Function CompressStringGZIP

src/StringCompression.cpp:56–114

int CompressStringGZIP(const char * a_Data, size_t a_Length, AString & a_Compressed)
{
	// Compress a_Data into a_Compressed using GZIP; return Z_XXX error constants same as zlib's compress2()

	a_Compressed.reserve(a_Length);

	char Buffer[64 KiB];
	z_stream strm;
	memset(&strm, 0, sizeof(strm));
	strm.next_in = (Bytef *)a_Data;
	strm.avail_in = a_Length;
	strm.next_out = (Bytef *)Buffer;
	strm.avail_out = sizeof(Buffer);
	
	int res = deflateInit2(&strm, 9, Z_DEFLATED, 31, 9, Z_DEFAULT_STRATEGY);
	if (res != Z_OK)
	{
		LOG("%s: compression initialization failed: %d (\"%s\").", __FUNCTION__, res, strm.msg);
		return res;
	}
	
	for (;;)
	{
		res = deflate(&strm, Z_FINISH);
		switch (res)
		{
			case Z_OK:
			{
				// Some data has been compressed. Consume the buffer and continue compressing
				a_Compressed.append(Buffer, sizeof(Buffer) - strm.avail_out);
				strm.next_out = (Bytef *)Buffer;
				strm.avail_out = sizeof(Buffer);
				if (strm.avail_in == 0)
				{
					// All data has been compressed
					deflateEnd(&strm);
					return Z_OK;
				}
				break;
			}
			
			case Z_STREAM_END:
			{
				// Finished compressing. Consume the rest of the buffer and return
				a_Compressed.append(Buffer, sizeof(Buffer) - strm.avail_out);
				deflateEnd(&strm);
				return Z_OK;
			}
			
			default:
			{
				// An error has occurred, log it and return the error value
				LOG("%s: compression failed: %d (\"%s\").", __FUNCTION__, res, strm.msg);
				deflateEnd(&strm);
				return res;
			}
		}  // switch (res)
	}  // while (true)