New: Ensure covers up to date with Goodreads

src/NzbDrone.Common/Http/Dispatchers/ManagedHttpDispatcher.cs

@@ -202,8 +202,6 @@ namespace NzbDrone.Common.Http.Dispatchers
                     case "If-Modified-Since":
                         webRequest.IfModifiedSince = HttpHeader.ParseDateTime(header.Value);
                         break;
-                    case "Range":
-                        throw new NotImplementedException();
                     case "Referer":
                         webRequest.Referer = header.Value;
                         break;

src/NzbDrone.Core.Test/MediaCoverTests/MediaCoverServiceFixture.cs

@@ -45,7 +45,7 @@ namespace NzbDrone.Core.Test.MediaCoverTests
                 .Build();
 
             _httpResponse = new HttpResponse(null, new HttpHeader(), "");
-            Mocker.GetMock<IHttpClient>().Setup(c => c.Head(It.IsAny<HttpRequest>())).Returns(_httpResponse);
+            Mocker.GetMock<IHttpClient>().Setup(c => c.Get(It.IsAny<HttpRequest>())).Returns(_httpResponse);
         }
 
         [TestCase(".png")]

src/NzbDrone.Core/MediaCover/CoverAlreadyExistsSpecification.cs

@@ -38,7 +38,7 @@ namespace NzbDrone.Core.MediaCover
                 return lastModifiedLocal.Value.ToUniversalTime() == serverModifiedDate.Value.ToUniversalTime();
             }
 
-            return true;
+            return false;
         }
     }
 }

src/NzbDrone.Core/MediaCover/MediaCoverService.cs

@@ -29,8 +29,7 @@ namespace NzbDrone.Core.MediaCover
         IHandleAsync<BookDeletedEvent>,
         IMapCoversToLocal
     {
-        private const double HTTP_RATE_LIMIT = 0;
-        private const string USER_AGENT = "Dalvik/2.1.0 (Linux; U; Android 10; Mi A2 Build/QKQ1.190910.002)";
+        private const string USER_AGENT = "Dalvik/2.1.0 (Linux; U; Android 10; SM-G975U Build/QP1A.190711.020)";
 
         private readonly IImageResizer _resizer;
         private readonly IBookService _bookService;
@@ -127,11 +126,13 @@ namespace NzbDrone.Core.MediaCover
 
                 try
                 {
-                    alreadyExists = _coverExistsSpecification.AlreadyExists(null, null, fileName);
+                    var serverFileHeaders = GetServerHeaders(cover.Url);
+
+                    alreadyExists = _coverExistsSpecification.AlreadyExists(serverFileHeaders.LastModified, GetContentLength(serverFileHeaders), fileName);
 
                     if (!alreadyExists)
                     {
-                        DownloadCover(author, cover, DateTime.Now);
+                        DownloadCover(author, cover, serverFileHeaders.LastModified ?? DateTime.Now);
                     }
                 }
                 catch (WebException e)
@@ -169,11 +170,13 @@ namespace NzbDrone.Core.MediaCover
                 var alreadyExists = false;
                 try
                 {
-                    alreadyExists = _coverExistsSpecification.AlreadyExists(null, null, fileName);
+                    var serverFileHeaders = GetServerHeaders(cover.Url);
+
+                    alreadyExists = _coverExistsSpecification.AlreadyExists(serverFileHeaders.LastModified, GetContentLength(serverFileHeaders), fileName);
 
                     if (!alreadyExists)
                     {
-                        DownloadAlbumCover(book, cover, DateTime.Now);
+                        DownloadAlbumCover(book, cover, serverFileHeaders.LastModified ?? DateTime.Now);
                     }
                 }
                 catch (WebException e)
@@ -269,6 +272,38 @@ namespace NzbDrone.Core.MediaCover
             }
         }
 
+        private HttpHeader GetServerHeaders(string url)
+        {
+            // Goodreads doesn't allow a HEAD, so request a zero byte range instead
+            var request = new HttpRequest(url)
+            {
+                AllowAutoRedirect = true,
+            };
+
+            request.Headers.Add("Range", "bytes=0-0");
+            request.Headers.Add("User-Agent", USER_AGENT);
+
+            return _httpClient.Get(request).Headers;
+        }
+
+        private long? GetContentLength(HttpHeader headers)
+        {
+            var range = headers.Get("content-range");
+
+            if (range == null)
+            {
+                return null;
+            }
+
+            var split = range.Split('/');
+            if (split.Length == 2 && long.TryParse(split[1], out long length))
+            {
+                return length;
+            }
+
+            return null;
+        }
+
         public void HandleAsync(AuthorRefreshCompleteEvent message)
         {
             EnsureArtistCovers(message.Author);