DagNode.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Runtime.Serialization;
using Google.Protobuf;

namespace Ipfs
{
    /// <summary>
    ///   A node in the IPFS Merkle DAG.
    /// </summary>
    /// <remarks>
    ///   A <b>DagNode</b> has opaque <see cref="DagNode.DataBytes"/>
    ///   and a set of navigable <see cref="DagNode.Links"/>.
    /// </remarks>
    [DataContract]
    public class DagNode : IMerkleNode<IMerkleLink>
    {
        private Cid? _id;
        private string _hashAlgorithm = MultiHash.DefaultAlgorithmName;
        private ulong? _size;

        /// <summary>
        ///   Create a new instance of a <see cref="DagNode"/> with the specified
        ///   <see cref="DagNode.DataBytes"/> and <see cref="DagNode.Links"/>
        /// </summary>
        /// <param name="data">
        ///   The opaque data, can be <b>null</b>.
        /// </param>
        /// <param name="links">
        ///   The links to other nodes.
        /// </param>
        /// <param name="hashAlgorithm">
        ///   The name of the hashing algorithm to use; defaults to 
        ///   <see cref="MultiHash.DefaultAlgorithmName"/>.
        /// </param>
        public DagNode(byte[]? data, IEnumerable<IMerkleLink>? links = null, string hashAlgorithm = MultiHash.DefaultAlgorithmName)
        {
            DataBytes = data ?? Array.Empty<byte>();
            Links = (links ?? Array.Empty<DagLink>())
                .OrderBy(link => link.Name ?? "");
            _hashAlgorithm = hashAlgorithm;
        }

        /// <summary>
        ///   Creates a new instance of the <see cref="DagNode"/> class from the
        ///   specified <see cref="Stream"/>.
        /// </summary>
        /// <param name="stream">
        ///   A <see cref="Stream"/> containing the binary representation of the
        ///   <b>DagNode</b>.
        /// </param>
        public DagNode(Stream stream)
        {
            Read(stream);
        }

        /// <summary>
        ///   Creates a new instance of the <see cref="DagNode"/> class from the
        ///   specified <see cref="CodedInputStream"/>.
        /// </summary>
        /// <param name="stream">(
        ///   A <see cref="CodedInputStream"/> containing the binary representation of the
        ///   <b>DagNode</b>.
        /// </param>
        public DagNode(CodedInputStream stream)
        {
            Read(stream);
        }

        /// <inheritdoc />
        [DataMember]
        public IEnumerable<IMerkleLink> Links { get; private set; } = Enumerable.Empty<IMerkleLink>();

        /// <inheritdoc />
        [DataMember]
        public byte[] DataBytes { get; private set; } = Array.Empty<byte>();

        /// <inheritdoc />
        public Stream DataStream => new MemoryStream(DataBytes, false);

        /// <summary>
        ///   The serialised size in bytes of the node.
        /// </summary>
        [DataMember]
        public ulong Size
        {
            get
            {
                _size ??= ComputeSize();
                return _size.Value;
            }
        }

        /// <inheritdoc />
        [DataMember]
        public Cid Id
        {
            get
            {
                _id ??= ComputeHash();
                return _id;
            }
            set
            {
                _id = value;
                _hashAlgorithm = _id.Hash.Algorithm.Name;
            }
        }

        /// <inheritdoc />
        public IMerkleLink ToLink(string name = "")
        {
            return new DagLink(name, Id, Size);
        }

        /// <summary>
        ///   Adds a link.
        /// </summary>
        /// <param name="link">
        ///   The link to add.
        /// </param>
        /// <returns>
        ///   A new <see cref="DagNode"/> with the existing and new
        ///   links.
        /// </returns>
        /// <remarks>
        ///   A <b>DagNode</b> is immutable.
        /// </remarks>
        public DagNode AddLink(IMerkleLink link)
        {
            return AddLinks(new[] { link });
        }

        /// <summary>
        ///   Adds a sequence of links.
        /// </summary>
        /// <param name="links">
        ///   The sequence of links to add.
        /// </param>
        /// <returns>
        ///   A new <see cref="DagNode"/> with the existing and new
        ///   links.
        /// </returns>
        /// <remarks>
        ///   A <b>DagNode</b> is immutable.
        /// </remarks>
        public DagNode AddLinks(IEnumerable<IMerkleLink> links)
        {
            var all = Links.Union(links);
            return new DagNode(DataBytes, all, _hashAlgorithm);
        }

