diff --git a/retroshare-gui/src/gui/common/RsCollection.cpp b/retroshare-gui/src/gui/common/RsCollection.cpp
index e7e329604..21079c114 100644
--- a/retroshare-gui/src/gui/common/RsCollection.cpp
+++ b/retroshare-gui/src/gui/common/RsCollection.cpp
@@ -45,19 +45,25 @@ RsCollection::RsCollection(QObject *parent)
 RsCollection::RsCollection(const RsFileTree& ft)
 {
     mFileTree = std::unique_ptr<RsFileTree>(new RsFileTree(ft));
+
+    for(uint64_t i=0;i<mFileTree->numFiles();++i)
+        mHashes.insert(std::make_pair(mFileTree->fileData(i).hash,i ));
 }
 
 RsCollection::RsCollection(const std::vector<DirDetails>& file_infos,FileSearchFlags flags, QObject *parent)
     : QObject(parent), mFileTree(new RsFileTree)
 {
-	if(! ( (flags & RS_FILE_HINTS_LOCAL) || (flags & RS_FILE_HINTS_REMOTE)))
-	{
-		std::cerr << "(EE) Wrong flags passed to RsCollection constructor. Please fix the code!" << std::endl;
-		return ;
-	}
+    if(! ( (flags & RS_FILE_HINTS_LOCAL) || (flags & RS_FILE_HINTS_REMOTE)))
+    {
+        std::cerr << "(EE) Wrong flags passed to RsCollection constructor. Please fix the code!" << std::endl;
+        return ;
+    }
 
-	for(uint32_t i = 0;i<file_infos.size();++i)
+    for(uint32_t i = 0;i<file_infos.size();++i)
         recursAddElements(mFileTree->root(),file_infos[i],flags) ;
+
+    for(uint64_t i=0;i<mFileTree->numFiles();++i)
+        mHashes.insert(std::make_pair(mFileTree->fileData(i).hash,i ));
 }
 
 RsCollection::~RsCollection()
@@ -67,88 +73,88 @@ RsCollection::~RsCollection()
 void RsCollection::downloadFiles() const
 {
 #ifdef TODO_COLLECTION
-	// print out the element names of all elements that are direct children
-	// of the outermost element.
-	QDomElement docElem = _xml_doc.documentElement();
+    // print out the element names of all elements that are direct children
+    // of the outermost element.
+    QDomElement docElem = _xml_doc.documentElement();
 
-	std::vector<ColFileInfo> colFileInfos ;
+    std::vector<ColFileInfo> colFileInfos ;
 
-	recursCollectColFileInfos(docElem,colFileInfos,QString(),false) ;
+    recursCollectColFileInfos(docElem,colFileInfos,QString(),false) ;
 
-	RsCollectionDialog(_fileName, colFileInfos, false).exec() ;
+    RsCollectionDialog(_fileName, colFileInfos, false).exec() ;
 #endif
 }
 
 void RsCollection::autoDownloadFiles() const
 {
 #ifdef TODO_COLLECTION
-	QDomElement docElem = _xml_doc.documentElement();
+    QDomElement docElem = _xml_doc.documentElement();
 
-	std::vector<ColFileInfo> colFileInfos;
+    std::vector<ColFileInfo> colFileInfos;
 
-	recursCollectColFileInfos(docElem,colFileInfos,QString(),false);
+    recursCollectColFileInfos(docElem,colFileInfos,QString(),false);
 
-	QString dlDir = QString::fromUtf8(rsFiles->getDownloadDirectory().c_str());
+    QString dlDir = QString::fromUtf8(rsFiles->getDownloadDirectory().c_str());
 
-	foreach(ColFileInfo colFileInfo, colFileInfos)
-	{
-		autoDownloadFiles(colFileInfo, dlDir);
-	}
+    foreach(ColFileInfo colFileInfo, colFileInfos)
+    {
+        autoDownloadFiles(colFileInfo, dlDir);
+    }
 #endif
 }
 
 void RsCollection::autoDownloadFiles(ColFileInfo colFileInfo, QString dlDir) const
 {
-	if (!colFileInfo.filename_has_wrong_characters)
-	{
-		QString cleanPath = dlDir + colFileInfo.path ;
-		std::cout << "making directory " << cleanPath.toStdString() << std::endl;
+    if (!colFileInfo.filename_has_wrong_characters)
+    {
+        QString cleanPath = dlDir + colFileInfo.path ;
+        std::cout << "making directory " << cleanPath.toStdString() << std::endl;
 
