Hello all, I am working on a pure Julia implementation of the arrow standard. Currently I am working on ingesting the metadata, and it seems to me that the output I'm creating with `pyarrow` is not matching the format, so I'm trying to figure out where I've misunderstood it.
I've written some arrow data to disk with the code you can find in [this gist](https://gist.github.com/ExpandingMan/4ef3cadab6f3e6d65e672a32b821654f). Reading the format, I expect each message to start with an `Int32` giving the size of the metadata flatbuffers, followed by the metadata flatbuffers themselves. The `Int32`'s indeed seem to be there, however the `Message` flatbuffers do not start where I expect. On the output from above, I find the first flatbuffers containing the `Message` with the `Schema` at byte 20. I am successfully able to construct all flatbuffer objects in Julia from byte 20, but I was expecting to find this flatbuffer at byte 4 immediately following the `Int32`. What is contained in bytes 4 to 19? Similarly, I can find the next `Int32` at byte 144 as expected, however I can't find the flatbuffers after that until byte 168. Again, I can successfully construct the metadata flatbuffers (in this case a `Message` containing a `RecordBatch`) in Julia, but I was expecting to do this from byte 148, not byte 168. What is contained in bytes 144 to 168? Note that this is now a 24 byte boundary, where as for the first `Message` it was only 16. What am I missing here? I have a suspicion that there is a small flatbuffer of some sort being contained in the mysterious extra bytes, but the format description makes no mention of that. Thanks!
