#!/usr/bin/env python3
#
# Wireshark - Network traffic analyzer
# By Gerald Combs <gerald@wireshark.org>
# Copyright 1998 Gerald Combs
#
# SPDX-License-Identifier: GPL-2.0-or-later
#
'''\
Generate Sysdig event dissector sections from the sysdig sources.

Reads driver/event_table.c and driver/ppm_events_public.h and generates
corresponding dissection code in packet-sysdig-event.c. Updates are
performed in-place in the dissector code.

Requires an Internet connection. Assets are loaded from GitHub over HTTPS, from falcosecurity/libs master.
'''

import logging
import os
import os.path
import re
import urllib.request, urllib.error, urllib.parse
import sys

sysdig_repo_pfx = 'https://raw.githubusercontent.com/falcosecurity/libs/master/'

def exit_msg(msg=None, status=1):
    if msg is not None:
        sys.stderr.write(msg + '\n\n')
    sys.stderr.write(__doc__ + '\n')
    sys.exit(status)

def get_url_lines(url):
    '''Open a URL.
    Returns the URL body as a list of lines.
    '''
    req_headers = { 'User-Agent': 'Wireshark generate-sysdig-event' }
    try:
        req = urllib.request.Request(url, headers=req_headers)
        response = urllib.request.urlopen(req)
        lines = response.read().decode().splitlines()
        response.close()
    except urllib.error.HTTPError as err:
        exit_msg("HTTP error fetching {0}: {1}".format(url, err.reason))
    except urllib.error.URLError as err:
        exit_msg("URL error fetching {0}: {1}".format(url, err.reason))
    except OSError as err:
        exit_msg("OS error fetching {0}: {1}".format(url, err.strerror))
    except Exception:
        exit_msg("Unexpected error:", sys.exc_info()[0])

    return lines


ppm_ev_pub_lines = get_url_lines(sysdig_repo_pfx + 'driver/ppm_events_public.h')

ppme_re = re.compile('^\s+PPME_([A-Z0-9_]+_[EX])\s*=\s*([0-9]+)\s*,')
ppm_sc_x_re = re.compile('^\s+PPM_SC_X\s*\(\s*(\S+)\s*,\s*(\d+)\s*\)')

event_info_d = {}

def get_event_defines():
    event_d = {}
    for line in ppm_ev_pub_lines:
        m = ppme_re.match(line)
        if m:
            event_d[int(m.group(2))] = m.group(1)
    return event_d

def get_syscall_code_defines():
    sc_d = {}
    for line in ppm_ev_pub_lines:
        m = ppm_sc_x_re.match(line)
        if m:
            sc_d[int(m.group(2))] = m.group(1)
    return sc_d

ppm_ev_table_lines = get_url_lines(sysdig_repo_pfx + 'driver/event_table.c')

hf_d = {}

event_info_re = re.compile('^\s+\[\s*PPME_.*\]\s*=\s*{\s*"([A-Za-z0-9_]+)"\s*,[^,]+,[^,]+,\s*([0-9]+)\s*[,{}]')
event_param_re = re.compile('{\s*"([A-Za-z0-9_ ]+)"\s*,\s*PT_([A-Z0-9_]+)\s*,\s*PF_([A-Z0-9_]+)\s*[,}]')

def get_event_names():
    '''Return a contiguous list of event names. Names are lower case.'''
    event_name_l = []
    for line in ppm_ev_table_lines:
        ei = event_info_re.match(line)
        if ei:
            event_name_l.append(ei.group(1))
    return event_name_l

# PT_xxx to FT_xxx
pt_to_ft = {
    'BYTEBUF': 'BYTES',
    'CHARBUF': 'STRING',
    'ERRNO': 'INT64',
    'FD': 'INT64',
    'FLAGS8': 'INT8',
    'FLAGS16': 'INT16',
    'FLAGS32': 'INT32',
    'FSPATH': 'STRING',
    'FSRELPATH': 'STRING',
    'GID': 'INT32',
    'MODE': 'INT32',
    'PID': 'INT64',
    'UID': 'INT32',
    'SYSCALLID': 'UINT16',
}

