JSON Meta Application Protocol (JMAP) Blob Management Extension

Internet Engineering Task Force (IETF)                  B. Gondwana, Ed.
Request for Comments: 9404                                      Fastmail
Updates: 8620                                                August 2023
Category: Standards Track
ISSN: 2070-1721


    JSON Meta Application Protocol (JMAP) Blob Management Extension

Abstract

   The JSON Meta Application Protocol (JMAP) base protocol (RFC 8620)
   provides the ability to upload and download arbitrary binary data via
   HTTP POST and GET on a 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 is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9404.

Copyright Notice

   Copyright (c) 2023 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 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.  Conventions Used in This Document
   3.  Addition to the Capabilities Object
     3.1.  urn:ietf:params:jmap:blob
       3.1.1.  Capability Example
   4.  Blob Methods
     4.1.  Blob/upload
       4.1.1.  Blob/upload Simple Example
       4.1.2.  Blob/upload Complex Example
     4.2.  Blob/get
       4.2.1.  Blob/get Simple Example
       4.2.2.  Blob/get Example with Range and Encoding Errors
     4.3.  Blob/lookup
       4.3.1.  Blob/lookup Example
   5.  Security Considerations
   6.  IANA Considerations
     6.1.  JMAP Capability Registration for "blob"
     6.2.  JMAP Error Codes Registration for "unknownDataType"
     6.3.  Creation of "JMAP Data Types" Registry
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Acknowledgements
   Author's Address

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 round trips.

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

   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.

   When JMAP is proxied through a system that applies additional access
   restrictions, it can be useful to know which objects reference any
   particular blob; 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 [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 presence of the capability urn:ietf:params:jmap:blob 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 MUST contain the following information on
   server capabilities and permissions for that account:

   *  maxSizeBlobSet: "UnsignedInt|null"

      The maximum size of the 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.

      If this value is null, then clients are not required to limit the
      size of the 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"

      The maximum number of DataSourceObjects allowed per creation in a
      Blob/upload.

      Servers MUST allow at least 64 DataSourceObjects per creation.

   *  supportedTypeNames: "String[]"

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

      Note that the supportedTypeNames list may include private types
      that are not in the "JMAP Data Types" registry defined by this
      document.  Clients MUST ignore type names they do not recognise.

   *  supportedDigestAlgorithms: "String[]"

      An array of supported digest algorithms that are supported for
      Blob/get.  If the server does not support calculating blob
      digests, then this will be the empty list.  Algorithms in this
      list MUST be present in the "HTTP Digest Algorithm Values"
      registry defined by [RFC3230]; however, in JMAP, they must be
      lowercased, e.g., "md5" rather than "MD5".

      Clients SHOULD prefer algorithms listed earlier in this list.

3.1.1.  Capability Example

   {
     "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.

   JMAP [RFC8620] defines the Blob/copy method, which is unchanged by
   this specification 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 in [RFC8620] in some ways.  However,
   blobs cannot be updated or deleted, so only create is allowed in the
   method call.  Also, blobs do not have state, so there is no state
   field present in the method response.

   *Parameters*

   *  accountId: "Id"

      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 creation id.

   The created objects contain:

   *  id: "Id"

      The blobId that was created.

   *  type: "String|null"

      The media type as given in the creation (if any).  If not
      provided, the server MAY perform content analysis and return one
      of the following: the calculated value, "application/octet-
      string", or null.

   *  size: "UnsignedInt"

      As per [RFC8620], the size of the created blob in octets.

   The created objects will also contain any other properties identical
   to those that would be returned in the JSON response of the upload
   endpoint described in [RFC8620].  This may be extended in the future;
   in this document, it is anticipated that implementations will extend
   both the upload endpoint and the Blob/upload responses in the same
   way.

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

   For each successful upload, servers MUST add an entry to the
   createdIds map ([RFC8620], Section 3.3) for the request; even if the
   caller did not explicitly pass a createdIds, the value must be
   available to later methods defined in the same Request Object.  This
   allows the blobId to be used via back-reference in subsequent method
   calls.

   The created blob will have the same lifetime and same expiry
   semantics as any other binary object created via the mechanism
   specified in [RFC8620], Section 6.

   Uploads using this mechanism will be restricted by the maxUploadSize
   limit for JMAP requests specified by the server, and clients SHOULD
   consider using the upload mechanism defined by [RFC8620] for blobs
   larger than a megabyte.

   *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
      in order to create the blob.

   *  type: "String|null" (default: null)

      A 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 cannot be fully satisfied (i.e., it 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 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 notCreated response.

   It is envisaged that the definition for DataSourceObject might be
   extended in the 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, the entire data:asBase64 field would be
   sent as a continuous string with no wrapping on the wire.

   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": {
       "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"
      ],
      "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": [
           {
             "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, the properties default to data and size.

   *Result Properties:*

   *  data:asText: "String|null"

      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 that 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.

4.2.1.  Blob/get Simple Example

   In this example, 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 the size and a short range of the data for
   one of the blobs.

   Method Calls:

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

   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 dog.", which contains an invalid UTF-8 sequence.

