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EricRosenfeld1 · Sep 13, 2019 · 69c82ba · 69c82ba
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diff --git a/.gitignore b/.gitignore
@@ -0,0 +1,5 @@
+.vs/
+bin/
+obj/
+*.user
+samples/Sample.WebAssembly/wwwroot/_content/
diff --git a/BlazorInputFile.sln b/BlazorInputFile.sln
@@ -0,0 +1,86 @@
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diff --git a/BlazorInputFile/BlazorInputFile.csproj b/BlazorInputFile/BlazorInputFile.csproj
@@ -0,0 +1,16 @@
+<Project Sdk="Microsoft.NET.Sdk.Razor">
+
+  <PropertyGroup>
+    <TargetFrameworks>netstandard2.0;netstandard2.1</TargetFrameworks>
+    <RazorLangVersion>3.0</RazorLangVersion>
+    <LangVersion>preview</LangVersion>
+    <PackageVersion>0.1.0-preview</PackageVersion>
+    <PackageLicenseExpression>Apache-2.0</PackageLicenseExpression>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.AspNetCore.Components" Version="$(ServerPackagesVersion)" />
+    <PackageReference Include="Microsoft.AspNetCore.Components.Web" Version="$(ServerPackagesVersion)" />
+  </ItemGroup>
+
+</Project>
diff --git a/BlazorInputFile/FileListEntryImpl.cs b/BlazorInputFile/FileListEntryImpl.cs
@@ -0,0 +1,40 @@
+using System;
+using System.IO;
+
+namespace BlazorInputFile
+{
+    // This is public only because it's used in a JSInterop method signature,
+    // but otherwise is intended as internal
+    public class FileListEntryImpl : IFileListEntry
+    {
+        internal InputFile Owner { get; set; }
+
+        private Stream _stream;
+
+        public event EventHandler OnDataRead;
+
+        public int Id { get; set; }
+
+        public DateTime LastModified { get; set; }
+
+        public string Name { get; set; }
+
+        public long Size { get; set; }
+
+        public string Type { get; set; }
+
+        public Stream Data
+        {
+            get
+            {
+                _stream ??= Owner.OpenFileStream(this);
+                return _stream;
+            }
+        }
+
+        internal void RaiseOnDataRead()
+        {
+            OnDataRead?.Invoke(this, null);
+        }
+    }
+}
diff --git a/BlazorInputFile/FileListEntryStream.cs b/BlazorInputFile/FileListEntryStream.cs
@@ -0,0 +1,80 @@
+using Microsoft.AspNetCore.Components;
+using Microsoft.JSInterop;
+using System;
+using System.IO;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace BlazorInputFile
+{
+    // TODO: When ReadAsync is called, don't just fetch the segment of data that's being requested.
+    // That will be very slow, as you may be doing a separate round-trip for each 1KB or so of data.
+    // Instead, have a larger buffer whose size == SignalR.MaxMessageSize and populate that. Then
+    // many of the ReadAsync calls can return immediately with already-loaded data.
+    //
+    // This is still not as fast as allowing the client to send as much data as it wants, and using
+    // TCP to apply backpressure. In the future we could achieve something closer to that by having
+    // an even larger buffer, and telling the client to send N messages in parallel. The ReadAsync
+    // calls would return whenever their portion of the buffer was populated. This is much more
+    // complicated to implement.
+
+    public abstract class FileListEntryStream : Stream
+    {
+        protected readonly IJSRuntime _jsRuntime;
+        protected readonly ElementReference _inputFileElement;
+        protected readonly FileListEntryImpl _file;
+        private long _position;
+
+        public FileListEntryStream(IJSRuntime jsRuntime, ElementReference inputFileElement, FileListEntryImpl file)
+        {
+            _jsRuntime = jsRuntime;
+            _inputFileElement = inputFileElement;
+            _file = file;
+        }
+
+        public override bool CanRead => true;
+
+        public override bool CanSeek => false;
+
+        public override bool CanWrite => false;
+
+        public override long Length => _file.Size;
+
+        public override long Position
+        {
+            get => _position;
+            set => throw new NotSupportedException();
+        }
+
+        public override void Flush()
+            => throw new NotSupportedException();
+
+        public override int Read(byte[] buffer, int offset, int count)
+            => throw new NotSupportedException("Synchronous reads are not supported");
+
+        public override long Seek(long offset, SeekOrigin origin)
+            => throw new NotSupportedException();
+
+        public override void SetLength(long value)
+            => throw new NotSupportedException();
+
+        public override void Write(byte[] buffer, int offset, int count)
+            => throw new NotSupportedException();
+
