Cosmos-sdk: coins exposed to clients should be map instead of array

[fedekunze]

Summary

Expose sdk.Coins as a map[string]sdk.Int instead of a slice of coins ([]sdk.Coin )

Problem Definition

currently sdk.Coins is defined as an array of sdk.Coin instead as a map (object), which makes it harder for clients to lookup a specific denomination since they have to filter the array

Proposal

sdk.Coin should remain as a it is rn, sdk.Coins should be refactored to a map[string]sdk.Int:

Proposed JSON

{
    "uatom": 10000000,
     "photon": 1500000
}

Current JSON

[
    {
        "denom": "uatom",
        "amount": 10000000
    },
   {
        "denom": "photon",
        "amount": 1500000
    }
]

I've experienced this pain point myself on Lunie as well as @sabau, @faboweb and @jbibla

---

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[alexanderbez]

I recall there was a reason we stuck with a slice instead of a map. For starters, maps are non-deterministic. So storing them as such may yield different application hashes. Not to mention, I doubt amino can even encode maps?

cc @ValarDragon

[fedekunze]

For starters, maps are non-deterministic.

yeah that's what @alessio told me

[alexanderbez]

Great! Want to close this?

[fedekunze]

oh, no, I meant that I think we should still export the map to clients. Even tho if we keep the slice internally

[alexanderbez]

You mean you want to implement Coins#ToMap? What would this provide? If you want to know if a denom exists or how much of a denom there is, use AmountOf (albeit it's slower).

[fedekunze]

to get the amount for a specific denom (eg uatom), clients need to implement a filter like the following:

const uatoms = coins.filter(coin => coin.denom === `uatom`)

[alexanderbez]

I understand now. What you're suggesting is creating a custom JSON encoder/decoder. However, I don't see anything inherently wrong with needing to filter imho. Now coins won't be a true representation of their internal structure.

[ValarDragon]

Surely theres a standard serializable golang hashmap?

[fedekunze]

I googled this and one of the top results was #553 lol

[fedekunze]

Also ref: https://github.com/cosmos/cosmos-sdk/issues/1273

[alexanderbez]

If you want simple JSON map just for the clients, I think the following will suffice:

types/coin.go

// ----------------------------------------------------------------------------
// Encoding

type CoinJSON map[string]Int

func (coins Coins) MarshalJSON() ([]byte, error) {
    cj := make(CoinJSON)

    for _, c := range coins {
        cj[c.Denom] = c.Amount
    }

    return json.Marshal(cj)
}

func (coins *Coins) UnmarshalJSON(b []byte) error {
    cj := make(CoinJSON)

    if err := json.Unmarshal(b, &cj); err != nil {
        return err
    }

    for denom, amount := range cj {
        (*coins) = append((*coins), NewCoin(denom, amount))
    }

    coins.Sort()
    return nil
}

[sabau]

I think this will make life slightly easier for clients.
We are talking just about REST interfaces or also CLI (if someone want to build some sort of local client that fetch data from CLI)?
RPC seems out of context here right?

[fedekunze]

Just REST would suffice for the scope of this issue I think

[alexanderbez]

With the code I showed above, it's as simple as that. You don't have to change anything else :)

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