AttachmentCacheItem.cs

using System;
using System.IO;
using System.Security.Cryptography;
using System.Threading.Tasks;
using Waher.Persistence.Attributes;
using Waher.Runtime.IO;
 
namespace Waher.Service.IoTBroker.Legal.Attachments
{
    [CollectionName("AttachmentCache")]
    [TypeName(TypeNameSerialization.None)]
    [Index("AttachmentId")]
    [Index("Expires")]
    public class AttachmentCacheItem
    {
        [ObjectId]
        public string ObjectId { get; set; }
 
        public string AttachmentId { get; set; }
 
        public DateTime Created { get; set; }
 
        public DateTime Expires { get; set; }
 
        public string ContentType { get; set; }
 
        [DefaultValueNull]
        public string LocalAttachmentId { get; set; }
 
        public string FileName { get; set; }
 
        public long Size { get; set; }
 
        public byte[] Salt { get; set; }
 
        public async Task<byte[]> LoadContent()
        {
            using FileStream AttachmentFile = File.OpenRead(this.FileName);
            Aes Aes = Aes.Create();
 
            Aes.BlockSize = 128;
            Aes.KeySize = 256;
            Aes.Mode = CipherMode.CBC;
            Aes.Padding = PaddingMode.Zeros;
 
            byte[] Key = new byte[32];
            byte[] IV = new byte[16];
 
            Buffer.BlockCopy(this.Salt, 0, Key, 0, 32);
            Buffer.BlockCopy(this.Salt, 32, IV, 0, 16);
 
            using ICryptoTransform Decryptor = Aes.CreateDecryptor(Key, IV);
            using CryptoStream DecryptedAttachmentFile = new CryptoStream(AttachmentFile, Decryptor, CryptoStreamMode.Read);
 
            if (this.Size > int.MaxValue)
                throw new InvalidOperationException("Attachment size exceeds maximum array size.");
 
            return await DecryptedAttachmentFile.ReadAllAsync((int)this.Size);
        }
    }
}