StreamWrapper.cs

using System;
using System.IO;

#if !NETSTANDARD1_0
using System.Net.Http;
#endif

using System.Threading;
using System.Threading.Tasks;
using Xamarin.Forms.Internals;

namespace Xamarin.Forms
{
	internal class StreamWrapper : Stream
	{
		readonly Stream _wrapped;
		IDisposable _additionalDisposable;

		public StreamWrapper(Stream wrapped) : this(wrapped, null)
		{
		}

		public StreamWrapper(Stream wrapped, IDisposable additionalDisposable)
		{
			if (wrapped == null)
				throw new ArgumentNullException("wrapped");

			_wrapped = wrapped;
			_additionalDisposable = additionalDisposable;
		}

		public override bool CanRead
		{
			get { return _wrapped.CanRead; }
		}

		public override bool CanSeek
		{
			get { return _wrapped.CanSeek; }
		}

		public override bool CanWrite
		{
			get { return _wrapped.CanWrite; }
		}

		public override long Length
		{
			get { return _wrapped.Length; }
		}

		public override long Position
		{
			get { return _wrapped.Position; }
			set { _wrapped.Position = value; }
		}

		public event EventHandler Disposed;

		public override void Flush()
		{
			_wrapped.Flush();
		}

		public override int Read(byte[] buffer, int offset, int count)
		{
			return _wrapped.Read(buffer, offset, count);
		}

		public override long Seek(long offset, SeekOrigin origin)
		{
			return _wrapped.Seek(offset, origin);
		}

		public override void SetLength(long value)
		{
			_wrapped.SetLength(value);
		}

		public override void Write(byte[] buffer, int offset, int count)
		{
			_wrapped.Write(buffer, offset, count);
		}

		protected override void Dispose(bool disposing)
		{
			_wrapped.Dispose();
			Disposed?.Invoke(this, EventArgs.Empty);
			_additionalDisposable?.Dispose();
			_additionalDisposable = null;

			base.Dispose(disposing);
		}

#if !NETSTANDARD1_0

		public static async Task<Stream> GetStreamAsync(Uri uri, CancellationToken cancellationToken, HttpClient client)
		{
			HttpResponseMessage response = await client.GetAsync(uri, cancellationToken).ConfigureAwait(false);
			if (!response.IsSuccessStatusCode)
			{
				Internals.Log.Warning("HTTP Request", $"Could not retrieve {uri}, status code {response.StatusCode}");
				return null;
			}

			// the HttpResponseMessage needs to be disposed of after the calling code is done with the stream
			// otherwise the stream may get disposed before the caller can use it
			return new StreamWrapper(await response.Content.ReadAsStreamAsync().ConfigureAwait(false), response);
		}
#endif

	}
}