Internet-Draft JMAP Blob December 2021
Gondwana Expires 23 June 2022 [Page]
Workgroup:
JMAP
Internet-Draft:
draft-ietf-jmap-blob-08
Updates:
8620 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Author:
B. Gondwana, Ed.
Fastmail

JMAP Blob management extension

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 23 June 2022.

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Table of Contents

1. Introduction

Sometimes JMAP ([RFC8620]) interactions require creating a blob and then referencing it. In the same way that IMAP Literals ([RFC7888]) were extended to reduce roundtrips for simple data, embedding simple small blobs into the JMAP method stream can reduce 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 could contain arbitrary binary data, this document allows the use of the base64 coding specified in [RFC4648].

Where JMAP is being proxied through a system which applies additional access restrictions, it can be useful to know where a blob is referenced in order to decide whether to allow it to be downloaded, so this document defines a way to look up where a particular blobId is referenced.

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.

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 set, gives the maximum size of a blob in octets that the server will allow to be created (size of the final output of catenate or of encoded forms).

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

    If this value is not set, clients MUST NOT attempt to create blobs larger than the value of maxSizeUpload specified in [RFC8620]. If neither of those limits are specified by the server, 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.

  • maxCatenateItems: UnsignedInt|null

    if set, gives the maximum number of of CatenateSourceObjects allowed per creation in a Blob/set. Servers MUST allow at least 64 items.

    If not set, clients SHOULD assume a limit of 64 items.

  • supportedTypeNames: [String]|null

    an array of data type names that are supported for Blob/lookup. May be null or not present if the account does not support reverse lookups.

3.1.1. Capability Example 

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

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/set

This is a standard JMAP set method.

4.1.1. create

Properties:

Exactly one of:

  • data:asText: String

    data which can be represented as utf-8 encoded text

  • data:asBase64: String

    binary data encoded as a ([RFC4648] Section 4) Base 64 string

  • catenate: [CatenateSourceObject]

    list of one or more octet sources in order

Also optionally:

  • type: String|null (default: null)

    hint for media type of the data

Result is:

  • 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/set responses in the same way)

CatenateSourceObject:

Exactly one of:

  • data:asText: String|null

  • data:asBase64: String|null

or a blobId source:

  • blobId: Id

  • offset: UnsignedInt|null (MAY be zero)

  • length: UnsignedInt|null (MUST NOT 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. extends past the end of the data in the blob) then the catenate itself is invalid and results in a notCreated response for this creation id.

If the data properties or catenate 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 legal to create a blob by calling catenate with a single CatenateSourceObject. Please note that a catenate source MUST NOT contain additional sub-catenates, only data or blob sources.

It is envisaged that catenate sources might be extended in future, for example to fetch external content.

A server SHOULD accept at least 64 catenate items.

4.1.2. update

It is not possible to update a Blob, so any update will result in a notUpdated response.

4.1.3. destroy

It is not possible to destroy a Blob, so any destroy will result in a notDestroyed response.

4.1.4. Blob/set 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.

Method Call:

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

Response:

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

4.1.5. Blob/set complex example with catenate 

Method Calls:

[
  [
    "Blob/set",
    {
      "create": {
        "b4": {
          "data:asText": "The quick brown fox jumped over the lazy dog."
        }
      }
    },
    "S4"
  ],
  [
    "Blob/set",
    {
      "create": {
        "cat": {
          "catenate": [
            {
              "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/set",
    {
      "oldState": null,
      "created": {
        "b4": {
          "id": "Gc0854fb9fb03c41cce3802cb0d220529e6eef94e",
          "size": 45,
          "type": "application/octet-stream"
        }
      },
      "updated": null,
      "destroyed": null,
      "notCreated": null,
      "notUpdated": null,
      "notDestroyed": null,
      "accountId": "account1"
    },
    "S4"
  ],
  [
    "Blob/set",
    {
      "oldState": null,
      "created": {
        "cat": {
          "id": "Gcc60576f036321ae6e8037ffc56bdee589bd3e23",
          "size": 19,
          "type": "application/octet-stream"
        }
      },
      "updated": null,
      "destroyed": null,
      "notCreated": null,
      "notUpdated": null,
      "notDestroyed": 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)
  • size

If not given, properties defaults 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

  • 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.

4.2.1. Blob/get simple example

Where a blob containing the string "The quick brown fox jumped over the lazy dog!" has blobId G6ec94756e3e046be78fcb33953b85b944e70673e.

Method Call:

[
  "Blob/get",
  {
    "accountId" : "account1",
    "ids" : [
      "G6ec94756e3e046be78fcb33953b85b944e70673e",
      "not-a-blob"
    ],
    "properties" : [
      "data:asText",
      "data:asBase64",
      "size"
    ],
    "offset" : 4,
    "length" : 9
  },
  "R1"
]

Response:

[
  "Blob/get",
  {
    "accountId": "account1",
    "list": [
      {
        "id": "G6ec94756e3e046be78fcb33953b85b944e70673e",
        "data:asText": "quick bro",
        "data:asBase64": "cXVpY2sgYnJvCg==",
        "size": 46
      }
    ],
    "notFound": [
      "not-a-blob"
    ]
  },
  "R1"
]

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.

  • 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/set",
    {
      "create": {
        "b1": {
          "data:asBase64": "VGhlIHF1aWNrIGJyb3duIGZveCBqdW1wZW
                            Qgb3ZlciB0aGUggYEgZG9nLg=="
        },
        "b2": {
          "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/set",
    {
      "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 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 List]

    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 

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

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/set 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/set catenate 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 blobId from a catenate 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

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:

Table 1
Type Name Can reference blobs Can use for state change Capability Reference
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]

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/

draft-ietf-jmap-blob-08:

draft-ietf-jmap-blob-07:

draft-ietf-jmap-blob-06:

draft-ietf-jmap-blob-05:

draft-ieft-jmap-blob-04:

draft-ieft-jmap-blob-03:

draft-ieft-jmap-blob-02:

draft-ieft-jmap-blob-01:

draft-ieft-jmap-blob-00:

draft-gondwana-jmap-blob-02

draft-gondwana-jmap-blob-01

draft-gondwana-jmap-blob-00

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

[RFC8620]
Jenkins, N. and C. Newman, "The JSON Meta Application Protocol (JMAP)", RFC 8620, DOI 10.17487/RFC8620, , <https://www.rfc-editor.org/info/rfc8620>.
[RFC4648]
Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, , <https://www.rfc-editor.org/info/rfc4648>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.

10. Informative References

[RFC7888]
Melnikov, A., Ed., "IMAP4 Non-synchronizing Literals", RFC 7888, DOI 10.17487/RFC7888, , <https://www.rfc-editor.org/info/rfc7888>.
[RFC8621]
Jenkins, N. and C. Newman, "The JSON Meta Application Protocol (JMAP) for Mail", RFC 8621, DOI 10.17487/RFC8621, , <https://www.rfc-editor.org/info/rfc8621>.

Author's Address

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