已写入标头.想要用500覆盖状态代码200

Question

这是我的gorilla-websocketwebsocket处理程序：

func wshandler(w http.ResponseWriter, r *http.Request) {
wsupgrader.CheckOrigin = func(r *http.Request) bool {
return true
}
c, err := wsupgrader.Upgrade(w, r, nil)
if err != nil {
fmt.Println(err)
return
}
for {
var m WebsocketGeneralClientMessage
err := c.ReadJSON(&m)
if err != nil {
log.Println(err)
break
}
switch m.Type {
case "register":
err := Register(c, m)
if err != nil {
log.Println(err)
}
}
}
}

根据type，我希望对不同类型的消息做出不同的响应。我只有register型。由于某种原因，Register函数给了我以下错误：

Headers were already written. Wanted to override status code 200 with 500

func Register(c *websocket.Conn, m WebsocketGeneralClientMessage) error {
var d RegisterData
json.Unmarshal(m.Data, &d)
if len(d.Email) < 6 || len(d.Email) > 64 {
_error := "The email length must be between 6 and 64 characters"
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": _error}})
return errors.New(_error)
}
if len(d.Password) < 6 || len(d.Password) > 32 {
_error := "The password length must be between 6 and 64 characters"
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": "The password length must be between 6 and 64 characters"}})
return errors.New(_error)
}
err := checkmail.ValidateFormat(d.Email)
if err != nil {
_error := "The email format is not correct"
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": _error}})
return errors.New(_error)
}
var rawUUID pgtype.UUID
var exists bool
err = Pool.QueryRow(context.Background(), `SELECT EXISTS(SELECT "email" FROM "account" WHERE "email"=$1)`, d.Email).Scan(&exists)
if err != nil {
_error := "An error occured while creating the account. Please send a message in #bugs at our Discord."
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": _error}})
return errors.New(_error)
}
if exists {
_error := "An error occured while creating the account. Please send a message in #bugs at our Discord."
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": _error}})
return errors.New(_error)
}
err = Pool.QueryRow(context.Background(), `INSERT INTO "account" ("email", "password") VALUES($1, $2) RETURNING "uuid"`, d.Email, d.Password).Scan(&rawUUID)
if err != nil {
_error := "An error occured while creating the account. Please send a message in #bugs at our Discord."
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": _error}})
return errors.New(_error)
}
uuid, err := rawUUID.Value()
if err != nil {
_error := "An error occured while saving the account to the database"
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "error", Data: map[string]interface{}{"text": _error}})
return errors.New(_error)
}
c.WriteJSON(WebsocketGeneralServerMessage{Type: "register", Status: "success", Data: map[string]interface{}{"uuid": uuid}})
return nil
}

我知道问题出在var exists bool之后的函数的后半部分，因为我删除了那个部分，程序没有给出错误。可能是什么问题？显然，出现错误是因为我应该覆盖响应，但每个c.WriterJSON都以return结束，所以不应该有任何响应覆盖。

以下是完整的错误：

2020/09/21 13:58:01 [Recovery] 2020/09/21 - 13:58:01 panic recovered:
GET /ws HTTP/1.1
Host: 192.168.0.41
Accept-Encoding: gzip
Connection: Upgrade
Origin: http://192.168.0.41
Sec-Websocket-Key: 9E7mNgJ4qH4VsbWDJuEaWQ==
Sec-Websocket-Version: 13
Upgrade: websocket
User-Agent: okhttp/3.14.4

runtime error: invalid memory address or nil pointer dereference
/usr/local/Cellar/go/1.15/libexec/src/runtime/panic.go:212 (0x104c992)
panicmem: panic(memoryError)
/usr/local/Cellar/go/1.15/libexec/src/runtime/signal_unix.go:720 (0x104c812)
sigpanic: panicmem()
/Users/virtumonde/go/pkg/mod/github.com/jackc/pgx/v4@v4.8.1/pgxpool/pool.go:355 (0x14c21ba)
(*Pool).Acquire: res, err := p.p.Acquire(ctx)
/Users/virtumonde/go/pkg/mod/github.com/jackc/pgx/v4@v4.8.1/pgxpool/pool.go:419 (0x14c2459)
(*Pool).QueryRow: c, err := p.Acquire(ctx)
/Users/virtumonde/Desktop/dev/terminus/terminus-server/ws_routes.go:46 (0x14cfa0b)
Register: err = Pool.QueryRow(context.Background(), `SELECT EXISTS(SELECT "email" FROM "account" WHERE "email"=$1)`, d.Email).Scan(&exists)
/Users/virtumonde/Desktop/dev/terminus/terminus-server/ws.go:34 (0x14cf3e4)
wshandler: err := Register(c, m)
/Users/virtumonde/Desktop/dev/terminus/terminus-server/main.go:44 (0x14d07ea)
main.func1: wshandler(c.Writer, c.Request)
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/context.go:161 (0x13a5eba)
(*Context).Next: c.handlers[c.index](c)
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/recovery.go:83 (0x13b1cc4)
RecoveryWithWriter.func1: c.Next()
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/context.go:161 (0x13a5eba)
(*Context).Next: c.handlers[c.index](c)
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/logger.go:241 (0x13b0dc4)
LoggerWithConfig.func1: c.Next()
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/context.go:161 (0x13a5eba)
(*Context).Next: c.handlers[c.index](c)
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/gin.go:409 (0x13a8c79)
(*Engine).handleHTTPRequest: c.Next()
/Users/virtumonde/go/pkg/mod/github.com/gin-gonic/gin@v1.6.3/gin.go:367 (0x13a84ec)
(*Engine).ServeHTTP: engine.handleHTTPRequest(c)
/usr/local/Cellar/go/1.15/libexec/src/net/http/server.go:2843 (0x12676a2)
serverHandler.ServeHTTP: handler.ServeHTTP(rw, req)
/usr/local/Cellar/go/1.15/libexec/src/net/http/server.go:1925 (0x1263c6c)
(*conn).serve: serverHandler{c.server}.ServeHTTP(w, w.req)
/usr/local/Cellar/go/1.15/libexec/src/runtime/asm_amd64.s:1374 (0x106bb60)
goexit: BYTE    $0x90   // NOP

Answer 1

我发现了问题。我的Pool变量(使用它连接到我的Postgres数据库(

var Pool *pgxpool.Pool

在初始化时被另一个局部变量盖过。

Pool, err := pgxpool.Connect(context.Background(), "postgres://postgres:@localhost:5432/database")

所以我把初始化改为

var err error
Pool, err = pgxpool.Connect(context.Background(), "postgres://postgres:@localhost:5432/database")

显然，由于这个原因，数据库代码执行了不止一次。