[smuxi: 9/15] [Common] IconCache: add method to download a particular image

[Mirco M. M. Bauer <mmmbauer src gnome org>]

commit 40f7a5b93eb46e5c60c02b2239b035b724364618
Author: Carlos Martín Nieto <cmn dwim me>
Date:   Sun Feb 1 18:26:10 2015 +0100

    [Common] IconCache: add method to download a particular image
    
    Instead of just downloading a favicon, download a particular image from
    a url directly. This will be useful for emoji and arbitrary external
    images.
    
    As this is the last part of what the favicon downloader does, we can
    extract that functionality as well and use it for the direct downloader.

 src/Common/IconCache.cs |  139 +++++++++++++++++++++++++++++++----------------
 1 files changed, 93 insertions(+), 46 deletions(-)
---
diff --git a/src/Common/IconCache.cs b/src/Common/IconCache.cs
index dddc077..f2d3f5a 100644
--- a/src/Common/IconCache.cs
+++ b/src/Common/IconCache.cs
@@ -73,33 +73,50 @@ namespace Smuxi.Common
         }
 
         /// <summary>
-        /// Download an icon into the cache.
-        ///
-        /// The download will happen in the background and onSuccess will be called
-        /// when done. If there is an error during the download, an error will be
-        /// logged and onSuccess will not be called.
-        ///
-        /// The callback will be called in the background thread. If you want to
-        /// update the GUI, make sure you schedule code to run in the main thread.
+        /// Download an image file into the cache
         /// </summary>
         /// <param name="protocol">The protocol of the channel or server</param>
-        /// <param name="iconName">Name of the icon, including extension</param>
-        /// <param name="websiteUrl">The url from which to download the icon</param>
-        /// <param name="onSuccess">Function to call after downloading the icon</param>
-        /// <param name="onError">Function to call if an error happens (optinal)</param>
+        /// <param name="iconName">Name of the image, including extension</param>
+        /// <param name="fileUrl">The url from which to download the image</param>
+        /// <param name="onSuccess">Function to call after downloading the image</param>
+        /// <param name="onError">Function to call if an error happens (optional)</param>
         /// <remarks>
         /// This method is thread safe
         /// </remarks>
-        public void DownloadIcon(string protocol, string iconName, string websiteUrl,
+        public void DownloadFile(string protocol, string iconName, string fileUrl,
             Action<string> onSuccess, Action<Exception> onError)
         {
+            EnqueueDownload(protocol, iconName, fileUrl, DownloadFileWorker, onSuccess, onError);
+        }
+
+        void DownloadFileWorker(string fileUrl, FileInfo imageFile)
+        {
+            Trace.Call(fileUrl, imageFile);
+
+            // download to a randomly-named file so we don't conflict with a concurrent download
+            var tempFile = new FileInfo(Path.Combine(imageFile.DirectoryName, Path.GetRandomFileName()));
+            DownloadFileFromUrl(fileUrl, tempFile);
+
+            // finally, rename atomically, giving up if someone beat us to downloading
+            // this file
+            try {
+                tempFile.MoveTo(imageFile.FullName);
+            } catch (IOException) {
+                // someone beat us to downloading the image, simply remove the temp file
+                tempFile.Delete();
+            }
+        }
+
+        void EnqueueDownload(string protocol, string iconName, string url,
+            Action<string, FileInfo> action, Action<string> onSuccess, Action<Exception> onError)
+        {
             ThreadPool.QueueUserWorkItem(delegate {
                 try {
                     var protocolPath = Path.Combine(f_IconsPath, protocol);
                     EnsureDirectoryExists(protocolPath);
                     var iconPath = Path.Combine(protocolPath, iconName);
                     var iconFile = new FileInfo(iconPath);
-                    DownloadServerIcon(websiteUrl, iconFile);
+                    action(url, iconFile);
                     iconFile.Refresh();
                     if (!iconFile.Exists || iconFile.Length == 0) {
                         return;
@@ -108,7 +125,7 @@ namespace Smuxi.Common
                     onSuccess(iconPath);
                 } catch (Exception ex) {
 #if LOG4NET
-                    f_Logger.Error("DownloadIcon(): Exception", ex);
+                    f_Logger.Error("IconCache: Exception", ex);
 #endif
                     if (onError != null) {
                         onError(ex);
@@ -117,6 +134,66 @@ namespace Smuxi.Common
             });
         }
 
