apj_tool.py

#!/usr/bin/env python3
'''
tool to manipulate ArduPilot firmware files, changing default parameters
'''

import os, sys, struct, json, base64, zlib, hashlib

import argparse

def to_ascii(s):
    '''get ascii string'''
    if sys.version_info.major >= 3:
        return str(s, 'ascii')
    else:
        return str(s)

def to_bytes(s):
    '''get bytes string'''
    if sys.version_info.major >= 3:
        if isinstance(s,bytes):
            return s
        if isinstance(s,int):
            s = chr(s)
        return bytes(s, 'ascii')
    else:
        return bytes(s)
    
class embedded_defaults(object):
    '''class to manipulate embedded defaults in a firmware'''
    def __init__(self, filename):
        self.filename = filename
        self.offset = 0
        self.max_len = 0
        self.extension = os.path.splitext(filename)[1]
        if self.extension.lower() in ['.apj', '.px4']:
            self.load_apj()
        elif self.extension.lower() in ['.abin']:
            self.load_abin()
        else:
            self.load_binary()

    def load_binary(self):
        '''load firmware from binary file'''
        f = open(self.filename,'rb')
        self.firmware = f.read()
        f.close()
        print("Loaded binary file of length %u" % len(self.firmware))

    def load_abin(self):
        '''load firmware from abin file'''
        f = open(self.filename,'r')
        self.headers = []
        while True:
            line = f.readline().rstrip()
            if line == '--':
                break
            self.headers.append(line)
            if len(self.headers) > 50:
                print("Error: too many abin headers")
                sys.exit(1)
        self.firmware = f.read()
        f.close()
        print("Loaded abin file of length %u" % len(self.firmware))

    def load_apj(self):
        '''load firmware from a json apj or px4 file'''
        f = open(self.filename,'r')
        self.fw_json = json.load(f)
        f.close()
        self.firmware = zlib.decompress(base64.b64decode(self.fw_json['image']))
        print("Loaded apj file of length %u" % len(self.firmware))

    def save_binary(self):
        '''save binary file'''
        f = open(self.filename, 'wb')
        f.write(self.firmware)
        f.close()
        print("Saved binary of length %u" % len(self.firmware))

    def save_apj(self):
        '''save apj file'''
        self.fw_json['image'] = to_ascii(base64.b64encode(zlib.compress(self.firmware, 9)))
        f = open(self.filename,'w')
        json.dump(self.fw_json,f,indent=4)
        f.truncate()
        f.close()
        print("Saved apj of length %u" % len(self.firmware))

    def save_abin(self):
        '''save abin file'''
        f = open(self.filename,'w')
        for i in range(len(self.headers)):
            line = self.headers[i]
            if line.startswith('MD5: '):
                h = hashlib.new('md5')
                h.update(self.firmware)
                f.write('MD5: %s\n' % h.hexdigest())
            else:
                f.write(line+'\n')
        f.write('--\n')
        f.write(self.firmware)
        f.close()
        print("Saved abin of length %u" % len(self.firmware))

    def find(self):
        '''find defaults in firmware'''
        # these are the magic headers from AP_Param.cpp
        magic_str = "PARMDEF".encode('ascii')
        param_magic = [ 0x55, 0x37, 0xf4, 0xa0, 0x38, 0x5d, 0x48, 0x5b ]
        def u_ord(c):
            return ord(c) if sys.version_info.major < 3 else c

        while True:
            i = self.firmware[self.offset:].find(magic_str)
            if i == -1:
                print("No param area found")
                return None
            matched = True
            for j in range(len(param_magic)):
                if u_ord(self.firmware[self.offset+i+j+8]) != param_magic[j]:
                    matched = False
                    break
            if not matched:
                self.offset += i+8
                continue
            self.offset += i
            self.max_len, self.length = struct.unpack("<HH", self.firmware[self.offset+16:self.offset+20])
            return True
    
    def contents(self):
        '''return current contents'''
        contents = self.firmware[self.offset+20:self.offset+20+self.length]
        # remove carriage returns
        contents = contents.replace(b'\r',b'')
        return contents

    def set_contents(self, contents):
        '''set new defaults as a string'''
        length = len(contents)
        if length > self.max_len:
            print("Error: Length %u larger than maximum %u" % (length, self.max_len))
            sys.exit(1)
        new_fw = self.firmware[:self.offset+18]
        new_fw += struct.pack("<H", length)
        new_fw += to_bytes(contents)
        new_fw += self.firmware[self.offset+20+length:]
        self.firmware = new_fw
        self.length = len(contents)

    def set_file(self, filename):
        '''set defaults to contents of a file'''
        print("Setting defaults from %s" % filename)
        f = open(filename, 'r')
        contents = f.read()
        f.close()
        # remove carriage returns from the file
        contents = contents.replace('\r','')
        self.set_contents(contents)

    def split_multi(self, s, separators):
        '''split a string, handling multiple separators'''
        for sep in separators:
            s = s.replace(to_bytes(sep), b' ')
        return s.split()

    def set_one(self, set):
        '''set a single parameter'''
        v = set.split('=')
        if len(v) != 2:
            print("Error: set takes form NAME=VALUE")
            sys.exit(1)
        param_name = to_bytes(v[0].upper())
        param_value = to_bytes(v[1])
        
        contents = self.contents()
        lines = contents.strip().split(b'\n')
        changed = False
        for i in range(len(lines)):
            a = self.split_multi(lines[i], b", =\t")
            if len(a) != 2:
                continue
            if a[0].upper() == param_name:
                separator = to_bytes(lines[i][len(param_name)])
                lines[i] = b'%s%s%s' % (param_name, separator, param_value)
                changed = True
        if not changed:
            lines.append(to_bytes('%s=%s' % (to_ascii(param_name), to_ascii(param_value))))
        contents = b'\n'.join(lines)
        contents = contents.lstrip() + b'\n'
        self.set_contents(contents)

    def save(self):
        '''save new firmware'''
        if self.extension.lower() in ['.apj', '.px4']:
            self.save_apj()
        elif self.extension.lower() in ['.abin']:
            self.save_abin()
        else:
            self.save_binary()

    def extract(self):
        '''extract firmware image to *.bin'''
        a = os.path.splitext(self.filename)
        if len(a) == 1:
            a.append('.bin')
        else:
            a = (a[0], '.bin')
            binfile = ''.join(a)
            print("Extracting firmware to %s" % binfile)
            f = open(binfile,'wb')
            f.write(self.firmware)
            f.close()
    

def defaults_contents(firmware, ofs, length):
    '''return current defaults contents'''
    return firmware

if __name__ == '__main__':
    parser = argparse.ArgumentParser(description='manipulate parameter defaults in an ArduPilot firmware')

    parser.add_argument('firmware_file')
    parser.add_argument('--set-file', type=str, default=None, help='replace parameter defaults from a file')
    parser.add_argument('--set', type=str, default=None, help='replace one parameter default, in form NAME=VALUE')
    parser.add_argument('--show', action='store_true', default=False, help='show current parameter defaults')
    parser.add_argument('--extract', action='store_true', default=False, help='extract firmware image to *.bin')

    args = parser.parse_args()

    defaults = embedded_defaults(args.firmware_file)

    have_defaults = defaults.find()

    if not have_defaults and not args.extract:
        print("Error: Param defaults support not found in firmware; see https://ardupilot.org/copter/docs/common-oem-customizations.html for embedding defaults.parm")
        sys.exit(1)

    if have_defaults:
        print("Found param defaults max_length=%u length=%u" % (defaults.max_len, defaults.length))

    if args.set_file:
        # load new defaults from a file
        defaults.set_file(args.set_file)
        defaults.save()

    if args.set:
        # set a single parameter
        defaults.set_one(args.set)
        defaults.save()

    if args.show:
        # show all defaults
        print(to_ascii(defaults.contents()))

    if args.extract:
        defaults.extract()