feat: implement nft module query server (cosmos#10462)

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## Description

QueryServer implementation and corresponding keeper methods,refer cosmos#9826

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---

### Author Checklist

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please add links to any relevant follow up issues.*

I have...

- [ ] included the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] added `!` to the type prefix if API or client breaking change
- [ ] targeted the correct branch (see [PR Targeting](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#pr-targeting))
- [ ] provided a link to the relevant issue or specification
- [ ] followed the guidelines for [building modules](https://github.com/cosmos/cosmos-sdk/blob/master/docs/building-modules)
- [ ] included the necessary unit and integration [tests](https://github.com/cosmos/cosmos-sdk/blob/master/CONTRIBUTING.md#testing)
- [ ] added a changelog entry to `CHANGELOG.md`
- [ ] included comments for [documenting Go code](https://blog.golang.org/godoc)
- [ ] updated the relevant documentation or specification
- [ ] reviewed "Files changed" and left comments if necessary
- [ ] confirmed all CI checks have passed

### Reviewers Checklist

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your handle next to the items reviewed if you only reviewed selected items.*

I have...

- [ ] confirmed the correct [type prefix](https://github.com/commitizen/conventional-commit-types/blob/v3.0.0/index.json) in the PR title
- [ ] confirmed `!` in the type prefix if API or client breaking change
- [ ] confirmed all author checklist items have been addressed 
- [ ] reviewed state machine logic
- [ ] reviewed API design and naming
- [ ] reviewed documentation is accurate
- [ ] reviewed tests and test coverage
- [ ] manually tested (if applicable)

x/nft/errors.go

@@ -12,4 +12,5 @@ var (
 	ErrNFTExists      = sdkerrors.Register(ModuleName, 5, "nft already exist")
 	ErrNFTNotExists   = sdkerrors.Register(ModuleName, 6, "nft does not exist")
 	ErrInvalidID      = sdkerrors.Register(ModuleName, 7, "invalid id")
+	ErrInvalidClassID = sdkerrors.Register(ModuleName, 8, "invalid class id")
 )

