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EventedStreamReader.cs
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EventedStreamReader.cs
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// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;
using System.Threading;
using System.Threading.Tasks;
namespace Microsoft.AspNetCore.NodeServices.Util
{
/// <summary>
/// Wraps a <see cref="StreamReader"/> to expose an evented API, issuing notifications
/// when the stream emits partial lines, completed lines, or finally closes.
/// </summary>
internal class EventedStreamReader
{
public delegate void OnReceivedChunkHandler(ArraySegment<char> chunk);
public delegate void OnReceivedLineHandler(string line);
public delegate void OnStreamClosedHandler();
public event OnReceivedChunkHandler OnReceivedChunk;
public event OnReceivedLineHandler OnReceivedLine;
public event OnStreamClosedHandler OnStreamClosed;
private readonly StreamReader _streamReader;
private readonly StringBuilder _linesBuffer;
public EventedStreamReader(StreamReader streamReader)
{
_streamReader = streamReader ?? throw new ArgumentNullException(nameof(streamReader));
_linesBuffer = new StringBuilder();
Task.Factory.StartNew(Run);
}
public Task<Match> WaitForMatch(Regex regex)
{
var tcs = new TaskCompletionSource<Match>();
var completionLock = new object();
OnReceivedLineHandler onReceivedLineHandler = null;
OnStreamClosedHandler onStreamClosedHandler = null;
void ResolveIfStillPending(Action applyResolution)
{
lock (completionLock)
{
if (!tcs.Task.IsCompleted)
{
OnReceivedLine -= onReceivedLineHandler;
OnStreamClosed -= onStreamClosedHandler;
applyResolution();
}
}
}
onReceivedLineHandler = line =>
{
var match = regex.Match(line);
if (match.Success)
{
ResolveIfStillPending(() => tcs.SetResult(match));
}
};
onStreamClosedHandler = () =>
{
ResolveIfStillPending(() => tcs.SetException(new EndOfStreamException()));
};
OnReceivedLine += onReceivedLineHandler;
OnStreamClosed += onStreamClosedHandler;
return tcs.Task;
}
private async Task Run()
{
var buf = new char[8 * 1024];
while (true)
{
var chunkLength = await _streamReader.ReadAsync(buf, 0, buf.Length);
if (chunkLength == 0)
{
OnClosed();
break;
}
OnChunk(new ArraySegment<char>(buf, 0, chunkLength));
var lineBreakPos = Array.IndexOf(buf, '\n', 0, chunkLength);
if (lineBreakPos < 0)
{
_linesBuffer.Append(buf, 0, chunkLength);
}
else
{
_linesBuffer.Append(buf, 0, lineBreakPos + 1);
OnCompleteLine(_linesBuffer.ToString());
_linesBuffer.Clear();
_linesBuffer.Append(buf, lineBreakPos + 1, chunkLength - (lineBreakPos + 1));
}
}
}
private void OnChunk(ArraySegment<char> chunk)
{
var dlg = OnReceivedChunk;
dlg?.Invoke(chunk);
}
private void OnCompleteLine(string line)
{
var dlg = OnReceivedLine;
dlg?.Invoke(line);
}
private void OnClosed()
{
var dlg = OnStreamClosed;
dlg?.Invoke();
}
}
}