+        void DownloadFileFromUrl(string url, FileInfo file)
+        {
+            var request = WebRequest.Create(url);
+            request.Proxy = Proxy;
+
+            if (request is HttpWebRequest) {
+                var iconHttpRequest = (HttpWebRequest) request;
+                if (file.Exists) {
+                    iconHttpRequest.IfModifiedSince = file.LastWriteTime;
+                }
+            }
+
+            WebResponse response;
+            try {
+                response = request.GetResponse();
+            } catch (WebException ex) {
+                if (ex.Response is HttpWebResponse) {
+                    var iconHttpResponse = (HttpWebResponse) ex.Response;
+                    if (iconHttpResponse.StatusCode == HttpStatusCode.NotModified) {
+                        // icon hasn't changed, nothing to do
+                        return;
+                    }
+                }
+                throw;
+            }
+
+            using (var fileStream = file.OpenWrite())
+            using (var httpStream = response.GetResponseStream()) {
+                byte[] buffer = new byte[4096];
+                int read;
+                while ((read = httpStream.Read(buffer, 0, buffer.Length)) > 0) {
+                    fileStream.Write(buffer, 0, read);
+                }
+            }
+        }
+
+        /// <summary>
+        /// Download an icon into the cache.
+        ///
+        /// The download will happen in the background and onSuccess will be called
+        /// when done. If there is an error during the download, an error will be
+        /// logged and onSuccess will not be called.
+        ///
+        /// The callback will be called in the background thread. If you want to
+        /// update the GUI, make sure you schedule code to run in the main thread.
+        /// </summary>
+        /// <param name="protocol">The protocol of the channel or server</param>
+        /// <param name="iconName">Name of the icon, including extension</param>
+        /// <param name="websiteUrl">The url from which to download the icon</param>
+        /// <param name="onSuccess">Function to call after downloading the icon</param>
+        /// <param name="onError">Function to call if an error happens (optinal)</param>
+        /// <remarks>
+        /// This method is thread safe
+        /// </remarks>
+        public void DownloadIcon(string protocol, string iconName, string websiteUrl,
+            Action<string> onSuccess, Action<Exception> onError)
+        {
+            EnqueueDownload(protocol, iconName, websiteUrl, DownloadServerIcon, onSuccess, onError);
+        }
+
         void DownloadServerIcon(string websiteUrl, FileInfo iconFile)
         {
             Trace.Call(websiteUrl, iconFile);
@@ -168,39 +245,9 @@ namespace Smuxi.Common
                 faviconUrl);
             #endif
 
-            var iconRequest = WebRequest.Create(faviconUrl);
-            iconRequest.Proxy = Proxy;
-
-            if (iconRequest is HttpWebRequest) {
-                var iconHttpRequest = (HttpWebRequest) iconRequest;
-                if (iconFile.Exists) {
-                    iconHttpRequest.IfModifiedSince = iconFile.LastWriteTime;
-                }
-            }
-
-            WebResponse iconResponse;
-            try {
-                iconResponse = iconRequest.GetResponse();
-            } catch (WebException ex) {
-                if (ex.Response is HttpWebResponse) {
-                    var iconHttpResponse = (HttpWebResponse) ex.Response;
-                    if (iconHttpResponse.StatusCode == HttpStatusCode.NotModified) {
-                        // icon hasn't changed, nothing to do
-                        return;
-                    }
-                }
-                throw;
-            }
 
             // save new or modified icon file
-            using (var iconStream = iconFile.OpenWrite())
-            using (var httpStream = iconResponse.GetResponseStream()) {
-                byte[] buffer = new byte[4096];
-                int read;
-                while ((read = httpStream.Read(buffer, 0, buffer.Length)) > 0) {
-                    iconStream.Write(buffer, 0, read);
-                }
-            }
+            DownloadFileFromUrl(faviconUrl, iconFile);
         }
 
         /// <summary>