public override void OnActionExecuting(ActionExecutingContext context)
{
    //在ASP.NET Core中Request Body是Stream的形式
    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = stream.ReadToEnd();
    _logger.LogDebug("body content:" + body);
    base.OnActionExecuting(context);
}

services.Configure<KestrelServerOptions>(options =>
{
    options.AllowSynchronousIO = true;
});

public override void OnActionExecuting(ActionExecutingContext context)
{
    var syncIOFeature = context.HttpContext.Features.Get<IHttpBodyControlFeature>();
    if (syncIOFeature != null)
    {
        syncIOFeature.AllowSynchronousIO = true;
    }
    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = stream.ReadToEnd();
    _logger.LogDebug("body content:" + body);
    base.OnActionExecuting(context);
}

public override void OnActionExecuting(ActionExecutingContext context)
{
    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = stream.ReadToEndAsync().GetAwaiter().GetResult();
    _logger.LogDebug("body content:" + body);
    base.OnActionExecuting(context);
}

public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = await stream.ReadToEndAsync();
    _logger.LogDebug("body content:" + body);
    await next();
}

public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = await stream.ReadToEndAsync();
    _logger.LogDebug("body content:" + body);

    StreamReader stream2 = new StreamReader(context.HttpContext.Request.Body);
    string body2 = await stream2.ReadToEndAsync();
    _logger.LogDebug("body2 content:" + body2);

    await next();
}

public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = await stream.ReadToEndAsync();
    _logger.LogDebug("body content:" + body);

    //或者使用重置Position的方式 context.HttpContext.Request.Body.Position = 0;
    //如果你確定上次讀取完之后已經(jīng)重置了Position那么這一句可以省略
    context.HttpContext.Request.Body.Seek(0, SeekOrigin.Begin);
    StreamReader stream2 = new StreamReader(context.HttpContext.Request.Body);
    string body2 = await stream2.ReadToEndAsync();
    //用完了我們盡量也重置一下，自己的坑自己填
    context.HttpContext.Request.Body.Seek(0, SeekOrigin.Begin);
    _logger.LogDebug("body2 content:" + body2);

    await next();
}

public override async Task OnActionExecutionAsync(ActionExecutingContext context, ActionExecutionDelegate next)
{
    //操作Request.Body之前加上EnableBuffering即可
    context.HttpContext.Request.EnableBuffering();

    StreamReader stream = new StreamReader(context.HttpContext.Request.Body);
    string body = await stream.ReadToEndAsync();
    _logger.LogDebug("body content:" + body);

    context.HttpContext.Request.Body.Seek(0, SeekOrigin.Begin);
    StreamReader stream2 = new StreamReader(context.HttpContext.Request.Body);
    //注意這里?。?！我已經(jīng)使用了同步讀取的方式
    string body2 = stream2.ReadToEnd();
    context.HttpContext.Request.Body.Seek(0, SeekOrigin.Begin);
    _logger.LogDebug("body2 content:" + body2);

    await next();
}

public override string ReadToEnd()
{
    ThrowIfDisposed();
    CheckAsyncTaskInProgress();
    // 調(diào)用ReadBuffer，然后從charBuffer中提取數(shù)據(jù)。 
    StringBuilder sb = new StringBuilder(_charLen - _charPos);
    do
    {
        //循環(huán)拼接讀取內(nèi)容
        sb.Append(_charBuffer, _charPos, _charLen - _charPos);
        _charPos = _charLen; 
        //讀取buffer，這是核心操作
        ReadBuffer();
    } while (_charLen > 0);
    //返回讀取內(nèi)容
    return sb.ToString();
}

