pbstream good() check

[DavidBrandes]

Hey everybody,

with the intention to alter the trajectory manually by myself (i.e. rotate it) I would like to create my own pbstream writer in python. However I am having issues with writing the output stream. I narrowed the problem down to how the new stream is written and saved in python. In the code example below I am trying to simply read an input pbstream and write it to a new output pbstream, so no (de)compression or (de)serialization is happening for now.

import struct

class ProtoStream:
    def __init__(self, input_pbstream_file, output_pbstream_file, header_size=8):
        self.header_size = header_size
        self.input_pbstream = open(input_pbstream_file, 'rb')
        self.output_pbstream = open(output_pbstream_file, 'wb')

    def copy(self):
        # read header
        self.input_pbstream.seek(self.header_size)
        header = self.read_message()

        # write header
        self.output_pbstream.seek(self.header_size)
        self.write_message(header)

        while True:
            # read other messages
            msg = self.read_message()

            if msg is None:
                break

            else:
                # write other messages
                self.write_message(msg)

        self.input_pbstream.close()

    def read_message(self):
        buf = self.input_pbstream.read(self.header_size)
        if len(buf) < self.header_size:
            return None

        else:
            size = struct.unpack_from("<Q", buf)[0]
            msg = self.input_pbstream.read(size)

            return msg

    def write_message(self, msg):
        self.output_pbstream.write(struct.pack('<Q', len(msg)))
        self.output_pbstream.write(msg)

input_pbstream_file = '/home/david/Desktop/proto/files/data.pbstream'
output_pbstream_file = '/home/david/Desktop/proto/files/new_data.pbstream'

PS = ProtoStream(input_pbstream_file, output_pbstream_file)
PS.copy()

The new pbstream is created with equal size to that of the input, however when I try to use it with Cartographer, I am getting the error message: 'protostream.cc:75 Check failed: in.good() Failed to open proto stream'. So I assume the problem lies somewhere in how the stream is written with python.

Does anyone know what exactly is triggering the good() check to fail and how to avoid it?

[DavidBrandes]

I could figure it out, if I leave out the seek() in both the writing and reading it now works. In particular if I use b'\xdb\x01\xf5[{\x1f\x1d{' as the header, Cartographer now accepts it