-		if(!QDir(QApplication::applicationDirPath()).mkpath(cleanPath))
-			std::cerr << "Unable to make path: " + cleanPath.toStdString() << std::endl;
+        if(!QDir(QApplication::applicationDirPath()).mkpath(cleanPath))
+            std::cerr << "Unable to make path: " + cleanPath.toStdString() << std::endl;
 
-		if (colFileInfo.type==DIR_TYPE_FILE)
-			rsFiles->FileRequest(colFileInfo.name.toUtf8().constData(),
-			                     RsFileHash(colFileInfo.hash.toStdString()),
-			                     colFileInfo.size,
-			                     cleanPath.toUtf8().constData(),
-			                     RS_FILE_REQ_ANONYMOUS_ROUTING,
-			                     std::list<RsPeerId>());
-	}
-	foreach(ColFileInfo colFileInfoChild, colFileInfo.children)
-	{
-		autoDownloadFiles(colFileInfoChild, dlDir);
-	}
+        if (colFileInfo.type==DIR_TYPE_FILE)
+            rsFiles->FileRequest(colFileInfo.name.toUtf8().constData(),
+                                 RsFileHash(colFileInfo.hash.toStdString()),
+                                 colFileInfo.size,
+                                 cleanPath.toUtf8().constData(),
+                                 RS_FILE_REQ_ANONYMOUS_ROUTING,
+                                 std::list<RsPeerId>());
+    }
+    foreach(ColFileInfo colFileInfoChild, colFileInfo.children)
+    {
+        autoDownloadFiles(colFileInfoChild, dlDir);
+    }
 }
 
 static QString purifyFileName(const QString& input,bool& bad)
 {
-	static const QString bad_chars = "/\\\"*:?<>|" ;
-	bad = false ;
-	QString output = input ;
+    static const QString bad_chars = "/\\\"*:?<>|" ;
+    bad = false ;
+    QString output = input ;
 
-	for(int i=0;i<output.length();++i)
-		for(int j=0;j<bad_chars.length();++j)
-			if(output[i] == bad_chars[j])
-			{
-				output[i] = '_' ;
-				bad = true ;
-			}
+    for(int i=0;i<output.length();++i)
+        for(int j=0;j<bad_chars.length();++j)
+            if(output[i] == bad_chars[j])
+            {
+                output[i] = '_' ;
+                bad = true ;
+            }
 
-	return output ;
+    return output ;
 }
 
 void RsCollection::merge_in(const QString& fname,uint64_t size,const RsFileHash& hash)
 {
     mFileTree->addFile(mFileTree->root(),fname.toStdString(),hash,size);
 #ifdef TO_REMOVE
-	ColFileInfo info ;
-	info.type = DIR_TYPE_FILE ;
-	info.name = fname ;
-	info.size = size ;
-	info.hash = QString::fromStdString(hash.toStdString()) ;
+    ColFileInfo info ;
+    info.type = DIR_TYPE_FILE ;
+    info.name = fname ;
+    info.size = size ;
+    info.hash = QString::fromStdString(hash.toStdString()) ;
 
-	recursAddElements(_xml_doc,info,_root) ;
+    recursAddElements(_xml_doc,info,_root) ;
 #endif
 }
 void RsCollection::merge_in(const RsFileTree& tree)
@@ -175,56 +181,56 @@ void RsCollection::recursMergeTree(RsFileTree::DirIndex parent,const RsFileTree&
 #ifdef TO_REMOVE
 void RsCollection::recursCollectColFileInfos(const QDomElement& e,std::vector<ColFileInfo>& colFileInfos,const QString& current_path, bool bad_chars_in_parent) const
 {
-	QDomNode n = e.firstChild() ;
+    QDomNode n = e.firstChild() ;
 #ifdef COLLECTION_DEBUG
-	std::cerr << "Parsing element " << e.tagName().toStdString() << std::endl;
+    std::cerr << "Parsing element " << e.tagName().toStdString() << std::endl;
 #endif
 
-	while(!n.isNull()) 
-	{
-		QDomElement ee = n.toElement(); // try to convert the node to an element.
+    while(!n.isNull())
+    {
+        QDomElement ee = n.toElement(); // try to convert the node to an element.
 
