运行时错误：内存地址无效或零指针取消引用【恐慌服务 54831】

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我目前正在开发一项功能，我将能够看到我关注的用户的所有推文，我正在使用 postman 测试它，但我无法弄清楚问题是什么，我知道这与零或指针引用，但尽管我仔细阅读了代码，但我仍无法弄清楚它。我对 go 还很陌生，这是我学习的第一种使用这种语法和指针的语言，所以如果我没有看到明显的东西，我提前道歉。 在我的数据库包上

package db

import (
    "context"
    "time"
    "fmt"
    "github.com/jeffersongarcia15/twitter-clone/models"
    "go.mongodb.org/mongo-driver/bson"
)

/*
readfollowerstweets reads the tweets from my followers
*/

func readfollowerstweets(id string, page int) ([]models.returnfollowerstweets, bool) {
    ctx, cancel := context.withtimeout(context.background(), 15*time.second)
    defer cancel()

    db := mongocn.database("twitter")
    col := db.collection("joins")

    skip := (page - 1) * 20

    conditions := make([]bson.m, 0)
    conditions = append(conditions, bson.m{"$match": bson.m{"userid": id}})
    conditions = append(conditions, bson.m{
        "$lookup": bson.m{
            "from":         "tweets",
            "localfield":   "userrelationid",
            "foreignfield": "userid",
            "as":           "tweets",
        }})
    conditions = append(conditions, bson.m{"unwind": "$tweets"}) //allows all the info to be repeated with the same structure for all tweets on same page
    conditions = append(conditions, bson.m{"$sort": bson.m{"date": "desc"}})
    conditions = append(conditions, bson.m{"$skip": skip})
    conditions = append(conditions, bson.m{"$limit": 20})

    cursor, err := col.aggregate(ctx, conditions)
    var result []models.returnfollowerstweets

    err := cursor.all(ctx, &result)
    if err != nil {
        fmt.println(err.error())
        return result, false
    }
    return result, true

}

在路由器上

封装路由器

import (
    "encoding/json"
    "net/http"
    "strconv"
    "github.com/jeffersongarcia15/twitter-clone/db"
)

/*
readfollowerstweets reads the tweets of all our followers
*/

func readfollowerstweets(w http.responsewriter, r *http.request) {
    if len(r.url.query().get("page")) < 1 {
        http.error(w, "you must send a page number", http.statusbadrequest)
        return
    }
    page, err := strconv.atoi(r.url.query().get("page"))
    if err != nil {
        http.error(w, "you must send a page number as an int greater than 0"+err.error(), http.statusbadrequest)
        return
    }
    response, correct := db.readfollowerstweets(iduser, page)
    if !correct {
        http.error(w, "an error occurred when reading the tweets", http.statusbadrequest)
        return
    }
    
    w.header().set("content-type", "application/json")
    w.writeheader(http.statuscreated)
    json.newencoder(w).encode(response)
}

