How to implement ZLIB encoding for VNC server?

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Hi,

While adding ZLIB encoding for my VNC server and I came across a problem. The issue is, only the very first framebuffer is accepted by the client (viewer) and subsequent framebuffers are plotted as blank screens. Somewhere I saw that we have to make use of a single ZLIB stream for a VNC session but I don't know how to implement it. Below is my code snippet sending a rectangle of pixel data in my VNC server.

C++

//==============================================================================
//Note: Rectangle header containing x, y, height, width and encoding is sent
//prior to this code.
//
//reduce the BMP header size from total length
uLongf sourceLen = DATA_SIZE-0x436;
//add sufficient length for encoding algorithm
uLongf destLen = (sourceLen*1.001)+12;
unsigned char* compressedBuffer = (unsigned char*)malloc(destLen);
zlibstream.next_in = (Bytef*)pixelDataBuffer;
zlibstream.avail_in = (uInt)sourceLen;
zlibstream.next_out = compressedBuffer;
zlibstream.avail_out = (uInt)destLen;
if ((uLong)zlibstream.avail_out != destLen) return 1;//Z_BUF_ERROR;

zlibstream.zalloc = (alloc_func)0;
zlibstream.zfree = (free_func)0;
zlibstream.opaque = (voidpf)0;

if(!bFirstUpdateSent)
{
	//Initialize the ZLIB ONLY for the first time
	printf("before deflateInit \r\n");
	zliberr = deflateInit(&zlibstream, Z_DEFAULT_COMPRESSION);
	if (zliberr != Z_OK) 
	{
		printf("deflateInit failed \r\n");
	}
}
bFirstUpdateSent = TRUE;

printf("before deflate \r\n");
//Apply ZLIB encoding to the pixel buffer
zliberr = deflate(&zlibstream, Z_FINISH);
if (zliberr != Z_STREAM_END) {
	return zliberr == Z_OK ? 0 : 1;
}
destLen = zlibstream.total_out;
	
printf("zlib data length = %d \r\n", zlibPixelBufferLength-4);
unsigned char zlibHeader[4]; 
UINT32 zlibLength = destLen;
zlibHeader[0] = zlibLength>>24; 
zlibHeader[1] = zlibLength>>16; 
zlibHeader[2] = zlibLength>>8; 
zlibHeader[3] = zlibLength;

//Send length of the zlib buffer
iSendResult = send( ClientSocket, (const char*)zlibHeader, 4, 0 );
if(iSendResult==SOCKET_ERROR){return 1;}

//send zlib encoded pixel data
iSendResult = send( ClientSocket, (const char*)compressedBuffer, destLen, 0 );
//==============================================================================

Please help.

Regards,

-KK-

Posted 3-Sep-13 0:41am

kdimunge

Updated 6-Sep-13 1:37am

v3

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2 solutions

Solution 1

I could resolve the issue by myself. I suppose to initialize zalloc, zfree and opaque before calling the init function and reset the stream after each deflate cycle. Following is the updated code.

C++

//==============================================================================
//Note: Rectangle header containing x, y, height, width and encoding is sent
//prior to this code.
//
//reduce the BMP header size from total length
uLongf sourceLen = DATA_SIZE-0x436;
//add sufficient length for encoding algorithm
uLongf destLen = (sourceLen*1.001)+12;
unsigned char* compressedBuffer = (unsigned char*)malloc(destLen);
zlibstream.next_in = (Bytef*)pixelDataBuffer;
zlibstream.avail_in = (uInt)sourceLen;
zlibstream.next_out = compressedBuffer;
zlibstream.avail_out = (uInt)destLen;

if ((uLong)zlibstream.avail_out != destLen) return 1;//Z_BUF_ERROR;
if(!bFirstUpdateSent)
{
	//must initialize zalloc, zfree and opaque before calling the init function
	zlibstream.zalloc = (alloc_func)0;
	zlibstream.zfree = (free_func)0;
	zlibstream.opaque = (voidpf)0;

