diff --git a/libgrive/src/drive/Drive.cc b/libgrive/src/drive/Drive.cc
index 1c34bb5..a025d5f 100644
--- a/libgrive/src/drive/Drive.cc
+++ b/libgrive/src/drive/Drive.cc
@@ -23,7 +23,7 @@
 #include "Entry.hh"
 
 #include "http/Agent.hh"
-// #include "http/ResponseLog.hh"
+#include "http/ResponseLog.hh"
 #include "http/XmlResponse.hh"
 #include "protocol/Json.hh"
 #include "protocol/OAuth2.hh"
@@ -56,8 +56,8 @@ Drive::Drive( OAuth2& auth, const Json& options ) :
 	m_auth( auth ),
 	m_state( state_file, options )
 {
-	m_http_hdr.push_back( "Authorization: Bearer " + m_auth.AccessToken() ) ;
-	m_http_hdr.push_back( "GData-Version: 3.0" ) ;
+	m_http_hdr.Add( "Authorization: Bearer " + m_auth.AccessToken() ) ;
+	m_http_hdr.Add( "GData-Version: 3.0" ) ;
 
 	Log( "Reading local directories", log::info ) ;
 	m_state.FromLocal( "." ) ;
@@ -127,7 +127,8 @@ void Drive::SyncFolders( http::Agent *http )
 	Log( "Synchronizing folders", log::info ) ;
 
 	http::XmlResponse xml ;
-	http->Get( feed_base + "/-/folder?max-results=50&showroot=true", &xml, m_http_hdr ) ;
+	http::ResponseLog log( "dir-", ".xml", &xml ) ;
+	http->Get( feed_base + "/-/folder?max-results=50&showroot=true", &log, m_http_hdr ) ;
 
 	xml::Node resp = xml.Response() ;
 
diff --git a/libgrive/src/drive/Drive.hh b/libgrive/src/drive/Drive.hh
index a7def44..c831f8a 100644
--- a/libgrive/src/drive/Drive.hh
+++ b/libgrive/src/drive/Drive.hh
@@ -21,6 +21,7 @@
 
 #include "State.hh"
 
+#include "http/Header.hh"
 #include "util/Exception.hh"
 
 #include <string>
@@ -52,11 +53,11 @@ private :
     void file();
 	
 private :
-	OAuth2&						m_auth ;
-	std::vector<std::string>	m_http_hdr ;
+	OAuth2&			m_auth ;
+	http::Header	m_http_hdr ;
 
-	std::string					m_resume_link ;
-	State						m_state ;
+	std::string		m_resume_link ;
+	State			m_state ;
 } ;
 
 } // end of namespace
diff --git a/libgrive/src/drive/Resource.cc b/libgrive/src/drive/Resource.cc
index c1f459c..bffc5cd 100644
--- a/libgrive/src/drive/Resource.cc
+++ b/libgrive/src/drive/Resource.cc
@@ -20,6 +20,7 @@
 #include "Resource.hh"
 #include "CommonUri.hh"
 
+#include "http/Agent.hh"
 #include "http/Download.hh"
 // #include "http/ResponseLog.hh"
 #include "http/StringResponse.hh"
@@ -33,6 +34,8 @@
 #include "xml/Node.hh"
 #include "xml/NodeSet.hh"
 
+#include <boost/exception/all.hpp>
+
 #include <cassert>
 
 // for debugging
@@ -291,7 +294,7 @@ Resource* Resource::FindChild( const std::string& name )
 }
 
 // try to change the state to "sync"
-void Resource::Sync( http::Agent *http, const http::Headers& auth )
+void Resource::Sync( http::Agent *http, const http::Header& auth )
 {
 	assert( m_state != unknown ) ;
 
@@ -370,25 +373,27 @@ void Resource::DeleteLocal()
 		fs::rename( Path(), dest ) ;
 }
 
-void Resource::DeleteRemote( http::Agent *http, const http::Headers& auth )
+void Resource::DeleteRemote( http::Agent *http, const http::Header& auth )
 {
-	http::Headers hdr( auth ) ;
-	hdr.push_back( "If-Match: " + m_entry.ETag() ) ;
+	http::Header hdr( auth ) ;
+	hdr.Add( "If-Match: " + m_entry.ETag() ) ;
 	http::StringResponse str ;
 	try
 	{
 		http->Custom( "DELETE", http->Unescape(m_entry.SelfHref()) , &str, hdr ) ;
 	}
-	catch ( Exception& )
+	catch ( Exception& e )
 	{
 		// don't rethrow here. there are some cases that I don't know why
 		// the delete will fail.
-		Trace( "response = %1%", str.Response() ) ;
+		Trace( "Exception %1% %2%",
+			boost::diagnostic_information(e),
+			str.Response() ) ;
 	}
 }
 
