DisableMultipleQueuedItemsFilter.cs

// Zero-Clause BSD (more permissive than MIT, doesn't require copyright notice)
// 
// Permission to use, copy, modify, and/or distribute this software for any purpose
// with or without fee is hereby granted.
// 
// THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
// WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT,
// INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS
// OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
// TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF
// THIS SOFTWARE.

// Source from:  https://gist.github.com/odinserj/a8332a3f486773baa009?permalink_comment_id=4051053#gistcomment-4051053

using Hangfire.Client;
using Hangfire.Common;
using Hangfire.States;
using Hangfire.Storage;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Security.Cryptography;

namespace Hangfire.Filters
{
    public class DisableMultipleQueuedItemsFilter : JobFilterAttribute, IClientFilter, IApplyStateFilter
    {
        private static readonly TimeSpan LockTimeout = TimeSpan.FromSeconds(5);
        private static readonly CultureInfo EnUs = new CultureInfo("en-US");

        /// <summary>
        /// Convert arguments into a culture-aware string
        /// </summary>
        ///<see cref="https://gist.github.com/odinserj/a8332a3f486773baa009?permalink_comment_id=4048344#gistcomment-4048344"/><see>
        private static string ConvertArgument(object obj)
        {
            switch (obj)
            {
                case null:
                    return string.Empty;
                case string s:
                    return s;
                case DateTime dt:
                    return dt.ToString("o"); // ISO8601 date format
                default:
                    return (string)Convert.ChangeType(obj, typeof(string), EnUs); // And force the rest to US English
            }
        }

        private static bool AddFingerprintIfNotExists(IStorageConnection connection, Job job)
        {
            var fingerprintKey = GetFingerprintKey(job);
            var finterprintLockKey = GetFingerprintLockKey(fingerprintKey);
            var distributedLock = connection.AcquireDistributedLock(finterprintLockKey, LockTimeout);
            using (distributedLock)
            {
                var fingerprint = connection.GetAllEntriesFromHash(fingerprintKey);

                if (fingerprint != null)
                {
                    // Actual fingerprint found, returning.
                    return false;
                }

                // Fingerprint does not exist, it is invalid (no `Timestamp` key),
                // or it is not actual (timeout expired).
                connection.SetRangeInHash(fingerprintKey, new Dictionary<string, string>
                    {
                        { "Timestamp", DateTimeOffset.UtcNow.ToString("o") }
                    });

                return true;
            }
        }

        private static void RemoveFingerprint(IStorageConnection connection, Job job)
        {
            var fingerprintKey = GetFingerprintKey(job);
            var finterprintLockKey = GetFingerprintLockKey(fingerprintKey);
            using (connection.AcquireDistributedLock(finterprintLockKey, LockTimeout))
            using (var transaction = connection.CreateWriteTransaction())
            {
                transaction.RemoveHash(fingerprintKey);
                transaction.Commit();
            }
        }

        private static string GetFingerprintLockKey(string fingerprintKey)
        {
            return string.Format("{0}:lock", fingerprintKey);
        }

        private static string GetFingerprintKey(Job job)
        {
            return string.Format("fingerprint:{0}", GetFingerprint(job));
        }

        private static string GetFingerprint(Job job)
        {
            string parameters = string.Empty;
            if (job?.Args != null)
            {
                parameters = string.Join(".", job.Args.Select(ConvertArgument));
            }
            if (job?.Type == null || job.Method == null)
            {
                return string.Empty;
            }

            //https://gist.github.com/odinserj/a8332a3f486773baa009#gistcomment-1898401
            var payload = $"{job.Type.FullName}.{job.Method.Name}.{parameters}";
            var hash = SHA256.Create().ComputeHash(System.Text.Encoding.UTF8.GetBytes(payload));
            var fingerprint = Convert.ToBase64String(hash);
            return fingerprint;
        }

        public void OnCreating(CreatingContext filterContext)
        {
            if (!AddFingerprintIfNotExists(filterContext.Connection, filterContext.Job))
            {
                filterContext.Canceled = true;
            }
        }

        public void OnCreated(CreatedContext filterContext)
        {
            //do nothing
        }


        public void OnStateApplied(ApplyStateContext context, IWriteOnlyTransaction transaction)
        {
            if (context.NewState.Name.Equals(Hangfire.States.SucceededState.StateName)
                || context.NewState.Name.Equals(Hangfire.States.FailedState.StateName))
            {
                RemoveFingerprint(context.Connection, context.BackgroundJob.Job);
            }
        }

        public void OnStateUnapplied(ApplyStateContext context, IWriteOnlyTransaction transaction)
        {
            // do nothing
        }
    }
}