   The results have the following properties:

   *  G1: Defaults to data and size, so b1 returns isEncodingProblem and
      a base64 value.

   *  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 wrapping 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",
           "#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",
       {
         "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==",
             "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
           }
         ],
         "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"
     ]
   ]

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
   that reference the provided blob.

   Since different datatypes will have different semantics of
   "contains", the definition of "reference" is somewhat loose but
   roughly means "you could discover this blobId by looking at this
   object or at other objects recursively contained within this object".

   For example, with a server that supports [RFC8621], if a Mailbox
   references a blob and if any Emails within that Mailbox reference the
   blobId, then the Mailbox references that blobId.  For any Thread that
   references an Email that references a blobId, it can be said that the
   Thread references the blobId.

   However, this does not mean that if an Email references a Mailbox in
   its mailboxIds property, then any blobId referenced by other Emails
   in that Mailbox are also referenced by the initial Email.

   *Parameters*

   *  accountId: "Id"

      The id of the account used for the call.

   *  typeNames: "String[]"

      A list of names from the "JMAP Data Types" registry or defined by
      private extensions that the client has requested.  Only names for
      which "Can reference blobs" is true may be specified, and the
      capability that 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 blobId.

   *  matchedIds: "String[Id[]]"

      A map from type name to a 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 or does not exist on the server at
   all, then the server MUST still return an empty array for each type
   as this doesn't leak any information about whether the blob is on the
   server but not visible to the requesting user.

4.3.1.  Blob/lookup Example

   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"
   ]

5.  Security Considerations

   All security considerations for JMAP [RFC8620] apply to this
   specification.  Additional considerations specific to the data types
   and functionality introduced by this document are described here.

   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
   that 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 cannot be discovered via a Blob/lookup.  For
   example, if an Email exists in a Mailbox that the authenticated user
   does not have access to see, then that emailId MUST NOT be returned
   in a lookup for a blob that is referenced by that email.

   The server MUST NOT trust that the data given to a Blob/upload is a
   well-formed instance of the specified media type.  Also, 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.

   With carefully chosen data sources, Blob/upload can be used to
   recreate dangerous content on the far side of security scanners
   (anti-virus or exfiltration scanners, for example) that 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.

   Digest algorithms can be expensive for servers to calculate.  Servers
   that share resources between multiple users should track resource
   usage by clients and rate-limit expensive operations to avoid
   resource starvation.

6.  IANA Considerations

6.1.  JMAP Capability Registration for "blob"

   IANA has registered the "blob" JMAP capability as follows:

   Capability Name:  urn:ietf:params:jmap:blob
   Specification document:  RFC 9404
   Intended use:  common
   Change Controller:  IETF
   Security and privacy considerations:  RFC 9404, Section 5

6.2.  JMAP Error Codes Registration for "unknownDataType"

   IANA has registered the "unknownDataType" JMAP error code as follows:

   JMAP Error Code:  unknownDataType
   Intended use:  common
   Change Controller:  IETF
   Reference:  RFC 9404
   Description:  The server does not recognise this data type, or the
      capability to enable it is not present in the current Request
      Object.

6.3.  Creation of "JMAP Data Types" Registry

   IANA has created a new registry called "JMAP Data Types".  Table 1
   shows the initial contents of this new registry.

   +================+=====+=======+=========================+=========+
   |Type Name       |Can  |Can Use|Capability               |Reference|
   |                |Ref  |for    |                         |         |
   |                |Blobs|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:    |[RFC8621]|
   |                |     |       |submission               |         |
   +----------------+-----+-------+-------------------------+---------+
   |EmailSubmission |No   |Yes    |urn:ietf:params:jmap:    |[RFC8621]|
   |                |     |       |submission               |         |
   +----------------+-----+-------+-------------------------+---------+
   |VacationResponse|No   |Yes    |urn:ietf:params:jmap:    |[RFC8621]|
   |                |     |       |vacationresponse         |         |
   +----------------+-----+-------+-------------------------+---------+
   |MDN             |No   |No     |urn:ietf:params:jmap:mdn |[RFC9007]|
   +----------------+-----+-------+-------------------------+---------+

                                 Table 1

   The registration policy for this registry is "Specification Required"
   [RFC8126].  Either an RFC or a similarly stable reference document
   defines a JMAP Data Type and associated capability.

   IANA will appoint designated experts to review requests for additions
   to this registry, with guidance to allow any registration that
   provides a stable document describing the capability and control over
   the URI namespace to which the capability URI points.

7.  References

7.1.  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>.

7.2.  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>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

   [RFC9007]  Ouazana, R., Ed., "Handling Message Disposition
              Notification with the JSON Meta Application Protocol
              (JMAP)", RFC 9007, DOI 10.17487/RFC9007, March 2021,
              <https://www.rfc-editor.org/info/rfc9007>.

Acknowledgements

   Joris Baum, Jim Fenton, Neil Jenkins, Alexey Melnikov, Ken Murchison,
   Robert Stepanek, and the JMAP Working Group in the IETF.

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