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if(offset >= buf->buffered_bytes) {
    return 0;
}

cursor = buf->first_ext;
bytes = 0;
while(cursor && bytes < offset) {
    bytes += cursor->len;
    cursor = cursor->next;
}

first_ext = cursor;
ext_count = 0;
for(; cursor; cursor = cursor->next) {
    ++ext_count;
}

if(0 == ext_count) {
    return 0;
}

assert(first_ext);

iov = (struct iovec*)malloc(sizeof(struct iovec) * ext_count);
if(!iov) {
    return MQTTERR_OUTOFMEMORY;
}

iov[0].iov_base = first_ext->payload + (offset - bytes);
iov[0].iov_len = first_ext->len - (offset - bytes);

i = 1;
for(cursor = first_ext->next; cursor; cursor = cursor->next) {
    iov[i].iov_base = cursor->payload;
    iov[i].iov_len = cursor->len;
    ++i;
}

i = ctx->writev_func(ctx->writev_func_arg, iov, ext_count);
free(iov);

return i;

3.2.2.2 Session Present 

Position: bit 0 of the Connect Acknowledge Flags. 

If the Server accepts a connection with CleanSession set to 1, the Server MUST set Session Present to 0 in the CONNACK packet in addition to setting a zero return code in the CONNACK packet [MQTT-3.2.2-1].

0x10 0x25 0x0 0x4 0x4d 0x51 0x54 0x54 0x4 0xc2 0x0 0x0 0x0 0x7 0x35 0x36 0x31 0x39 0x31 0x30 0x39 0x0 0x5 0x38 0x35 0x35 0x37 0x34 0x0 0x9 0x68 0x65 0x6c 0x6c 0x6f ......

0x20 0x02 0x01 0x00

0x20 0x02 0x00 0x00