To turn the semantics into a real file format, we need to define what they look like as actual data. How do you write an SDBD to a stream or a disk? How do we turn our HTTP-like semantics into a real document? That question almost answers itself. I'll keep stealing from HTTP.
## Consider the options
There are three versions of HTTP that each represent headers in a different format. HTTP/1.1 uses a human-readable plain text format. It's basically the format you'll see in browser development tools and blog posts about HTTP headers. HTTP/2 uses a compressible binary format called HPACK. HTTP/3 uses a variant of HPACK called QPACK that's designed to be less trouble for the underlying QUIC protocol.
I'm going to decide that SDBD will be a binary format. No part of it needs to be plain text. I'm going to choose HPACK over QPACK. Mostly that's because I think it should be easier to implement the proof of concept with HPACK due to available tools.
## Represent
It's time to put it together. I already have plans for updating the format, so the very first byte of SDBD will be a version number. We'll start simply with `0x01`. The rest of this section will describe a `version 1` document.
Next comes the metadata. We need to know how long the metadata is, so we'll use two bytes to store an unsigned int to tell us the length of the metadata section in bytes. (But what happens if the metadata is more than 64KB? We'll worry about that later.) The metadata headers will be encoded with HPACK.
After the metadata comes the data, which better be the exact length defined by `content-length`, or bad things will happen.
That's it. If we encode the original example with this format, this is the result:
