checked MD5 checksum before downloading

CMakeLists.txt

@@ -1,12 +1,18 @@
 project(grive)
 
+cmake_minimum_required(VERSION 2.8)
+
+include(FindOpenSSL)
+
 add_executable( grive
 	src/main.cc
 	src/OAuth2.cc
 	src/HTTP.cc
 	src/Json.cc
-	src/Drive.cc )
+	src/Drive.cc
+	src/Download.cc )
 
 target_link_libraries( grive
 	curl
-	json )
+	json
+	${OPENSSL_LIBRARIES} )

src/Download.cc

@@ -0,0 +1,90 @@
+/*
+	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; either version 2
+	of the License, or (at your option) any later version.
+
+	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 "Download.hh"
+
+#include <openssl/evp.h>
+
+#include <cassert>
+#include <new>
+#include <stdexcept>
+
+namespace gr {
+
+Download::Download( const std::string& filename ) :
+	m_file( filename.c_str(), std::ios::out | std::ios::binary ),
+	m_mdctx( ::EVP_MD_CTX_create() )
+{
+	if ( m_mdctx == 0 )
+		throw std::bad_alloc() ;
+	
+	if ( ::EVP_DigestInit_ex( m_mdctx, ::EVP_md5(), 0 ) != 1 )
+		throw std::runtime_error( "cannot create MD5 digest context" ) ;
+
+	if ( !m_file )
+		throw std::runtime_error( "cannot open file " + filename + " for writing" ) ;
+}
+
+Download::Download( const std::string& filename, NoChecksum ) :
+	m_file( filename.c_str(), std::ios::out | std::ios::binary ),
+	m_mdctx( 0 )
+{
+	if ( !m_file )
+		throw std::runtime_error( "cannot open file " + filename + " for writing" ) ;
+}
+
+Download::~Download( )
+{
+	if ( m_mdctx != 0 )
+		::EVP_MD_CTX_destroy( m_mdctx ) ;
+}
+
+std::string Download::Finish() const
+{
+	std::string result ;
+
+	// get the checksum and return it ;
+	if ( m_mdctx != 0 )
+	{
+		unsigned int size = EVP_MAX_MD_SIZE ;
+		result.resize( size ) ;
+		
+		if ( ::EVP_DigestFinal_ex( m_mdctx, reinterpret_cast<unsigned char*>(&result[0]), &size ) != 1 )
+			throw std::runtime_error( "cannot calculate checksum" ) ;
+		
+		result.resize( size ) ;
+	}
+
+	return result ;
+}
+
+std::size_t Download::Callback( char *data, std::size_t size, std::size_t nmemb, Download *pthis )
+{
+	assert( pthis != 0 ) ;
+	assert( data != 0 ) ;
+	
+	std::size_t count = size * nmemb ;
+	
+	if ( pthis->m_mdctx != 0 )
+		::EVP_DigestUpdate( pthis->m_mdctx, data, count ) ;
+	
+	return pthis->m_file.rdbuf()->sputn( data, count ) ;
+}
+
+} // end of namespace

src/Download.hh

@@ -0,0 +1,46 @@
+/*
+	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; either version 2
+	of the License, or (at your option) any later version.
+
+	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 <string>
+#include <fstream>
+
+#include <openssl/evp.h>
+
+namespace gr {
+
+class Download
+{
+public :
+	struct NoChecksum {} ;
+	Download( const std::string& filename ) ;
+	Download( const std::string& filename, NoChecksum ) ;
+	~Download( ) ;
+	
+	std::string Finish() const ;
+	
+	static std::size_t Callback( char *data, std::size_t size, std::size_t nmemb, Download *pthis ) ;
+	
+private :
+	std::ofstream	m_file ;
+	EVP_MD_CTX		*m_mdctx ;
+} ;
+
+} // end of namespace

src/Drive.cc

@@ -23,11 +23,42 @@
 #include "Json.hh"
 #include "OAuth2.hh"
 
+#include <openssl/evp.h>
+
+#include <algorithm>
+#include <fstream>
+#include <iomanip>
+#include <sstream>
+
 // for debugging only
 #include <iostream>
 
 namespace gr {
 
+std::string MD5( std::streambuf *file )
+{
+	char buf[64 * 1024] ;
+	EVP_MD_CTX	md ;
+	EVP_MD_CTX_init( &md );
+	EVP_DigestInit_ex( &md, EVP_md5(), 0 ) ;
+	
+	std::size_t count = 0 ;
+	while ( (count = file->sgetn( buf, sizeof(buf) )) > 0 )
+	{
+		EVP_DigestUpdate( &md, buf, count ) ;
+	}
+	
+	unsigned int md5_size = EVP_MAX_MD_SIZE ;
+	unsigned char md5[EVP_MAX_MD_SIZE] ;
+	EVP_DigestFinal_ex( &md, md5, &md5_size ) ;
+	
+	std::ostringstream ss ;
+	for ( unsigned int i = 0 ; i < md5_size ; i++ )
+		ss << std::hex << std::setw(2) << std::setfill('0') << static_cast<int>(md5[i]) ;
+	
+	return ss.str() ;
+}
+
 Drive::Drive( OAuth2& auth ) :
 	m_auth( auth )
 {
@@ -51,11 +82,11 @@ Drive::Drive( OAuth2& auth ) :
 
 void Drive::DownloadEntry( const Json& entry )
 {
-	Json::Object map = entry.As<Json::Object>() ;
-	for ( Json::Object::iterator i = map.begin() ; i != map.end() ; ++i )
-	{
-//		std::cout << i->first << "\t" << i->second.DataType() << std::endl ;
-	}
+// 	Json::Object map = entry.As<Json::Object>() ;
+// 	for ( Json::Object::iterator i = map.begin() ; i != map.end() ; ++i )
+// 	{
+// 		std::cout << i->first << "\t" << i->second.DataType() << std::endl ;
+// 	}
 	
 	// only handle uploaded files
 	if ( entry.Has( "docs$filename" ) )
@@ -64,9 +95,25 @@ void Drive::DownloadEntry( const Json& entry )
 		std::string filename	= entry["docs$filename"]["$t"].As<std::string>() ;
 		std::string url			= entry["content"]["src"].As<std::string>() ;
 		
-		std::cout << "downloading " << filename << " from " << url << std::endl ;
+		bool changed = true ;
 		
-		HttpGetFile( url, filename, m_http_hdr ) ;
+		// compare checksum first if file exists
+		std::ifstream ifile( filename.c_str(), std::ios::binary | std::ios::out ) ;
+		if ( ifile && entry.Has("docs$md5Checksum") )
+		{
+			std::string remote_md5	= entry["docs$md5Checksum"]["$t"].As<std::string>() ;
+			std::string local_md5	= MD5( ifile.rdbuf() ) ;
+			
+			std::transform( remote_md5.begin(), remote_md5.end(), remote_md5.begin(), tolower ) ;
+			if ( local_md5 == remote_md5 )
+				changed = false ;
+		}
+		
+		if ( changed )
+		{
+std::cout << "downloading " << filename << std::endl ;
+			HttpGetFile( url, filename, m_http_hdr ) ;
+		}
 	}
 }
 

src/HTTP.cc

@@ -19,9 +19,12 @@
 
 #include "HTTP.hh"
 
+#include "Download.hh"
+
+// dependent libraries
 #include <curl/curl.h>
+
 #include <cassert>
-#include <fstream>
 #include <iostream>
 #include <sstream>
 #include <streambuf>
@@ -51,15 +54,6 @@ std::size_t WriteCallback( char *data, size_t size, size_t nmemb, std::string *r
 	return count ;
 }
 
-// libcurl callback to write to a file
-std::size_t DownloadCallback( char *data, size_t size, size_t nmemb, std::streambuf *file )
-{
-	assert( file != 0 ) ;
-	assert( data != 0 ) ;
-	
-	return file->sputn( data, size * nmemb ) ;
-}
-
 CURL* InitCurl( const std::string& url, std::string *resp, const Headers& hdr )
 {
 	CURL *curl = curl_easy_init();
@@ -122,17 +116,23 @@ void HttpGetFile(
 	const std::string&	filename,
 	const Headers& 		hdr )
 {
-	std::ofstream file( filename.c_str(), std::ios::binary | std::ios::out ) ;
-	if ( !file )
-		throw std::runtime_error( "cannot open file " + filename + " for writing" ) ;
-
+	Download dl( filename, Download::NoChecksum() ) ;
+		
 	CURL *curl = InitCurl( url, 0, hdr ) ;
-	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION,	DownloadCallback);
-	curl_easy_setopt(curl, CURLOPT_WRITEDATA,		file.rdbuf() ) ;
+	curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION,	&Download::Callback);
+	curl_easy_setopt(curl, CURLOPT_WRITEDATA,		&dl ) ;
 	curl_easy_setopt(curl, CURLOPT_HTTPGET, 1L);
 	DoCurl( curl ) ;
 }
 
+void HttpGetFile(
+	const std::string&	url,
+	const std::string&	filename,
+	std::string&		md5sum,
+	const Headers& 		hdr )
+{
+}
+
 std::string HttpPostData( const std::string& url, const std::string& data, const Headers& hdr )
 {
 	std::string resp ;

src/HTTP.hh

@@ -33,6 +33,12 @@ namespace gr
 		const std::string&	filename,
 		const Headers& 		hdr = Headers() ) ;
 	
+	void HttpGetFile(
+		const std::string&	url,
+		const std::string&	filename,
+		std::string&		md5sum,
+		const Headers& 		hdr = Headers() ) ;
+	
 	std::string HttpPostData(
 		const std::string&	url,
 		const std::string&	data,

src/main.cc

@@ -40,7 +40,6 @@ namespace gr
 
 	Json ReadConfig()
 	{
-		std::cout << ConfigFilename() << std::endl ;
 		std::ifstream ifile( ConfigFilename().c_str() ) ;
 		
 		if ( ifile )