# handle.go

> Loc: x/stake/handler.go

handler.go是模块逻辑的核心，所有的模块功能都在handler内部实现。

```go
package stake

import (
    "bytes"

    sdk "github.com/cosmos/cosmos-sdk/types"
    abci "github.com/tendermint/abci/types"
)

//nolint
const (
    GasDeclareCandidacy int64 = 20
    GasEditCandidacy    int64 = 20
    GasDelegate         int64 = 20
    GasUnbond           int64 = 20
)

func NewHandler(k Keeper) sdk.Handler {
    return func(ctx sdk.Context, msg sdk.Msg) sdk.Result {
        // NOTE msg already has validate basic run
        switch msg := msg.(type) {
        case MsgDeclareCandidacy:
            return handleMsgDeclareCandidacy(ctx, msg, k)
        case MsgEditCandidacy:
            return handleMsgEditCandidacy(ctx, msg, k)
        case MsgDelegate:
            return handleMsgDelegate(ctx, msg, k)
        case MsgUnbond:
            return handleMsgUnbond(ctx, msg, k)
        default:
            return sdk.ErrTxDecode("invalid message parse in staking module").Result()
        }
    } 
}
```

NewHandler在内部主要实现了根据模块的msg的具体type来返回不同的handler。stake一共有四种message，所以对应了上面四种类型，然后他返回的也是输入为sdk.Context,sdk.Msg,返回为sdk.Result的函数。下面就是具体handler的实现

```go
// now we just perform action and save
func handleMsgDeclareCandidacy(ctx sdk.Context, msg MsgDeclareCandidacy, k Keeper) sdk.Result {

    // check to see if the pubkey or sender has been registered before
    _, found := k.GetCandidate(ctx, msg.CandidateAddr)
    if found {
        return ErrCandidateExistsAddr(k.codespace).Result()
    }
    if msg.Bond.Denom != k.GetParams(ctx).BondDenom {
        return ErrBadBondingDenom(k.codespace).Result()
    }
    if ctx.IsCheckTx() {
        return sdk.Result{
            GasUsed: GasDeclareCandidacy,
        }
    }

    candidate := NewCandidate(msg.CandidateAddr, msg.PubKey, msg.Description)
    k.setCandidate(ctx, candidate)
    tags := sdk.NewTags("action", []byte("declareCandidacy"), "candidate", msg.CandidateAddr.Bytes(), "moniker", []byte(msg.Description.Moniker), "identity", []byte(msg.Description.Identity))

    // move coins from the msg.Address account to a (self-bond) delegator account
    // the candidate account and global shares are updated within here
    delegateTags, err := delegate(ctx, k, msg.CandidateAddr, msg.Bond, candidate)
    if err != nil {
        return err.Result()
    }
    tags = tags.AppendTags(delegateTags)
    return sdk.Result{
        Tags: tags,
    }
}
```

整个handler函数代码，由`IsCheckTx()`分隔，当checktx调用的时候，返回`true`，当是deliverTx调用的时刻，返回`false`。换句话说，`IsCheckTx()`上面部分是checkTx处理的逻辑，用来检查交易的合法性，然后deliverTx处理的逻辑是包含checkTx的，还多加了具体模块的应用逻辑 ，对KVStore进行读写操作。最后就是返回`sdk.Result`。注意每个handler末尾都有Tag，记录handler处理的信息返回给tendermintCore。`sdk.NewTags`的输入是`string`类型然后接`[]bytes`类型，成对出现的变长参数列表。


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://mikexu.gitbook.io/cosmossdk-in-action/module-create/message-handler-handler/handle.go.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.