Inheritance: System.IO.IOException
        private void DownloadObject(ProgressMonitor pm, AnyObjectId id)
        {
            if (_local.HasObject(id)) return;

            while (true)
            {
                if (DownloadPackedObject(pm, id))
                    return;

                string idStr = id.Name;
                string subdir = idStr.Slice(0, 2);
                string file = idStr.Substring(2);
                string looseName = subdir + "/" + file;

                for (int i = _lastRemoteIdx; i < _remotes.Count; i++)
                {
                    if (DownloadLooseObject(id, looseName, _remotes[i]))
                    {
                        _lastRemoteIdx = i;
                        return;
                    }
                }

                for (int i = 0; i < _lastRemoteIdx; i++)
                {
                    if (DownloadLooseObject(id, looseName, _remotes[i]))
                    {
                        _lastRemoteIdx = i;
                        return;
                    }
                }

                while (_noPacksYet.Count > 0)
                {
                    WalkRemoteObjectDatabase wrr = _noPacksYet.First.Value;
                    _noPacksYet.RemoveFirst();
                    List<string> packNameList;
                    try
                    {
                        pm.BeginTask("Listing packs", ProgressMonitor.UNKNOWN);
                        packNameList = wrr.getPackNames();
                    }
                    catch (IOException e)
                    {
                        RecordError(id, e);
                        continue;
                    }
                    finally
                    {
                        pm.EndTask();
                    }

                    if (packNameList == null || packNameList.Count == 0)
                        continue;
                    foreach (string packName in packNameList)
                    {
                        if (!_packsConsidered.Contains(packName))
                        {
                            _packsConsidered.Add(packName);
                            _unfetchedPacks.AddLast(new RemotePack(_lockMessage, _packLocks, _objCheck, _local, wrr, packName));
                        }
                    }
                    if (DownloadPackedObject(pm, id))
                        return;
                }

                List<WalkRemoteObjectDatabase> al = ExpandOneAlternate(id, pm);
                if (al != null && al.Count > 0)
                {
                    foreach (WalkRemoteObjectDatabase alt in al)
                    {
                        _remotes.Add(alt);
                        _noPacksYet.AddLast(alt);
                        _noAlternatesYet.AddLast(alt);
                    }
                    continue;
                }

                List<Exception> failures = null;
                if (_fetchErrors.ContainsKey(id.Copy()))
                {
                    failures = _fetchErrors[id.Copy()];
                }

                TransportException te = null;
                if (failures != null && failures.Count > 0)
                {
                    te = failures.Count == 1 ?
                        new TransportException("Cannot get " + id.Name + ".", failures[0]) :
                        new TransportException("Cannot get " + id.Name + ".", new CompoundException(failures));
                }

                if (te == null)
                {
                    te = new TransportException("Cannot get " + id.Name + ".");
                }

                throw te;
            }
        }
        private void DownloadObject(ProgressMonitor pm, AnyObjectId id)
        {
            if (_local.HasObject(id)) return;

            while (true)
            {
                // Try a pack file we know about, but don't have yet. Odds are
                // that if it has this object, it has others related to it so
                // getting the pack is a good bet.
                //
                if (DownloadPackedObject(pm, id))
                    return;

                // Search for a loose object over all alternates, starting
                // from the one we last successfully located an object through.
                //
                string idStr = id.Name;
                string subdir = idStr.Slice(0, 2);
                string file = idStr.Substring(2);
                string looseName = subdir + "/" + file;

                for (int i = _lastRemoteIdx; i < _remotes.Count; i++)
                {
                    if (DownloadLooseObject(id, looseName, _remotes[i]))
                    {
                        _lastRemoteIdx = i;
                        return;
                    }
                }

                for (int i = 0; i < _lastRemoteIdx; i++)
                {
                    if (DownloadLooseObject(id, looseName, _remotes[i]))
                    {
                        _lastRemoteIdx = i;
                        return;
                    }
                }

                // Try to obtain more pack information and search those.
                //
                while (_noPacksYet.Count > 0)
                {
                    WalkRemoteObjectDatabase wrr = _noPacksYet.First.Value;
                    _noPacksYet.RemoveFirst();
                    ICollection<string> packNameList;
                    try
                    {
                        pm.BeginTask("Listing packs", ProgressMonitor.UNKNOWN);
                        packNameList = wrr.getPackNames();
                    }
                    catch (IOException e)
                    {
                        // Try another repository.
                        //
                        RecordError(id, e);
                        continue;
                    }
                    finally
                    {
                        pm.EndTask();
                    }

                    if (packNameList == null || packNameList.Count == 0)
                        continue;
                    foreach (string packName in packNameList)
                    {
                        bool contains = _packsConsidered.Contains(packName);
                        _packsConsidered.Add(packName);
                        if (!contains)
                        {
                            _unfetchedPacks.AddLast(new RemotePack(_lockMessage, _packLocks, _objCheck, _local, wrr, packName));
                        }
                    }
                    if (DownloadPackedObject(pm, id))
                        return;
                }

                // Try to expand the first alternate we haven't expanded yet.
                //
                ICollection<WalkRemoteObjectDatabase> al = ExpandOneAlternate(id, pm);
                if (al != null && al.Count > 0)
                {
                    foreach (WalkRemoteObjectDatabase alt in al)
                    {
                        _remotes.Add(alt);
                        _noPacksYet.AddLast(alt);
                        _noAlternatesYet.AddLast(alt);
                    }
                    continue;
                }

                // We could not obtain the object. There may be reasons why.
                //
                List<Exception> failures = _fetchErrors.get(id.Copy());

                var te = new TransportException("Cannot get " + id.Name + ".");

                if (failures != null && failures.Count > 0)
                {
                    te = failures.Count == 1 ?
                        new TransportException("Cannot get " + id.Name + ".", failures[0]) :
                        new TransportException("Cannot get " + id.Name + ".", new CompoundException(failures));
                }

                throw te;
            }
        }