 #ifdef COLLECTION_DEBUG
-		std::cerr << "  Seeing child " << ee.tagName().toStdString() << std::endl;
+        std::cerr << "  Seeing child " << ee.tagName().toStdString() << std::endl;
 #endif
 
-		if(ee.tagName() == QString("File"))
-		{
-			ColFileInfo newChild ;
-			newChild.hash = ee.attribute(QString("sha1")) ;
-			bool bad_chars_detected = false ;
-			newChild.name = purifyFileName(ee.attribute(QString("name")), bad_chars_detected) ;
-			newChild.filename_has_wrong_characters = bad_chars_detected || bad_chars_in_parent ;
-			newChild.size = ee.attribute(QString("size")).toULongLong() ;
-			newChild.path = current_path ;
-			newChild.type = DIR_TYPE_FILE ;
+        if(ee.tagName() == QString("File"))
+        {
+            ColFileInfo newChild ;
+            newChild.hash = ee.attribute(QString("sha1")) ;
+            bool bad_chars_detected = false ;
+            newChild.name = purifyFileName(ee.attribute(QString("name")), bad_chars_detected) ;
+            newChild.filename_has_wrong_characters = bad_chars_detected || bad_chars_in_parent ;
+            newChild.size = ee.attribute(QString("size")).toULongLong() ;
+            newChild.path = current_path ;
+            newChild.type = DIR_TYPE_FILE ;
 
-			colFileInfos.push_back(newChild) ;
-		}
-		else if(ee.tagName() == QString("Directory"))
-		{
-			ColFileInfo newParent ;
-			bool bad_chars_detected = false ;
-			QString cleanDirName = purifyFileName(ee.attribute(QString("name")),bad_chars_detected) ;
-			newParent.name=cleanDirName;
-			newParent.filename_has_wrong_characters = bad_chars_detected || bad_chars_in_parent ;
-			newParent.size = 0;
-			newParent.path = current_path ;
-			newParent.type = DIR_TYPE_DIR ;
+            colFileInfos.push_back(newChild) ;
+        }
+        else if(ee.tagName() == QString("Directory"))
+        {
+            ColFileInfo newParent ;
+            bool bad_chars_detected = false ;
+            QString cleanDirName = purifyFileName(ee.attribute(QString("name")),bad_chars_detected) ;
+            newParent.name=cleanDirName;
+            newParent.filename_has_wrong_characters = bad_chars_detected || bad_chars_in_parent ;
+            newParent.size = 0;
+            newParent.path = current_path ;
+            newParent.type = DIR_TYPE_DIR ;
 
-			recursCollectColFileInfos(ee,newParent.children,current_path + "/" + cleanDirName, bad_chars_in_parent || bad_chars_detected) ;
-			uint32_t size = newParent.children.size();
-			for(uint32_t i=0;i<size;++i)
-			{
-				const ColFileInfo &colFileInfo = newParent.children[i];
-				newParent.size +=colFileInfo.size ;
-			}
+            recursCollectColFileInfos(ee,newParent.children,current_path + "/" + cleanDirName, bad_chars_in_parent || bad_chars_detected) ;
+            uint32_t size = newParent.children.size();
+            for(uint32_t i=0;i<size;++i)
+            {
+                const ColFileInfo &colFileInfo = newParent.children[i];
+                newParent.size +=colFileInfo.size ;
+            }
 
-			colFileInfos.push_back(newParent) ;
-		}
+            colFileInfos.push_back(newParent) ;
+        }
 
-		n = n.nextSibling() ;
-	}
+        n = n.nextSibling() ;
+    }
 }
 #endif
 
@@ -234,82 +240,82 @@ void RsCollection::recursAddElements(RsFileTree::DirIndex parent, const DirDetai
     if (dd.type == DIR_TYPE_FILE)
         mFileTree->addFile(parent,dd.name,dd.hash,dd.size);
     else if (dd.type == DIR_TYPE_DIR)
-	{
+    {
         RsFileTree::DirIndex new_dir_index = mFileTree->addDirectory(parent,dd.name);
 
         for(uint32_t i=0;i<dd.children.size();++i)
-		{
+        {
             if (!dd.children[i].ref)
-				continue;
+                continue;
 
-			DirDetails subDirDetails;
+            DirDetails subDirDetails;
 
             if (!rsFiles->RequestDirDetails(dd.children[i].ref, subDirDetails, flags))
-				continue;
+                continue;
 
             recursAddElements(new_dir_index,subDirDetails,flags) ;
-		}
-	}
+        }
+    }
 }
 
 #ifdef TO_REMOVE
 void RsCollection::recursAddElements(QDomDocument& doc,const ColFileInfo& colFileInfo,QDomElement& e) const
 {
-	if (colFileInfo.type == DIR_TYPE_FILE)
-	{
-		QDomElement f = doc.createElement("File") ;
+    if (colFileInfo.type == DIR_TYPE_FILE)
+    {
+        QDomElement f = doc.createElement("File") ;
 
