-15): 0x00000000

   CAS          (16-23): 0x0000000000000000

   Extras              :

     Flags      (24-27): 0xdeadbeef

     Expiry     (28-31): 0x00001c20

   Key          (32-36): The textual string "Hello"

   Value        (37-41): The textual string "World"

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   The response-packet contains no extra data, and the result of the

   operation is signaled through the status code.  If the command

   succeeds, the CAS value for the item is returned in the CAS-field of

   the packet.

   Successful add response:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x81          | 0x02          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      4| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x01          |

       +---------------+---------------+---------------+---------------+

       Total 24 bytes

   Field        (offset) (value)

   Magic        (0)    : 0x81

   Opcode       (1)    : 0x02

   Key length   (2,3)  : 0x0000

   Extra length (4)    : 0x00

   Data type    (5)    : 0x00

   Status       (6,7)  : 0x0000

   Total body   (8-11) : 0x00000000

   Opaque       (12-15): 0x00000000

   CAS          (16-23): 0x0000000000000001

   Extras              : None

   Key                 : None

   Value               : None

4.4.  Delete

      MUST NOT have extras.

      MUST have key.

      MUST NOT have value.

   Delete the item with the specific key.

Stone & Norbye            Expires March 1, 2009                [Page 15]

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4.4.1.  Example

   The following figure shows a delete message for the item "Hello".

   Delete request:

     Byte/     0       |       1       |       2       |       3       |

        /              |               |               |               |

       |0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|0 1 2 3 4 5 6 7|

       +---------------+---------------+---------------+---------------+

      0| 0x80          | 0x04          | 0x00          | 0x05          |

       +---------------+---------------+---------------+---------------+

      4| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

      8| 0x00          | 0x00          | 0x00          | 0x05          |

       +---------------+---------------+---------------+---------------+

     12| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     16| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     20| 0x00          | 0x00          | 0x00          | 0x00          |

       +---------------+---------------+---------------+---------------+

     24| 0x48 ('H')    | 0x65 ('e')    | 0x6c ('l')    | 0x6c ('l')    |

       +---------------+---------------+---------------+---------------+

     28| 0x6f ('o')    |

       +---------------+

       Total 29 bytes (24 byte header, 5 byte value)

   Field        (offset) (value)

   Magic        (0)    : 0x80

   Opcode       (1)    : 0x04

   Key length   (2,3)  : 0x0005

   Extra length (4)    : 0x00

   Data type    (5)    : 0x00

   Reserved     (6,7)  : 0x0000