# FT_xxx to BASE_xxx
force_param_formats = {
    'STRING': 'NONE',
    'INT.*': 'DEC',
}

def get_event_params():
    '''Return a list of dictionaries containing event names and parameter info.'''
    event_param_l = []
    event_num = 0
    force_string_l = ['args', 'env']
    for line in ppm_ev_table_lines:
        ei = event_info_re.match(line)
        ep = event_param_re.findall(line)
        if ei and ep:
            event_name = ei.group(1)
            src_param_count = int(ei.group(2))
            if len(ep) != src_param_count:
                err_msg = '{}: found {} parameters. Expected {}. Params: {}'.format(
                    event_name, len(ep), src_param_count, repr(ep))
                if len(ep) > src_param_count:
                    logging.warning(err_msg)
                    del ep[src_param_count:]
                else:
                    raise NameError(err_msg)
            for p in ep:
                if p[0] in force_string_l:
                    param_type = 'STRING'
                elif p[1] in pt_to_ft:
                    param_type = pt_to_ft[p[1]]
                elif p[0] == 'flags' and p[1].startswith('INT') and 'HEX' in p[2]:
                    param_type = 'U' + p[1]
                elif 'INT' in p[1]:
                    # Ints
                    param_type = p[1]
                else:
                    print(f"p fallback {p}")
                    # Fall back to bytes
                    param_type = 'BYTES'

                if p[2] == 'NA':
                    if 'INT' in param_type:
                        param_format = 'DEC'
                    else:
                        param_format = 'NONE'
                elif param_type == 'BYTES':
                    param_format = 'NONE'
                else:
                    param_format = p[2]

                for pt_pat, force_pf in force_param_formats.items():
                    if re.match(pt_pat, param_type) and param_format != force_pf:
                        err_msg = 'Forcing {} {} format to {}. Params: {}'.format(
                            event_name, param_type, force_pf, repr(ep))
                        logging.warning(err_msg)
                        param_format = force_pf

                param_d = {
                    'event_name': event_name,
                    'event_num': event_num,
                    # use replace() to account for "plugin ID" param name (ie: param names with space)
                    'param_name': p[0].replace(" ", "_"),
                    'param_type': param_type,
                    'param_format': param_format,
                }
                event_param_l.append(param_d)
        if ei:
            event_num += 1
    return event_param_l

def param_to_hf_name(param):
    return 'hf_param_{}_{}'.format(param['param_name'], param['param_type'].lower())

def param_to_value_string_name(param):
    return '{}_{}_vals'.format(param['param_name'], param['param_type'].lower())

def get_param_desc(param):
    # Try to coerce event names and parameters into human-friendly
    # strings.
    # XXX This could use some work.

    # Specific descriptions. Event name + parameter name.
    param_descs = {
        'accept.queuepct': 'Accept queue per connection',
        'execve.args': 'Program arguments',
        'execve.comm': 'Command',
        'execve.cwd': 'Current working directory',
    }
    # General descriptions. Event name only.
    event_descs = {
        'ioctl': 'I/O control',
    }

    event_name = param['event_name']
    param_id = '{}.{}'.format(event_name, param['param_name'])
    if param_id in param_descs:
        param_desc = param_descs[param_id]
    elif event_name in event_descs:
        param_desc = '{}: {}'.format(event_descs[event_name], param['param_name'])
    else:
        param_desc = param['param_name']
    return param_desc

def main():
    logging.basicConfig(format='%(levelname)s: %(message)s')

    # Event list
    event_d = get_event_defines()
    event_nums = list(event_d.keys())
    event_nums.sort()

    event_name_l = get_event_names()
    event_param_l = get_event_params()

    hf_d = {}
    for param in event_param_l:
        hf_name = param_to_hf_name(param)
        hf_d[hf_name] = param

    idx_id_to_name = { '': 'no' }
    parameter_index_l = []

    for en in range (0, len(event_nums)):
        param_id = ''
        param_l = []
        event_var = event_d[en].lower()
        for param in event_param_l:
            if param['event_num'] == en:
                hf_name = param_to_hf_name(param)
                param_l.append(hf_name)
                param_id += ':' + param['param_name'] + '_' + param['param_type']

        ei_str = ''
        if param_id not in idx_id_to_name:
            idx_id_to_name[param_id] = event_var
            ei_str = 'static int * const {}_indexes[] = {{ &{}, NULL }};'.format(
                event_var,
                ', &'.join(param_l)
            )
        else:
            ei_str = '#define {}_indexes {}_indexes'.format(event_var, idx_id_to_name[param_id])

        parameter_index_l.append(ei_str)

    dissector_path = os.path.join(os.path.dirname(__file__),
        '..', 'epan', 'dissectors', 'packet-sysdig-event.c')
    dissector_f = open(dissector_path, 'r')
    dissector_lines = list(dissector_f)
    dissector_f = open(dissector_path, 'w+')

    # Strip out old content
    strip_re_l = []
    strip_re_l.append(re.compile('^static\s+int\s+hf_param_.*;'))
    strip_re_l.append(re.compile('^#define\s+EVT_STR_[A-Z0-9_]+\s+"[A-Za-z0-9_]+"'))
    strip_re_l.append(re.compile('^#define\s+EVT_[A-Z0-9_]+\s+[0-9]+'))
    strip_re_l.append(re.compile('^\s*{\s*EVT_[A-Z0-9_]+\s*,\s*EVT_STR_[A-Z0-9_]+\s*}'))
    strip_re_l.append(re.compile('^static\s+const\s+int\s+\*\s*[a-z0-9_]+_[ex]_indexes\[\]\s*=\s*\{\s*&hf_param_.*NULL\s*\}\s*;'))
    strip_re_l.append(re.compile('^static\s+int\s*\*\s+const\s+[a-z0-9_]+_[ex]_indexes\[\]\s*=\s*\{\s*&hf_param_.*NULL\s*\}\s*;'))
    strip_re_l.append(re.compile('^\s*#define\s+[a-z0-9_]+_[ex]_indexes\s+[a-z0-9_]+_indexes'))
    strip_re_l.append(re.compile('^\s*\{\s*EVT_[A-Z0-9_]+_[EX]\s*,\s*[a-z0-9_]+_[ex]_indexes\s*}\s*,'))
    strip_re_l.append(re.compile('^\s*\{\s*\d+\s*,\s*"\S+"\s*}\s*,\s*//\s*PPM_SC_\S+'))
    strip_re_l.append(re.compile('^\s*{\s*&hf_param_.*},')) # Must all be on one line

    for strip_re in strip_re_l:
        dissector_lines = [line for line in dissector_lines if not strip_re.search(line)]

    # Find our value strings
    value_string_re = re.compile('static\s+const\s+value_string\s+([A-Za-z0-9_]+_vals)')
    value_string_l = []
    for line in dissector_lines:
        vs = value_string_re.match(line)
        if vs:
            value_string_l.append(vs.group(1))

    # Add in new content after comments.

    header_fields_c = 'Header fields'
    header_fields_re = re.compile('/\*\s+' + header_fields_c, flags = re.IGNORECASE)
    header_fields_l = []
    for hf_name in sorted(hf_d.keys()):
        header_fields_l.append('static int {};'.format(hf_name))

    event_names_c = 'Event names'
    event_names_re = re.compile('/\*\s+' + event_names_c, flags = re.IGNORECASE)
    event_names_l = []
    event_str_l = list(set(event_name_l))
    event_str_l.sort()
    for evt_str in event_str_l:
        event_names_l.append('#define EVT_STR_{0:24s} "{1:s}"'.format(evt_str.upper(), evt_str))

    event_definitions_c = 'Event definitions'
    event_definitions_re = re.compile('/\*\s+' + event_definitions_c, flags = re.IGNORECASE)
    event_definitions_l = []
    for evt in event_nums:
        event_definitions_l.append('#define EVT_{0:24s} {1:3d}'.format(event_d[evt], evt))