-		f.setAttribute(QString("name"),colFileInfo.name) ;
-		f.setAttribute(QString("sha1"),colFileInfo.hash) ;
-		f.setAttribute(QString("size"),QString::number(colFileInfo.size)) ;
+        f.setAttribute(QString("name"),colFileInfo.name) ;
+        f.setAttribute(QString("sha1"),colFileInfo.hash) ;
+        f.setAttribute(QString("size"),QString::number(colFileInfo.size)) ;
 
-		e.appendChild(f) ;
-	}
-	else if (colFileInfo.type == DIR_TYPE_DIR)
-	{
-		QDomElement d = doc.createElement("Directory") ;
+        e.appendChild(f) ;
+    }
+    else if (colFileInfo.type == DIR_TYPE_DIR)
+    {
+        QDomElement d = doc.createElement("Directory") ;
 
-		d.setAttribute(QString("name"),colFileInfo.name) ;
+        d.setAttribute(QString("name"),colFileInfo.name) ;
 
-		for (std::vector<ColFileInfo>::const_iterator it = colFileInfo.children.begin(); it != colFileInfo.children.end(); ++it)
-			recursAddElements(doc,(*it),d) ;
+        for (std::vector<ColFileInfo>::const_iterator it = colFileInfo.children.begin(); it != colFileInfo.children.end(); ++it)
+            recursAddElements(doc,(*it),d) ;
 
-		e.appendChild(d) ;
-	}
+        e.appendChild(d) ;
+    }
 }
 
 void RsCollection::recursAddElements(
         QDomDocument& doc, const RsFileTree& ft, uint32_t index,
         QDomElement& e ) const
 {
-	std::vector<uint64_t> subdirs;
-	std::vector<RsFileTree::FileData> subfiles ;
-	std::string name;
-	if(!ft.getDirectoryContent(name, subdirs, subfiles, index)) return;
+    std::vector<uint64_t> subdirs;
+    std::vector<RsFileTree::FileData> subfiles ;
+    std::string name;
+    if(!ft.getDirectoryContent(name, subdirs, subfiles, index)) return;
 
-	QDomElement d = doc.createElement("Directory") ;
-	d.setAttribute(QString("name"),QString::fromUtf8(name.c_str())) ;
-	e.appendChild(d) ;
+    QDomElement d = doc.createElement("Directory") ;
+    d.setAttribute(QString("name"),QString::fromUtf8(name.c_str())) ;
+    e.appendChild(d) ;
 
-	for (uint32_t i=0;i<subdirs.size();++i)
-		recursAddElements(doc,ft,subdirs[i],d) ;
+    for (uint32_t i=0;i<subdirs.size();++i)
+        recursAddElements(doc,ft,subdirs[i],d) ;
 
-	for(uint32_t i=0;i<subfiles.size();++i)
-	{
-		QDomElement f = doc.createElement("File") ;
+    for(uint32_t i=0;i<subfiles.size();++i)
+    {
+        QDomElement f = doc.createElement("File") ;
 
-		f.setAttribute(QString("name"),QString::fromUtf8(subfiles[i].name.c_str())) ;
-		f.setAttribute(QString("sha1"),QString::fromStdString(subfiles[i].hash.toStdString())) ;
-		f.setAttribute(QString("size"),QString::number(subfiles[i].size)) ;
+        f.setAttribute(QString("name"),QString::fromUtf8(subfiles[i].name.c_str())) ;
+        f.setAttribute(QString("sha1"),QString::fromStdString(subfiles[i].hash.toStdString())) ;
+        f.setAttribute(QString("size"),QString::number(subfiles[i].size)) ;
 
-		d.appendChild(f) ;
-	}
+        d.appendChild(f) ;
+    }
 }
 
 static void showErrorBox(const QString& fileName, const QString& error)
 {
-	QMessageBox mb(QMessageBox::Warning, QObject::tr("Failed to process collection file"), QObject::tr("The collection file %1 could not be opened.\nReported error is: \n\n%2").arg(fileName).arg(error), QMessageBox::Ok);
-	mb.exec();
+    QMessageBox mb(QMessageBox::Warning, QObject::tr("Failed to process collection file"), QObject::tr("The collection file %1 could not be opened.\nReported error is: \n\n%2").arg(fileName).arg(error), QMessageBox::Ok);
+    mb.exec();
 }
 #endif
 
