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https://github.com/RedWizardsLab/EchoHub.git
synced 2026-09-04 08:36:11 +02:00
feat: implement link embed functionality to enhance message previews with metadata and thumbnails
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HueByte
@@ -0,0 +1,268 @@
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using System.Net;
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using System.Text;
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using System.Text.RegularExpressions;
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using EchoHub.Core.Constants;
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using EchoHub.Core.DTOs;
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using Microsoft.Extensions.Logging;
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namespace EchoHub.Server.Services;
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public partial class LinkEmbedService
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{
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private readonly IHttpClientFactory _httpClientFactory;
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private readonly ImageToAsciiService _asciiService;
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private readonly ILogger<LinkEmbedService> _logger;
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public LinkEmbedService(
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IHttpClientFactory httpClientFactory,
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ImageToAsciiService asciiService,
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ILogger<LinkEmbedService> logger)
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{
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_httpClientFactory = httpClientFactory;
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_asciiService = asciiService;
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_logger = logger;
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}
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/// <summary>
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/// Detect the first URL in message content and attempt to fetch OG embed data.
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/// Returns null if no URL found, fetch fails, or no useful OG data.
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/// Never throws — all errors are caught internally.
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/// </summary>
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public async Task<EmbedDto?> TryGetEmbedAsync(string content)
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{
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try
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{
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var url = ExtractFirstUrl(content);
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if (url is null)
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return null;
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if (!Uri.TryCreate(url, UriKind.Absolute, out var uri))
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return null;
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if (uri.Scheme is not ("http" or "https"))
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return null;
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if (IsPrivateHost(uri))
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return null;
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using var cts = new CancellationTokenSource(
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TimeSpan.FromSeconds(HubConstants.EmbedFetchTimeoutSeconds));
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var client = _httpClientFactory.CreateClient("OgFetch");
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using var request = new HttpRequestMessage(HttpMethod.Get, uri);
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using var response = await client.SendAsync(request,
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HttpCompletionOption.ResponseHeadersRead, cts.Token);
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if (!response.IsSuccessStatusCode)
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return null;
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var contentType = response.Content.Headers.ContentType?.MediaType;
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if (contentType is null || !contentType.StartsWith("text/html", StringComparison.OrdinalIgnoreCase))
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return null;
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var html = await ReadLimitedAsync(response, HubConstants.EmbedMaxHtmlBytes, cts.Token);
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if (string.IsNullOrWhiteSpace(html))
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return null;
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var ogTags = ParseOgTags(html);
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// Try og:title, fallback to <title> tag
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var title = ogTags.GetValueOrDefault("title");
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if (string.IsNullOrWhiteSpace(title))
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{
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var titleMatch = TitleTagRegex().Match(html);
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if (titleMatch.Success)
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title = WebUtility.HtmlDecode(titleMatch.Groups[1].Value.Trim());
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}
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// If no title at all, nothing useful to show
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if (string.IsNullOrWhiteSpace(title))
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return null;
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var siteName = ogTags.GetValueOrDefault("site_name");
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var description = ogTags.GetValueOrDefault("description");
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// Truncate description
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if (description is not null && description.Length > HubConstants.EmbedMaxDescriptionLength)
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description = description[..(HubConstants.EmbedMaxDescriptionLength - 3)] + "...";
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// HTML decode text fields
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title = WebUtility.HtmlDecode(title);
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siteName = siteName is not null ? WebUtility.HtmlDecode(siteName) : null;
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description = description is not null ? WebUtility.HtmlDecode(description) : null;
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// Attempt to fetch OG image thumbnail
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string? imageAscii = null;
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var imageUrl = ogTags.GetValueOrDefault("image");
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if (!string.IsNullOrWhiteSpace(imageUrl))
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{
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imageAscii = await FetchImageThumbnailAsync(imageUrl, uri, cts.Token);
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}
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return new EmbedDto(siteName, title, description, imageAscii, url);
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}
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catch (OperationCanceledException)
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{
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_logger.LogDebug("Embed fetch timed out for message content");
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return null;
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}
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catch (Exception ex)
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{
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_logger.LogDebug(ex, "Failed to fetch embed");
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return null;
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}
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}
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private static string? ExtractFirstUrl(string content)
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{
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var match = UrlRegex().Match(content);
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if (!match.Success)
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return null;
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var url = match.Value;
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// Strip trailing punctuation that's likely not part of the URL
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url = url.TrimEnd('.', ',', '!', '?', ')', ']', ';', ':');
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return url;
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}
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private static bool IsPrivateHost(Uri uri)
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{
