如何通过Azure函数从Blob存储流式传输二进制文件

问题描述

我正在尝试通过将Azure函数与HTTP触发器结合使用，通过Azure API管理从Blob存储中获取二进制文件。应该如何实施Azure功能以达到最小的内存占用？

此实现有效，但似乎需要大量内存，当处理太多并发请求时，会导致内存不足异常：

public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Function,"get","post",Route = "dbrevisions/{dbRevision}")] HttpRequestMessage request,[Blob("typedatadev/typedata_{dbRevision}.db",FileAccess.Read)] Stream blobStream,string dbRevision,ILogger log)
{
    var memoryBlobStream = new MemoryStream();
    blobStream.copyTo(memoryBlobStream);

    var result = new FileStreamResult(memoryBlobStream,"application/octet-stream");
    result.FileStream.Flush();
    result.FileStream.Seek(0,SeekOrigin.Begin);
    return result;
}

这将最终变为状态502（也没有“冲洗”调用）：

public static async Task<IActionResult> Run(
    [HttpTrigger(AuthorizationLevel.Function,ILogger log)
{
    var result = new FileStreamResult(blobStream,SeekOrigin.Begin);
    return result;
}

这也会失败：

var response = new HttpResponseMessage(HttpStatusCode.OK)
{
    Content = new StreamContent(blobStream)
};
response.Content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/octet-stream");
return response;

解决方法

我想像下面那样将内存占用最小化。请注意，不是绑定到流，而是绑定到ICloudBlob实例（幸运的是，C＃函数支持blob input binding的几种风格）并返回开放流。使用内存分析器对其进行了测试，即使对于较大的Blob，也可以正常工作且没有内存泄漏。

注意：您无需寻求流位置0或刷新或处置（处置将在响应端自动完成）；

using System.IO;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Azure.WebJobs;
using Microsoft.Azure.WebJobs.Extensions.Http;
using Microsoft.AspNetCore.Http;
using Microsoft.Extensions.Logging;
using Microsoft.Azure.Storage.Blob;

namespace TestFunction1
{
   public static class MyFunction
   {
        [FunctionName("MyFunction")]
        public static async Task<IActionResult> Run(
            [HttpTrigger(AuthorizationLevel.Anonymous,"get","post",Route = "dbrevisions/{dbRevision}")] HttpRequest req,[Blob("typedatadev/typedata_{dbRevision}.db",FileAccess.Read,Connection = "BlobConnection")] ICloudBlob blob,string dbRevision,ILogger log)
        {
            var blobStream = await blob.OpenReadAsync().ConfigureAwait(false);
            return new FileStreamResult(blobStream,"application/octet-stream");
        }
   }
}