@@ -441,25 +447,25 @@ bool RsCollection::checkFile(const QString& fileName, RsCollectionErrorCode& err
 #ifdef TO_REMOVE
 bool RsCollection::load(QWidget *parent)
 {
-	QString fileName;
-	if (!misc::getOpenFileName(parent, RshareSettings::LASTDIR_EXTRAFILE, QApplication::translate("RsCollectionFile", "Open collection file"), QApplication::translate("RsCollectionFile", "Collection files") + " (*." + RsCollection::ExtensionString + ")", fileName))
-		return false;
+    QString fileName;
+    if (!misc::getOpenFileName(parent, RshareSettings::LASTDIR_EXTRAFILE, QApplication::translate("RsCollectionFile", "Open collection file"), QApplication::translate("RsCollectionFile", "Collection files") + " (*." + RsCollection::ExtensionString + ")", fileName))
+        return false;
 
-	std::cerr << "Got file name: " << fileName.toStdString() << std::endl;
+    std::cerr << "Got file name: " << fileName.toStdString() << std::endl;
 
-	return load(fileName, true);
+    return load(fileName, true);
 }
 #endif
 
 bool RsCollection::save(const QString& fileName) const
 {
-	QFile file(fileName);
+    QFile file(fileName);
 
-	if (!file.open(QIODevice::WriteOnly))
-	{
-		std::cerr << "Cannot write to file " << fileName.toStdString() << " !!" << std::endl;
-		return false;
-	}
+    if (!file.open(QIODevice::WriteOnly))
+    {
+        std::cerr << "Cannot write to file " << fileName.toStdString() << " !!" << std::endl;
+        return false;
+    }
 
     QDomDocument xml_doc ;
     QDomElement root = xml_doc.createElement("RsCollection");
@@ -472,12 +478,12 @@ bool RsCollection::save(const QString& fileName) const
     xml_doc.appendChild(root);
 
     QTextStream stream(&file) ;
-	stream.setCodec("UTF-8") ;
+    stream.setCodec("UTF-8") ;
 
     stream << xml_doc.toString() ;
-	file.close();
+    file.close();
 
-	return true;
+    return true;
 }
 
 bool RsCollection::recursParseXml(QDomDocument& doc,const QDomNode& e,const RsFileTree::DirIndex parent)
@@ -545,6 +551,10 @@ bool RsCollection::recursParseXml(QDomDocument& doc,const QDomNode& e,const RsFi
 
         n = n.nextSibling() ;
     }
+    mHashes.clear();
+    for(uint64_t i=0;i<mFileTree->numFiles();++i)
+        mHashes.insert(std::make_pair(mFileTree->fileData(i).hash,i ));
+
     return true;
 }
 bool RsCollection::recursExportToXml(QDomDocument& doc,QDomElement& e,const RsFileTree::DirData& dd) const
@@ -581,16 +591,16 @@ bool RsCollection::recursExportToXml(QDomDocument& doc,QDomElement& e,const RsFi
 #ifdef TO_REMOVE
 bool RsCollection::save(QWidget *parent) const
 {
-	QString fileName;
-	if(!misc::getSaveFileName(parent, RshareSettings::LASTDIR_EXTRAFILE, QApplication::translate("RsCollectionFile", "Create collection file"), QApplication::translate("RsCollectionFile", "Collection files") + " (*." + RsCollection::ExtensionString + ")", fileName))
-		return false;
+    QString fileName;
+    if(!misc::getSaveFileName(parent, RshareSettings::LASTDIR_EXTRAFILE, QApplication::translate("RsCollectionFile", "Create collection file"), QApplication::translate("RsCollectionFile", "Collection files") + " (*." + RsCollection::ExtensionString + ")", fileName))
+        return false;
 
-	if (!fileName.endsWith("." + RsCollection::ExtensionString))
-		fileName += "." + RsCollection::ExtensionString ;
+    if (!fileName.endsWith("." + RsCollection::ExtensionString))
+        fileName += "." + RsCollection::ExtensionString ;
 
-	std::cerr << "Got file name: " << fileName.toStdString() << std::endl;
+    std::cerr << "Got file name: " << fileName.toStdString() << std::endl;
 
-	return save(fileName);
+    return save(fileName);
 }
 
 
@@ -606,38 +616,59 @@ qulonglong RsCollection::size()
     return mFileTree->totalFileSize();
 
 #ifdef TO_REMOVE
-	QDomElement docElem = _xml_doc.documentElement();
+    QDomElement docElem = _xml_doc.documentElement();
 
-	std::vector<ColFileInfo> colFileInfos;
-	recursCollectColFileInfos(docElem, colFileInfos, QString(),false);
+    std::vector<ColFileInfo> colFileInfos;
+    recursCollectColFileInfos(docElem, colFileInfos, QString(),false);
 
-	uint64_t size = 0;
+    uint64_t size = 0;
 
