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JMAP Blob management extension
draft-ietf-jmap-blob-13

Document Type Active Internet-Draft (jmap WG)
Author Bron Gondwana
Last updated 2022-10-07 (Latest revision 2022-09-13)
Replaces draft-gondwana-jmap-blob
Stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Formats
Stream WG state WG Consensus: Waiting for Write-Up
Doc Shepherd Follow-up Underway
Associated WG milestone
Aug 2022
Submit document for Blobs via JMAP to the IESG
Document shepherd Jim Fenton
IESG IESG state I-D Exists
Consensus boilerplate Yes
Telechat date (None)
Responsible AD (None)
Send notices to fenton@bluepopcorn.net
draft-ietf-jmap-blob-13
JMAP                                                    B. Gondwana, Ed.
Internet-Draft                                                  Fastmail
Updates: 8620 (if approved)                            14 September 2022
Intended status: Standards Track                                        
Expires: 18 March 2023

                     JMAP Blob management extension
                        draft-ietf-jmap-blob-13

Abstract

   The JMAP base protocol (RFC8620) provides the ability to upload and
   download arbitrary binary data via HTTP POST and GET on defined
   endpoint.  This binary data is called a "blob".

   This extension adds additional ways to create and access blobs, by
   making inline method calls within a standard JMAP request.

   This extension also adds a reverse lookup mechanism to discover where
   blobs are referenced within other data types.

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 https://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 18 March 2023.

Copyright Notice

   Copyright (c) 2022 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 (https://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

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   and restrictions with respect to this document.  Code Components
   extracted from this document must include Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used In This Document . . . . . . . . . . . . . .   3
   3.  Addition to the Capabilities Object . . . . . . . . . . . . .   3
     3.1.  urn:ietf:params:jmap:blob . . . . . . . . . . . . . . . .   3
       3.1.1.  Capability Example  . . . . . . . . . . . . . . . . .   4
   4.  Blob Methods  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Blob/upload . . . . . . . . . . . . . . . . . . . . . . .   5
       4.1.1.  Blob/upload simple example  . . . . . . . . . . . . .   7
       4.1.2.  Blob/upload complex example . . . . . . . . . . . . .   8
     4.2.  Blob/get  . . . . . . . . . . . . . . . . . . . . . . . .  11
       4.2.1.  Blob/get simple example . . . . . . . . . . . . . . .  13
       4.2.2.  Blob/get example with range and encoding errors . . .  14
     4.3.  Blob/lookup . . . . . . . . . . . . . . . . . . . . . . .  20
       4.3.1.  Blob/lookup example . . . . . . . . . . . . . . . . .  21
   5.  Security considerations . . . . . . . . . . . . . . . . . . .  23
   6.  IANA considerations . . . . . . . . . . . . . . . . . . . . .  23
     6.1.  JMAP Capability registration for "blob" . . . . . . . . .  23
     6.2.  JMAP Error Codes Registration for "unknownDataType" . . .  24
     6.3.  Creation of "JMAP Data Types" Registry  . . . . . . . . .  24
   7.  Changes . . . . . . . . . . . . . . . . . . . . . . . . . . .  25
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  28
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  28
   10. Informative References  . . . . . . . . . . . . . . . . . . .  28
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Sometimes JMAP ([RFC8620]) interactions require creating a blob and
   then referencing it.  In the same way that IMAP Literals were
   extended by [RFC7888], embedding small blobs directly into the JMAP
   method calls array can be an option for reducing roundtrips.

   Likewise, when fetching an object, it can be useful to also fetch the
   raw content of that object without a separate roundtrip.

   Since raw blobs may contain arbitrary binary data, this document
   defines a use of the base64 coding specified in [RFC4648] for both
   creating and fetching blob data.

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   Where JMAP is being proxied through a system which applies additional
   access restrictions, it can be useful to know which objects reference
   any particular blob, and this document defines a way to discover
   those references.

2.  Conventions Used In This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

   The definitions of JSON keys and datatypes in the document follow the
   conventions described in the core JMAP specification [RFC8620].

3.  Addition to the Capabilities Object

   The capabilities object is returned as part of the JMAP Session
   object; see [RFC8620], Section 2.

