CBOR encoding of date-time

[martin-lindstrom]

CBOR can represent a time stamp both as an int and as a string. However, the schema states that timestamps should be strings:

       "sc": {
          "description": "Date/Time of Sample Collection",
          "type": "string",
          "format": "date-time"
        },
        "dr": {
          "description": "Date/Time of Test Result",
          "type": "string",
          "format": "date-time"
        },

For the sake of interoperability and to smoothen the differences between JSON and CBOR I think that we need to have a writing (in the wiki or somewhere else) that clarifies this. My suggestion is to be clear that date-time fields should be CBOR encoded using the string representation. Otherwise we'll introduce completely unnecessary interop-problems when going from CBOR to JSON and back.

Also, see https://github.com/eu-digital-green-certificates/dgc-testdata/issues/30.

[jschlyter]

Does 9bcbc70b52b0a70160ad8ec3cf6ca86812eddd3d work for you @martin-lindstrom ?

[martin-lindstrom]

Does 9bcbc70 work for you @martin-lindstrom ?

Actually, we should say something about tagging also. See section 3.4.1 of RFC8949.

[gabywh]

So this is getting a bit messy with spec in README.md and wiki - one of the reasons I wanted to keep it all in one place and didn't choose for wiki.

Does 9bcbc70 work for you @martin-lindstrom ?

doesn't work for me -> SHOULD -> SHALL

[gabywh]

Decision from eHN meeting 2021-05-07: CBOR timestamp is ISO8601.

[jschlyter]

doesn't work for me -> SHOULD -> SHALL

Was later on fixed in 59ed31c72f06dd4e5278da7ccd038635a3080c17. Complete text for next release is currently as below. Timestamps encoded as defined in RFC 3339, i.e. a profile of ISO8601, something that was already enforced by the JSON schema.

CBOR Encoding

Concise Binary Object Representation (CBOR), specified in RFC7049, defines a number of major data types. The following types are REQUIRED to be used by parties creating electronic health certificates payloads:

• Integers are encoded as CBOR major type 0, an unsigned integer.
• Strings are encoded as CBOR major type 3, a text string.
• Arrays are encoded as CBOR major type 4, an array of data items.
• Objects are encoded as CBOR major type 5, a map of pairs of data items.

Timestamps (defined by JSON type string and format date-time) MUST be encoded as CBOR major type 3, a text string, and formatted per RFC 3339, section 5.6, with tag 0 as specified by RFC 8949, section 3.4.1.