# -*- coding: utf-8 -*-
"""
pcapy clone in pure python
This module aims to support exactly the same interface as pcapy,
so that it can be used as a drop-in replacement. This means the module
does not and probably will never support live captures. Offline file
support should match the original though.
"""

# Copyright 2010 Stanisław Pitucha. All rights reserved.
#
# Redistribution and use in source and binary forms, with or without modification, are
# permitted provided that the following conditions are met:
#
# 1. Redistributions of source code must retain the above copyright notice, this list of
# 	conditions and the following disclaimer.
#
# 2. Redistributions in binary form must reproduce the above copyright notice, this list
# 	of conditions and the following disclaimer in the documentation and/or other materials
# 	provided with the distribution.
#
# THIS SOFTWARE IS PROVIDED BY Stanisław Pitucha ``AS IS'' AND ANY EXPRESS OR IMPLIED
# WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
# FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR
# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
# ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
# NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
# ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
#
# The views and conclusions contained in the software and documentation are those of the
# authors and should not be interpreted as representing official policies, either expressed
# or implied, of Stanisław Pitucha.


import struct

DLT_NULL = 0
DLT_EN10MB = 1
DLT_IEEE802 = 6
DLT_ARCNET = 7
DLT_SLIP = 8
DLT_PPP = 9
DLT_FDDI = 10
DLT_ATM_RFC1483 = 11
DLT_RAW = 12
DLT_PPP_SERIAL = 50
DLT_PPP_ETHER = 51
DLT_C_HDLC = 104
DLT_IEEE802_11 = 105
DLT_LOOP = 108
DLT_LINUX_SLL = 113
DLT_LTALK = 114

class PcapError(Exception):
	""" General Pcap module exception class """
	pass

def fixup_identical_short(short):
	""" noop for "fixing" big/little endian """
	return short
def fixup_identical_long(long_int):
	""" noop for "fixing" big/little endian """
	return long_int
def fixup_swapped_short(short):
	""" swap bytes in a 16b short """
	return ((short&0xff) << 8) | ((short&0xff00) >> 8)
def fixup_swapped_long(long_int):
	""" swap swapped shorts in a 32b int """
	bottom = fixup_swapped_short(long_int & 0xffff)
	top = fixup_swapped_short((long_int >> 16) & 0xffff)
	return ((bottom << 16) & 0xffff0000) | top

fixup_sets = {
		b"\xd4\xc3\xb2\xa1": (fixup_identical_short, fixup_identical_long),
		b"\xa1\xb2\xc3\xd4": (fixup_swapped_short, fixup_swapped_long),
		}

def open_offline(filename):
	""" opens the pcap file indicated by `filename` and returns a Reader object """
	if filename == "-":
		import sys
		source = sys.stdin
	else:
		try:
			source = open(filename, "rb")
		except IOError as error:
			if error.args[0] == 21:
				raise PcapError("error reading dump file: %s" % (error.args[1]))
			else:
				raise PcapError("%s: %s" % (filename, error.args[1]))

	return Reader(source)

def open_live(_device, _snaplen, _promisc, _to_ms):
	raise NotImplementedError("This function is only available in pcapy")

def lookupdev():
	raise NotImplementedError("This function is only available in pcapy")

def findalldevs():
	raise NotImplementedError("This function is only available in pcapy")

def compile(_linktype, _snaplen, _filter, _optimize, _netmask):
	raise NotImplementedError("not implemented yet")

class Reader(object):
	"""
	An interface for reading an open pcap file.
	This object can either read a single packet via `next()`, a series
	via `loop()` or `dispatch()`, or by iterating over the object.
	"""

	__GLOBAL_HEADER_LEN = 24
	__PACKET_HEADER_LEN = 16

	def __init__(self, source):
		""" creates a Reader instance from an open file object """

		self.__source = source
		header = self.__source.read(self.__GLOBAL_HEADER_LEN)
		if len(header) < self.__GLOBAL_HEADER_LEN:
			raise PcapError(
					"truncated dump file; tried to read %i file header bytes, only got %i" %
					(self.__GLOBAL_HEADER_LEN, len(header)))

		hdr_values = struct.unpack("IHHIIII", header)
		if header[:4] in fixup_sets:
			self.fixup_short, self.fixup_long = fixup_sets[header[:4]]
		else:
			raise PcapError("bad dump file format")

		self.version_major, self.version_minor = [self.fixup_short(x)
				for x in hdr_values[1:3]]
		self.thiszone, self.sigfigs, self.snaplen, self.network = [self.fixup_long(x)
				for x in hdr_values[3:]]