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if (uri.IsLoopback)
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return true;
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if (IPAddress.TryParse(uri.Host, out var ip))
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{
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var bytes = ip.GetAddressBytes();
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if (bytes.Length == 4)
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{
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if (bytes[0] == 10) return true;
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if (bytes[0] == 172 && bytes[1] >= 16 && bytes[1] <= 31) return true;
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if (bytes[0] == 192 && bytes[1] == 168) return true;
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if (bytes[0] == 127) return true;
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if (bytes[0] == 0) return true;
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}
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}
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// Also check hostname-based loopback
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if (uri.Host.Equals("localhost", StringComparison.OrdinalIgnoreCase))
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return true;
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return false;
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}
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private static Dictionary<string, string> ParseOgTags(string html)
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{
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var tags = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
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// Match: <meta property="og:key" content="value" />
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foreach (Match match in OgTagRegex().Matches(html))
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{
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var key = match.Groups[1].Value;
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var value = match.Groups[2].Value;
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tags.TryAdd(key, value);
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}
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// Match reversed order: <meta content="value" property="og:key" />
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foreach (Match match in OgTagReversedRegex().Matches(html))
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{
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var value = match.Groups[1].Value;
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var key = match.Groups[2].Value;
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tags.TryAdd(key, value);
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}
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return tags;
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}
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private async Task<string?> FetchImageThumbnailAsync(string imageUrl, Uri pageUri, CancellationToken ct)
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{
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try
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{
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// Resolve relative image URLs against the page URI
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if (!Uri.TryCreate(imageUrl, UriKind.Absolute, out var imageUri))
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{
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if (!Uri.TryCreate(pageUri, imageUrl, out imageUri))
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return null;
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}
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if (imageUri.Scheme is not ("http" or "https"))
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return null;
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if (IsPrivateHost(imageUri))
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return null;
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var client = _httpClientFactory.CreateClient("OgFetch");
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using var response = await client.GetAsync(imageUri, ct);
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if (!response.IsSuccessStatusCode)
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return null;
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var contentType = response.Content.Headers.ContentType?.MediaType;
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if (contentType is null || !contentType.StartsWith("image/", StringComparison.OrdinalIgnoreCase))
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return null;
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await using var stream = await response.Content.ReadAsStreamAsync(ct);
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// Buffer into a MemoryStream for validation + conversion
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using var memoryStream = new MemoryStream();
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await stream.CopyToAsync(memoryStream, ct);
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if (memoryStream.Length == 0 || memoryStream.Length > HubConstants.MaxFileSizeBytes)
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return null;
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memoryStream.Position = 0;
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if (!FileValidationHelper.IsValidImage(memoryStream))
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return null;
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memoryStream.Position = 0;
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return _asciiService.ConvertToAscii(memoryStream,
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HubConstants.EmbedThumbnailWidth,
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HubConstants.EmbedThumbnailHeight);
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}
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catch (Exception ex)
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{
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_logger.LogDebug(ex, "Failed to fetch OG image thumbnail from {Url}", imageUrl);
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return null;
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}
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}
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private static async Task<string> ReadLimitedAsync(HttpResponseMessage response, int maxBytes, CancellationToken ct)
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{
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await using var stream = await response.Content.ReadAsStreamAsync(ct);
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var buffer = new byte[maxBytes];
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var totalRead = 0;
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while (totalRead < maxBytes)
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{
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var read = await stream.ReadAsync(buffer.AsMemory(totalRead, maxBytes - totalRead), ct);
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if (read == 0) break;
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totalRead += read;
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}
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// Try to detect encoding from Content-Type, default to UTF-8
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var charset = response.Content.Headers.ContentType?.CharSet;
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var encoding = charset is not null
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? Encoding.GetEncoding(charset)
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: Encoding.UTF8;
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return encoding.GetString(buffer, 0, totalRead);
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}
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[GeneratedRegex(@"https?://[^\s<>""')\]]+", RegexOptions.IgnoreCase)]
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private static partial Regex UrlRegex();
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[GeneratedRegex(@"<meta\s+[^>]*?property\s*=\s*[""']og:(\w+)[""'][^>]*?content\s*=\s*[""']([^""']*)[""'][^>]*/?>",
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RegexOptions.IgnoreCase | RegexOptions.Singleline)]
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private static partial Regex OgTagRegex();
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[GeneratedRegex(@"<meta\s+[^>]*?content\s*=\s*[""']([^""']*)[""'][^>]*?property\s*=\s*[""']og:(\w+)[""'][^>]*/?>",
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RegexOptions.IgnoreCase | RegexOptions.Singleline)]
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private static partial Regex OgTagReversedRegex();
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[GeneratedRegex(@"<title[^>]*>([^<]+)</title>", RegexOptions.IgnoreCase)]
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private static partial Regex TitleTagRegex();
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}
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