adds config and method to verify that a url exists (returns success status code) when selecting provider

Author: skttl

src/ImageSharpCommunity.Providers.Remote/Configuration/RemoteImageProviderSetting.cs

@@ -57,5 +57,10 @@ public RemoteImageProviderSetting(string prefix)
     /// </summary>
     public bool AllowAllDomains { get; set; }
 
+    /// <summary>
+    /// Verify that the input url returns a succesful status code.
+    /// </summary>
+    public bool VerifyUrl { get; set; } = true;
+
     internal string ClientDictionaryKey => $"{HttpClientName}_{UserAgent}_{Timeout}_{MaxBytes}";
 }

src/ImageSharpCommunity.Providers.Remote/RemoteImageProvider.cs

@@ -1,5 +1,6 @@
 using ImageSharpCommunity.Providers.Remote.Configuration;
 using Microsoft.AspNetCore.Http;
+using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using SixLabors.ImageSharp.Web.Providers;
@@ -13,13 +14,15 @@ public class RemoteImageProvider : IImageProvider
     private readonly RemoteImageProviderOptions _options;
     private readonly ILogger<RemoteImageProvider> _logger;
     private readonly ILogger<RemoteImageResolver> _resolverLogger;
+    private readonly IMemoryCache _cache;
 
-    public RemoteImageProvider(IHttpClientFactory clientFactory, IOptions<RemoteImageProviderOptions> options, ILogger<RemoteImageProvider> logger, ILogger<RemoteImageResolver> resolverLogger)
+    public RemoteImageProvider(IHttpClientFactory clientFactory, IOptions<RemoteImageProviderOptions> options, ILogger<RemoteImageProvider> logger, ILogger<RemoteImageResolver> resolverLogger, IMemoryCache cache)
     {
         _clientFactory = clientFactory;
         _options = options.Value;
         _logger = logger;
         _resolverLogger = resolverLogger;
+        _cache = cache;
     }
 
     public ProcessingBehavior ProcessingBehavior => ProcessingBehavior.All;
@@ -37,7 +40,8 @@ public bool IsValidRequest(HttpContext context)
             context.Request.Path.GetMatchingRemoteImageProviderSetting(_options) is RemoteImageProviderSetting setting
             && context.Request.Path.GetSourceUrlForRemoteImageProviderUrl(_options) is string url
             && Uri.TryCreate(url, UriKind.Absolute, out Uri? uri) && uri != null
-            && uri.IsValidForSetting(setting);
+            && uri.IsValidForSetting(setting)
+            && UrlReturnsSuccess(setting, uri);
     }
 
     public Task<IImageResolver?> GetAsync(HttpContext context)
@@ -60,4 +64,30 @@ private bool IsMatch(HttpContext context)
     {
         return context.Request.Path.GetMatchingRemoteImageProviderSetting(_options) != null;
     }
+
+    private bool UrlReturnsSuccess(RemoteImageProviderSetting setting, Uri uri)
+    {
+        if (setting.VerifyUrl == false)
+        {
+            _logger.LogDebug("Skipping verification of URL {Url} as VerifyUrl is set to false", uri);
+            return true;
+        }
+
+        if (_cache.TryGetValue(nameof(RemoteImageProvider) + uri, out bool cachedResult))
+        {
+            _logger.LogDebug("Using cached result for URL {Url}", uri);
+            return cachedResult;
+        }
+
+        var client = _clientFactory.GetRemoteImageProviderHttpClient(setting);
+        var request = new HttpRequestMessage(HttpMethod.Head, uri);
+        var response = client.SendAsync(request).Result;
+
+        if (response.Headers.CacheControl?.MaxAge is not null)
+        {
+            _cache.Set(nameof(RemoteImageProvider) + uri, response.IsSuccessStatusCode, response.Headers.CacheControl.MaxAge ?? TimeSpan.Zero);
+        }
+
+        return response.IsSuccessStatusCode;
+    }
 }