		self.last_good_position = self.__GLOBAL_HEADER_LEN

	def __loop_and_count(self, maxcant, callback):
		"""
		reads up to `maxcant` packets and runs callback for each of them
		returns the number of packets processed
		"""

		i = 0
		while True:
			if i >= maxcant and maxcant > -1:
				break

			hdr, data = self.next()
			if hdr is None:
				break
			else:
				callback(hdr, data)

			i += 1

		return i

	def dispatch(self, maxcant, callback):
		"""
		reads up to `maxcant` packets and runs callback for each of them
		returns the number of packets processed or 0 if no limit was specified
		"""

		i = self.__loop_and_count(maxcant, callback)

		if maxcant > -1:
			return i
		else:
			return 0

	def loop(self, maxcant, callback):
		"""
		reads up to `maxcant` packets and runs callback for each of them
		does not return a value
		"""
		self.__loop_and_count(maxcant, callback)

	def __iter__(self):
	    return self

	def next(self):
		""" reads the next packet from file and returns a (Pkthdr, data) tuple """

		header = self.__source.read(self.__PACKET_HEADER_LEN)

		if len(header) == 0:
			return (None, '')
		if len(header) < self.__PACKET_HEADER_LEN:
			raise PcapError(
					"truncated dump file; tried to read %i header bytes, only got %i" %
					(self.__PACKET_HEADER_LEN, len(header)))

		hdr_values = struct.unpack("IIII", header)
		ts_sec, ts_usec, incl_len, orig_len = [self.fixup_long(x) for x in hdr_values]

		data = self.__source.read(incl_len)
		if len(data) < incl_len:
			raise PcapError(
					"truncated dump file; tried to read %i captured bytes, only got %i" %
					(incl_len, len(data)))

		pkthdr = Pkthdr(ts_sec, ts_usec, incl_len, orig_len)
		return (pkthdr, data)

	def getnet(self):
		raise NotImplementedError("This function is only available in pcapy")

	def getmask(self):
		raise NotImplementedError("This function is only available in pcapy")

	def datalink(self):
		""" returns the datalink type used in the current file """
		return self.network

	def getnonblock(self):
		"""
		shows whether the operations are nonblocking, which is always 0 for files
		"""
		return 0

	def setnonblock(self, state):
		""" this has no effect on savefiles, so is not implemented in pure-pcapy """
		pass

	def dump_open(self, filename):
		"""
		create a new dumper object which inherits the network and snaplen information
		from the original reader
		"""
		return Dumper(filename, self.snaplen, self.network)

class Dumper(object):
	"""
	Interface for pcap files, which can be used for creating new files.
	Although this is accessible only through `Reader.dump_open()` in the
	original pcapy, there's no good reason for that limitation and this object
	can be used directly. It implements some sanity checking before the packet
	is written to the file.
	Files created this way are always stored using the native byte order.
	"""

	def __init__(self, filename, snaplen, network):
		""" creates a new dumper object which can be used for writing pcap files """
		self.store = open(filename, "wb")
		self.store.write(struct.pack("IHHIIII", 0xa1b2c3d4, 2, 4, 0, 0,
			snaplen, network))
		self.store.flush() # have to flush, since there's no close

	def dump(self, header, data):
		""" writes a new header and packet to the file, then forces a file flush """
		if not isinstance(header, Pkthdr):
			raise PcapError("not a proper Pkthdr")

		if type(data) != bytes:
			raise PcapError("can dump only bytes")

		if header.getcaplen() != len(data):
			raise PcapError("capture length not equal to length of data")

		fields = list(header.getts()) + [header.getcaplen(), header.getlen()]
		self.store.write(struct.pack("IIII", *fields))
		self.store.write(data)
		self.store.flush()

class Pkthdr(object):
	"""
	Packet header, as used in the pcap files before each data segment.
	This class is a simple data wrapper.
	"""

	def __init__(self, ts_sec, ts_usec, incl_len, orig_len):
		self.ts = (ts_sec, ts_usec)
		self.incl_len = incl_len
		self.orig_len = orig_len

	def getts(self):
		""" returns a (seconds, microseconds) tuple for the capture time"""
		return self.ts

	def getcaplen(self):
		""" returns the captured length of the packet """
		return self.incl_len

	def getlen(self):
		""" returns the original length of the packet """
		return self.orig_len

class Bpf(object):
	def __init__(self):
		raise NotImplementedError("not implemented yet")

	def filter(self, packet):
		raise NotImplementedError("not implemented yet")