How to read packet saved in a file with Python? -

i have c++ code generates ip packet header. code use struct representing each field in packet:

struct cip {    uint8_t        ip_hl:4, /* both fields 4 bytes */                   ip_v:4;    uint8_t        ip_tos;    uint16_t       ip_len;    uint16_t       ip_id;    uint16_t       ip_off;    uint8_t        ip_ttl;    uint8_t        ip_p;    uint16_t       ip_sum;    struct in_addr ip_src;    struct in_addr ip_dst;    char       head[100]; }; 

the user prompt input message enter values each variable in struct:

enter filename save packet: packet

enter ip version(0-15): 4

enter header length(5-15): 5

enter type of service(0-255): 55

enter packet total size(bytes, 20, 200): 25

the packet created , saved in file:

file* f = fopen(file, "w"); int success = fwrite(&packet, sizeof(char), ((unsigned int)packet.ip_hl)*4,f); if(success <= 0) {     printf("error writing packet header"); } success = fwrite(&data, sizeof(char),ntohs(packet.ip_len)-(4*packet.ip_hl),f); if(success < 0) {     printf("error writing packet data"); } fflush(f); fclose(f); printf("\npacket written.\n"); 

i didn't create code, gave me code can create other program in python validate packet created program above. validation includes verifying checksum generated packet, version of ip packet, protocol, length of header , on.

so know if can me figuring out how can read file , parse frame. tried read line in file string, problem i'm having file looks after creation: (it unreadable)

o È ,@ šÀ¨À¨ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxdata_______________________data____________ ô·

i don't understand why: (i'm guessing because variables bigger 1 byte converted big endian function "htons":

printf("\nenter ip id number(0-65535):\n"); scanf("%d", &input); packet.ip_id = htons(input); 

i tried search option dealing socket.makefile(), me socket in program file, need parse frame gave me in file.

any ideas?

thanks.

p.s.: can give me link can find how convert integer big endian small endian , vicerversa in python. thanks!

you should read file usual (specifying "binary" mode windows):

with open("test.txt", 'br') f:     line in f.readlines():         # process lines 

to unpack binary data should use struct package, can handle big , little endian , on. example struct:

print struct.unpack('bbhhhbbh100s', line) 

i omitted ip_src , ip_dst unpacking since didn't specify contents of struct. least possible value read 1 byte, split first field 2 parts can use:

(ip_hl, ip_v) = (value >> 4, value & 15) 

of course, order of 8-bit component depends on struct endianess.