Golang API遇到奇怪错误：curl和Bruno测试正常但JavaScript fetch无法使用

Golang API遇到奇怪错误：curl和Bruno测试正常但JavaScript fetch无法使用 我是Go语言的新手。我很喜欢Go，但这个问题让我快疯了。

以下是相关的Go代码。它的作用仅仅是发送一个TCP字符串命令。

type CasparRequest struct {
		Command string
	}
	mux.HandleFunc("/casparconnecting", func(w http.ResponseWriter, req *http.Request) {
		enableCors(&w)

		connection, err := amcp.Dial("127.0.0.1:5250")
		if err != nil {

			// log.Fatal(err)

			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)

		}

		if connection == nil {

			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
			w.Write([]byte("Connection has not been established"))
			return
		}
		defer connection.Close()
		var command CasparRequest

		err1 := json.NewDecoder(req.Body).Decode(&command)

		if err1 != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}

		fmt.Println("the command sent", command.Command)

		code, replyData, err := connection.Do(command.Command)

		if err != nil {
			log.Fatal(err)

			w.Header().Set("Content-Type", "application/json")
			w.WriteHeader(http.StatusBadRequest)
		}
		fmt.Println("replyCode", code)
		fmt.Println("replyCode", replyData)

		replyString := fmt.Sprintf("%v", replyData)

		w.Header().Set("Content-Type", "application/json")
		w.WriteHeader(http.StatusOK) // Set your code here, after setting your headers
		w.Write([]byte(replyString))
		// defer c.Close()
	})

以下的curl请求可以正常工作： curl --header "Content-Type: application/json" --request POST --data '{"command":"PLAY 1-1 myfile000.mp4"}' http://localhost:8080/casparconnecting

然而，一旦我从浏览器发起请求，服务器就会发生恐慌（panic）。

const fetched = await fetch("http://localhost:8080/casparconnecting", {
            headers: {
                "Content-Type": "application/json",
            },
            method: "POST",
            body: JSON.stringify({ command: "PLAY 1-1 myfile000.mp4" }),
        });

这是JavaScript POST请求的详细信息：

{
  "args": {}, 
  "data": "{\"command\":\"PLAY 1-1 myfile000.mp4\"}", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Accept": "*/*", 
    "Accept-Encoding": "gzip, deflate, br, zstd", 
    "Accept-Language": "en-GB,en-US;q=0.9,en;q=0.8", 
    "Connection": "keep-alive", 
    "Content-Length": "36", 
    "Content-Type": "application/json", 
    "Host": "localhost:9090", 
    "Origin": "http://localhost:5173", 
    "Referer": "http://localhost:5173/", 
    "Sec-Ch-Ua": "\"Chromium\";v=\"128\", \"Not;A=Brand\";v=\"24\", \"Google Chrome\";v=\"128\"", 
    "Sec-Ch-Ua-Mobile": "?0", 
    "Sec-Ch-Ua-Platform": "\"Linux\"", 
    "Sec-Fetch-Dest": "empty", 
    "Sec-Fetch-Mode": "cors", 
    "Sec-Fetch-Site": "same-site", 
    "User-Agent": "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/128.0.0.0 Safari/537.36"
  }, 
  "json": {
    "command": "PLAY 1-1 myfile000.mp4"
  }, 
  "method": "POST", 
  "origin": "172.17.0.1", 
  "url": "http://localhost:9090/anything"
}

这是curl请求的详细信息：

{
  "args": {}, 
  "data": "{\"command\":\"play 1-1 myfile000.mp4\"}", 
  "files": {}, 
  "form": {}, 
  "headers": {
    "Accept": "*/*", 
    "Content-Length": "36", 
    "Content-Type": "application/json", 
    "Host": "localhost:9090", 
    "User-Agent": "curl/7.81.0"
  }, 
  "json": {
    "command": "play 1-1 myfile000.mp4"
  }, 
  "method": "POST", 
  "origin": "172.17.0.1", 
  "url": "http://localhost:9090/anything"
}

为什么JavaScript请求会在这里导致问题？即使我从浏览器复制请求作为curl命令，它也能工作。但我不明白这怎么会导致后端出错。 以下是我的Go代码失败的方式：

2024/09/04 12:58:22 http: panic serving [::1]:34408: runtime error: invalid memory address or nil pointer dereference goroutine 6 [running]: net/http.(*conn).serve.func1() /usr/local/go/src/net/http/server.go:1898 +0xbe panic({0x6b2360?, 0x93e4f0?}) /usr/local/go/src/runtime/panic.go:770 +0x132 main.main.func3({0x785120, 0xc0000e6620}, 0xc0000ca360) /home/john_doe/repos/basketball-backend-go/main.go:139 +0x7f5 net/http.HandlerFunc.ServeHTTP(0xc0000bab60?, {0x785120?, 0xc0000e6620?}, 0x651dda?) /usr/local/go/src/net/http/server.go:2166 +0x29 net/http.(*ServeMux).ServeHTTP(0x467db9?, {0x785120, 0xc0000e6620}, 0xc0000ca360) /usr/local/go/src/net/http/server.go:2683 +0x1ad net/http.serverHandler.ServeHTTP({0xc0000b8cf0?}, {0x785120?, 0xc0000e6620?}, 0x6?) /usr/local/go/src/net/http/server.go:3137 +0x8e net/http.(*conn).serve(0xc0000fe000, {0x7856b0, 0xc0000b8c00}) /usr/local/go/src/net/http/server.go:2039 +0x5e8 created by net/http.(*Server).Serve in goroutine 1 /usr/local/go/src/net/http/server.go:3285 +0x4b4

请帮帮我。我不明白问题可能出在哪里。