 
-void Resource::Download( http::Agent* http, const fs::path& file, const http::Headers& auth ) const
+void Resource::Download( http::Agent* http, const fs::path& file, const http::Header& auth ) const
 {
 	http::Download dl( file.string(), http::Download::NoChecksum() ) ;
 	long r = http->Get( m_entry.ContentSrc(), &dl, auth ) ;
@@ -396,7 +401,7 @@ void Resource::Download( http::Agent* http, const fs::path& file, const http::He
 		os::SetFileTime( file, m_entry.MTime() ) ;
 }
 
-bool Resource::EditContent( http::Agent* http, const http::Headers& auth )
+bool Resource::EditContent( http::Agent* http, const http::Header& auth )
 {
 	assert( m_parent != 0 ) ;
 
@@ -414,7 +419,7 @@ bool Resource::EditContent( http::Agent* http, const http::Headers& auth )
 	return Upload( http, m_entry.EditLink(), auth, false ) ;
 }
 
-bool Resource::Create( http::Agent* http, const http::Headers& auth )
+bool Resource::Create( http::Agent* http, const http::Header& auth )
 {
 	assert( m_parent != 0 ) ;
 	assert( m_parent->IsFolder() ) ;
@@ -431,8 +436,8 @@ bool Resource::Create( http::Agent* http, const http::Headers& auth )
 		
 		std::string meta = (boost::format(xml_meta) % "folder" % Name() ).str() ;
 		
-		http::Headers hdr( auth ) ;
-		hdr.push_back( "Content-Type: application/atom+xml" ) ;
+		http::Header hdr( auth ) ;
+		hdr.Add( "Content-Type: application/atom+xml" ) ;
 		
 		http::XmlResponse xml ;
 // 		http::ResponseLog log( "create", ".xml", &xml ) ;
@@ -452,7 +457,7 @@ bool Resource::Create( http::Agent* http, const http::Headers& auth )
 	}
 }
 
-bool Resource::Upload( http::Agent* http, const std::string& link, const http::Headers& auth, bool post )
+bool Resource::Upload( http::Agent* http, const std::string& link, const http::Header& auth, bool post )
 {
 	StdioFile file( Path() ) ;
 	
@@ -466,12 +471,12 @@ bool Resource::Upload( http::Agent* http, const std::string& link, const http::H
 	std::ostringstream xcontent_len ;
 	xcontent_len << "X-Upload-Content-Length: " << data.size() ;
 	
-	http::Headers hdr( auth ) ;
-	hdr.push_back( "Content-Type: application/atom+xml" ) ;
-	hdr.push_back( "X-Upload-Content-Type: application/octet-stream" ) ;
-	hdr.push_back( xcontent_len.str() ) ;
-  	hdr.push_back( "If-Match: " + m_entry.ETag() ) ;
-	hdr.push_back( "Expect:" ) ;
+	http::Header hdr( auth ) ;
+	hdr.Add( "Content-Type: application/atom+xml" ) ;
+	hdr.Add( "X-Upload-Content-Type: application/octet-stream" ) ;
+	hdr.Add( xcontent_len.str() ) ;
+  	hdr.Add( "If-Match: " + m_entry.ETag() ) ;
+	hdr.Add( "Expect:" ) ;
 	
 	std::string meta = (boost::format( xml_meta ) % m_entry.Kind() % Name()).str() ;
 	
@@ -481,9 +486,9 @@ bool Resource::Upload( http::Agent* http, const std::string& link, const http::H
 	else
 		http->Put( link, meta, &str, hdr ) ;
 	
-	http::Headers uphdr ;
-	uphdr.push_back( "Expect:" ) ;
-	uphdr.push_back( "Accept:" ) ;
+	http::Header uphdr ;
+	uphdr.Add( "Expect:" ) ;
+	uphdr.Add( "Accept:" ) ;
 
 	// the content upload URL is in the "Location" HTTP header
 	std::string uplink = http->RedirLocation() ;
diff --git a/libgrive/src/drive/Resource.hh b/libgrive/src/drive/Resource.hh
index 1c3a4e4..968b6f5 100644
--- a/libgrive/src/drive/Resource.hh
+++ b/libgrive/src/drive/Resource.hh
@@ -20,7 +20,6 @@
 #pragma once
 
 #include "Entry.hh"
-#include "http/Agent.hh"
 #include "util/Exception.hh"
 #include "util/FileSystem.hh"
 
