config: backport the rename of fastsync to blocksync (#9259)

This is largely a cherry pick of #6755 with some additional fixups added where detected. 
This change moves the blockchain package to a package called blocksync. Additionally, it renames the relevant uses of the term `fastsync` to `blocksync`.

closes: #9227 

#### PR checklist

- [ ] Tests written/updated, or no tests needed
- [x] `CHANGELOG_PENDING.md` updated, or no changelog entry needed
- [x] Updated relevant documentation (`docs/`) and code comments, or no
      documentation updates needed

blocksync/msgs.go

@@ -0,0 +1,110 @@
+package blocksync
+
+import (
+	"errors"
+	"fmt"
+
+	"github.com/gogo/protobuf/proto"
+
+	bcproto "github.com/tendermint/tendermint/proto/tendermint/blocksync"
+	"github.com/tendermint/tendermint/types"
+)
+
+const (
+	// NOTE: keep up to date with bcproto.BlockResponse
+	BlockResponseMessagePrefixSize   = 4
+	BlockResponseMessageFieldKeySize = 1
+	MaxMsgSize                       = types.MaxBlockSizeBytes +
+		BlockResponseMessagePrefixSize +
+		BlockResponseMessageFieldKeySize
+)
+
+// EncodeMsg encodes a Protobuf message
+func EncodeMsg(pb proto.Message) ([]byte, error) {
+	msg := bcproto.Message{}
+
+	switch pb := pb.(type) {
+	case *bcproto.BlockRequest:
+		msg.Sum = &bcproto.Message_BlockRequest{BlockRequest: pb}
+	case *bcproto.BlockResponse:
+		msg.Sum = &bcproto.Message_BlockResponse{BlockResponse: pb}
+	case *bcproto.NoBlockResponse:
+		msg.Sum = &bcproto.Message_NoBlockResponse{NoBlockResponse: pb}
+	case *bcproto.StatusRequest:
+		msg.Sum = &bcproto.Message_StatusRequest{StatusRequest: pb}
+	case *bcproto.StatusResponse:
+		msg.Sum = &bcproto.Message_StatusResponse{StatusResponse: pb}
+	default:
+		return nil, fmt.Errorf("unknown message type %T", pb)
+	}
+
+	bz, err := proto.Marshal(&msg)
+	if err != nil {
+		return nil, fmt.Errorf("unable to marshal %T: %w", pb, err)
+	}
+
+	return bz, nil
+}
+
+// DecodeMsg decodes a Protobuf message.
+func DecodeMsg(bz []byte) (proto.Message, error) {
+	pb := &bcproto.Message{}
+
+	err := proto.Unmarshal(bz, pb)
+	if err != nil {
+		return nil, err
+	}
+
+	switch msg := pb.Sum.(type) {
+	case *bcproto.Message_BlockRequest:
+		return msg.BlockRequest, nil
+	case *bcproto.Message_BlockResponse:
+		return msg.BlockResponse, nil
+	case *bcproto.Message_NoBlockResponse:
+		return msg.NoBlockResponse, nil
+	case *bcproto.Message_StatusRequest:
+		return msg.StatusRequest, nil
+	case *bcproto.Message_StatusResponse:
+		return msg.StatusResponse, nil
+	default:
+		return nil, fmt.Errorf("unknown message type %T", msg)
+	}
+}
+
+// ValidateMsg validates a message.
+func ValidateMsg(pb proto.Message) error {
+	if pb == nil {
+		return errors.New("message cannot be nil")
+	}
+
+	switch msg := pb.(type) {
+	case *bcproto.BlockRequest:
+		if msg.Height < 0 {
+			return errors.New("negative Height")
+		}
+	case *bcproto.BlockResponse:
+		_, err := types.BlockFromProto(msg.Block)
+		if err != nil {
+			return err
+		}
+	case *bcproto.NoBlockResponse:
+		if msg.Height < 0 {
+			return errors.New("negative Height")
+		}
+	case *bcproto.StatusResponse:
+		if msg.Base < 0 {
+			return errors.New("negative Base")
+		}
+		if msg.Height < 0 {
+			return errors.New("negative Height")
+		}
+		if msg.Base > msg.Height {
+			return fmt.Errorf("base %v cannot be greater than height %v", msg.Base, msg.Height)
+		}
+	case *bcproto.StatusRequest:
+		return nil
+	default:
+		return fmt.Errorf("unknown message type %T", msg)
+	}
+	return nil
+}