Stop requesting URL previews if the feature has been disabled on the homeserver.

Riot/Managers/URLPreviews/URLPreviewService.swift

@@ -15,6 +15,7 @@
 //
 
 import Foundation
+import AFNetworking
 
 enum URLPreviewServiceError: Error {
     case missingResponse
@@ -74,7 +75,10 @@ class URLPreviewService: NSObject {
                 success(previewData)
             }
             
-        }, failure: failure)
+        }, failure: { error in
+            self.checkForDisabledAPI(in: error)
+            failure(error)
+        })
     }
     
     /// Removes any cached preview data that has expired.
@@ -156,4 +160,21 @@ class URLPreviewService: NSObject {
         
         return components?.url ?? url
     }
+    
+    /// Checks an error returned from `MXRestClient` to see whether the previews API
+    /// has been disabled on the homeserver. If this is true, link detection will be disabled
+    /// to prevent further requests being made and stop any previews loaders being presented.
+    private func checkForDisabledAPI(in error: Error?) {
+        // The error will contain a 404 and no matrix error code.
+        guard
+            let error = error as NSError?,
+            error.userInfo[kMXErrorCodeKey] == nil,
+            let response = error.userInfo[AFNetworkingOperationFailingURLResponseErrorKey] as? HTTPURLResponse
+        else { return }
+        
+        if response.statusCode == 404 {
+            MXLog.debug("[URLPreviewService] Disabling link detection as homeserver does not support URL previews.")
+            MXKAppSettings.standard().enableBubbleComponentLinkDetection = false
+        }
+    }
 }