Add a Layout.read_bytes() method that reads a layout from a byte array

[rocallahan]

This is much more convenient and a bit more efficient than writing the bytes to a temporary file and reading that back in. It's useful when we have received a layout over the network or embedded in some file.

This makes a copy of the bytes but there doesn't seem to be any way to avoid that currently.

[rocallahan]

An even better API (for Python) would be to accept a Python io.BufferedIOBase which we would wrap in a tl::InputStreamBase but that's far more work.

[klayoutmatthias]

Thanks for this PR. This makes sense.

Version will be 0.29.9 - if you like, I can change that.

Basically, the reader can take data from "data:" stream "paths", but true bytes are easier to work with.

For symmetry, a writer to bytes would be needed too, right?

Matthias

[klayoutmatthias]

Another comment: Currently, passing the byte array as std::vector<char> involves a memory copy. So this facility is not good for passing huge files.

[rocallahan]

For symmetry, a writer to bytes would be needed too, right?

Yes, although we don't need that at the moment.

Currently, passing the byte array as std::vector involves a memory copy. So this facility is not good for passing huge files.

Yes, I guess there is no way around that without extending your bindings infrastructure.

[rocallahan]

I should mention that after submitting this PR I worked out another approach: use mkfifo to create a FIFO, and have KLayout read from that FIFO while another Python thread writes bytes into it. Compared to this PR, it would use less memory for large files but requires more system calls and is a lot more complicated for users. Compared to a temporary file, it doesn't require space on the filesystem and is probably a bit faster, but is also more complicated for users. So I still think this PR is useful.

[klayoutmatthias]

Would you like to add a byte writer too? I feel it would look better that way.