-	for (uint32_t i = 0; i < colFileInfos.size(); ++i) {
-		size += colFileInfos[i].size;
-	}
+    for (uint32_t i = 0; i < colFileInfos.size(); ++i) {
+        size += colFileInfos[i].size;
+    }
 
-	return size;
+    return size;
 #endif
 }
 
 bool RsCollection::isCollectionFile(const QString &fileName)
 {
-	QString ext = QFileInfo(fileName).suffix().toLower();
+    QString ext = QFileInfo(fileName).suffix().toLower();
 
-	return (ext == RsCollection::ExtensionString);
+    return (ext == RsCollection::ExtensionString);
 }
 
+void RsCollection::updateHashes(const std::map<RsFileHash,RsFileHash>& old_to_new_hashes)
+{
+    for(auto it:old_to_new_hashes)
+    {
+        auto fit = mHashes.find(it.first);
+
+        if(fit == mHashes.end())
+        {
+            RsErr() << "Could not find hash " << it.first << " in RsCollection list of hashes. This is a bug." ;
+            return ;
+        }
+        const auto& fd(mFileTree->fileData(fit->second));
+
+        if(fd.hash != it.first)
+        {
+            RsErr() << "Mismatch hash for file " << fd.name << " (found " << fd.hash << " instead of " << it.first << ") in RsCollection list of hashes. This is a bug." ;
+            return ;
+        }
+        mFileTree->updateFile(fit->second,fd.name,it.second,fd.size);
+    }
+}
 #ifdef TO_REMOVE
 void RsCollection::saveColl(std::vector<ColFileInfo> colFileInfos, const QString &fileName)
 {
 
-	QDomElement root = _xml_doc.elementsByTagName("RsCollection").at(0).toElement();
-	while (root.childNodes().count()>0) root.removeChild(root.firstChild());
-	for(uint32_t i = 0;i<colFileInfos.size();++i)
-		recursAddElements(_xml_doc,colFileInfos[i],root) ;
+    QDomElement root = _xml_doc.elementsByTagName("RsCollection").at(0).toElement();
+    while (root.childNodes().count()>0) root.removeChild(root.firstChild());
+    for(uint32_t i = 0;i<colFileInfos.size();++i)
+        recursAddElements(_xml_doc,colFileInfos[i],root) ;
 
-	_saved=save(fileName);
+    _saved=save(fileName);
 
 }
 #endif
diff --git a/retroshare-gui/src/gui/common/RsCollection.h b/retroshare-gui/src/gui/common/RsCollection.h
index 745a4c764..bc9ff2a28 100644
--- a/retroshare-gui/src/gui/common/RsCollection.h
+++ b/retroshare-gui/src/gui/common/RsCollection.h
@@ -103,6 +103,7 @@ public:
 
 	static bool isCollectionFile(const QString& fileName);
 
+    void updateHashes(const std::map<RsFileHash,RsFileHash>& old_to_new_hashes);
 private:
 
     bool recursExportToXml(QDomDocument& doc,QDomElement& e,const RsFileTree::DirData& dd) const;
@@ -130,6 +131,8 @@ private:
 	void autoDownloadFiles(ColFileInfo colFileInfo, QString dlDir) const ;
 
     std::unique_ptr<RsFileTree> mFileTree;
+    std::map<RsFileHash,RsFileTree::FileIndex> mHashes;	// used to efficiently update files being hashed
+
 #ifdef TO_REMOVE
 	QDomDocument _xml_doc ;
 	QString _fileName ;
diff --git a/retroshare-gui/src/gui/common/RsCollectionDialog.cpp b/retroshare-gui/src/gui/common/RsCollectionDialog.cpp
index 71e1c2c75..d6ec70f22 100644
--- a/retroshare-gui/src/gui/common/RsCollectionDialog.cpp
+++ b/retroshare-gui/src/gui/common/RsCollectionDialog.cpp
@@ -23,6 +23,7 @@
 
 #include "RsCollection.h"
 #include "util/misc.h"
+#include "util/rsdir.h"
 
 #include <QCheckBox>
 #include <QDateTime>
@@ -738,7 +739,7 @@ void RsCollectionDialog::addSelectionRecursive()
     addSelection(true);
 }
 
-static void recursBuildFileTree(const QString& path,RsFileTree& tree,RsFileTree::DirIndex dir_index,bool recursive)
+static void recursBuildFileTree(const QString& path,RsFileTree& tree,RsFileTree::DirIndex dir_index,bool recursive,QSet<QString>& paths_to_hash)
 {
     QFileInfo fileInfo = path;
 