    value_strings_c = 'Value strings'
    value_strings_re = re.compile('/\*\s+' + value_strings_c, flags = re.IGNORECASE)
    value_strings_l = []
    for evt in event_nums:
        evt_num = 'EVT_{},'.format(event_d[evt])
        evt_str = 'EVT_STR_' + event_name_l[evt].upper()
        value_strings_l.append('    {{ {0:<32s} {1:s} }},'.format(evt_num, evt_str))

    parameter_index_c = 'Parameter indexes'
    parameter_index_re = re.compile('/\*\s+' + parameter_index_c, flags = re.IGNORECASE)
    # parameter_index_l defined above.

    event_tree_c = 'Event tree'
    event_tree_re = re.compile('/\*\s+' + event_tree_c, flags = re.IGNORECASE)
    event_tree_l = []
    for evt in event_nums:
        evt_num = 'EVT_{}'.format(event_d[evt])
        evt_idx = '{}_indexes'.format(event_d[evt].lower())
        event_tree_l.append('    {{ {}, {} }},'.format(evt_num, evt_idx))

    # Syscall codes
    syscall_code_d = get_syscall_code_defines()
    syscall_code_c = 'Syscall codes'
    syscall_code_re = re.compile('/\*\s+' + syscall_code_c, flags = re.IGNORECASE)
    syscall_code_l = []
    for sc_num in syscall_code_d:
        syscall_code_l.append(f'    {{ {sc_num:3}, "{syscall_code_d[sc_num].lower()}" }}, // PPM_SC_{syscall_code_d[sc_num]}')

    header_field_reg_c = 'Header field registration'
    header_field_reg_re = re.compile('/\*\s+' + header_field_reg_c, flags = re.IGNORECASE)
    header_field_reg_l = []
    for hf_name in sorted(hf_d.keys()):
        param = hf_d[hf_name]
        event_name = param['event_name']
        param_desc = get_param_desc(param)
        param_name = param['param_name']
        param_type = param['param_type']
        param_format = param['param_format']
        fieldconvert = 'NULL'
        vs_name = param_to_value_string_name(param)
        if vs_name in value_string_l and 'INT' in param_type:
            fieldconvert = 'VALS({})'.format(vs_name)
        header_field_reg_l.append('        {{ &{}, {{ "{}", "sysdig.param.{}.{}", FT_{}, BASE_{}, {}, 0, NULL, HFILL }} }},'.format(
            hf_name,
            param_desc,
            event_name,
            param_name,
            param_type,
            param_format,
            fieldconvert
            ))

    for line in dissector_lines:
        fill_comment = None
        fill_l = []

        if header_fields_re.match(line):
            fill_comment = header_fields_c
            fill_l = header_fields_l
        elif event_names_re.match(line):
            fill_comment = event_names_c
            fill_l = event_names_l
        elif event_definitions_re.match(line):
            fill_comment = event_definitions_c
            fill_l = event_definitions_l
        elif value_strings_re.match(line):
            fill_comment = value_strings_c
            fill_l = value_strings_l
        elif parameter_index_re.match(line):
            fill_comment = parameter_index_c
            fill_l = parameter_index_l
        elif event_tree_re.match(line):
            fill_comment = event_tree_c
            fill_l = event_tree_l
        elif syscall_code_re.match(line):
            fill_comment = syscall_code_c
            fill_l = syscall_code_l
        elif header_field_reg_re.match(line):
            fill_comment = header_field_reg_c
            fill_l = header_field_reg_l

        if fill_comment is not None:
            # Write our comment followed by the content
            print(('Generating {}, {:d} lines'.format(fill_comment, len(fill_l))))
            dissector_f.write('/* {}. Automatically generated by tools/{} */\n'.format(
                fill_comment,
                os.path.basename(__file__)
                ))
            for line in fill_l:
                dissector_f.write('{}\n'.format(line))
            # Fill each section only once
            del fill_l[:]
        else:
            # Existing content
            dissector_f.write(line)

    dissector_f.close()

#
# On with the show
#

if __name__ == "__main__":
    sys.exit(main())