   This document defines an additional capability URI.

3.1.  urn:ietf:params:jmap:blob

   The capability urn:ietf:params:jmap:blob being present in the
   "accountCapabilities" property of an account represents support for
   additional API methods on the Blob datatype.  Servers that include
   the capability in one or more "accountCapabilities" properties MUST
   also include the property in the "capabilities" property.

   The value of this property in the JMAP session "capabilities"
   property MUST be an empty object.

   The value of this property in an account's "accountCapabilities"
   property is an object that MAY contain the following information on
   server capabilities and permissions for that account:

   *  maxSizeBlobSet: UnsignedInt|null

      If present, this is the maximum size of blob (in octets) that the
      server will allow to be created (including blobs created by
      concatenating multiple data sources together).

      Clients MUST NOT attempt to create blobs larger than this size.

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      If this value is not present or null, then clients are not
      required to limit the size of blob they try to create, though
      servers can always reject creation of blobs regardless of size;
      e.g. due to lack of disk space, or per-user rate limits.

   *  maxDataSources: UnsignedInt|null

      If present, gives the maximum number of of DataSourceObjects
      allowed per creation in a Blob/upload.  Servers MUST allow at
      least 64 items.

      If this value is not present or null, then clients SHOULD assume a
      limit of 64 items.

   *  supportedTypeNames: String[]|null

      An array of data type names that are supported for Blob/lookup.
      If the server does not support lookups then this could be the
      empty list, not present or null.

   *  supportedDigestAlgorithms String[]|null

      An array of supported digest algorithms that are supported for
      Blob/get.  If the server does not support calculating blob
      digests, then this could be the empty list, not present, or null.
      Algorithms on this list _MUST_ be present in the HTTP Digest
      Alogirthms registry defined by [RFC3230], and are always
      lowercased.

3.1.1.  Capability Example

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   {
     "capabilities": {
       ...,
       "urn:ietf:params:jmap:blob": {}
     },
     "accounts": {
       "A13842": {
         ...
         "accountCapabilities": {
           "urn:ietf:params:jmap:blob": {
             "maxSizeBlobSet": 50000000,
             "maxDataSources": 100,
             "supportedTypeNames" : [
               "Mailbox",
               "Thread",
               "Email"
             ],
             "supportedDigestAlgorithms" : [
               "sha",
               "sha-256"
             ]
           }
         }
       }
     }
   }

4.  Blob Methods

   A blob is a sequence of zero or more octets.

   The JMAP base spec [RFC8620] defines the Blob/copy method, which is
   unchanged by this specfication, and is selected by the
   urn:ietf:params:jmap:core capability.

   The following JMAP Methods are selected by the
   urn:ietf:params:jmap:blob capability.

4.1.  Blob/upload

   This is similar to a Foo/set from [RFC8620] in some ways, however
   blobs can't be updated or deleted, so only create is allowed in the
   method call, and blobs don't have state, so there is no state field
   present in the method response.

   *Parameters*

   *  accountId: Id

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      The id of the account in which the blobs will be created.

   *  create: Id[UploadObject]

      A map of creation id to UploadObjects.

   *Result*

   The result is the same as for Foo/set in RFC8620, with created and
   notCreated objects mapping from the creationId.

   The created objects contain:

   *  id: Id

      the blobId which was created

   *  type: String|null

      the media type as given in the creation (if any); or detected from
      content; or null

   *  size: UnsignedInt

      as per RFC8620 - the size of the created blob in octets

   Plus any other properties identical to those that would be returned
   in the JSON response of the RFC8620 upload endpoint (which may be
   extended in the future - this document anticipates that
   implementations will extend both the upload endpoint and the Blob/
   upload responses in the same way)

   Or if there is a problem with a creation, then the server will return
   a notCreated response with a map from the failed creationId to a
   SetError object.

   For each sucessful upload, servers MUST add an entry to the
   creationIds map for the request.  This allows the blob id to be used
   via back-reference in subsequent method calls.

   *UploadObject*

   *  data: DataSourceObject[]

      an array of zero or more octet sources in order (zero to create an
      empty blob).  The result of each of these sources is concatenated
      together in order to create the blob.

