Add FromFile to BinaryData

[manandre]

Closes #106203

[huoyaoyuan]

Should temp files be cleaned up?

[manandre]

Indeed!
Also fixed for the existing test that I took as reference.

[lilinus]

Would it be better to use File.ReadAllBytes? Since it has that tries to minimize allocations of the byte array if the file-size is determinable.

[manandre]

Good question!

• The file-size optimization is also supported in the FromStream flow.

• The ReadAllBytesAsync method is not available for the net462 and netstandard2.0 TFMs. Can we then fallback to the synchronous implementation for these TFMs?

• The ReadAllBytes{Async} flow may be more efficient to avoid the intermediate copy buffer of the CopyTo{Async} flow.

Here would be the corresponding code:

        private static
#if NET6_0_OR_GREATER
        async
#endif
        Task<BinaryData> FromFileAsync(string path, bool async, string? mediaType = default, CancellationToken cancellationToken = default)
        {
#if NET6_0_OR_GREATER
            byte[] bytes;

            if (async)
            {
                bytes = await File.ReadAllBytesAsync(path, cancellationToken).ConfigureAwait(false);
            }
            else
            {
                bytes = File.ReadAllBytes(path);
            }

            return new BinaryData(bytes, mediaType);
#else
            byte[] bytes = File.ReadAllBytes(path);

            return Task.FromResult(new BinaryData(bytes, mediaType));
#endif
        }

Better?

[lilinus]

Ah I see. Thanks for looking into it. Personally I don't think the potential benefit outweighs the added complexity, I would keep it as it is then.

[stephentoub]

The FileStream should be opened for asynchronous use when async: true. The way this is written, it'll always use synchronous I/O, which means async operations on it will end up being sync calls queued to the pool.

[manandre]

Replaced with the FileStream constructor enabling async calls.