将 JSON 解码为接口值

Question

由于 encoding/json 需要一个非 nil 接口来解组：我如何可靠地制作用户提供的指针类型的（完整）副本，将其存储在我的User接口中，然后 JSON 解码为该临时？

注意：这里的目标是实现“无人值守”——即从 Redis/BoltDB 中提取字节，解码为接口类型，然后检查GetID()接口定义的方法是否返回非空字符串，以及请求中间件。

游乐场：http : //play.golang.org/p/rYODiNrfWw

package main

import (

    "bytes"

    "encoding/json"

    "fmt"

    "log"

    "net/http"

    "os"

    "time"

)

type session struct {

    ID      string

    User    User

    Expires int64

}

type User interface {

    GetID() string

}

type LocalUser struct {

    ID      string

    Name    string

    Created time.Time

}

func (u *LocalUser) GetID() string {

    return u.ID

}

type Auth struct {

    key []byte

    // We store an instance of userType here so we can unmarshal into it when

    // deserializing from JSON (or other non-gob decoders) into *session.User.

    // Attempting to unmarshal into a nil session.User would otherwise fail.

    // We do this so we can unmarshal from our data-store per-request *without

    // the package user having to do so manually* in the HTTP middleware. We can't

    // rely on the user passing in an fresh instance of their User satisfying type.

    userType User

}

func main() {

    // auth is a pointer to avoid copying the struct per-request: although small

    // here, it contains a 32-byte key, options fields, etc. outside of this example.

    var auth = &Auth{key: []byte("abc")}

    local := &LocalUser{"19313", "Matt", time.Now()}

    b, _, _, err := auth.SetUser(local)

    if err != nil {

        log.Fatalf("SetUser: %v", err)

    }

    user, err := auth.GetUser(b)

    if err != nil {

        log.Fatalf("GetUser: %#v", err)

    }

    fmt.Fprintf(os.Stdout, "%v\n", user)

}

Answer 1

如果您需要深度复制接口，请将该方法添加到您的接口中。type User interface {  GetID() string  Copy() User}type LocalUser struct {  ID string  Name string  Created time.Time}// Copy receives a copy of LocalUser and returns a pointer to it.func (u LocalUser) Copy() User {  return &u}

Answer 2

因为应用程序将解码为 aUser并且 JSON 解码器的参数必须是指针值，所以我们可以假设User值是指针值。鉴于此假设，以下代码可用于为解码创建新的零值：uzero := reflect.New(reflect.TypeOf(u).Elem()).Interface().(User)