if (_checkPreamble)
{
    //通過這里我們可以知道本質(zhì)就是使用要讀取的Stream里的Read方法
    int len = _stream.Read(_byteBuffer, _bytePos, _byteBuffer.Length - _bytePos);
    if (len == 0)
    {
        if (_byteLen > 0)
        {
            _charLen += _decoder.GetChars(_byteBuffer, 0, _byteLen, _charBuffer, _charLen);
            _bytePos = _byteLen = 0;
        }
        return _charLen;
    }
    _byteLen += len;
}
else
{
    //通過這里我們可以知道本質(zhì)就是使用要讀取的Stream里的Read方法
    _byteLen = _stream.Read(_byteBuffer, 0, _byteBuffer.Length);
    if (_byteLen == 0) 
    {
        return _charLen;
    }
}

public override Task<string> ReadToEndAsync()
{
    if (GetType() != typeof(StreamReader))
    {
        return base.ReadToEndAsync();
    }
    ThrowIfDisposed();
    CheckAsyncTaskInProgress();
    //本質(zhì)是ReadToEndAsyncInternal方法
    Task<string> task = ReadToEndAsyncInternal();
    _asyncReadTask = task;

    return task;
}

private async Task<string> ReadToEndAsyncInternal()
{
    //也是循環(huán)拼接讀取的內(nèi)容
    StringBuilder sb = new StringBuilder(_charLen - _charPos);
    do
    {
        int tmpCharPos = _charPos;
        sb.Append(_charBuffer, tmpCharPos, _charLen - tmpCharPos);
        _charPos = _charLen; 
        //核心操作是ReadBufferAsync方法
        await ReadBufferAsync(CancellationToken.None).ConfigureAwait(false);
    } while (_charLen > 0);
    return sb.ToString();
}

byte[] tmpByteBuffer = _byteBuffer;
//Stream賦值給tmpStream 
Stream tmpStream = _stream;
if (_checkPreamble)
{
    int tmpBytePos = _bytePos;
    //本質(zhì)是調(diào)用Stream的ReadAsync方法
    int len = await tmpStream.ReadAsync(new Memory<byte>(tmpByteBuffer, tmpBytePos, tmpByteBuffer.Length - tmpBytePos), cancellationToken).ConfigureAwait(false);
    if (len == 0)
    {
        if (_byteLen > 0)
        {
            _charLen += _decoder.GetChars(tmpByteBuffer, 0, _byteLen, _charBuffer, _charLen);
            _bytePos = 0; _byteLen = 0;
        }
        return _charLen;
    }
    _byteLen += len;
}
else
{
    //本質(zhì)是調(diào)用Stream的ReadAsync方法
    _byteLen = await tmpStream.ReadAsync(new Memory<byte>(tmpByteBuffer), cancellationToken).ConfigureAwait(false);
    if (_byteLen == 0) 
    {
        return _charLen;
    }
}

public override int Read(byte[] buffer, int offset, int count)
{
    //知道同步讀取Body為啥報(bào)錯(cuò)了吧
    if (!_bodyControl.AllowSynchronousIO)
    {
        throw new InvalidOperationException(CoreStrings.SynchronousReadsDisallowed);
    }
    //本質(zhì)是調(diào)用ReadAsync
    return ReadAsync(buffer, offset, count).GetAwaiter().GetResult();
}

public override ValueTask<int> ReadAsync(Memory<byte> destination, CancellationToken cancellationToken = default)
{
    return ReadAsyncWrapper(destination, cancellationToken);
}

private readonly HttpRequestPipeReader _pipeReader;
private readonly IHttpBodyControlFeature _bodyControl;
public HttpRequestStream(IHttpBodyControlFeature bodyControl, HttpRequestPipeReader pipeReader)
{
    _bodyControl = bodyControl;
    _pipeReader = pipeReader;
}

private readonly HttpRequestStream _request;
public BodyControl(IHttpBodyControlFeature bodyControl, IHttpResponseControl responseControl)
{
    _request = new HttpRequestStream(bodyControl, _requestReader);
}

public void InitializeBodyControl(MessageBody messageBody)
{
    if (_bodyControl == null)
    {
        //這里傳遞的是bodyControl傳遞的是this
        _bodyControl = new BodyControl(bodyControl: this, this);
    }
    (RequestBody, ResponseBody, RequestBodyPipeReader, ResponseBodyPipeWriter) = _bodyControl.Start(messageBody);
    _requestStreamInternal = RequestBody;
    _responseStreamInternal = ResponseBody;
}