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   *  type: String|null (default: null)

      hint for media type of the data

   *DataSourceObject*

   Exactly one of:

   *  data:asText: String|null (raw octets, must be UTF-8)

   *  data:asBase64: String|null (base64 representation of octets)

   or a blobId source:

   *  blobId: Id

   *  offset: UnsignedInt|null (MAY be zero)

   *  length: UnsignedInt|null (MAY be zero)

   If null then offset is assumed to be zero.

   If null then length is the remaining octets in the blob.

   If the range can not be fully satisfied (i.e. begins or extends past
   the end of the data in the blob) then the DataSourceObject is invalid
   and results in a notCreated response for this creation id.

   If the data properties have any invalid references or invalid data
   contained in them, the server MUST NOT guess as to the user's intent,
   and MUST reject the creation and return a notCreated response for
   that creation id.

   Likewise, invalid characters in the base64 of data:asBase64, or
   invalid UTF-8 in data:asText MUST result in a nonCreated response.

   It is envisaged that the definition for DataSourceObject might be
   extended in future, for example to fetch external content.

   A server MUST accept at least 64 DataSourceObjects per create, as
   described in Section 3.1 of this document.

4.1.1.  Blob/upload simple example

   The data:asBase64 field is set over multiple lines for ease of
   publication here, however all data:asBase64 would be sent as a
   continuous string with no whitespace on the wire.

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Method Call:

[
  "Blob/upload",
  {
    "accountId": "account1",
    "create": {
      "1": {
        "data" : [
          {
            "data:asBase64": "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABAQMAAAAl21bKA
                              AAAA1BMVEX/AAAZ4gk3AAAAAXRSTlN/gFy0ywAAAApJRE
                              FUeJxjYgAAAAYAAzY3fKgAAAAASUVORK5CYII=",
          }
        ],
        "type": "image/png"
      },
    },
  },
  "R1"
]

Response:

[
  "Blob/upload",
  {
    "accountId" : "account1",
    "created" : {
      "1": {
        "id" : "G4c6751edf9dd6903ff54b792e432fba781271beb",
        "type" : "image/png",
        "size" : 95
      },
    },
  },
  "R1"
]

4.1.2.  Blob/upload complex example

Method Calls:

[
  [
    "Blob/upload",
    {
      "create": {

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        "b4": {
          "data": [
            {
              "data:asText": "The quick brown fox jumped over the lazy dog."
            }
          ]
        }
      }
    },
    "S4"
  ],
  [
    "Blob/upload",
    {
      "create": {
        "cat": {
          "data": [
            {
              "data:asText": "How"
            },
            {
              "blobId": "#b4",
              "length": 7,
              "offset": 3
            },
            {
              "data:asText": "was t"
            },
            {
              "blobId": "#b4",
              "length": 1,
              "offset": 1
            },
            {
              "data:asBase64": "YXQ/"
            }
          ]
        }
      }
    },
    "CAT"
  ],
  [
    "Blob/get",
    {
      "properties": [
        "data:asText",
        "size"

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      ],
      "ids": [
        "#cat"
      ]
    },
    "G4"
  ]
]

Responses:

[
  [
    "Blob/upload",
    {
      "oldState": null,
      "created": {
        "b4": {
          "id": "Gc0854fb9fb03c41cce3802cb0d220529e6eef94e",
          "size": 45,
          "type": "application/octet-stream"
        }
      },
      "notCreated": null,
      "accountId": "account1"
    },
    "S4"
  ],
  [
    "Blob/upload",
    {
      "oldState": null,
      "created": {
        "cat": {
          "id": "Gcc60576f036321ae6e8037ffc56bdee589bd3e23",
          "size": 19,
          "type": "application/octet-stream"
        }
      },
      "notCreated": null,
      "accountId": "account1"
    },
    "CAT"
  ],
  [
    "Blob/get",
    {
      "list": [

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        {
          "id": "Gcc60576f036321ae6e8037ffc56bdee589bd3e23",
          "data:asText": "How quick was that?",
          "size": 19
        }
      ],
      "notFound": [],
      "accountId": "account1"
    },
    "G4"
  ]
]

4.2.  Blob/get

   A standard JMAP get, with two additional optional parameters:

   *  offset: UnsignedInt|null

      start this many octets into the blob data.  If null or
      unspecified, this defaults to zero.

