BuyName
Msg
现在来定义购买域名的Msg，并加在./x/nameservice/msgs.go文件中。代码同SetName非常相似：
// MsgBuyName defines the BuyName message
type MsgBuyName struct {
Name string
Bid sdk.Coins
Buyer sdk.AccAddress
}
// NewMsgBuyName is the constructor function for MsgBuyName
func NewMsgBuyName(name string, bid sdk.Coins, buyer sdk.AccAddress) MsgBuyName {
return MsgBuyName{
Name: name,
Bid: bid,
Buyer: buyer,
}
}
// Route should return the name of the module
func (msg MsgBuyName) Route() string { return "nameservice" }
// Type should return the action
func (msg MsgBuyName) Type() string { return "buy_name" }
// ValidateBasic runs stateless checks on the message
func (msg MsgBuyName) ValidateBasic() sdk.Error {
if msg.Buyer.Empty() {
return sdk.ErrInvalidAddress(msg.Buyer.String())
}
if len(msg.Name) == 0 {
return sdk.ErrUnknownRequest("Name cannot be empty")
}
if !msg.Bid.IsAllPositive() {
return sdk.ErrInsufficientCoins("Bids must be positive")
}
return nil
}
// GetSignBytes encodes the message for signing
func (msg MsgBuyName) GetSignBytes() []byte {
b, err := json.Marshal(msg)
if err != nil {
panic(err)
}
return sdk.MustSortJSON(b)
}
// GetSigners defines whose signature is required
func (msg MsgBuyName) GetSigners() []sdk.AccAddress {
return []sdk.AccAddress{msg.Buyer}
}
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接着，在./x/nameservice/handler.go文件中，把MsgBuyName加入到模块路由器中：
// NewHandler returns a handler for "nameservice" type messages.
func NewHandler(keeper Keeper) sdk.Handler {
return func(ctx sdk.Context, msg sdk.Msg) sdk.Result {
switch msg := msg.(type) {
case MsgSetName:
return handleMsgSetName(ctx, keeper, msg)
case MsgBuyName:
return handleMsgBuyName(ctx, keeper, msg)
default:
errMsg := fmt.Sprintf("Unrecognized nameservice Msg type: %v", msg.Type())
return sdk.ErrUnknownRequest(errMsg).Result()
}
}
}
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最后，定义BuyName的handler，该函数执行由msg触发的状态转换。请记住，此时msg已运行其ValidateBasic函数，因此已进行了一些输入验证。但是，ValidateBasic无法查询应用程序状态。应在handler中执行依赖于网络状态（例如帐户余额）的验证逻辑。
// Handle a message to buy name
func handleMsgBuyName(ctx sdk.Context, keeper Keeper, msg MsgBuyName) sdk.Result {
if keeper.GetPrice(ctx, msg.Name).IsAllGT(msg.Bid) { // Checks if the the bid price is greater than the price paid by the current owner
return sdk.ErrInsufficientCoins("Bid not high enough").Result() // If not, throw an error
}
if keeper.HasOwner(ctx, msg.Name) {
_, err := keeper.coinKeeper.SendCoins(ctx, msg.Buyer, keeper.GetOwner(ctx, msg.Name), msg.Bid)
if err != nil {
return sdk.ErrInsufficientCoins("Buyer does not have enough coins").Result()
}
} else {
_, _, err := keeper.coinKeeper.SubtractCoins(ctx, msg.Buyer, msg.Bid) // If so, deduct the Bid amount from the sender
if err != nil {
return sdk.ErrInsufficientCoins("Buyer does not have enough coins").Result()
}
}
keeper.SetOwner(ctx, msg.Name, msg.Buyer)
keeper.SetPrice(ctx, msg.Name, msg.Bid)
return sdk.Result{}
}
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首先确保出价高于当前价格。然后，检查域名是否已有所有者。如果有，之前的所有者将会收到Buyer的钱。
如果没有所有者，你的nameservice模块会把Buyer的资金“燃烧”（即发送到不可恢复的地址）。
如果SubtractCoins或SendCoins返回一个非空错误，handler会抛出一个错误，回退状态转变。没有的话，使用之前在Keeper上定义的 getter 和 setter，handler 将买方设置为新所有者，并将新价格设置为当前出价。
注意：此handler使用
coinKeeper中的函数执行货币相关操作。如果你的应用程序正在执行货币相关操作，你可能需要查看此模块的文档，以查看它提供的功能。