        /// <summary>
        ///   Removes a link.
        /// </summary>
        /// <param name="link">
        ///   The <see cref="IMerkleLink"/> to remove.
        /// </param>
        /// <returns>
        ///   A new <see cref="DagNode"/> with the <paramref name="link"/>
        ///   removed.
        /// </returns>
        /// <remarks>
        ///   A <b>DagNode</b> is immutable.
        ///   <para>
        ///   No exception is raised if the <paramref name="link"/> does
        ///   not exist.
        ///   </para>
        /// </remarks>
        public DagNode RemoveLink(IMerkleLink link)
        {
            return RemoveLinks(new[] { link });
        }

        /// <summary>
        ///   Remove a sequence of links.
        /// </summary>
        /// <param name="links">
        ///   The sequence of <see cref="IMerkleLink"/> to remove.
        /// </param>
        /// <returns>
        ///   A new <see cref="DagNode"/> with the <paramref name="links"/>
        ///   removed.
        /// </returns>
        /// <remarks>
        ///   A <b>DagNode</b> is immutable.
        ///   <para>
        ///   No exception is raised if any of the <paramref name="links"/> do
        ///   not exist.
        ///   </para>
        /// </remarks>
        public DagNode RemoveLinks(IEnumerable<IMerkleLink> links)
        {
            var ignore = links.ToLookup(link => link.Id);
            var some = Links.Where(link => !ignore.Contains(link.Id));
            return new DagNode(DataBytes, some, _hashAlgorithm);
        }

        /// <summary>
        ///   Writes the binary representation of the node to the specified <see cref="Stream"/>.
        /// </summary>
        /// <param name="stream">
        ///   The <see cref="Stream"/> to write to.
        /// </param>
        public void Write(Stream stream)
        {
            using var cos = new CodedOutputStream(stream, true);
            Write(cos);
        }

        /// <summary>
        ///   Writes the binary representation of the node to the specified <see cref="CodedOutputStream"/>.
        /// </summary>
        /// <param name="stream">
        ///   The <see cref="CodedOutputStream"/> to write to.
        /// </param>
        public void Write(CodedOutputStream stream)
        {
            foreach (var link in Links.Select(l => new DagLink(l)))
            {
                using var linkStream = new MemoryStream();
                link.Write(linkStream);
                var msg = linkStream.ToArray();
                stream.WriteTag(2, WireFormat.WireType.LengthDelimited);
                stream.WriteLength(msg.Length);
                stream.WriteSomeBytes(msg);
            }
            
            if (DataBytes.Length > 0)
            {
                stream.WriteTag(1, WireFormat.WireType.LengthDelimited);
                stream.WriteLength(DataBytes.Length);
                stream.WriteSomeBytes(DataBytes);
            }
        }

        private void Read(Stream stream)
        {
            using var cis = new CodedInputStream(stream, true);
            Read(cis);
        }

        private void Read(CodedInputStream stream)
        {
            var links = new List<DagLink>();
            bool done = false;

            while (!stream.IsAtEnd && !done)
            {
                var tag = stream.ReadTag();
                switch(WireFormat.GetTagFieldNumber(tag))
                {
                    case 1:
                        DataBytes = stream.ReadSomeBytes(stream.ReadLength());
                        done = true;
                        break;
                    case 2:
                        using (var ms = new MemoryStream(stream.ReadSomeBytes(stream.ReadLength())))
                        {
                            links.Add(new DagLink(ms));
                        }
                        break;
                    default:
                        throw new InvalidDataException("Unknown field number");
                }
            }

            DataBytes ??= Array.Empty<byte>();
            Links = links.ToArray();
        }

        /// <summary>
        ///   Returns the IPFS binary representation as a byte array.
        /// </summary>
        /// <returns>
        ///   A byte array.
        /// </returns>
        public byte[] ToArray()
        {
            using var ms = new MemoryStream();
            Write(ms);
            return ms.ToArray();
        }

        private MultiHash ComputeHash()
        {
            using var ms = new MemoryStream();
            Write(ms);
            _size = (ulong?)ms.Position;
            ms.Position = 0;
            return MultiHash.ComputeHash(ms, _hashAlgorithm);
        }

        private ulong ComputeSize()
        {
            using var ms = new MemoryStream();
            Write(ms);
            return (ulong)ms.Position;
        }
    }
}