msg native reader fails on full disk image

[sjoro]

Code Sample, a minimal, complete, and verifiable piece of code

nat = Scene(f,reader='native_msg')

Problem description

MSG Native reader gets a ValueError when using a full disk image file

Expected Output

no error

Actual Result, Traceback if applicable

~/fork/satpy/satpy/readers/native_msg.py in _get_memmap(self)
     99             hdr_size = self.header.dtype.itemsize
    100             import ipdb; ipdb.set_trace()
--> 101             return np.memmap(fp_, dtype=dt, shape=(self.data_len,),
    102                              offset=hdr_size, mode="r")
    103 

~/dev/lib/python3.4/site-packages/numpy-1.14.2-py3.4-linux-x86_64.egg/numpy/core/memmap.py in __new__(subtype, filename, dtype, mode, offset, shape, order)
    262         bytes -= start
    263         array_offset = offset - start
--> 264         mm = mmap.mmap(fid.fileno(), bytes, access=acc, offset=start)
    265 
    266         self = ndarray.__new__(subtype, shape, dtype=descr, buffer=mm,

ValueError: mmap length is greater than file size

Versions of Python, package at hand and relevant dependencies

3.4.6
Thank you for reporting an issue !

[sjoro]

Fixed and merged to develop