.NET 5 Azure Functions从HttpRequestData读取multipart/form-data参数报错

• 手动实例化的StreamContent对象未继承原HTTP请求的Content-Type请求头，ReadAsMultipartAsync方法只能从传入的HttpContent对象的头中读取内容类型，不会读取原HttpRequestData的头，因此触发类型校验失败异常
• 现有代码存在语法错误：代码中调用ReadAsMultipartAsync的stream变量未声明，实际声明的变量名为contentStream；方法使用了await关键字但未添加async修饰符
• 流资源释放时机不合理，可能在读取未完成时就释放流导致后续操作异常

需提前安装NuGet包Microsoft.AspNet.WebApi.Client

/* Azure Function, HTTP Trigger, .NET 5 Isolated : Update.cs */
[Function("Update")]
public static async Task<HttpResponseData> Run([HttpTrigger(AuthorizationLevel.Function, "get", "post")]
        HttpRequestData req,
        FunctionContext executionContext)
{
    Dictionary<string, string> formDataDict = new Dictionary<string, string>();
    // 实例化StreamContent并复制原请求的Content-Type头
    using var contentStream = new StreamContent(req.Body);
    if (req.Headers.TryGetValues("Content-Type", out var contentTypeValues))
    {
        contentStream.Headers.TryAddWithoutValidation("Content-Type", contentTypeValues.First());
    }

    // 解析multipart/form-data内容
    var multipartProvider = await contentStream.ReadAsMultipartAsync();
    foreach (var httpContent in multipartProvider.Contents)
    {
        var formData = await httpContent.ReadAsFormDataAsync();
        foreach (string key in formData.AllKeys)
        {
            if (!string.IsNullOrEmpty(key))
            {
                formDataDict.TryAdd(key, formData[key]);
            }
        }
    }

    // 后续业务逻辑，构造返回值示例
    var response = req.CreateResponse(HttpStatusCode.OK);
    await response.WriteAsJsonAsync(new { Success = true, FormData = formDataDict });
    return response;
}

可使用.NET自带的MultipartReader完成解析，仅需引用命名空间Microsoft.AspNetCore.WebUtilities

[Function("Update")]
public static async Task<HttpResponseData> Run([HttpTrigger(AuthorizationLevel.Function, "get", "post")]
        HttpRequestData req,
        FunctionContext executionContext)
{
    Dictionary<string, string> formDataDict = new Dictionary<string, string>();
    var contentType = req.Headers.GetValues("Content-Type").FirstOrDefault();
    var boundary = HeaderUtilities.RemoveQuotes(MediaTypeHeaderValue.Parse(contentType).Boundary).Value;
    var reader = new MultipartReader(boundary, req.Body);

    var section = await reader.ReadNextSectionAsync();
    while (section != null)
    {
        var hasContentDisposition = ContentDispositionHeaderValue.TryParse(section.ContentDisposition, out var contentDisposition);
        if (hasContentDisposition && contentDisposition.IsFormDisposition())
        {
            var key = HeaderUtilities.RemoveQuotes(contentDisposition.Name).Value;
            using var streamReader = new StreamReader(section.Body);
            var value = await streamReader.ReadToEndAsync();
            formDataDict.TryAdd(key, value);
        }
        section = await reader.ReadNextSectionAsync();
    }

    var response = req.CreateResponse(HttpStatusCode.OK);
    await response.WriteAsJsonAsync(new { Success = true, FormData = formDataDict });
    return response;
}

内容的提问来源于stack exchange，提问作者Belle 'Sandon' Ling