@@ -30,6 +29,12 @@
 
 namespace gr {
 
+namespace http
+{
+	class Agent ;
+	class Header ;
+}
+
 class Json ;
 
 /*!	\brief	A resource can be a file or a folder in the google drive
@@ -72,7 +77,7 @@ public :
 	void FromRemote( const Entry& remote, const DateTime& last_sync ) ;
 	void FromLocal( const DateTime& last_sync ) ;
 	
-	void Sync( http::Agent *http, const http::Headers& auth ) ;
+	void Sync( gr::http::Agent* http, const http::Header& auth ) ;
 
 	Json Serialize() const ;
 	
@@ -119,16 +124,16 @@ private :
 	friend std::ostream& operator<<( std::ostream& os, State s ) ;
 	
 private :
-	void Download( http::Agent* http, const fs::path& file, const http::Headers& auth ) const ;
-	bool EditContent( http::Agent* http, const http::Headers& auth ) ;
-	bool Create( http::Agent* http, const http::Headers& auth ) ;
-	bool Upload( http::Agent* http, const std::string& link, const http::Headers& auth, bool post ) ;
+	void Download( http::Agent* http, const fs::path& file, const http::Header& auth ) const ;
+	bool EditContent( http::Agent* http, const http::Header& auth ) ;
+	bool Create( http::Agent* http, const http::Header& auth ) ;
+	bool Upload( http::Agent* http, const std::string& link, const http::Header& auth, bool post ) ;
 	
 	void FromRemoteFolder( const Entry& remote, const DateTime& last_sync ) ;
 	void FromRemoteFile( const Entry& remote, const DateTime& last_sync ) ;
 	
 	void DeleteLocal() ;
-	void DeleteRemote( http::Agent* http, const http::Headers& auth ) ;
+	void DeleteRemote( http::Agent* http, const http::Header& auth ) ;
 	
 private :
 	Entry					m_entry ;
diff --git a/libgrive/src/drive/State.cc b/libgrive/src/drive/State.cc
index 192b053..bdf5bac 100644
--- a/libgrive/src/drive/State.cc
+++ b/libgrive/src/drive/State.cc
@@ -22,6 +22,7 @@
 #include "Resource.hh"
 #include "CommonUri.hh"
 
+#include "http/Agent.hh"
 #include "util/Crypt.hh"
 #include "util/Log.hh"
 #include "protocol/Json.hh"
@@ -219,7 +220,7 @@ void State::Write( const fs::path& filename ) const
 	fs << result ;
 }
 
-void State::Sync( http::Agent *http, const http::Headers& auth )
+void State::Sync( http::Agent *http, const http::Header& auth )
 {
 	std::for_each( m_res.begin(), m_res.end(),
 		boost::bind( &Resource::Sync, _1, http, auth ) ) ;
diff --git a/libgrive/src/drive/State.hh b/libgrive/src/drive/State.hh
index c17699f..7a8fc68 100644
--- a/libgrive/src/drive/State.hh
+++ b/libgrive/src/drive/State.hh
@@ -21,7 +21,6 @@
 
 #include "ResourceTree.hh"
 
-#include "http/Agent.hh"
 #include "util/DateTime.hh"
 #include "util/FileSystem.hh"
 
@@ -29,6 +28,12 @@
 
 namespace gr {
 
+namespace http
+{
+	class Agent ;
+	class Header ;
+}
+
 class Json ;
 class Resource ;
 class Entry ;
@@ -52,7 +57,7 @@ public :
 	Resource* FindByID( const std::string& id ) ;
 	Resource* Find( const fs::path& path ) ;
 
-	void Sync( http::Agent *http, const http::Headers& auth ) ;
+	void Sync( http::Agent *http, const http::Header& auth ) ;
 	
 	iterator begin() ;
 	iterator end() ;
diff --git a/libgrive/src/http/Agent.cc b/libgrive/src/http/Agent.cc
index c12905b..0866826 100644
--- a/libgrive/src/http/Agent.cc
+++ b/libgrive/src/http/Agent.cc
@@ -126,9 +126,9 @@ std::size_t Agent::Receive( void* ptr, size_t size, size_t nmemb, Receivable *re
 }
 
 long Agent::ExecCurl(
-	const std::string&		url,
-	Receivable				*dest,
-	const http::Headers&	hdr )
+	const std::string&	url,
+	Receivable			*dest,
+	const http::Header&	hdr )
 {
 	CURL *curl = m_pimpl->curl ;
 	assert( curl != 0 ) ;
@@ -158,6 +158,7 @@ long Agent::ExecCurl(
 				<< HttpResponse( http_code )
 				<< Url( url )
 				<< expt::ErrMsg( error )
+				<< HttpHeader( hdr )
 		) ;
 	}
 
