> For the complete documentation index, see [llms.txt](https://mikexu.gitbook.io/cosmossdk-in-action/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mikexu.gitbook.io/cosmossdk-in-action/module-create/message-handler-handler/handle.go.md).

# 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。