[gnome-boxes] downloader: Write chunks to file instead of memory

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 3eabdb1c6479473a53d660bb1c15f1c75748e012
Author: Lasse Schuirmann <lasse schuirmann gmail com>
Date:   Tue Jul 15 18:10:04 2014 +0200

    downloader: Write chunks to file instead of memory
    
    This makes the downloader suitable for downloading large files and
    additionally prevents that all downloaded data is hold in the memory
    until the program terminates.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=733170

 src/downloader.vala |   27 +++++++++++++++++++++++----
 1 files changed, 23 insertions(+), 4 deletions(-)
---
diff --git a/src/downloader.vala b/src/downloader.vala
index fa8373d..6aff83f 100644
--- a/src/downloader.vala
+++ b/src/downloader.vala
@@ -110,6 +110,7 @@ private class Boxes.Downloader : GLib.Object {
 
     private async void download_from_http (Download download) throws GLib.Error {
         var msg = new Soup.Message ("GET", download.uri);
+        msg.response_body.set_accumulate (false);
         var address = msg.get_address ();
         var connectable = new NetworkAddress (address.name, (uint16) address.port);
         var network_monitor = NetworkMonitor.get_default ();
@@ -121,22 +122,40 @@ private class Boxes.Downloader : GLib.Object {
             total_num_bytes =  msg.response_headers.get_content_length ();
         });
 
+        var cached_file_stream = yield download.cached_file.create_async (FileCreateFlags.NONE);
+        GLib.Error? err = null;
+
         int64 current_num_bytes = 0;
+        // FIXME: Reduce lambda nesting by splitting out downloading to Download class
         msg.got_chunk.connect ((msg, chunk) => {
             if (total_num_bytes <= 0)
                 return;
 
             current_num_bytes += chunk.length;
-            download.progress.progress = (double) current_num_bytes / total_num_bytes;
+            try {
+                // Write synchronously as we have no control over order of async
+                // calls and we'll end up writing bytes out in wrong order. Besides
+                // we are writing small chunks so it wouldn't really block the UI.
+                cached_file_stream.write (chunk.data);
+                download.progress.progress = (double) current_num_bytes / total_num_bytes;
+            } catch (GLib.Error e) {
+                err = e;
+                session.cancel_message (msg, Soup.Status.CANCELLED);
+            }
         });
 
         session.queue_message (msg, (session, msg) => {
             download_from_http.callback ();
         });
+
         yield;
-        if (msg.status_code != Soup.Status.OK)
-            throw new Boxes.Error.INVALID (msg.reason_phrase);
-        yield download.cached_file.replace_contents_async (msg.response_body.data, null, false, 0, null, 
null);
+        if (msg.status_code != Soup.Status.OK) {
+            download.cached_file.delete ();
+            if (err == null)
+                err = new GLib.Error (Soup.http_error_quark (), (int)msg.status_code, msg.reason_phrase);
+
+            throw err;
+        }
     }
 
     public static async void fetch_os_logo (Gtk.Image image, Osinfo.Os os, int size) {