internal partial class HttpProtocol : IHttpRequestFeature, 
 IHttpRequestBodyDetectionFeature, 
 IHttpResponseFeature, 
 IHttpResponseBodyFeature, 
 IRequestBodyPipeFeature, 
 IHttpUpgradeFeature, 
 IHttpConnectionFeature, 
 IHttpRequestLifetimeFeature, 
 IHttpRequestIdentifierFeature, 
 IHttpRequestTrailersFeature, 
 IHttpBodyControlFeature, 
 IHttpMaxRequestBodySizeFeature, 
 IEndpointFeature, 
 IRouteValuesFeature 
 { 
     bool IHttpBodyControlFeature.AllowSynchronousIO 
     { 
         get => AllowSynchronousIO; 
         set => AllowSynchronousIO = value; 
     } 
 }

private HttpConnectionContext _context;
//ServiceContext初始化來自HttpConnectionContext 
public ServiceContext ServiceContext => _context.ServiceContext;
protected KestrelServerOptions ServerOptions { get; set; } = default!;
public void Initialize(HttpConnectionContext context)
{
    _context = context;
    //來自ServiceContext
    ServerOptions = ServiceContext.ServerOptions;
    Reset();
    HttpResponseControl = this;
}

public KestrelServerImpl(
   IOptions<KestrelServerOptions> options,
   IEnumerable<IConnectionListenerFactory> transportFactories,
   ILoggerFactory loggerFactory)     
   //注入進(jìn)來的IOptions<KestrelServerOptions>調(diào)用了CreateServiceContext
   : this(transportFactories, null, CreateServiceContext(options, loggerFactory))
{
}

private static ServiceContext CreateServiceContext(IOptions<KestrelServerOptions> options, ILoggerFactory loggerFactory)
{
    //值來自于IOptions<KestrelServerOptions> 
    var serverOptions = options.Value ?? new KestrelServerOptions();
    return new ServiceContext
    {
        Log = trace,
        HttpParser = new HttpParser<Http1ParsingHandler>(trace.IsEnabled(LogLevel.Information)),
        Scheduler = PipeScheduler.ThreadPool,
        SystemClock = heartbeatManager,
        DateHeaderValueManager = dateHeaderValueManager,
        ConnectionManager = connectionManager,
        Heartbeat = heartbeat,
        //賦值操作
        ServerOptions = serverOptions,
    };
}

//不能使用Seek操作
public override bool CanSeek => false;
//允許讀
public override bool CanRead => true;
//不允許寫
public override bool CanWrite => false;
//不能獲取長(zhǎng)度
public override long Length => throw new NotSupportedException();
//不能讀寫Position
public override long Position
{
    get => throw new NotSupportedException();
    set => throw new NotSupportedException();
}
//不能使用Seek方法
public override long Seek(long offset, SeekOrigin origin)
{
    throw new NotSupportedException();
}

/// <summary>
/// 確保Request.Body可以被多次讀取
/// </summary>
/// <param name="request"></param>
public static void EnableBuffering(this HttpRequest request)
{
    BufferingHelper.EnableRewind(request);
}

/// <summary>
/// 確保Request.Body可以被多次讀取
/// </summary>
/// <param name="request"></param>
/// <param name="bufferThreshold">內(nèi)存中用于緩沖流的最大大?。ㄗ止?jié)）。較大的請(qǐng)求主體被寫入磁盤。</param>
/// <param name="bufferLimit">請(qǐng)求正文的最大大?。ㄗ止?jié)）。嘗試讀取超過此限制將導(dǎo)致異常</param>
public static void EnableBuffering(this HttpRequest request, int bufferThreshold, long bufferLimit)
{
    BufferingHelper.EnableRewind(request, bufferThreshold, bufferLimit);
}

