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/*
* Copyright (c) 2024 Vaughn Nugent
*
* Library: VNLib
* Package: VNLib.Plugins.Essentials
* File: SemiConsistentVeTable.cs
*
* SemiConsistentVeTable.cs is part of VNLib.Plugins.Essentials which
* is part of the larger VNLib collection of libraries and utilities.
*
* VNLib.Plugins.Essentials is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as
* published by the Free Software Foundation, either version 3 of the
* License, or (at your option) any later version.
*
* VNLib.Plugins.Essentials is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see https://www.gnu.org/licenses/.
*/
using System;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.Collections.Frozen;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using VNLib.Net.Http;
using VNLib.Plugins.Essentials.Endpoints;
namespace VNLib.Plugins.Essentials
{
internal class SemiConsistentVeTable : IVirtualEndpointTable
{
/*
* The VE table is read-only for the processor and my only
* be updated by the application via the methods below
*
* Since it would be very inefficient to track endpoint users
* using locks, we can assume any endpoint that is currently
* processing requests cannot be stopped, so we just focus on
* swapping the table when updates need to be made.
*
* This means calls to modify the table will read the table
* (clone it), modify the local copy, then exhange it for
* the active table so new requests will be processed on the
* new table.
*
* To make the calls to modify the table thread safe, a lock is
* held while modification operations run, then the updated
* copy is published. Any threads reading the old table
* will continue to use a stale endpoint.
*/
/// <summary>
/// A "lookup table" that represents virtual endpoints to be processed when an
/// incomming connection matches its path parameter
/// </summary>
private FrozenDictionary<string, IVirtualEndpoint<HttpEntity>> VirtualEndpoints =
new Dictionary<string, IVirtualEndpoint<HttpEntity>>(StringComparer.OrdinalIgnoreCase)
.ToFrozenDictionary();
private bool _isEmpty = true;
/*
* A lock that is held by callers that intend to
* modify the vep table at the same time
*/
private readonly object VeUpdateLock = new();
///<inheritdoc/>
public bool IsEmpty => _isEmpty;
///<inheritdoc/>
public void AddEndpoint(params IEndpoint[] endpoints)
{
//Check
ArgumentNullException.ThrowIfNull(endpoints);
//Make sure all endpoints specify a path
if (endpoints.Any(static e => string.IsNullOrWhiteSpace(e?.Path)))
{
throw new ArgumentException("Endpoints array contains one or more empty endpoints");
}
if (endpoints.Length == 0)
{
return;
}
//Get virtual endpoints
IEnumerable<IVirtualEndpoint<HttpEntity>> eps = endpoints
.Where(static e => e is IVirtualEndpoint<HttpEntity>)
.Select(static e => (IVirtualEndpoint<HttpEntity>)e);
//Get http event endpoints and create wrapper classes for conversion
IEnumerable<IVirtualEndpoint<HttpEntity>> evs = endpoints
.Where(static e => e is IVirtualEndpoint<IHttpEvent>)
.Select(static e => new EvEndpointWrapper((e as IVirtualEndpoint<IHttpEvent>)!));
//Uinion endpoints by their paths to combine them
IEnumerable<IVirtualEndpoint<HttpEntity>> allEndpoints = eps.UnionBy(evs, static s => s.Path);
//Only allow 1 thread at a time to mutate the table
lock (VeUpdateLock)
{
//Clone the current dictonary
Dictionary<string, IVirtualEndpoint<HttpEntity>> newTable = new(VirtualEndpoints, StringComparer.OrdinalIgnoreCase);
//Insert the new eps, and/or overwrite old eps
foreach (IVirtualEndpoint<HttpEntity> ep in allEndpoints)
{
newTable.Add(ep.Path, ep);
}
//Update is-empty flag
_isEmpty = newTable.Count == 0;
//Create the new table and store the entire table
_ = Interlocked.Exchange(ref VirtualEndpoints, newTable.ToFrozenDictionary(StringComparer.OrdinalIgnoreCase));
}
}
///<inheritdoc/>
public void RemoveEndpoint(params IEndpoint[] eps)
{
ArgumentNullException.ThrowIfNull(eps);
//Call remove on path
RemoveEndpoint(eps.Select(static s => s.Path).ToArray());
}
///<inheritdoc/>
public void RemoveEndpoint(params string[] paths)
{
ArgumentNullException.ThrowIfNull(paths);
//Make sure all endpoints specify a path
if (paths.Any(static e => string.IsNullOrWhiteSpace(e)))
{
throw new ArgumentException("Paths array contains one or more empty strings");
}
if (paths.Length == 0)
{
return;
}
//take update lock
lock (VeUpdateLock)
{
//Clone the current dictonary
Dictionary<string, IVirtualEndpoint<HttpEntity>> newTable = new(VirtualEndpoints, StringComparer.OrdinalIgnoreCase);
foreach (string eps in paths)
{
_ = newTable.Remove(eps);
}
//Update is-empty flag
_isEmpty = newTable.Count == 0;
//Store the new table
_ = Interlocked.Exchange(ref VirtualEndpoints, newTable.ToFrozenDictionary(StringComparer.OrdinalIgnoreCase));
}
}
///<inheritdoc/>
public bool TryGetEndpoint(string path, [NotNullWhen(true)] out IVirtualEndpoint<HttpEntity>? endpoint)
=> VirtualEndpoints.TryGetValue(path, out endpoint);
/*
* Wrapper class for converting IHttpEvent endpoints to
* httpEntityEndpoints
*/
private sealed class EvEndpointWrapper(IVirtualEndpoint<IHttpEvent> Wrapped) : IVirtualEndpoint<HttpEntity>
{
string IEndpoint.Path => Wrapped.Path;
ValueTask<VfReturnType> IVirtualEndpoint<HttpEntity>.Process(HttpEntity entity) => Wrapped.Process(entity);
}
}
}
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