keep the balance query endpoint compatible with legacy blocks

Closes: cosmos#13296

A temporary solution before the proxy tool developed, since the balance endpoint is too important.

CHANGELOG.md

@@ -85,6 +85,7 @@ Ref: https://keepachangelog.com/en/1.0.0/
 * [#13178](https://github.com/cosmos/cosmos-sdk/pull/13178) Add `cosmos.msg.v1.service` protobuf annotation to allow tooling to distinguish between Msg and Query services via reflection. 
 * [#13233](https://github.com/cosmos/cosmos-sdk/pull/13233) Add `--append` to `add-genesis-account` sub-command to append new tokens after an account is already created.
 * [#13236](https://github.com/cosmos/cosmos-sdk/pull/13236) Integrate Filter Logging
+* [#]() Keep the balance query endpoint compatible with legacy blocks
 
 ### State Machine Breaking
 

x/bank/keeper/grpc_query.go

@@ -62,11 +62,12 @@ func (k BaseKeeper) AllBalances(ctx context.Context, req *types.QueryAllBalances
 	accountStore := k.getAccountStore(sdkCtx, addr)
 
 	pageRes, err := query.Paginate(accountStore, req.Pagination, func(key, value []byte) error {
-		var amount math.Int
-		if err := amount.Unmarshal(value); err != nil {
+		denom := string(key)
+		balance, err := UnmarshalBalanceCompat(k.cdc, value, denom)
+		if err != nil {
 			return err
 		}
-		balances = append(balances, sdk.NewCoin(string(key), amount))
+		balances = append(balances, balance)
 		return nil
 	})
 	if err != nil {

x/bank/keeper/view.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 
 	"cosmossdk.io/math"
+
 	"github.com/tendermint/tendermint/libs/log"
 
 	"github.com/cosmos/cosmos-sdk/codec"
@@ -100,17 +101,13 @@ func (k BaseViewKeeper) GetAccountsBalances(ctx sdk.Context) []types.Balance {
 // by address.
 func (k BaseViewKeeper) GetBalance(ctx sdk.Context, addr sdk.AccAddress, denom string) sdk.Coin {
 	accountStore := k.getAccountStore(ctx, addr)
-	amount := math.ZeroInt()
 	bz := accountStore.Get([]byte(denom))
-	if bz == nil {
-		return sdk.NewCoin(denom, amount)
-	}
-
-	if err := amount.Unmarshal(bz); err != nil {
+	balance, err := UnmarshalBalanceCompat(k.cdc, bz, denom)
+	if err != nil {
 		panic(err)
 	}
 
-	return sdk.NewCoin(denom, amount)
+	return balance
 }
 
 // IterateAccountBalances iterates over the balances of a single account and
@@ -123,12 +120,13 @@ func (k BaseViewKeeper) IterateAccountBalances(ctx sdk.Context, addr sdk.AccAddr
 	defer iterator.Close()
 
 	for ; iterator.Valid(); iterator.Next() {
-		var amount math.Int
-		if err := amount.Unmarshal(iterator.Value()); err != nil {
+		denom := string(iterator.Key())
+		balance, err := UnmarshalBalanceCompat(k.cdc, iterator.Value(), denom)
+		if err != nil {
 			panic(err)
 		}
 
-		if cb(sdk.NewCoin(string(iterator.Key()), amount)) {
+		if cb(balance) {
 			break
 		}
 	}
@@ -153,12 +151,12 @@ func (k BaseViewKeeper) IterateAllBalances(ctx sdk.Context, cb func(sdk.AccAddre
 			panic(err)
 		}
 
-		var amount math.Int
-		if err := amount.Unmarshal(iterator.Value()); err != nil {
+		balance, err := UnmarshalBalanceCompat(k.cdc, iterator.Value(), denom)
+		if err != nil {
 			panic(err)
 		}
 
-		if cb(address, sdk.NewCoin(denom, amount)) {
+		if cb(address, balance) {
 			break
 		}
 	}
@@ -252,3 +250,23 @@ func (k BaseViewKeeper) getAccountStore(ctx sdk.Context, addr sdk.AccAddress) pr
 func (k BaseViewKeeper) getDenomAddressPrefixStore(ctx sdk.Context, denom string) prefix.Store {
 	return prefix.NewStore(ctx.KVStore(k.storeKey), types.CreateDenomAddressPrefix(denom))
 }
+
+// UnmarshalBalanceCompat unmarshal sdk.Coin from storage, it's backward-compatible with the legacy format.
+func UnmarshalBalanceCompat(cdc codec.BinaryCodec, bz []byte, denom string) (sdk.Coin, error) {
+	amount := math.ZeroInt()
+	if bz == nil {
+		return sdk.NewCoin(denom, amount), nil
+	}
+
+	if err := amount.Unmarshal(bz); err != nil {
+		// try to unmarshal with the legacy format.
+		var balance sdk.Coin
+		if cdc.Unmarshal(bz, &balance) != nil {
+			// return with the original error
+			return sdk.Coin{}, err
+		}
+		return balance, nil
+	}
+
+	return sdk.NewCoin(denom, amount), nil
+}