//默認(rèn)內(nèi)存中可緩存的大小為30K,超過這個(gè)大小將會(huì)被存儲(chǔ)到磁盤
internal const int DefaultBufferThreshold = 1024 * 30;

/// <summary>
/// 這個(gè)方法也是HttpRequest擴(kuò)展方法
/// </summary>
/// <returns></returns>
public static HttpRequest EnableRewind(this HttpRequest request, int bufferThreshold = DefaultBufferThreshold, long? bufferLimit = null)
{
    if (request == null)
    {
        throw new ArgumentNullException(nameof(request));
    }
    //先獲取Request Body
    var body = request.Body;
    //默認(rèn)情況Body是HttpRequestStream這個(gè)類CanSeek是false所以肯定會(huì)執(zhí)行到if邏輯里面
    if (!body.CanSeek)
    {
        //實(shí)例化了FileBufferingReadStream這個(gè)類，看來這是關(guān)鍵所在
        var fileStream = new FileBufferingReadStream(body, bufferThreshold,bufferLimit,AspNetCoreTempDirectory.TempDirectoryFactory);
        //賦值給Body，也就是說開啟了EnableBuffering之后Request.Body類型將會(huì)是FileBufferingReadStream
        request.Body = fileStream;
        //這里要把fileStream注冊(cè)給Response便于釋放
        request.HttpContext.Response.RegisterForDispose(fileStream);
    }
    return request;
}

public class FileBufferingReadStream : Stream
{
}

/// <summary>
/// 允許讀
/// </summary>
public override bool CanRead
{
    get { return true; }
}
/// <summary>
/// 允許Seek
/// </summary>
public override bool CanSeek
{
    get { return true; }
}
/// <summary>
/// 不允許寫
/// </summary>
public override bool CanWrite
{
    get { return false; }
}
/// <summary>
/// 可以獲取長(zhǎng)度
/// </summary>
public override long Length
{
    get { return _buffer.Length; }
}
/// <summary>
/// 可以讀寫Position
/// </summary>
public override long Position
{
    get { return _buffer.Position; }
    set
    {
        ThrowIfDisposed();
        _buffer.Position = value;
    }
}

public override long Seek(long offset, SeekOrigin origin)
{
    //如果Body已釋放則異常
    ThrowIfDisposed();
    //特殊情況拋出異常
    //_completelyBuffered代表是否完全緩存一定是在原始的HttpRequestStream讀取完成后才置為true
    //出現(xiàn)沒讀取完成但是原始位置信息和當(dāng)前位置信息不一致則直接拋出異常
    if (!_completelyBuffered && origin == SeekOrigin.End)
    {
        throw new NotSupportedException("The content has not been fully buffered yet.");
    }
    else if (!_completelyBuffered && origin == SeekOrigin.Current && offset + Position > Length)
    {
        throw new NotSupportedException("The content has not been fully buffered yet.");
    }
    else if (!_completelyBuffered && origin == SeekOrigin.Begin && offset > Length)
    {
        throw new NotSupportedException("The content has not been fully buffered yet.");
    }
    //充值buffer的Seek
    return _buffer.Seek(offset, origin);
}

private readonly ArrayPool<byte> _bytePool;
private const int _maxRentedBufferSize = 1024 * 1024; //1MB
private Stream _buffer;
public FileBufferingReadStream(int memoryThreshold)
{
    //即使我們?cè)O(shè)置memoryThreshold那么它最大也不能超過1MB否則也會(huì)存儲(chǔ)在磁盤上
    if (memoryThreshold <= _maxRentedBufferSize)
    {
        _rentedBuffer = bytePool.Rent(memoryThreshold);
        _buffer = new MemoryStream(_rentedBuffer);
        _buffer.SetLength(0);
    }
    else
    {
        //超過1M將緩存到磁盤所以僅僅初始化
        _buffer = new MemoryStream();
    }
}

private readonly Stream _inner;
public FileBufferingReadStream(Stream inner)
{
    //接收原始的Request.Body
    _inner = inner;
}
public override int Read(Span<byte> buffer)
{
    ThrowIfDisposed();

