def poll_next_packet
if @packet.nil?
minimum = server.block_size < 4 ? 4 : server.block_size
return nil if available < minimum
data = read_available(minimum)
@packet = Net::SSH::Buffer.new(server.update_cipher(data))
@packet_length = @packet.read_long
end
need = @packet_length + 4 - server.block_size
raise Net::SSH::Exception, "padding error, need #{need} block #{server.block_size}" if need % server.block_size != 0
return nil if available < need + server.hmac.mac_length
if need > 0
data = read_available(need)
@packet.append(server.update_cipher(data))
end
real_hmac = read_available(server.hmac.mac_length) || ""
@packet.append(server.final_cipher)
padding_length = @packet.read_byte
payload = @packet.read(@packet_length - padding_length - 1)
padding = @packet.read(padding_length) if padding_length > 0
my_computed_hmac = server.hmac.digest([server.sequence_number, @packet.content].pack("NA*"))
raise Net::SSH::Exception, "corrupted mac detected" if real_hmac != my_computed_hmac
payload = server.decompress(payload)
debug { "received packet nr #{server.sequence_number} type #{payload.getbyte(0)} len #{@packet_length}" }
server.increment(@packet_length)
@packet = nil
return Packet.new(payload)
end