+        public override async Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            var maxBytesToRead = (int)Math.Min(count, Length - Position);
+            if (maxBytesToRead == 0)
+            {
+                return 0;
+            }
+
+            var actualBytesRead = await CopyFileDataIntoBuffer(_position, buffer, offset, maxBytesToRead, cancellationToken);
+            _position += actualBytesRead;
+            _file.RaiseOnDataRead();
+            return actualBytesRead;
+        }
+
+        protected abstract Task<int> CopyFileDataIntoBuffer(long sourceOffset, byte[] destination, int destinationOffset, int maxBytes, CancellationToken cancellationToken);
+    }
+}
diff --git a/BlazorInputFile/IFileListEntry.cs b/BlazorInputFile/IFileListEntry.cs
@@ -0,0 +1,20 @@
+using System;
+using System.IO;
+
+namespace BlazorInputFile
+{
+    public interface IFileListEntry
+    {
+        DateTime LastModified { get; }
+
+        string Name { get; }
+
+        long Size { get; }
+
+        string Type { get; }
+
+        Stream Data { get; }
+
+        event EventHandler OnDataRead;
+    }
+}
diff --git a/BlazorInputFile/InputFile.razor b/BlazorInputFile/InputFile.razor
@@ -0,0 +1,47 @@
+@implements IDisposable
+@inject IJSRuntime JSRuntime
+
+<input type="file" @ref="inputFileElement" @attributes="UnmatchedParameters" />
+
+@code {
+    [Parameter(CaptureUnmatchedValues = true)] public Dictionary<string, object> UnmatchedParameters { get; set; }
+    [Parameter] public EventCallback<IFileListEntry[]> OnChange { get; set; }
+    [Parameter] public int MaxMessageSize { get; set; } = 20 * 1024; // TODO: Use SignalR default
+    [Parameter] public int MaxBufferSize { get; set; } = 1024 * 1024;
+
+    ElementReference inputFileElement;
+    IDisposable thisReference;
+
+    [JSInvokable]
+    public Task NotifyChange(FileListEntryImpl[] files)
+    {
+        foreach (var file in files)
+        {
+            // So that method invocations on the file can be dispatched back here
+            file.Owner = (InputFile)(object)this;
+        }
+
+        return OnChange.InvokeAsync(files);
+    }
+
+    protected override async Task OnAfterRenderAsync(bool firstRender)
+    {
+        if (firstRender)
+        {
+            thisReference = DotNetObjectReference.Create(this);
+            await JSRuntime.InvokeAsync<object>("BlazorInputFile.init", inputFileElement, thisReference);
+        }
+    }
+
+    internal Stream OpenFileStream(FileListEntryImpl file)
+    {
+        return SharedMemoryFileListEntryStream.IsSupported(JSRuntime)
+            ? (Stream)new SharedMemoryFileListEntryStream(JSRuntime, inputFileElement, file)
+            : new RemoteFileListEntryStream(JSRuntime, inputFileElement, file, MaxMessageSize, MaxBufferSize);
+    }
+
+    void IDisposable.Dispose()
+    {
+        thisReference?.Dispose();
+    }
+}
diff --git a/BlazorInputFile/PreFetchingSequence.cs b/BlazorInputFile/PreFetchingSequence.cs
@@ -0,0 +1,58 @@
+using System;
+using System.Collections.Generic;
+using System.Threading;
+
+namespace BlazorInputFile
+{
+    internal class PreFetchingSequence<T>
+    {
+        private readonly Func<long, CancellationToken, T> _fetchCallback;
+        private readonly int _maxBufferCapacity;
+        private readonly long _totalFetchableItems;
+        private readonly Queue<T> _buffer;
+        private long _maxFetchedIndex;
+
+        public PreFetchingSequence(Func<long, CancellationToken, T> fetchCallback, long totalFetchableItems, int maxBufferCapacity)
+        {
+            _fetchCallback = fetchCallback;
+            _buffer = new Queue<T>();
+            _maxBufferCapacity = maxBufferCapacity;
+            _totalFetchableItems = totalFetchableItems;
+        }
+
+        public T ReadNext(CancellationToken cancellationToken)
+        {
+            EnqueueFetches(cancellationToken);
+            if (_buffer.Count == 0)
+            {
+                throw new InvalidOperationException("There are no more entries to read");
+            }
+
+            var next = _buffer.Dequeue();
+            EnqueueFetches(cancellationToken);
+            return next;
+        }
+
+        public bool TryPeekNext(out T result)
+        {
+            if (_buffer.Count > 0)
+            {
+                result = _buffer.Peek();
+                return true;
+            }
+            else
+            {
+                result = default;
+                return false;
+            }
+        }
+
+        private void EnqueueFetches(CancellationToken cancellationToken)
+        {
+            while (_buffer.Count < _maxBufferCapacity && _maxFetchedIndex < _totalFetchableItems)
+            {
+                _buffer.Enqueue(_fetchCallback(_maxFetchedIndex++, cancellationToken));
+            }
+        }
+    }
+}