   *  length: UnsignedInt|null

      return at most this many octets of the blob data.  If null or
      unspecified, then all remaining octets in the blob are returned.
      This can be considered equivalent to an infinitely large length
      value, except that the isTruncated warning is not given unless the
      start offset is past the end of the blob.

   *Request Properties:*

   Any of

   *  data:asText
   *  data:asBase64
   *  data (returns data:asText if the selected octets are valid UTF-8,
      or data:asBase64)
   *  digest:<algorithm> (where <algorithm> is one of the named
      algorithms in the supportedDigestAlgorithms capability)
   *  size

   If not given, properties defaults to data and size.

   *Result Properties:*

   *  data:asText: String|null

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      the raw octets of the selected range if they are valid UTF-8,
      otherwise null

   *  data:asBase64: String

      the base64 encoding of the octets in the selected range

   *  digest:<algorithm> String

      the base64 encoding of the digest of the octets in the selected
      range, calculated using the named algorithm

   *  isEncodingProblem: Boolean (default: false)

   *  isTruncated: Boolean (default: false)

   *  size: UnsignedInt

      the number of octets in the entire blob

   The size value MUST always be the number of octets in the underlying
   blob, regardless of offset and length.

   The data fields contain a representation of the octets within the
   selected range that are present in the blob.  If the octets selected
   are not valid UTF-8 (including truncating in the middle of a multi-
   octet sequence) and data or data:asText was requested, then the key
   isEncodingProblem MUST be set to true and the data:asText response
   value MUST be null.  In the case where data was requested and the
   data is not valid UTF-8, then data:asBase64 MUST be returned.

   If the selected range requests data outside the blob (i.e. the
   offset+length is larger than the blob) then the result is either just
   the octets from the offset to the end of the blob, or an empty string
   if the offset is past the end of the blob.  Either way, the
   isTruncated property in the result MUST be set to true to tell the
   client that the requested range could not be fully satisfied.  If
   digest was requested, any digest is calculated on the octets that
   would be returned for a data field.

   Servers SHOULD store the size for blobs in a format which is
   efficient to read, and clients SHOULD limit their request to just the
   size parameter if that is all they need, as fetching blob content
   could be significantly more expensive and slower for the server.

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4.2.1.  Blob/get simple example

   Where a blob containing the string "The quick brown fox jumped over
   the lazy dog." has blobId Gc0854fb9fb03c41cce3802cb0d220529e6eef94e.

   The first method call requests just the size for multiple blobs, and
   the second requests both size and a short range of the data for one
   of the blobs.

Method Calls:

[
  [
    "Blob/get",
    {
      "ids" : [
        "Gc0854fb9fb03c41cce3802cb0d220529e6eef94e"
        "not-a-blob"
      ],
      "properties" : [
        "data:asText",
        "digest:sha",
        "size"
      ]
    },
    "R1"
  ],
  [
    "Blob/get",
    {
      "accountId" : "account1",
      "ids" : [
        "Gc0854fb9fb03c41cce3802cb0d220529e6eef94e"
      ],
      "properties" : [
        "data:asText",
        "data:asBase64",
        "digest:sha",
        "digest:sha-256",
        "size"
      ],
      "offset" : 4,
      "length" : 9
    },
    "R2"
  ]
]

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Responses:

[
  [
    "Blob/get",
    {
      "accountId": "account1",
      "list": [
        {
          "id": "Gc0854fb9fb03c41cce3802cb0d220529e6eef94e",
          "data:asText": "The quick brown fox jumped over the lazy dog.",
          "digest:sha": "wIVPufsDxBzOOALLDSIFKebu+U4=",
          "size": 45
        }
      ],
      "notFound": [
        "not-a-blob"
      ]
    },
    "R1"
  ],
  [
    "Blob/get",
    {
      "accountId": "account1",
      "list": [
        {
          "id": "Gc0854fb9fb03c41cce3802cb0d220529e6eef94e",
          "data:asText": "quick bro",
          "digest:sha": "QiRAPtfyX8K6tm1iOAtZ87Xj3Ww=",
          "digest:sha-256": "gdg9INW7lwHK6OQ9u0dwDz2ZY/gubi0En0xlFpKt0OA=",
          "size": 45
        }
      ]
    },
    "R2"
  ]
]

4.2.2.  Blob/get example with range and encoding errors

   The b1 value is the text: "The quick brown fox jumped over the
   \x81\x81 fox" which contains an invalid utf8 sequence.

