Prowlarr/src/NzbDrone.Core/Download/NzbValidationService.cs

using System;
using System.IO;
using System.Linq;
using System.Xml;
using System.Xml.Linq;
using NzbDrone.Common.Extensions;

namespace NzbDrone.Core.Download
{
    public interface IValidateNzbs
    {
        void Validate(byte[] fileContent);
    }

    public class NzbValidationService : IValidateNzbs
    {
        public void Validate(byte[] fileContent)
        {
            try
            {
                var reader = new StreamReader(new MemoryStream(fileContent));

                using (var xmlTextReader = XmlReader.Create(reader,
                           new XmlReaderSettings { DtdProcessing = DtdProcessing.Ignore, IgnoreComments = true }))
                {
                    var xDoc = XDocument.Load(xmlTextReader);
                    var nzb = xDoc.Root;

                    if (nzb == null)
                    {
                        throw new InvalidNzbException("Invalid NZB: No Root element");
                    }

                    // nZEDb has a bug in their error reporting code spitting out invalid http status codes
                    if (nzb.Name.LocalName.Equals("error") &&
                        nzb.TryGetAttributeValue("code", out var code) &&
                        nzb.TryGetAttributeValue("description", out var description))
                    {
                        throw new InvalidNzbException("Invalid NZB: Contains indexer error: {0} - {1}", code, description);
                    }

                    if (!nzb.Name.LocalName.Equals("nzb"))
                    {
                        throw new InvalidNzbException(
                            "Invalid NZB: Unexpected root element. Expected 'nzb' found '{0}'", nzb.Name.LocalName);
                    }

                    var ns = nzb.Name.Namespace;
                    var files = nzb.Elements(ns + "file").ToList();

                    if (files.Empty())
                    {
                        throw new InvalidNzbException("Invalid NZB: No files");
                    }
                }
            }
            catch (InvalidNzbException)
            {
                // Throw the original exception
                throw;
            }
            catch (Exception ex)
            {
                throw new InvalidNzbException("Invalid NZB: Unable to parse", ex);
            }
        }
    }
}