使用 golang 和 gorilla websocket 库，为什么 WriteJson return 会出错？

Question

我正在按照此处的说明进行操作：

https://testnet.bitmex.com/app/wsAPI

并且我已经确认以下 Python 实施有效（即我这边没有网络问题等），因为：

python wsdump.py \
  wss://testnet.bitmex.com/realtime

> {"op":"subscribe","args":["orderBookL2_25:XBTUSD"]}

结果

{"success":true,"subscribe":"orderBookL2_25:XBTUSD","request":{"op":"subscribe","args":["orderBookL2_25:XBTUSD"]}}

我已经尝试修改大猩猩示例代码来组合一个基本客户端：

package main

import (
    "encoding/json"
    "flag"
    "fmt"
    "log"
    "net/url"
    "os"
    "os/signal"
    "time"

    "github.com/gorilla/websocket"
)

var addr = flag.String("addr", "testnet.bitmex.com", "http service address")

func main() {
    flag.Parse()
    log.SetFlags(0)

    interrupt := make(chan os.Signal, 1)
    signal.Notify(interrupt, os.Interrupt)

    u := url.URL{Scheme: "wss", Host: *addr, Path: "/realtime"}
    log.Printf("connecting to %s", u.String())

    c, _, err := websocket.DefaultDialer.Dial(u.String(), nil)
    if err != nil {
        log.Fatal("dial:", err)
    }
    defer c.Close()

    done := make(chan struct{})

    go func() {
        defer close(done)
        for {
            _, message, err := c.ReadMessage()
            if err != nil {
                log.Println("read:", err)
                return
            }
            log.Printf("recv: %s", message)
        }
    }()

    type commandStruct struct {
        Op   string   `json:"op"`
        Args []string `json:"args"`
    }
    command := &commandStruct{
        Op:   "subscribe",
        Args: []string{"orderBookL2_25:XBTUSD"}}
    json, _ := json.Marshal(command)
    stringJSON := string(json)
    fmt.Println("JSON:", stringJSON)
    connectionErr := c.WriteJSON(stringJSON)
    if connectionErr != nil {
        log.Println("write:", connectionErr)
    }

    for {
        select {
        case <-done:
            return
        case <-interrupt:
            log.Println("interrupt")

            // Cleanly close the connection by sending a close message and then
            // waiting (with timeout) for the server to close the connection.
            err := c.WriteMessage(websocket.CloseMessage, websocket.FormatCloseMessage(websocket.CloseNormalClosure, ""))
            if err != nil {
                log.Println("write close:", err)
                return
            }
            select {
            case <-done:
            case <-time.After(time.Second):
            }
            return
        }
    }
}

我的程序将以下内容打印到控制台：

{"op":"subscribe","args":["orderBookL2_25:XBTUSD"]}

与上面 Python 示例中的 JSON 相同。但随后我收到一条错误消息：

recv: {"status":400,"error":"Unrecognized request. See the docs or send 'help' for more details.","meta":{},"request":"{\"op\":\"subscribe\",\"args\":[\"orderBookL2_25:XBTUSD\"]}"}

为什么我得到不同的结果？

Answer 1

问题是应用程序将值双重编码为 JSON:

对 json.Marshal(command) 的调用将 command 结构编码为 JSON:

{"op":"subscribe","args":["orderBookL2_25:XBTUSD"]}

调用 c.WriteJSON(stringJSON) 将该文本编码为 JSON 并将其写入网络。双重编码的 JSON 是：

"{\"op\":\"subscribe\",\"args\":[\"orderBookL2_25:XBTUSD\"]}"

请改用以下代码：

connectionErr := c.WriteJSON(command)

Answer 2

我知道这是一个有点老的话题，我的回答并没有直接解决操作员提出的问题，但由于我有一个非常相似的问题，我想提出一个稍微不同的解决方案：

下面可以使用WriteMessage更直接的编码，而不是WriteJSON

  type commandStruct struct {
        Op   string   `json:"op"`
        Args []string `json:"args"`
    }
    command := &commandStruct{
        Op:   "subscribe",
        Args: []string{"orderBookL2_25:XBTUSD"}}
    json, _ := json.Marshal(command)
    stringJSON := string(json)
    fmt.Println("JSON:", stringJSON)
    connectionErr := c.WriteJSON(stringJSON)

使用两层衬垫，如下：

stringJSON := `{"op":"subscribe","args":["orderBookL2_25:XBTUSD"]}`
connectionErr := c.WriteMessage(websocket.TextMessage, []byte(stringJSON))

使用 golang 和 gorilla websocket 库，为什么 WriteJson return 会出错？

Using golang with the gorilla websocket library, why does WriteJson return an error?

go

websocket

gorilla