   The results have the following interesting properties:

   *  G1: defaults to data and size - so b1 returns isEncodingProblem
      and a base64 value.

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   *  G2: since data:asText was explicitly selected, does not attempt to
      return a value for the data, just isEncodingProblem for b1.

   *  G3: since only data:asBase64 was requested, there is no encoding
      problem and both values are returned.

   *  G4: since the requested range could be satisfied as text, both
      blobs are returned as data:asText and there is no encoding
      problem.

   *  G5: both blobs cannot satisfy the requested range, so isTruncated
      is true for both.

   Note: some values have been wrapped for line length - there would be
   no whitespace in the data:asBase64 values on the wire

   Method calls:

   [
     [
       "Blob/upload",
       {
         "create": {
           "b1": {
             "data": [
               {
                 "data:asBase64": "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZW
                                   Qgb3ZlciB0aGUggYEgZG9nLg=="
               }
             ]
           },
           "b2": {
             "data": [
               {
                 "data:asText": "hello world"
               }
             ],
             "type" : "text/plain"
           }
         }
       },
       "S1"
     ],
     [
       "Blob/get",
       {
         "ids": [
           "#b1",

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           "#b2"
         ]
       },
       "G1"
     ],
     [
       "Blob/get",
       {
         "ids": [
           "#b1",
           "#b2"
         ],
         "properties": [
           "data:asText",
           "size"
         ]
       },
       "G2"
     ],
     [
       "Blob/get",
       {
         "ids": [
           "#b1",
           "#b2"
         ],
         "properties": [
           "data:asBase64",
           "size"
         ]
       },
       "G3"
     ],
     [
       "Blob/get",
       {
         "offset": 0,
         "length": 5,
         "ids": [
           "#b1",
           "#b2"
         ]
       },
       "G4"
     ],
     [
       "Blob/get",
       {

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         "offset": 20,
         "length": 100,
         "ids": [
           "#b1",
           "#b2"
         ]
       },
       "G5"
     ]
   ]

   Responses:

   [
     [
       "Blob/upload",
       {
         "oldState": null,
         "created": {
           "b2": {
             "id": "G2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
             "size": 11,
             "type": "application/octet-stream"
           },
           "b1": {
             "id": "G72cfa4804194563685d9a4b695f7ba20e7739576",
             "size": 43,
             "type": "text/plain"
           }
         },
         "updated": null,
         "destroyed": null,
         "notCreated": null,
         "notUpdated": null,
         "notDestroyed": null,
         "accountId": "account1"
       },
       "S1"
     ],
     [
       "Blob/get",
       {
         "list": [
           {
             "id": "G72cfa4804194563685d9a4b695f7ba20e7739576",
             "isEncodingProblem": true,
             "data:asBase64": "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZW
                               Qgb3ZlciB0aGUggYEgZG9nLg==",

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             "size": 43
           },
           {
             "id": "G2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
             "data:asText": "hello world",
             "size": 11
           }
         ],
         "notFound": [],
         "accountId": "account1"
       },
       "G1"
     ],
     [
       "Blob/get",
       {
         "list": [
           {
             "id": "G72cfa4804194563685d9a4b695f7ba20e7739576",
             "isEncodingProblem": true,
             "size": 43
           },
           {
             "id": "G2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
             "data:asText": "hello world",
             "size": 11
           }
         ],
         "notFound": [],
         "accountId": "account1"
       },
       "G2"
     ],
     [
       "Blob/get",
       {
         "list": [
           {
             "id": "G72cfa4804194563685d9a4b695f7ba20e7739576",
             "data:asBase64": "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZW
                               Qgb3ZlciB0aGUggYEgZG9nLg==",
             "size": 43
           },
           {
             "id": "G2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
             "data:asBase64": "aGVsbG8gd29ybGQ=",
             "size": 11
           }

