Create API address derivation path type.

[jonathanknowles]

Context

We need to be able to represent address derivation paths in the API.

Decision

Create type ApiAddressDerivationPath that can encode an address derivation path.

A derivation path should be serialized to JSON as a list.

For example, the path 1852H/1815H/0H/0/0 should have the following JSON representation:

[
  {
    "derivation_index": 1852,
    "derivation_type": "hardened"
  },
  {
    "derivation_index": 1815,
    "derivation_type": "hardened"
  },
  {
    "derivation_index": 0,
    "derivation_type": "hardened"
  },
  {
    "derivation_index": 0,
    "derivation_type": "soft"
  },
  {
    "derivation_index": 0,
    "derivation_type": "soft"
  }
]

Each entry in the list should have the following pair of fields:

Field name	Type	Domain
derivation_index	natural number	[ 0 .. 2^31 − 1 ]
derivation_type	enumeration	[ hardened | soft ]

Acceptance Criteria

• There must be an ApiAddressDerivation type.
• Values of the ApiAddressDerivation type must be serializable to JSON and deserializable from JSON.
• Deserialization of a previously serialized value must yield the original value.
• The JSON representation of an ApiAddressDerivation value should be a list.

---

Development

• Create API address derivation path type. #2177

QA

See #2177, which includes:

• JSON roundtrip encoding/decoding tests for all types.
• JSON golden tests for all types.
• negative tests for the ApiRelativeAddressIndex type.

[paweljakubas]

I wonder if first three paths, ie., are not superfluous 1852H/1815H/0H. the first two for sure if we are dealing with ada. Last one depicting account maybe also... On the other hand, it is only presentation layer so maybe the full information does not hurt.

Another thing : we want to use relative indexes (counting from 0) also for hardened index?

[rvl]

Was there anything wrong with just using a string to represent derivation path?
It's pretty simple to parse.

[jonathanknowles]

Was there anything wrong with just using a string to represent derivation path?
It's pretty simple to parse.

Hi @rvl.

We could indeed have used a string, and you're right, it would not be very hard to parse.

The use of a JSON list was requested here: https://input-output-rnd.slack.com/archives/GBT05825V/p1600859749018000?thread_ts=1600843830.004300&cid=GBT05825V

[jonathanknowles]

@paweljakubas

Another thing : we want to use relative indexes (counting from 0) also for hardened index?

Good point! I've updated the task description to specify that we will use relative indices, ranging from 0 to 2^31 - 1.

[rvl]

In that slack thread, a JSON list of strings was requested, not a list of objects. I fail to see how a list of objects like this will help the user.

[piotr-iohk]

lgtm