@@ -746,17 +747,28 @@ static void recursBuildFileTree(const QString& path,RsFileTree& tree,RsFileTree:
     {
         auto di = tree.addDirectory(dir_index,fileInfo.fileName().toUtf8().constData());
 
-        QDir dirParent = fileInfo.absoluteFilePath();
-        dirParent.setFilter(QDir::AllEntries | QDir::NoSymLinks | QDir::NoDotAndDotDot);
-        QFileInfoList childrenList = dirParent.entryInfoList();
+        if(recursive)
+        {
+            QDir dirParent = fileInfo.absoluteFilePath();
+            dirParent.setFilter(QDir::AllEntries | QDir::NoSymLinks | QDir::NoDotAndDotDot);
+            QFileInfoList childrenList = dirParent.entryInfoList();
 
-        for(QFileInfo f:childrenList)
-            recursBuildFileTree(f.absoluteFilePath(),tree,di,recursive);
+            for(QFileInfo f:childrenList)
+                recursBuildFileTree(f.absoluteFilePath(),tree,di,recursive,paths_to_hash);
+        }
     }
     else
     {
-#warning TODO: compute the hash
-        tree.addFile(dir_index,fileInfo.fileName().toUtf8().constData(),RsFileHash(),fileInfo.size());
+        // Here we use a temporary hash that serves two purposes:
+        // 1 - identify the file in the RsFileTree of the collection so that we can update its hash when calculated
+        // 2 - mark the file as being processed
+        // The hash s is computed to be the hash of the path of the file. The collection must take care of multiple instances.
+
+        Sha1CheckSum s = RsDirUtil::sha1sum((uint8_t*)(fileInfo.filePath().toUtf8().constData()),fileInfo.filePath().toUtf8().size());
+
+        tree.addFile(dir_index,fileInfo.fileName().toUtf8().constData(),s,fileInfo.size());
+
+        paths_to_hash.insert(fileInfo.filePath().toUtf8().constData());
     }
 }
 /**
@@ -768,7 +780,6 @@ static void recursBuildFileTree(const QString& path,RsFileTree& tree,RsFileTree:
  */
 void RsCollectionDialog::addSelection(bool recursive)
 {
-	QStringList fileToHash;
 	QMap<QString, QString > dirToAdd;
     int count=0;//to not scan all items on list .count()
 
@@ -776,11 +787,13 @@ void RsCollectionDialog::addSelection(bool recursive)
 
     mCollectionModel->preMods();
 
+    QSet<QString> paths_to_hash;	// sha1sum of the paths to hash
+
 	foreach (QModelIndex index, milSelectionList)
         if(index.column()==0)    //Get only FileName
         {
             RsFileTree tree;
-            recursBuildFileTree(_dirModel->filePath(_tree_proxyModel->mapToSource(index)),tree,tree.root(),recursive);
+            recursBuildFileTree(_dirModel->filePath(_tree_proxyModel->mapToSource(index)),tree,tree.root(),recursive,paths_to_hash);
 
             mCollection->merge_in(tree);
 
@@ -852,9 +865,18 @@ void RsCollectionDialog::addSelection(bool recursive)
 	// Process Files once all done
 	ui._hashBox->addAttachments(fileToHash,RS_FILE_REQ_ANONYMOUS_ROUTING /*, 0*/);
 #endif
+//    std::map<Sha1CheckSum,QString> paths_and_hashes;
+//    for(auto path:paths_to_hash)
+//        paths_and_hashes.insert(std::make_pair(RsDirUtil::sha1sum((uint8_t*)path.toUtf8().constData(),path.toUtf8().size()),path));
+
+//    mCollectionModel->addFilesToHash(paths_and_hashes);
+
     mCollectionModel->postMods();
+
+    ui._hashBox->addAttachments(QStringList(paths_to_hash.begin(),paths_to_hash.end()),RS_FILE_REQ_ANONYMOUS_ROUTING /*, 0*/);
 }
 
+#ifdef TO_REMOVE
 /**
  * @brief RsCollectionDialog::addAllChild: Add children to RsCollection
  * @param fileInfoParent: Parent's QFileInfo to scan
@@ -910,6 +932,7 @@ bool RsCollectionDialog::addAllChild(QFileInfo &fileInfoParent
 	}
 	return true;
 }
+#endif
 
 /**
  * @brief RsCollectionDialog::remove: Remove selected Items in RSCollection
@@ -1186,6 +1209,7 @@ void RsCollectionDialog::makeDir()
  */
 void RsCollectionDialog::fileHashingFinished(QList<HashedFile> hashedFiles)
 {
+#ifdef TO_REMOVE
 	std::cerr << "RsCollectionDialog::fileHashingFinished() started." << std::endl;
 