    //如果讀取完成過則直接在buffer中獲取信息直接返回
    if (_buffer.Position < _buffer.Length || _completelyBuffered)
    {
        return _buffer.Read(buffer);
    }

    //未讀取完成才會(huì)走到這里
    //_inner正是接收的原始的RequestBody
    //讀取的RequestBody放入buffer中
    var read = _inner.Read(buffer);
    //超過設(shè)定的長(zhǎng)度則會(huì)拋出異常
    if (_bufferLimit.HasValue && _bufferLimit - read < _buffer.Length)
    {
        throw new IOException("Buffer limit exceeded.");
    }
    //如果設(shè)定存儲(chǔ)在內(nèi)存中并且Body長(zhǎng)度大于設(shè)定的可存儲(chǔ)在內(nèi)存中的長(zhǎng)度,則存儲(chǔ)到磁盤中
    if (_inMemory && _memoryThreshold - read < _buffer.Length)
    {
        _inMemory = false;
        //緩存原始的Body流
        var oldBuffer = _buffer;
        //創(chuàng)建緩存文件
        _buffer = CreateTempFile();
        //超過內(nèi)存存儲(chǔ)限制，但是還未寫入過臨時(shí)文件
        if (_rentedBuffer == null)
        {
            oldBuffer.Position = 0;
            var rentedBuffer = _bytePool.Rent(Math.Min((int)oldBuffer.Length, _maxRentedBufferSize));
            try
            {
                //將Body流讀取到緩存文件流中
                var copyRead = oldBuffer.Read(rentedBuffer);
                //判斷是否讀取到結(jié)尾
                while (copyRead > 0)
                {
                    //將oldBuffer寫入到緩存文件流_buffer當(dāng)中
                    _buffer.Write(rentedBuffer.AsSpan(0, copyRead));
                    copyRead = oldBuffer.Read(rentedBuffer);
                }
            }
            finally
            {
                //讀取完成之后歸還臨時(shí)緩沖區(qū)到ArrayPool中
                _bytePool.Return(rentedBuffer);
            }
        }
        else
        {
            
            _buffer.Write(_rentedBuffer.AsSpan(0, (int)oldBuffer.Length));
            _bytePool.Return(_rentedBuffer);
            _rentedBuffer = null;
        }
    }

    //如果讀取RequestBody未到結(jié)尾,則一直寫入到緩存區(qū)
    if (read > 0)
    {
        _buffer.Write(buffer.Slice(0, read));
    }
    else
    {
        //如果已經(jīng)讀取RequestBody完畢，也就是寫入到緩存完畢則更新_completelyBuffered
        //標(biāo)記為以全部讀取RequestBody完成，后續(xù)在讀取RequestBody則直接在_buffer中讀取
        _completelyBuffered = true;
    }
    //返回讀取的byte個(gè)數(shù)用于外部StreamReader判斷讀取是否完成
    return read;
}

private Stream CreateTempFile()
{
    //判斷是否制定過緩存目錄，沒有的話則使用系統(tǒng)臨時(shí)文件目錄
    if (_tempFileDirectory == null)
    {
        Debug.Assert(_tempFileDirectoryAccessor != null);
        _tempFileDirectory = _tempFileDirectoryAccessor();
        Debug.Assert(_tempFileDirectory != null);
    }
    //臨時(shí)文件的完整路徑
    _tempFileName = Path.Combine(_tempFileDirectory, "ASPNETCORE_" + Guid.NewGuid().ToString() + ".tmp");
    //返回臨時(shí)文件的操作流
    return new FileStream(_tempFileName, FileMode.Create, FileAccess.ReadWrite, FileShare.Delete, 1024 * 16,
        FileOptions.Asynchronous | FileOptions.DeleteOnClose | FileOptions.SequentialScan);
}