为 http PostAsync 重用序列化的 StringContent答案

【问题标题】：Re-use of serialized StringContent for http PostAsync为 http PostAsync 重用序列化的 StringContent
【发布时间】：2020-12-06 01:02:52
【问题描述】：

我正在对具有相同内容的不同 URI 进行 2 次 httpclient PostAsync 调用。如果我没有第二次序列化 StringContent，我的异步任务似乎永远不会执行完成。请忽略我没有在异步调用中使用“等待”运算符的事实 - 除非这会以某种方式影响结果。我的理解是它不应该，但显然如果这是错误的，请帮助我的误解？

private static List<string> validPackageType = new List<string>(new string[] { "A", "B", "C"});
private static shipmentValidationURL = "https://shipment.com.au/v1/shipmentvalidation";
private static shipmentURL = "https://shipment.com.au/v1/shipment";

    public void Controller (){
        PostContent();
        logger.Trace("Sleep");
    }

    private async PostContent(){
        var json = JsonConvert.SerializeObject(validPackageType );
        var data = new StringContent(json, Encoding.UTF8, "application/json");
        var datastring = data.ReadAsStringAsync().Result;
        logger.Trace("data:{data}", datastring);
        logger.Trace("Shipment validation Posting to:{shipmentValidationURL}", shipmentValidationURL);
        var response = client.PostAsync(shipmentValidationURL, data);
        var respcontent = response.Result.Content.ReadAsStringAsync().Result;

        if (response.Result.IsSuccessStatusCode != true)
        {
            logger.Error("Validation Error:{errorxml}", respcontent);
            return;
        }
        else 
        {
            logger.Trace("Validation success");
        }

        logger.Trace("Calling Shipment Creation");
        data = new StringContent(json, Encoding.UTF8, "application/json"); //2nd StringContent()
        logger.Trace("data:{data}", datastring);
        var result = client.PostAsync(shipmentURL, data);
        var resultcontent = result.Result.Content.ReadAsStringAsync().Result;
        logger.Trace("Calling Shipment done");
        
        if (result.Result.IsSuccessStatusCode == true)
        {
            logger.Trace("Shipment success");

        }else{
            logger.Trace("Shipment failed");
        }
    }

输出：

The output WITHOUT the 2nd StringContent() call looks like:
11:01:07.1060 TRACE data:"{ A,B,C....}"
11:01:07.1060 TRACE Shipment validation Posting to:"https://shipment.com.au/v1/shipmentvalidation"
11:01:07.4680 TRACE Validation success
11:01:07.4680 TRACE Shipment update Posting to:"https://shipment.com.au/v1/shipment"
11:01:07.4680 TRACE Calling Shipment Creation
11:01:17.4865 TRACE Sleep

However if the 2nd StringContent call is made, it all executes as expected.
11:01:07.1060 TRACE data:"{ A,B,C....}"
11:01:07.1060 TRACE Shipment validation Posting to:"https://shipment.com.au/v1/shipmentvalidation"
11:01:07.4680 TRACE Validation success
11:01:07.4680 TRACE Shipment update Posting to:"https://shipment.com.au/v1/shipment"
11:01:07.4680 TRACE Calling Shipment Creation
11:01:07.1060 TRACE data:"{ A,B,C....}"
11:01:07.4680 TRACE Calling Shipment done
11:01:07.4680 TRACE Shipment success
11:01:17.4865 TRACE Sleep

【问题讨论】：

“除非以某种方式影响结果”您是否尝试等待一切？虽然可能不是你的问题，但不要阻塞异步方法。

标签： c# json asynchronous dotnet-httpclient

【解决方案1】：

显然PostAsync 处理了Content，因此在第一次PostAsync 调用后不再可以使用它。这在多个线程中进行了简要讨论，例如：

我没有深入研究为什么这是最佳行为或最佳实践（除了重新创建内容）。

奇怪的是，Visual Studio 调试器没有在上面提供的示例中发布异常。我摆弄了另一个带有“等待”的版本并强制Task.Wait()，然后那个版本警告我ObjectDisposedException()。我想这是另一个问题...

【讨论】：