@@ -168,7 +169,7 @@ long Agent::Put(
 	const std::string&		url,
 	const std::string&		data,
 	Receivable				*dest,
-	const http::Headers&	hdr )
+	const Header&			hdr )
 {
 	Trace("HTTP PUT \"%1%\"", url ) ;
 	
@@ -189,7 +190,7 @@ long Agent::Put(
 long Agent::Get(
 	const std::string& 		url,
 	Receivable				*dest,
-	const http::Headers&	hdr )
+	const Header&			hdr )
 {
 	Trace("HTTP GET \"%1%\"", url ) ;
 	
@@ -206,7 +207,7 @@ long Agent::Post(
 	const std::string& 		url,
 	const std::string&		data,
 	Receivable				*dest,
-	const http::Headers&	hdr )
+	const Header&			hdr )
 {
 	Trace("HTTP POST \"%1%\" with \"%2%\"", url, data ) ;
 
@@ -228,22 +229,23 @@ long Agent::Custom(
 	const std::string&		method,
 	const std::string&		url,
 	Receivable				*dest,
-	const http::Headers&	hdr )
+	const Header&			hdr )
 {
 	Trace("HTTP %2% \"%1%\"", url, method ) ;
 
 	CURL *curl = m_pimpl->curl ;
 
 	::curl_easy_setopt(curl, CURLOPT_CUSTOMREQUEST, method.c_str() );
+	::curl_easy_setopt(curl, CURLOPT_VERBOSE,		1 );
 
 	return ExecCurl( url, dest, hdr ) ;
 }
 
-void Agent::SetHeader( const http::Headers& hdr )
+void Agent::SetHeader( const Header& hdr )
 {
 	// set headers
 	struct curl_slist *curl_hdr = 0 ;
-    for ( Headers::const_iterator i = hdr.begin() ; i != hdr.end() ; ++i )
+    for ( Header::iterator i = hdr.begin() ; i != hdr.end() ; ++i )
 		curl_hdr = curl_slist_append( curl_hdr, i->c_str() ) ;
 	
 	::curl_easy_setopt( m_pimpl->curl, CURLOPT_HTTPHEADER, curl_hdr ) ;
diff --git a/libgrive/src/http/Agent.hh b/libgrive/src/http/Agent.hh
index 59e1ba2..b764b62 100644
--- a/libgrive/src/http/Agent.hh
+++ b/libgrive/src/http/Agent.hh
@@ -19,14 +19,14 @@
 
 #pragma once
 
+#include "Header.hh"
+
 #include <memory>
 #include <string>
 #include <vector>
 
 namespace gr { namespace http {
 
-typedef std::vector<std::string> Headers ;
-
 class Receivable ;
 
 /*!	\class	Agent
@@ -44,27 +44,27 @@ public :
 	void SetLogFile( const std::string& prefix ) ;
 	
 	long Put(
-		const std::string&		url,
-		const std::string&		data,
-		Receivable				*dest,
-		const http::Headers&	hdr = http::Headers() ) ;
+		const std::string&	url,
+		const std::string&	data,
+		Receivable			*dest,
+		const Header&		hdr = Header() ) ;
 
 	long Get(
-		const std::string& 		url,
-		Receivable				*dest,
-		const http::Headers&	hdr = http::Headers() ) ;
+		const std::string& 	url,
+		Receivable			*dest,
+		const Header&		hdr = Header() ) ;
 	
 	long Post(
-		const std::string& 		url,
-		const std::string&		data,
-		Receivable				*dest,
-		const http::Headers&	hdr = http::Headers() ) ;
+		const std::string& 	url,
+		const std::string&	data,
+		Receivable			*dest,
+		const Header&		hdr = Header() ) ;
 	
 	long Custom(
-		const std::string&		method,
-		const std::string&		url,
-		Receivable				*dest,
-		const http::Headers&	hdr = http::Headers() ) ;
+		const std::string&	method,
+		const std::string&	url,
+		Receivable			*dest,
+		const Header&		hdr = Header() ) ;
 	
 	std::string RedirLocation() const ;
 	
@@ -75,11 +75,11 @@ private :
 	static std::size_t HeaderCallback( void *ptr, size_t size, size_t nmemb, Agent *pthis ) ;
 	static std::size_t Receive( void* ptr, size_t size, size_t nmemb, Receivable *recv ) ;
 	
