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/*
* Copyright (c) 2023 Vaughn Nugent
*
* Library: VNLib
* Package: Emails.Transactional
* File: ResendMta.cs
*
* ResendMta.cs is part of Emails.Transactional which is part of the larger
* VNLib collection of libraries and utilities.
*
* Emails.Transactional is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published
* by the Free Software Foundation, either version 2 of the License,
* or (at your option) any later version.
*
* Emails.Transactional 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
* General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with Emails.Transactional. If not, see http://www.gnu.org/licenses/.
*/
using System;
using System.Net;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.Text.Json.Serialization;
using RestSharp;
using VNLib.Net.Http;
using VNLib.Utils.Logging;
using VNLib.Utils.Extensions;
using VNLib.Net.Rest.Client.Construction;
using VNLib.Net.Rest.Client;
using VNLib.Plugins;
using VNLib.Plugins.Extensions.Loading;
using VNLib.Plugins.Extensions.Loading.Events;
using ContentType = VNLib.Net.Http.ContentType;
namespace Emails.Transactional.Mta
{
[ConfigurationName("resend")]
internal sealed class ResendMta : IMailTransferAgent
{
const int ResendMaxPerSecond = 10;
/*
* Resend has a rate limit of 10 request per second,
* this timer resets the request counter every second
*/
private int _remainingRequests;
Task ResetRateLimitAsync(ILogProvider log, CancellationToken pluginExitToken)
{
//Reset the request counter
_remainingRequests = ResendMaxPerSecond;
return Task.CompletedTask;
}
private readonly ResendSiteAdapter _resendAdapter;
private readonly TimeSpan _rateLimitDelay;
private readonly int _rateLimitRetry;
public ResendMta(PluginBase plugin, IConfigScope config)
{
int timeoutMs = config.GetRequiredProperty("timeout_ms", e => e.GetInt32());
int maxClients = config.GetRequiredProperty("max_clients", e => e.GetInt32());
string? userAgent = config.GetProperty("user_agent", e => e.GetString());
_rateLimitDelay = config["rate_limit_delay_ms"].GetTimeSpan(TimeParseType.Milliseconds);
_rateLimitRetry = config["rate_limit_retry"].GetInt32();
//Create the resend adapter
_resendAdapter = new ResendSiteAdapter(timeoutMs, maxClients, userAgent);
//Retrieve the access token
IAsyncLazy<string> authToken = plugin.GetSecretAsync("resend_token").ToLazy(p => p.Result.ToString());
//Define the send endpoint
//https://resend.com/docs/api-reference/emails/send-email
_resendAdapter.DefineSingleEndpoint()
.WithEndpoint<ResendEmail>()
.WithMethod(Method.Post)
.WithUrl("/emails")
.WithHeader("Accept", "application/json")
.WithHeader("Content-Type", HttpHelpers.GetContentTypeString(ContentType.Json))
//Add authorization header on requests
.WithHeader("Authorization", e => $"Bearer {authToken.Value}")
//Add message body
.WithModifier(static (re, r) => r.AddJsonBody(re));
//Schedule timer to reset the rate limit
plugin.ScheduleInterval(ResetRateLimitAsync, TimeSpan.FromSeconds(1));
}
///<inheritdoc/>
public async Task<MtaResult> SendEmailAsync(EmailTransaction transaction, IEmailMessageData message, CancellationToken cancellation = default)
{
int retryCount = 0;
while (retryCount < _rateLimitRetry)
{
//Increment the request counter
int newCount = Interlocked.Increment(ref _remainingRequests);
//if rate limit hasn't been reached, break
if (newCount >= 0)
{
break;
}
retryCount++;
//Wait for the rate limit delay
await Task.Delay(_rateLimitDelay, cancellation);
}
//Create the resend email object
ResendEmail email = new(transaction)
{
Html = message.GetHtml(),
};
//Execute the request
RestResponse<ResendResponse> response = await _resendAdapter.ExecuteAsync<ResendEmail, ResendResponse>(email, cancellation);
if(response.IsSuccessful)
{
//Store the raw response content data
transaction.Result = response.Content;
return new MtaResult(true, response.Data?.Id);
}
else
{
switch (response.StatusCode)
{
case HttpStatusCode.UnprocessableEntity:
return new MtaResult(false, response.Data?.StatusText);
default:
return new MtaResult(false, response.Content);
}
}
}
private sealed record class ResendEmail(EmailTransaction Transaction)
{
[JsonPropertyName("from")]
public string From => $"{Transaction.FromName} <{Transaction.From}>";
[JsonPropertyName("subject")]
public string? Subject => Transaction.Subject;
[JsonPropertyName("to")]
public string[]? To => Transaction.ToAddresses?.Select(static t => $"{t.Value} <{t.Key}>").ToArray();
[JsonPropertyName("bcc")]
public string[]? Bcc => Transaction.BccAddresses?.Select(static t => $"{t.Value} <{t.Key}>").ToArray();
[JsonPropertyName("cc")]
public string[]? Cc => Transaction.CcAddresses?.Select(static t => $"{t.Value} <{t.Key}>").ToArray();
[JsonPropertyName("reply_to")]
public string? ReplyTo => Transaction.ReplyTo == null ? null : $"{Transaction.ReplyToName} <{Transaction.ReplyTo}>";
[JsonPropertyName("html")]
public string Html { get; init; } = "";
}
private sealed class ResendResponse
{
[JsonPropertyName("id")]
public string Id { get; set; } = null!;
[JsonPropertyName("name")]
public string? Name { get; set; }
[JsonPropertyName("statusCode")]
public int StatusCpde { get; set; }
[JsonPropertyName("message")]
public string? StatusText { get; set; }
}
private sealed class ResendSiteAdapter : RestSiteAdapterBase
{
//Fixed resend api url
private const string BaseUrl = "https://api.resend.com";
///<inheritdoc/>
protected override RestClientPool Pool { get; }
public ResendSiteAdapter(int maxTimeoutMs, int maxClients, string? userAgent)
{
RestClientOptions options = new(BaseUrl)
{
AutomaticDecompression = DecompressionMethods.All,
Encoding = Encoding.UTF8,
FollowRedirects = false,
MaxTimeout = maxTimeoutMs,
UserAgent = userAgent,
};
//Create client pool
Pool = new RestClientPool(maxClients, options);
}
///<inheritdoc/>
public override void OnResponse(RestResponse response)
{ }
///<inheritdoc/>
public override Task WaitAsync(CancellationToken cancellation = default)
{
//TODO implement rate limit wait
return Task.CompletedTask;
}
}
}
}
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