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         ],
         "notFound": [],
         "accountId": "account1"
       },
       "G3"
     ],
     [
       "Blob/get",
       {
         "list": [
           {
             "id": "G72cfa4804194563685d9a4b695f7ba20e7739576",
             "data:asText": "The q",
             "size": 43
           },
           {
             "id": "G2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
             "data:asText": "hello",
             "size": 11
           }
         ],
         "notFound": [],
         "accountId": "account1"
       },
       "G4"
     ],
     [
       "Blob/get",
       {
         "list": [
           {
             "id": "G72cfa4804194563685d9a4b695f7ba20e7739576",
             "isTruncated": true,
             "isEncodingProblem": true,
             "data:asBase64": "anVtcGVkIG92ZXIgdGhlIIGBIGRvZy4=",
             "size": 43
           },
           {
             "id": "G2aae6c35c94fcfb415dbe95f408b9ce91ee846ed",
             "isTruncated": true,
             "data:asText": "",
             "size": 11
           }
         ],
         "notFound": [],
         "accountId": "account1"
       },
       "G5"

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     ]
   ]

4.3.  Blob/lookup

   Given a list of blobIds, this method does a reverse lookup in each of
   the provided type names to find the list of Ids within that data type
   which reference the provided blob.

   The definition of reference is somewhat loosely defined, but roughly
   means "you could discover this blobId by looking inside this object",
   for example if a Mailbox contains an Email which references the
   blobId, then it references that blobId.  Likewise for a Thread.

   *Parameters*

   *  accountId: Id

      The id of the account used for the call.

   *  typeNames: String[]

      A list of names from the "JMAP Data Types" registry.  Only names
      for which "Can reference blobs" is true may be specified, and the
      capability which defines each type must also be used by the
      overall JMAP request in which this method is called.

      If a type name is not known by the server, or the associated
      capability has not been requested, then the server returns an
      "unknownDataType" error.

   *  ids: Id[]

      A list of blobId values to be looked for.

   *Response*

   *  list: BlobInfo[]

      A list of BlobInfo objects.

   *BlobInfo Object*

   *  id: Id

      The Blob Identifier.

   *  matchedIds: String[Id[]]

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      A map from type name to list of Ids of that data type (e.g. the
      name "Email" maps to a list of emailIds)

   If a blob is not visible to a user at all, then the server SHOULD
   return that blobId in the notFound array, however it may also return
   an empty list for each type name, as it may not be able to know if
   other data types do reference that blob.

4.3.1.  Blob/lookup example

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   Method call:

   [
     "Blob/lookup",
     {
       "typeNames": [
         "Mailbox",
         "Thread",
         "Email"
       ],
       "ids": [
         "Gd2f81008cf07d2425418f7f02a3ca63a8bc82003",
         "not-a-blob"
       ]
     },
     "R1"
   ]

   Response:

   [
     "Blob/lookup",
     {
       "list": [
         {
           "id": "Gd2f81008cf07d2425418f7f02a3ca63a8bc82003",
           "matchedIds": {
             "Mailbox": [
               "M54e97373",
               "Mcbe6b662"
             ],
             "Thread": [
               "T1530616e"
             ],
             "Email": [
               "E16e70a73eb4",
               "E84b0930cf16"
             ]
           }
         }
       ],
       "notFound": [
         "not-a-blob"
       ]
     },
     "R1"
   ]

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5.  Security considerations

   JSON parsers are not all consistent in handling non-UTF-8 data.  JMAP
   requires that all JSON data be UTF-8 encoded, so servers MUST only
   return a null value if data:asText is requested for a range of octets
   which is not valid UTF-8, and set isEncodingProblem: true.

   Servers MUST apply any access controls, such that if the
   authenticated user would be unable to discover the blobId by making
   queries, then this fact can't be discovered via a Blob/lookup.  For
   example, if an Email exists in a Mailbox which the authenticated user
   does not have access to see, then that emailId MUST not be returned
   in a lookup for a blob which is referenced by that email.

