Use a pcap wrapper instead of tcpdump (#10)

README.md

@@ -17,7 +17,8 @@ Additionally, IGMPv2 and MLDv1 are implemented alongside with PIM-DM to detect i
  - Unicast routing protocol
  - Python3 (we have written all code to be compatible with at least Python v3.3)
  - pip (to install all dependencies)
- - tcpdump
+ - libpcap-dev
+ - python3-dev
 
 
 # Installation

filter.h

+/* based on https://github.com/the-tcpdump-group/tcpdump */
+
+#ifndef FILTER_H
+#define FILTER_H
+
+#define MAXIMUM_SNAPLEN    262144
+
+#include <stdio.h>
+#include <pcap.h>
+
+int filter_try_compile(struct bpf_program *fp, const char *cmdbuf)
+{
+  int dump_dlt, ret;
+  pcap_t *pd;
+
+  dump_dlt = DLT_EN10MB;
+  fprintf(stderr, "Warning: assuming Ethernet\n");
+  pd = pcap_open_dead(dump_dlt, MAXIMUM_SNAPLEN);
+
+  ret = pcap_compile(pd, fp, cmdbuf, 1, 0);
+  if (ret < 0)
+    fprintf(stderr, "%s", pcap_geterr(pd));
+
+  pcap_close(pd);
+  return (ret);
+}
+
+#endif /* FILTER_H */

pcap.pyx

+#include <pcap.h>
+
+import struct
+
+ctypedef unsigned int u_int
+ctypedef unsigned char u_char
+ctypedef unsigned short int u_short
+ctypedef u_int bpf_u_int32
+
+cdef extern from "pcap.h":
+    struct bpf_insn:
+        u_short code
+        u_char jt
+        u_char jf
+        bpf_u_int32 k
+    struct bpf_program:
+        bpf_insn *bf_insns
+        u_int bf_len
+
+cdef extern from "pcap.h":
+    void    pcap_freecode(bpf_program *fp)
+
+cdef extern from "filter.h":
+    int    filter_try_compile(bpf_program *fp, const char *cmdbuf)
+
+
+cdef class bpf:
+    """bpf(filter) -> BPF filter object"""
+
+    cdef bpf_program fcode
+
+    def __init__(self, char *filter):
+        if filter_try_compile(&self.fcode, filter) < 0:
+            raise IOError, 'bad filter'
+
+    def compiled_filter(self):
+        cdef bpf_insn *bf_insns
+        bf_insns = self.fcode.bf_insns
+        size = self.fcode.bf_len
+
+        return size, b''.join(
+            struct.pack('HBBI', bf_insns[i].code, bf_insns[i].jt, bf_insns[i].jf, bf_insns[i].k)
+            for i in range(size)
+        )
+
+    def dump(self):
+        cdef bpf_insn *bf_insns
+        cdef bpf_insn bf_insn
+        bf_insns = self.fcode.bf_insns
+        for i in range(self.fcode.bf_len):
+            bf_insn = bf_insns[i]
+            print("{ 0x%x, %d, %d, 0x%08x }," % (bf_insn.code, bf_insn.jt, bf_insn.jf, bf_insn.k))
+
+    def __dealloc__(self):
+        pcap_freecode(&self.fcode)

pimdm/tree/data_packets_socket.py

 import struct
 import socket
 import ipaddress
-import subprocess
 from ctypes import create_string_buffer, addressof
+from pcap_wrapper import bpf
 
 SO_ATTACH_FILTER = 26
 ETH_P_IP = 0x0800    # Internet Protocol packet
@@ -14,25 +14,17 @@ def get_s_g_bpf_filter_code(source, group, interface_name):
     ip_source_version = ipaddress.ip_address(source).version
     ip_group_version = ipaddress.ip_address(group).version
     if ip_source_version == ip_group_version == 4:
-        # cmd = "tcpdump -ddd \"(udp or icmp) and host %s and dst %s\"" % (source, group)
-        cmd = "tcpdump -ddd \"(ip proto not 2) and host %s and dst %s\"" % (source, group)
+        # bpf_filter_str = "(udp or icmp) and host %s and dst %s" % (source, group)
+        bpf_filter_str = "(ip proto not 2) and host %s and dst %s" % (source, group)
         protocol = ETH_P_IP
     elif ip_source_version == ip_group_version == 6:
         # TODO: allow ICMPv6 echo request/echo response to be considered multicast packets
-        cmd = "tcpdump -ddd \"(ip6 proto not 58) and host %s and dst %s\"" % (source, group)
+        bpf_filter_str = "(ip6 proto not 58) and host %s and dst %s" % (source, group)
         protocol = ETH_P_IPV6
     else:
         raise Exception("Unknown IP family")
 
-    result = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
-    bpf_filter = b''
-
-    tmp = result.stdout.read().splitlines()
-    num = int(tmp[0])
-    for line in tmp[1:]:
-        print(line)
-        bpf_filter += struct.pack("HBBI", *tuple(map(int, line.split(b' '))))
-
+    num, bpf_filter = bpf(bpf_filter_str.encode()).compiled_filter()
     print(num)
 
     # defined in linux/filter.h.

setup.py

 import sys
-from setuptools import setup, find_packages
+from setuptools import setup, find_packages, Extension
 
 # we only support Python 3 version >= 3.3
 if len(sys.argv) >= 2 and sys.argv[1] == "install" and sys.version_info < (3, 3):
@@ -26,6 +26,11 @@ setup(
         'igmp==1.0.2',
     ],
     packages=find_packages(exclude=["docs"]),
+    ext_modules = [Extension(
+        name="pcap_wrapper",
+        sources = ["pcap.c"],
+        libraries=["pcap"],
+    )],
     entry_points={
         "console_scripts": [
             "pim-dm = pimdm.Run:main",