JSON field ordering

When serializing JSON, monerod has the behavior to order key fields within a scope alphabetically.

For example:

{
  "id": "0",
  "jsonrpc": "2.0",
  "result": {
    "blockhashing_blob": "...",
    "blocktemplate_blob": "...",
    "difficulty": 283305047039,
    "difficulty_top64": 0,
    "expected_reward": 600000000000,
    "height": 3195018,
    "next_seed_hash": "",
    "prev_hash": "9d648e741d85ca0e7acb4501f051b27e9b107d3cd7a3f03aa7f776089117c81a",
    "reserved_offset": 131,
    "seed_hash": "e2aa0b7b55042cd48b02e395d78fa66a29815ccc1584e38db2d1f0e8485cd44f",
    "seed_height": 3194880,
    "status": "OK",
    "untrusted": false,
    "wide_difficulty": "0x41f64bf3ff"
  }
}

In the main {}, id comes before jsonrpc, which comes before result.

The same alphabetical ordering is applied to the fields within result.

Cuprate uses serde for JSON serialization, which serializes fields based on the definition order, i.e. whatever order the fields are defined in the code, is the order they will appear in JSON.

Some struct fields within Cuprate's RPC types happen to be alphabetical, but this is not a guarantee.

As these are JSON maps, the ordering of fields should not matter, although this is something to note as the output will technically differ.

Example incompatibility

An example of where this leads to incompatibility is if specific line numbers are depended on to contain specific fields.

For example, this will print the 10th line:

curl http://127.0.0.1:18081/json_rpc -d '{"jsonrpc":"2.0","id":"0","method":"get_block_template","params":{"wallet_address":"44GBHzv6ZyQdJkjqZje6KLZ3xSyN1hBSFAnLP6EAqJtCRVzMzZmeXTC2AHKDS9aEDTRKmo6a6o9r9j86pYfhCWDkKjbtcns","reserve_size":60}' -H 'Content-Type: application/json' | sed -n 10p

It will be "height": 3195018 in monerod's case, but may not necessarily be for Cuprate.

By all means, this should not be relied upon in the first place, although it is shown as an example.