   If a server might sometimes return all names empty rather than
   putting a blobId in the notFound response to a Blob/get, then the
   server SHOULD always return the same type of response, regardless of
   whether a blob exists but the user can't access it, or doesn't exist
   at all.  This avoids leaking information about the existence of the
   blob.

   The server MUST NOT trust that the data given to a Blob/upload is a
   well formed instance of the specified media type, and if the server
   attempts to parse the given blob, only hardened parsers designed to
   deal with arbitrary untrusted data should be used.  The server SHOULD
   NOT reject data on the grounds that it is not a valid specimen of the
   stated type.

   Blob/upload with carefully chosen data sources can be used to
   recreate dangerous content on the far side of security scanners
   (anti-virus or exfiltration scanners for example) which may be
   watching the upload endpoint.  Server implementations SHOULD provide
   a hook to allow security scanners to check the resulting blob after
   concatenating the data sources in the same way that they do for the
   upload endpoint.

6.  IANA considerations

6.1.  JMAP Capability registration for "blob"

   IANA is requested to register the "blob" JMAP Capability as follows:

   Capability Name: urn:ietf:params:jmap:blob

   Specification document: this document

   Intended use: common

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   Change Controller: IETF

   Security and privacy considerations: this document, Section XXX

6.2.  JMAP Error Codes Registration for "unknownDataType"

   IANA is requested to register the "unknownDataType" JMAP Error Code
   as follows:

   JMAP Error Code: unknownDataType

   Intended use: common

   Change Controller: IETF

   Reference: this document

   Description: The server does not recognise this data type, or the
   capability to enable it was not present.

6.3.  Creation of "JMAP Data Types" Registry

   IANA is requested to create a new registry "JMAP Data Types" with the
   initial content:

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   +================+=========+======+=====================================+=========+
   |Type Name       |Can      |Can   |Capability                           |Reference|
   |                |reference|use   |                                     |         |
   |                |blobs    |for   |                                     |         |
   |                |         |state |                                     |         |
   |                |         |change|                                     |         |
   +================+=========+======+=====================================+=========+
   |Core            |No       |No    |urn:ietf:params:jmap:core            |[RFC8620]|
   +----------------+---------+------+-------------------------------------+---------+
   |PushSubscription|No       |No    |urn:ietf:params:jmap:core            |[RFC8620]|
   +----------------+---------+------+-------------------------------------+---------+
   |Mailbox         |Yes      |Yes   |urn:ietf:params:jmap:mail            |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |Thread          |Yes      |Yes   |urn:ietf:params:jmap:mail            |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |Email           |Yes      |Yes   |urn:ietf:params:jmap:mail            |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |EmailDelivery   |No       |Yes   |urn:ietf:params:jmap:mail            |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |SearchSnippet   |No       |No    |urn:ietf:params:jmap:mail            |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |Identity        |No       |Yes   |urn:ietf:params:jmap:submission      |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |EmailSubmission |No       |Yes   |urn:ietf:params:jmap:submission      |[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |VacationResponse|No       |Yes   |urn:ietf:params:jmap:vacationresponse|[RFC8621]|
   +----------------+---------+------+-------------------------------------+---------+
   |MDN             |No       |No    |urn:ietf:params:jmap:mdn             |[RFC9007]|
   +----------------+---------+------+-------------------------------------+---------+

                                  Table 1

   This policy for this registry is "Specification required", either an
   RFC or a simiarly stable reference document which defines a JMAP Data
   Type and associated capability.

7.  Changes

   EDITOR: please remove this section before publication.

   The source of this document exists on github at:
   https://github.com/brong/draft-gondwana-jmap-blob/
   (https://github.com/brong/draft-gondwana-jmap-blob/)

   *draft-ietf-jmap-blob-13*

   *  added examples of digest responses

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   *draft-ietf-jmap-blob-12*

   *  updates based on Neil Jenkins' feedback:
      -  fixed [] positions for type specs
      -  documented delta between /upload and /set better
      -  allowed zero-length blobId sources
      -  fixed examples with /set leftovers
      -  documented datatypes registry policy
   *  added optional "digest" support

   *draft-ietf-jmap-blob-11*:

   *  updates based on IETF113 feedback:
      -  added wording to suggest the a Blob/get of just size might be
         faster
      -  added an example with just the size field being selected

   *draft-ietf-jmap-blob-10*:

   *  removed remaining references to catenate.