控制台出错

2021/10/04 10:24:46 http: panic serving [::1]:55085: runtime error: invalid memory address or nil pointer dereference
goroutine 164 [running]:
net/http.(*conn).serve.func1()
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:1801 +0xb9
panic({0x14bbac0, 0x1985c40})
        /usr/local/Cellar/go/1.17/libexec/src/runtime/panic.go:1047 +0x266
go.mongodb.org/mongo-driver/mongo.(*Cursor).closeImplicitSession(0x10526ff)
        /Users/jeffersonlopezgarcia/go/pkg/mod/go.mongodb.org/[email protected]/mongo/cursor.go:267 +0x14
panic({0x14bbac0, 0x1985c40})
        /usr/local/Cellar/go/1.17/libexec/src/runtime/panic.go:1038 +0x215
go.mongodb.org/mongo-driver/mongo.(*Cursor).Close(0x0, {0x16755a8, 0xc000416360})
        /Users/jeffersonlopezgarcia/go/pkg/mod/go.mongodb.org/[email protected]/mongo/cursor.go:180 +0x5f
panic({0x14bbac0, 0x1985c40})
        /usr/local/Cellar/go/1.17/libexec/src/runtime/panic.go:1038 +0x215
go.mongodb.org/mongo-driver/mongo.(*Cursor).All(0x0, {0x16755a8, 0xc000416360}, {0x1487380, 0xc00000e600})
        /Users/jeffersonlopezgarcia/go/pkg/mod/go.mongodb.org/[email protected]/mongo/cursor.go:209 +0x1fe
github.com/JeffersonGarcia15/Twitter-Clone/db.ReadFollowersTweets({0xc0000fc0c0, 0x18}, 0x1)
        /Users/jeffersonlopezgarcia/go/src/github.com/JeffersonGarcia15/Twitter-Clone/db/readFollowersTweets.go:41 +0x8c9
github.com/JeffersonGarcia15/Twitter-Clone/routers.ReadFollowersTweets({0x1673cd0, 0xc000588700}, 0xc000684300)
        /Users/jeffersonlopezgarcia/go/src/github.com/JeffersonGarcia15/Twitter-Clone/routers/readFollowersTweets.go:24 +0x10a
net/http.HandlerFunc.ServeHTTP(...)
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:2046
github.com/JeffersonGarcia15/Twitter-Clone/middlew.ValidJWT.func1({0x1673cd0, 0xc000588700}, 0xc000684300)
        /Users/jeffersonlopezgarcia/go/src/github.com/JeffersonGarcia15/Twitter-Clone/middlew/validJWT.go:20 +0xb2
net/http.HandlerFunc.ServeHTTP(...)
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:2046
github.com/JeffersonGarcia15/Twitter-Clone/middlew.CheckDB.func1({0x1673cd0, 0xc000588700}, 0xc00059a600)
        /Users/jeffersonlopezgarcia/go/src/github.com/JeffersonGarcia15/Twitter-Clone/middlew/checkDB.go:18 +0xa9
net/http.HandlerFunc.ServeHTTP(0xc000684200, {0x1673cd0, 0xc000588700}, 0xc0000a2701)
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:2046 +0x2f
github.com/gorilla/mux.(*Router).ServeHTTP(0xc0004ba240, {0x1673cd0, 0xc000588700}, 0xc000684100)
        /Users/jeffersonlopezgarcia/go/pkg/mod/github.com/gorilla/[email protected]/mux.go:210 +0x1cf
github.com/rs/cors.(*Cors).Handler.func1({0x1673cd0, 0xc000588700}, 0xc000684100)
        /Users/jeffersonlopezgarcia/go/pkg/mod/github.com/rs/[email protected]/cors.go:219 +0x1bd
net/http.HandlerFunc.ServeHTTP(0xc000559819, {0x1673cd0, 0xc000588700}, 0x106236e)
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:2046 +0x2f
net/http.serverHandler.ServeHTTP({0xc00059a450}, {0x1673cd0, 0xc000588700}, 0xc000684100)
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:2878 +0x43b
net/http.(*conn).serve(0xc00031d4a0, {0x16755e0, 0xc00059a2d0})
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:1929 +0xb08
created by net/http.(*Server).Serve
        /usr/local/Cellar/go/1.17/libexec/src/net/http/server.go:3033 +0x4e8

正确答案

代码中堆栈跟踪的最后一行是：

/users/jeffersonlopezgarcia/go/src/github.com/jeffersongarcia15/twitter-clone/db/readfollowerstweets.go:41

从引用的代码来看，这似乎是：

err := cursor.all(ctx, &result)

让我们看看，这怎么会导致 nil 指针？我们来看看相关部分是在哪里初始化的。

cursor, _ := col.Aggregate(ctx, conditions)

您在这里丢弃了一个错误，因此这很可能是您的原因。 永远不要放弃你的错误，尤其是当某些事情失败并且你无法找出原因时。这应该始终是您要寻找的第一件事。

今天关于《运行时错误：内存地址无效或零指针取消引用【恐慌服务 54831】》的内容就介绍到这里了，是不是学起来一目了然！想要了解更多关于的内容请关注golang学习网公众号！