pushpool's client developing issues

Developing pushpool client

Hello,
I'm really interested in jgarzik's pushpool (it's binary protocol in particular) and writing Qt-based client.

Problem is that I can't make it through LOGIN step.
As far as I undestand from forum's threads and (mostly) pushpool's source code, I need to send ubbp_header with BC_OP_LOGIN operation code and message's length in bytes. Message is SHA256 of compressed json updated with userpass following compressed json.

Json looks something like this (protocol is always 1, config is always null):

Code: (json)

{"protocol":1, "user":"username", "config":null}

And I'm doing following (higlighted version):

Code:

ubbp_header header;
   strcpy((char*)header.magic, PUSHPOOL_UBBP_MAGIC);

   QSocket socket;
   socket.connectToHost("my.pushpool.host", 8336);
   socket.waitForConnected();

   // add compressed json to data
   dataToSend = json.toUtf8();
   dataToSend = (qCompress(dataToSend, 9));

   // Since qCompress() adding length (first 4 bytes in dataToSend) in Big-Endian,
   // but server uses le32toh() to get it, change endianness to Little-Endian:
   dataToSend.remove(0, 4);
   uint32_t len = json.length();
   dataToSend.insert(0, (char*)&len;, sizeof(uint32_t));

   // add compressed json digest
   char pass[] = "test";
   uchar md[SHA256_DIGEST_LENGTH];
   SHA256_CTX ctx;
   SHA256_Init(&ctx;);
   SHA256_Update(&ctx;, dataToSend.data(), dataToSend.size());
   SHA256_Update(&ctx;, pass, strlen(pass));
   SHA256_Final(md, &ctx;);
   dataToSend.append((char*)md, SHA256_DIGEST_LENGTH);

   // Send operation code & message size
   header.op_size = UBBP_OP_SIZE(BC_OP_LOGIN, dataToSend.size());
   socket.write((char*)&header;, sizeof(ubbp_header));
   socket.waitForBytesWritten();

   // Send message
   socket.write(dataToSend);
   socket.waitForBytesWritten();

   // Here's a problem:
   // after message sent, I get
   // QAbstractSocket::error() with 'Remote host closed connection'

My assumptions:

JSON compressed by qCompress() cannot be uncompressed by zlib (even after my manipulation)
I'm calculating wrong SHA256
Something wrong with json (i.e. config must not be null)

After puzzling for almost whole day, I'm writing here.
Guys, please help.