add fragment store draft doc

src/fragment_store/README.md

@@ -0,0 +1,72 @@
+# Fragment Store
+
+Fragments are are pieces of information split into Metadata and Data.
+They can be stored seperated or together.
+They can be used as a Transport protocol/logic too.
+
+# Store types
+
+### Object Store
+
+Fragment files are stored with the first 2 hex chars as sub folders:
+eg:
+objects/ (object store root)
+  - 5f/ (first 2hex subfolder)
+    - 4fffffff (the fragment file without the first 2 hexchars)
+
+### Split Object Store
+
+Same as Object Store, but medadata and data stored in seperate files.
+Metadata files have the `.meta` suffix. They also have a filetype specific suffix, like `.json`, `.msgpack` etc.
+
+### Memory Store
+
+Just keeps the Fragments in memory.
+
+
+# File formats
+
+Files can be compressed and encrypted. Since compression needs the data structure to funcion, it is applied before it is encrypted.
+
+### Text Json
+
+Text json only makes sense for metadata if it's neither compressed nor encrypted. (otherwise its binary on disk anyway, so why waste bytes).
+Since the content of data is not looked at, nothing stops you from using text json and ecrypt it, but atleast basic compression is advised.
+
+A Metadata json object has the following keys:
+- `enc` Encryption type of the data, if any
+- `comp` Compression type of the data, if any
+
+## Binary file headers
+
+### Split Metadata
+
+file magic bytes `SOLMET` (6 bytes)
+
+1 byte encryption type (0x00 is none)
+
+1 byte compression type (0x00 is none)
+
+...metadata here...
+
+note that the ecnryption and compression are for the metadata only.
+The metadata itself contains encryption and compression about the data.
+
+### Split Data
+
+(none) all the data is in the metadata file.
+This is mostly to allow direct storage for files in the Fragment store without excessive duplication.
+Keep in mind to not use the actual file name as the data/meta file name.
+
+### Single fragment
+
+file magic bytes `SOLFIL` (6 bytes)
+
+1 byte encryption type (0x00 is none)
+
+1 byte compression type (0x00 is none)
+
+...metadata here...
+
+...data here...
+