def ip_packet(payload, src_ip, dst_ip, protocol=chr(ip_constants.IPV4_PROTOCOL_UDP)):
"""
Create an IPv4 packet.
:type payload: str
:param payload: Contents of next layer up.
:type src_ip: str
:param src_ip: 4-byte source IP address.
:type dst_ip: str
:param dst_ip: 4-byte destination IP address.
:type protocol: str
:param protocol: Single-byte string identifying next layer's protocol. Default "\x11" UDP.
:return: IPv4 packet.
:rtype: str
"""
ip_header = "\x45" # Version | Header Length
ip_header += "\x00" # "Differentiated Services Field"
ip_header += struct.pack(">H", IP_HEADER_LEN + len(payload)) # Length
ip_header += "\x00\x01" # ID Field
ip_header += "\x40\x00" # Flags, Fragment Offset
ip_header += "\x40" # Time to live
ip_header += protocol
ip_header += "\x00\x00" # Header checksum (fill in zeros in order to compute checksum)
ip_header += src_ip
ip_header += dst_ip
checksum = struct.pack(">H", helpers.ipv4_checksum(ip_header))
ip_header = ip_header[:10] + checksum + ip_header[12:]
return ip_header + payload
def ip_packet(payload, src_ip, dst_ip, protocol=six.int2byte(ip_constants.IPV4_PROTOCOL_UDP)):
"""
Create an IPv4 packet.
:type payload: bytes
:param payload: Contents of next layer up.
:type src_ip: bytes
:param src_ip: 4-byte source IP address.
:type dst_ip: bytes
:param dst_ip: 4-byte destination IP address.
:type protocol: bytes
:param protocol: Single-byte string identifying next layer's protocol. Default "\x11" UDP.
:return: IPv4 packet.
:rtype: bytes
"""
ip_header = b"\x45" # Version | Header Length
ip_header += b"\x00" # "Differentiated Services Field"
ip_header += struct.pack(">H", IP_HEADER_LEN + len(payload)) # Length
ip_header += b"\x00\x01" # ID Field
ip_header += b"\x40\x00" # Flags, Fragment Offset
ip_header += b"\x40" # Time to live
ip_header += protocol
ip_header += b"\x00\x00" # Header checksum (fill in zeros in order to compute checksum)
ip_header += src_ip
ip_header += dst_ip
checksum = struct.pack(">H", helpers.ipv4_checksum(ip_header))
ip_header = ip_header[:10] + checksum + ip_header[12:]
return ip_header + payload
