如何写入从 WebRequest.GetRequestStream() 返回的 Stream 对象答案

【问题标题】：How to write to Stream object returned from WebRequest.GetRequestStream()如何写入从 WebRequest.GetRequestStream() 返回的 Stream 对象
【发布时间】：2020-11-18 03:11:10
【问题描述】：

我正在尝试使用 C# 中的 HTTP 请求将 FCM 推送警报发送到 Android 应用程序。我看过一些例子并写了它们作为参考，但我遇到了我没想到的问题。

我得到一个通过HTTP请求返回的数据流，我用Write()方法向它写入数据，但是发生了异常。
这是我的代码。

public void PushNotification()
    {
        const string FCM_URL = "https://fcm.googleapis.com/v1/projects/xxx/messages:send HTTP/1.1";
        const string SERVER_KEY = "xxxxxx";
        const string SENDER_ID = "xxxxx";
        
        string postbody;
        Byte[] byteArr;
        object payload;
        WebRequest wReq;

        wReq = WebRequest.Create(FCM_URL);
        wReq.Method = "post";
        wReq.Headers.Add(string.Format("Autorization:key={0}", SERVER_KEY));
        wReq.Headers.Add(string.Format("Sender:id={0}", SENDER_ID));
        wReq.ContentType = "application/json";

        payload = new
        {
            to = "/topics/all",
            priority = "high",
            content_available = true,
            notification = new
            {
                body = "Test",
                title = "Test",
                badge = 1
            },
            data = new
            {
                key1 = "val1",
                key2 = "val2"
            }
        };

        postbody = JsonConvert.SerializeObject(payload).ToString();
        byteArr = Encoding.UTF8.GetBytes(postbody);
        wReq.ContentLength = byteArr.Length;

        using (Stream dStream = wReq.GetRequestStream())
        {
            dStream.Write(byteArr, 0, byteArr.Length);
            using (WebResponse wResp = wReq.GetResponse()) //Exception: You must write ContentLength bytes to the request stream before calling [Begin]GetResponse.
            {
                using (Stream dStreamResp = wResp.GetResponseStream())
                {
                    if (dStreamResp != null) using (StreamReader wReader = new StreamReader(dStreamResp))
                        {
                            string sRespFromServer = wReader.ReadToEnd();
                        }
                }
            }
        }
    }

我是怎么解决的？？？

【问题讨论】：

标签： c# firebase-cloud-messaging

【解决方案1】：

我认为我犯了一个错误，因为我不熟悉 C#。由于使用了 'using' 关键字，因此流在写入后没有关闭。于是我将代码修改为：

    public void PushData(string messageTitle, string messageText)
    {
        string postbody;
        object payload;
        Byte[] byteArr;

        WebRequest wReq;
        WebResponse wResp;
        Stream dataStream, dataRespStream;
        
        wReq = WebRequest.Create(FCM_ENDPOINT);
        wReq.Method = "POST";
        wReq.Headers.Add(string.Format("Authorization: key={0}", serverApiKey));
        wReq.Headers.Add(string.Format("Sender: id={0}", senderID));
        wReq.ContentType = "application/json";

        payload = new
        {
            to = "/topics/" + _receiverGrpID,
            priority = "high",
            content_available = true,
            data = new
            {
                title = messageTitle,
                body = messageText
            }
        };

        postbody = JsonConvert.SerializeObject(payload).ToString();
        byteArr = Encoding.UTF8.GetBytes(postbody);
        wReq.ContentLength = byteArr.Length;

        dataStream = wReq.GetRequestStream();
        dataStream.Write(byteArr, 0, byteArr.Length);
        dataStream.Close();

        wResp = wReq.GetResponse();
        dataRespStream = wResp.GetResponseStream();
        if(dataRespStream != null)
        {
            StreamReader streamReader = new StreamReader(dataRespStream);
            _respFromFCMServer = streamReader.ReadToEnd();
        }
        dataRespStream.Close();
    }

即使我的请求 URL 有误。这不起作用是很自然的。
解决这些之后，就可以了！

【讨论】：