ftpfs possible issue with openbin

[al8ba]

Recently, while trying out the ftpfs, I've noticed that to open a binary file-like object for writing by some third-party packages I have to do this:

with open_fs("ftp://anonymous:anonymous@localhost:8021") as fs:
    with fs.openbin("test.bin", "wb") as f:
        ...

Note in the above the mode param used in openbin includes b: Looking at the docs for the mode param it suggests the b is implied via openbin, but b isn't implicitly added to the mode of the file-like that is returned by openbin - this means that, unless b is explicitly provided as above, third-party packages that inspect the mode of the file-like may complain that it is not opened in binary mode.

Should openbin not reflect the implied b by implicitly adding b to the mode?

[lurch]

Yeah, perhaps FTPFS should also be doing this? https://github.com/PyFilesystem/pyfilesystem2/blob/master/fs/osfs.py#L360

[al8ba]

Yes, I was thinking of mentioning use of to_platform_bin in a similar manner.

I guess another way of putting the question is that, given the "b is implied by openbin" in the docs, then for a file f opened via it should "b" in f.mode hold true? Sounds almost like a unit test...

[willmcgugan]

The base class only guarantees that openbin will return a BinaryIO, which doesn't contain a "mode" attribute. Only the io.FileIO class can be sure of having mode.

So it would be a mistake to assume that all file-like objects have a "mode" attribute. But people do write broken code because they make reasonable assumptions and the specifications are too difficult to understand, so perhaps it would be a good idea for ftp files to add a mode attribute.

[al8ba]

so perhaps it would be a good idea for ftp files to add a mode attribute.

The FTPFile object does have a mode attribute - the issue I'm bringing up is that if the FTPFile instance comes from a call to openbin then the mode within it will not contain b, unless b was explicitly supplied in the call to openbin.

I think a solution to this, similar to the previous note about osfs, would be to have the final two lines of openbin look more akin to this:

        ...
        ftp_file = FTPFile(self, _path, mode.to_platform_bin())
    return ftp_file  # type: ignore

[althonos]

Actually, it is reasonable to expect FS.openbin to return an object with a mode attribute (containing a "b" flag), since it all filesystems are doing it but FTPFile and _MemoryFile. I patched them in #435