x/nft/keeper/grpc_query.go

@@ -0,0 +1,192 @@
+package keeper
+
+import (
+	"context"
+
+	"github.com/cosmos/cosmos-sdk/store/prefix"
+	sdk "github.com/cosmos/cosmos-sdk/types"
+	sdkerrors "github.com/cosmos/cosmos-sdk/types/errors"
+	"github.com/cosmos/cosmos-sdk/types/query"
+	"github.com/cosmos/cosmos-sdk/x/nft"
+)
+
+var _ nft.QueryServer = Keeper{}
+
+// Balance return the number of NFTs of a given class owned by the owner, same as balanceOf in ERC721
+func (k Keeper) Balance(goCtx context.Context, r *nft.QueryBalanceRequest) (*nft.QueryBalanceResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	if err := nft.ValidateClassID(r.ClassId); err != nil {
+		return nil, err
+	}
+
+	owner, err := sdk.AccAddressFromBech32(r.Owner)
+	if err != nil {
+		return nil, err
+	}
+
+	ctx := sdk.UnwrapSDKContext(goCtx)
+	balance := k.GetBalance(ctx, r.ClassId, owner)
+	return &nft.QueryBalanceResponse{Amount: balance}, nil
+}
+
+// Owner return the owner of the NFT based on its class and id, same as ownerOf in ERC721
+func (k Keeper) Owner(goCtx context.Context, r *nft.QueryOwnerRequest) (*nft.QueryOwnerResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	if err := nft.ValidateClassID(r.ClassId); err != nil {
+		return nil, err
+	}
+
+	if err := nft.ValidateNFTID(r.Id); err != nil {
+		return nil, err
+	}
+
+	ctx := sdk.UnwrapSDKContext(goCtx)
+	owner := k.GetOwner(ctx, r.ClassId, r.Id)
+	return &nft.QueryOwnerResponse{Owner: owner.String()}, nil
+}
+
+// Supply return the number of NFTs from the given class, same as totalSupply of ERC721.
+func (k Keeper) Supply(goCtx context.Context, r *nft.QuerySupplyRequest) (*nft.QuerySupplyResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	if err := nft.ValidateClassID(r.ClassId); err != nil {
+		return nil, err
+	}
+	ctx := sdk.UnwrapSDKContext(goCtx)
+	supply := k.GetTotalSupply(ctx, r.ClassId)
+	return &nft.QuerySupplyResponse{Amount: supply}, nil
+}
+
+// NFTsOfClass return all NFTs of a given class or optional owner, similar to tokenByIndex in ERC721Enumerable
+func (k Keeper) NFTsOfClass(goCtx context.Context, r *nft.QueryNFTsOfClassRequest) (*nft.QueryNFTsOfClassResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	if err := nft.ValidateClassID(r.ClassId); err != nil {
+		return nil, err
+	}
+
+	var nfts []*nft.NFT
+	ctx := sdk.UnwrapSDKContext(goCtx)
+
+	// if owner is not empty, filter nft by owner
+	if len(r.Owner) > 0 {
+		owner, err := sdk.AccAddressFromBech32(r.Owner)
+		if err != nil {
+			return nil, err
+		}
+
+		ownerStore := k.getClassStoreByOwner(ctx, owner, r.ClassId)
+		pageRes, err := query.Paginate(ownerStore, r.Pagination, func(key []byte, _ []byte) error {
+			nft, has := k.GetNFT(ctx, r.ClassId, string(key))
+			if has {
+				nfts = append(nfts, &nft)
+			}
+			return nil
+		})
+
+		if err != nil {
+			return nil, err
+		}
+		return &nft.QueryNFTsOfClassResponse{
+			Nfts:       nfts,
+			Pagination: pageRes,
+		}, nil
+	}
+
+	nftStore := k.getNFTStore(ctx, r.ClassId)
+	pageRes, err := query.Paginate(nftStore, r.Pagination, func(_ []byte, value []byte) error {
+		var nft nft.NFT
+		if err := k.cdc.Unmarshal(value, &nft); err != nil {
+			return err
+		}
+		nfts = append(nfts, &nft)
+		return nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+	return &nft.QueryNFTsOfClassResponse{
+		Nfts:       nfts,
+		Pagination: pageRes,
+	}, nil
+}
+
+// NFT return an NFT based on its class and id.
+func (k Keeper) NFT(goCtx context.Context, r *nft.QueryNFTRequest) (*nft.QueryNFTResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	if err := nft.ValidateClassID(r.ClassId); err != nil {
+		return nil, err
+	}
+	if err := nft.ValidateNFTID(r.Id); err != nil {
+		return nil, err
+	}
+
+	ctx := sdk.UnwrapSDKContext(goCtx)
+	n, has := k.GetNFT(ctx, r.ClassId, r.Id)
+	if !has {
+		return nil, sdkerrors.Wrapf(nft.ErrNFTNotExists, "not found nft: class: %s, id: %s", r.ClassId, r.Id)
+	}
+	return &nft.QueryNFTResponse{Nft: &n}, nil
+
+}
+
+// Class return an NFT class based on its id
+func (k Keeper) Class(goCtx context.Context, r *nft.QueryClassRequest) (*nft.QueryClassResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	if err := nft.ValidateClassID(r.ClassId); err != nil {
+		return nil, err
+	}
+
+	ctx := sdk.UnwrapSDKContext(goCtx)
+	class, has := k.GetClass(ctx, r.ClassId)
+	if !has {
+		return nil, sdkerrors.Wrapf(nft.ErrClassNotExists, "not found class: %s", r.ClassId)
+	}
+	return &nft.QueryClassResponse{Class: &class}, nil
+}
+
+// Classes return all NFT classes
+func (k Keeper) Classes(goCtx context.Context, r *nft.QueryClassesRequest) (*nft.QueryClassesResponse, error) {
+	if r == nil {
+		return nil, sdkerrors.Wrap(sdkerrors.ErrInvalidRequest, "empty request")
+	}
+
+	ctx := sdk.UnwrapSDKContext(goCtx)
+	store := ctx.KVStore(k.storeKey)
+	classStore := prefix.NewStore(store, ClassKey)
+
+	var classes []*nft.Class
+	pageRes, err := query.Paginate(classStore, r.Pagination, func(_ []byte, value []byte) error {
+		var class nft.Class
+		if err := k.cdc.Unmarshal(value, &class); err != nil {
+			return err
+		}
+		classes = append(classes, &class)
+		return nil
+	})
+
+	if err != nil {
+		return nil, err
+	}
+	return &nft.QueryClassesResponse{
+		Classes:    classes,
+		Pagination: pageRes,
+	}, nil
+}