c# - 如何使用 PipeReader 读取 JSON 平面文件？

Question

我正在尝试学习这个新的 system.io.pipelines，以及用于反序列化 json 的新 webapi 策略...

我编写了自己的 JsonConverter，但我无法找出从 json 平面文件固定装置初始化 Utf9JsonReader 的正确方法。

这是测试:

    [Fact]
    public void WhenGivenJsonObjectThenEntityDTOReturned() {
                    
        using(var stream = new FileStream("Fixtures/BookStoreJson.json", FileMode.Open))
        {
            var pipe = PipeReader.Create(stream);
            ReadResult bytes;
            pipe.TryRead(out bytes);
            var reader = new Utf8JsonReader(bytes.Buffer);
            var target = new EntityDTOConverter();
            reader.Read();
            var actual = target.Read(ref reader, typeof(EntityDTO), new JsonSerializerOptions());
            
            Assert.True(actual.Props.ContainsKey("name"));
        }
    

    }

当我调试此问题时，bytes.buffer 设置为 0 字节，即使 BookStoreJson.json 文件包含以下内容:

{
    "name": "Tattered Cover",
    "store":{
       "book":[
          {
             "category":"reference",
             "author":"Nigel Rees",
             "title":"Sayings of the Century",
             "price":8.95
          },
          {
             "category":"fiction",
             "author":"Evelyn Waugh",
             "title":"Sword of Honour",
             "price":12.99
          },
          {
             "category":"fiction",
             "author":"J. R. R. Tolkien",
             "title":"The Lord of the Rings",
             "isbn":"0-395-19395-8",
             "price":22.99
          }
       ],
       "bicycle":{
          "color":"red",
          "price":19.95
       }
    }
 }

Answer 1

抱歉，我没有意识到异步过程，我正在从控制台应用程序进行测试。除了不确定这个答案会对您有多大帮助之外，基本上您可以通过访问结果来运行同步异步任务。缓冲区大小也有限制，如果 json 文件大小较大，您可能需要创建自定义池并使用 AdvanceTo 选项读取缓冲区末尾以获取流。

using System;
using System.Buffers;
using System.IO;
using System.IO.Pipelines;
using System.Text;
using System.Text.Json;
using System.Threading.Tasks;
using Xunit;
 

            public class Person
            {
                public string Email { get; set; }
                public bool Active { get; set; }
                public string CreatedDate { get; set; }
                public string[] Roles { get; set; }
            }
    
            [Fact]
            public void WhenGivenJsonObjectThenEntityDTOReturned()
            {
                //{
                //    "Email": "<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="8ce6ede1e9ffcce9f4ede1fce0e9a2efe3e1" rel="noreferrer noopener nofollow">[email protected]</a>",
                //    "Active": true,
                //    "CreatedDate": "2013-01-20T00: 00: 00Z",
                //    "Roles": [
                //    "User",
                //    "Admin"
                //    ]
                //}
    
                using (var stream = new FileStream(@"c:\temp\json.json", FileMode.Open))
                {
                    var reader = PipeReader.Create(stream, 
                        new StreamPipeReaderOptions(bufferSize:4096 *2));
    
                    ValueTask<ReadResult> readResult = reader.ReadAsync();
                    ReadOnlySequence<byte> buffer = readResult.Result.Buffer;
                    Assert.True(readResult.IsCompleted);
                    var jsonStreamReader = new Utf8JsonReader(buffer);
                    var expectedJson = JsonSerializer
                        .Deserialize<Person>(Encoding.UTF8.GetString(buffer.ToArray()));
                    Assert.Equal("<a href="https://stackoverflow.com/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="fd979c90988ebd98859c908d9198d39e9290" rel="noreferrer noopener nofollow">[email protected]</a>", expectedJson.Email);
                }
            }