	//Initialize the ZLIB for the first time
	printf("before deflateInit \r\n");
	zliberr = deflateInit(&zlibstream, Z_DEFAULT_COMPRESSION);
	if (zliberr != Z_OK) 
	{
		printf("deflateInit failed \r\n");
	}
}
bFirstUpdateSent = TRUE;
printf("before deflate \r\n");
//Apply ZLIB encoding to the pixel buffer
zliberr = deflate(&zlibstream, Z_FINISH);
if (zliberr != Z_STREAM_END) {
	return zliberr == Z_OK ? 0 : 1;
}
destLen = zlibstream.total_out;
unsigned char zlibHeader[4]; 
UINT32 zlibLength = destLen;
zlibHeader[0] = zlibLength>>24; zlibHeader[1] = zlibLength>>16; zlibHeader[2] = zlibLength>>8; zlibHeader[3] = zlibLength;
//Send length of the zlib buffer
iSendResult = send( ClientSocket, (const char*)zlibHeader, 4, 0 );
if(iSendResult==SOCKET_ERROR){return 1;}
//send zlib encoded pixel data
iSendResult = send( ClientSocket, (const char*)compressedBuffer, destLen, 0 );

//Reset the stream for next cycle
zliberr = deflateReset(&zlibstream);
//==============================================================================

Regards,

-KK-

Posted 4-Sep-13 0:18am

kdimunge

Comments

kdimunge 5-Sep-13 9:47am

This issue is not fully resolved it seems. Though it works with Ultra VNC, eggplant viewer still draws empty screen for subsequent framebuffer updates.

-KK-

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kdimunge · Accepted Answer · 2013-09-06T01:33:00

Finally the issue is resolved and here is the updated code if someone is interested in.

C++

//==============================================================================
if(!bFirstUpdateSent)
{
	zlibstream.zalloc = (alloc_func)0;
	zlibstream.zfree = (free_func)0;
	zlibstream.opaque = (voidpf)0;

	//Initialize the ZLIB for the first time
	printf("before deflateInit \r\n");
	zliberr = deflateInit(&zlibstream, Z_DEFAULT_COMPRESSION);
	if (zliberr != Z_OK) 
	{
		printf("deflateInit failed \r\n");
	}
}
bFirstUpdateSent = TRUE;

//reduce the BMP header size from total length
uLongf sourceLen = DATA_SIZE-0x436;
//add sufficient length for encoding algorithm
uLongf destLen = (sourceLen*1.001)+12;
unsigned char* compressedBuffer = (unsigned char*)malloc(destLen);
zlibstream.next_in = (Bytef*)pixelDataBuffer;
zlibstream.avail_in = (uInt)sourceLen;
zlibstream.next_out = compressedBuffer;
zlibstream.avail_out = (uInt)destLen;		
previous_out = zlibstream.total_out; 

printf("before deflate \r\n");
//Apply ZLIB encoding to the pixel buffer
zliberr = deflate(&zlibstream, Z_SYNC_FLUSH);
	
destLen = zlibstream.total_out - previous_out;

printf("zlib data length = %d \r\n", destLen);
unsigned char zlibHeader[4]; 
UINT32 zlibLength = destLen;
zlibHeader[0] = zlibLength>>24; zlibHeader[1] = zlibLength>>16; zlibHeader[2] = zlibLength>>8; zlibHeader[3] = zlibLength;

//Send length of the zlib buffer
iSendResult = send( ClientSocket, (const char*)zlibHeader, 4, 0 );
if(iSendResult==SOCKET_ERROR){return 1;}

//send zlib encoded pixel data
iSendResult = send( ClientSocket, (const char*)compressedBuffer, destLen, 0 );

//Free the buffer
free(compressedBuffer);
//==============================================================================

Regards,

-KK-