 	QString message;
@@ -1211,8 +1235,26 @@ void RsCollectionDialog::fileHashingFinished(QList<HashedFile> hashedFiles)
 		_newColFileInfos.push_back(colFileInfo);
 #endif
 	}
+#endif
+    // build a map of old-hash to new-hash for the hashed files, so that it can be passed to the mCollection for update
 
-	std::cerr << "RsCollectionDialog::fileHashingFinished message : " << message.toStdString() << std::endl;
+    std::map<RsFileHash,RsFileHash> old_to_new_hashes;
+
+    for(auto f:hashedFiles)
+    {
+        auto it = mFilesBeingHashed.find(f.filepath);
+
+        if(it == mFilesBeingHashed.end())
+        {
+            RsErr() << "Could not find hash-ID correspondence for path " << f.filepath.toUtf8().constData() << ". This is a bug." << std::endl;
+            continue;
+        }
+        old_to_new_hashes.insert(std::make_pair(it->second,f.hash));
+        mFilesBeingHashed.erase(it);
+    }
+    mCollectionModel->preMods();
+    mCollection->updateHashes(old_to_new_hashes);
+    mCollectionModel->postMods();
 
 	updateList();
 }
diff --git a/retroshare-gui/src/gui/common/RsCollectionDialog.h b/retroshare-gui/src/gui/common/RsCollectionDialog.h
index 71c261cb4..9ba3ac857 100644
--- a/retroshare-gui/src/gui/common/RsCollectionDialog.h
+++ b/retroshare-gui/src/gui/common/RsCollectionDialog.h
@@ -18,6 +18,7 @@
  *                                                                             *
  *******************************************************************************/
 
+#include <set>
 #include "ui_RsCollectionDialog.h"
 #include "RsCollection.h"
 #include "RsCollectionModel.h"
@@ -90,12 +91,12 @@ private:
     bool addChild(QTreeWidgetItem *parent, const std::vector<ColFileInfo> &child);
 	bool removeItem(QTreeWidgetItem *item, bool &removeOnlyFile) ;
     void saveChild(QTreeWidgetItem *parentItem, ColFileInfo *parentInfo = NULL);
-#endif
-    void addSelection(bool recursive) ;
 	bool addAllChild(QFileInfo &fileInfoParent
 	                 , QMap<QString, QString > &dirToAdd
 	                 , QStringList &fileToHash
 	                 , int &count);
+#endif
+    void addSelection(bool recursive) ;
 
 	Ui::RsCollectionDialog ui;
 	QString _fileName ;
@@ -110,4 +111,6 @@ private:
 
     RsCollectionModel *mCollectionModel;
     RsCollection *mCollection;
+
+    std::map<QString,RsFileHash> mFilesBeingHashed; // map of file path vs. temporary ID used for the file while hashing
 };
diff --git a/retroshare-gui/src/gui/common/RsCollectionModel.cpp b/retroshare-gui/src/gui/common/RsCollectionModel.cpp
index f05e25231..6e8352339 100644
--- a/retroshare-gui/src/gui/common/RsCollectionModel.cpp
+++ b/retroshare-gui/src/gui/common/RsCollectionModel.cpp
@@ -252,9 +252,9 @@ bool RsCollectionModel::setData(const QModelIndex& index,const QVariant& value,i
 
     if(role==Qt::CheckStateRole && convertInternalIdToIndex(index.internalId(), e))
     {
-//#ifdef DEBUG_COLLECTION_MODEL
+#ifdef DEBUG_COLLECTION_MODEL
         std::cerr << "Setting check state of item " << index << " to " << value.toBool() << std::endl;
-//#endif
+#endif
         RsFileTree::DirIndex dir_index ;
 
         if(e.is_file)
@@ -370,7 +370,6 @@ QVariant RsCollectionModel::checkStateRole(const EntryIndex& i,int col) const
     {
         if(i.is_file)
         {
-            std::cerr<< "entry is file, checkstate = " << (int)mFileInfos[i.index].is_checked << std::endl;
             if(mFileInfos[i.index].is_checked)
                 return QVariant(Qt::Checked);
             else
@@ -378,8 +377,6 @@ QVariant RsCollectionModel::checkStateRole(const EntryIndex& i,int col) const
         }
         else
         {
-            std::cerr<< "entry is dir, checkstate = " << (int)mDirInfos[i.index].check_state << std::endl;
-
             switch(mDirInfos[i.index].check_state)
             {
             case SELECTED: return QVariant::fromValue((int)Qt::Checked);