-	void SetHeader( const http::Headers& hdr ) ;
+	void SetHeader( const Header& hdr ) ;
 	long ExecCurl(
-		const std::string&		url,
-		Receivable				*dest,
-		const http::Headers&	hdr) ;
+		const std::string&	url,
+		Receivable			*dest,
+		const Header&		hdr ) ;
 
 	void Init() ;
 	
diff --git a/libgrive/src/http/Error.hh b/libgrive/src/http/Error.hh
index 94b2c44..a513f5f 100644
--- a/libgrive/src/http/Error.hh
+++ b/libgrive/src/http/Error.hh
@@ -19,6 +19,7 @@
 
 #pragma once
 
+#include "Header.hh"
 #include "util/Exception.hh"
 
 namespace gr { namespace http {
@@ -37,4 +38,7 @@ typedef boost::error_info<struct HttpResponseStrTag, std::string>	HttpResponseTe
 // URL
 typedef boost::error_info<struct UrlTag, std::string>		Url ;
 
+// HTTP headers
+typedef boost::error_info<struct HeaderTag, Header>		HttpHeader ;
+
 } } // end of namespace
diff --git a/libgrive/src/http/Header.cc b/libgrive/src/http/Header.cc
new file mode 100644
index 0000000..36bd245
--- /dev/null
+++ b/libgrive/src/http/Header.cc
@@ -0,0 +1,53 @@
+/*
+	grive: an GPL program to sync a local directory with Google Drive
+	Copyright (C) 2012  Wan Wai Ho
+
+	This program is free software; you can redistribute it and/or
+	modify it under the terms of the GNU General Public License
+	as published by the Free Software Foundation version 2
+	of the License.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program; if not, write to the Free Software
+	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+
+#include "Header.hh"
+
+#include <algorithm>
+#include <iterator>
+#include <ostream>
+
+namespace gr { namespace http {
+
+Header::Header()
+{
+}
+
+void Header::Add( const std::string& str )
+{
+	m_vec.push_back( str ) ;
+}
+
+Header::iterator Header::begin() const
+{
+	return m_vec.begin() ;
+}
+
+Header::iterator Header::end() const
+{
+	return m_vec.end() ;
+}
+
+std::ostream& operator<<( std::ostream& os, const Header& h )
+{
+	std::copy( h.begin(), h.end(), std::ostream_iterator<std::string>( os, "\n" ) ) ;
+	return os ;
+}
+
+} } // end of namespace
diff --git a/libgrive/src/http/Header.hh b/libgrive/src/http/Header.hh
new file mode 100644
index 0000000..c581d7d
--- /dev/null
+++ b/libgrive/src/http/Header.hh
@@ -0,0 +1,50 @@
+/*
+	grive: an GPL program to sync a local directory with Google Drive
+	Copyright (C) 2012  Wan Wai Ho
+
+	This program is free software; you can redistribute it and/or
+	modify it under the terms of the GNU General Public License
+	as published by the Free Software Foundation version 2
+	of the License.
+
+	This program is distributed in the hope that it will be useful,
+	but WITHOUT ANY WARRANTY; without even the implied warranty of
+	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+	GNU General Public License for more details.
+
+	You should have received a copy of the GNU General Public License
+	along with this program; if not, write to the Free Software
+	Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+*/
+
+#pragma once
+
+#include <iosfwd>
+#include <string>
+#include <vector>
+
+namespace gr { namespace http {
+
+class Header
+{
+private :
+	typedef std::vector<std::string>	Vec ;
+
+public :
+	typedef Vec::const_iterator	iterator ;
+
+public :
+	Header() ;
+	
+	void Add( const std::string& str ) ;
+	
+	iterator begin() const ;
+	iterator end() const ;
+
+private :
+	Vec	m_vec ;
+} ;
+
+std::ostream& operator<<( std::ostream& os, const Header& h ) ;
+
+}} // end of namespace
diff --git a/libgrive/src/util/DefaultLog.cc b/libgrive/src/util/DefaultLog.cc
index d52b356..dbecb90 100644
--- a/libgrive/src/util/DefaultLog.cc
+++ b/libgrive/src/util/DefaultLog.cc
@@ -39,7 +39,7 @@ DefaultLog::DefaultLog( const std::string& filename ) :
 	m_file( filename.c_str() ),
 	m_log( m_file )
 {
-	m_enabled[log::debug]		= false ;
+	m_enabled[log::debug]		= true ;
 	m_enabled[log::verbose]		= true ;
 	m_enabled[log::info]		= true ;
 	m_enabled[log::warning]		= true ;