   *draft-ietf-jmap-blob-09*:

   *  tidied up introduction text
   *  replaced Blob/set with Blob/upload
   *  made all upload creates take an array of sources to normalise
      behaviour at the cost of a slightly more complex default case.

   *draft-ietf-jmap-blob-08*:

   *  Fixed spelling of Neil's name in acknowledgements
   *  Last call review (thanks Jim Fenton)
      -  fixed mmark sillyness causing RFC8620 to be non-normative in
         the references
      -  clarified the capability object and accountCapability object
         requirements
      -  made capability keys much more tightly defined, with mandatory
         minimum catenate limit and default values.
      -  increased use of normative language generally
      -  lowercased 'blob' anywhere it wasn't explicitly the object
      -  lowercased titles of the columns in the registry

   *draft-ietf-jmap-blob-07*:

   *  more examples to cover the interactions of offset, length and
      encoding checks.

   *draft-ietf-jmap-blob-06*:

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   *  removed asHex - we only need base64 and text
   *  added reference to where base64 is defined
   *  made 'destroy' not be allowed
   *  expanded JSON examples for readability
   *  removed 'expires' from examples

   *draft-ietf-jmap-blob-05*:

   *  discovered I hadn't actually included typeNames and matchedIds
      anywhere except the updates section, oops!
   *  added a catenate example
   *  tightened up some text

   *draft-ieft-jmap-blob-04*:

   *  added security considerations for scanning catenate results

   *draft-ieft-jmap-blob-03*:

   *  added capabilities object
   *  renamed types to typeNames and matchedIds
   *  added details of how to handle non-UTF8 data and truncation in
      Blob/get
   *  added isTruncated and isEncodingProblem to Blob/get to tell the
      client if the request wasn't entirely satisfied.

   *draft-ieft-jmap-blob-02*:

   *  fixed incorrect RFC number in reference and HTTP PUT -> POST,
      thanks Ken.
   *  added acknowledgements section
   *  removed all 'datatype' text and changed to 'data type' or 'type
      name' as appropriate (issue #1 proposal)
   *  expanded security considerations section and moved optional Blob/
      lookup empty case into Blob/lookup section

   *draft-ieft-jmap-blob-01*:

   *  renamed 'datatypes' to 'types' to align with PushSubscription from
      RFC8620.
   *  added example for Blob/get
   *  specified offset and length precisely

   *draft-ieft-jmap-blob-00*:

   *  initial adoption as an IETF document, otherwise identical to
      draft-gondwana-jmap-blob-02

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   *draft-gondwana-jmap-blob-02*

   *  renamed 'objects' to 'datatypes'
   *  specified Blob/lookup
   *  added IANA registry for datatypes

   *draft-gondwana-jmap-blob-01*

   *  added an example

   *draft-gondwana-jmap-blob-00*

   *  initial proposal

8.  Acknowledgements

   Joris Baum, Jim Fenton, Neil Jenkins, Alexey Melnikov, Ken Murchison,
   Robert Stepanek and the JMAP working group at the IETF.

9.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC3230]  Mogul, J. and A. Van Hoff, "Instance Digests in HTTP",
              RFC 3230, DOI 10.17487/RFC3230, January 2002,
              <https://www.rfc-editor.org/info/rfc3230>.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
              <https://www.rfc-editor.org/info/rfc4648>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8620]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, July
              2019, <https://www.rfc-editor.org/info/rfc8620>.

10.  Informative References

   [RFC7888]  Melnikov, A., Ed., "IMAP4 Non-synchronizing Literals",
              RFC 7888, DOI 10.17487/RFC7888, May 2016,
              <https://www.rfc-editor.org/info/rfc7888>.

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   [RFC8621]  Jenkins, N. and C. Newman, "The JSON Meta Application
              Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621,
              August 2019, <https://www.rfc-editor.org/info/rfc8621>.

Author's Address

   Bron Gondwana (editor)
   Fastmail
   Level 2, 114 William St
   Melbourne  VIC 3000
   Australia
   Email: brong@fastmailteam.com
   URI:   https://www.fastmail.com

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