add project documentation

README.md

@@ -1,12 +1,72 @@
 [![build](https://github.com/falk-werner/webfuse/actions/workflows/build.yml/badge.svg)](https://github.com/falk-werner/webfuse/actions/workflows/build.yml)
 
-# webfuse2
+# webfuse
 
-Reimplementation of webfuse.
+webfuse combines libwebsockets and libfuse. It allows to attach a remote filesystem via websockets.
 
-## Build
+## Motivation
 
-````
-cmake -B build
-cmake --build build
-````
+Many embedded devices, such as smart home or [IoT](https://en.wikipedia.org/wiki/Internet_of_things) devices are very limited regarding to their (non-volatile) memory resources. Such devices are typically comprised of an embedded linux and a small web server, providing an interface for maintenance purposes.
+
+Some use cases, such as firmware update, require to transfer (larger) files to the device. The firmware file is often stored multiple times on the device:
+
+1.  cached by the web server, e.g. [lighttpd](https://redmine.lighttpd.net/boards/2/topics/3451)
+2.  copied to locally, e.g. /tmp
+3.  uncompressed, also to /tmp
+
+Techniques like [SquashFS](https://en.wikipedia.org/wiki/SquashFS) help to avoid the third step, since the upgrade file can be mounted directly. [RAUC](https://rauc.io/) shows the use of SquashFS within an update facility.  
+However at least one (unecessary) copy of the upload file is needed on the device.
+
+To avoid Steps 1 and 2, it would be great to keep the update file entirely in web server, just like [NFS](https://en.wikipedia.org/wiki/Network_File_System) or [WebDAV](https://wiki.archlinux.org/index.php/WebDAV). Unfortunately, NFS is not based on any protocol, natively usable by a web application. WebDAV is based on HTTP, but it needs a server providing the update file.
+
+webfuse solves this problem by using the [WebSocket](https://en.wikipedia.org/wiki/WebSocket) protocol. The emdedded device runs a service, known as webfuse adapter, awaiting incoming connections, e.g. from a web browser. The browser acts as a file system provider, providing the update file to the device.
+
+## Concept
+
+![concept](doc/concept.png)
+
+With webfuse it is possible to implement remote filesystems based on websockets.
+Therefore, webfuse defined two roles participating in a webfuse connection:
+
+- webfuse service
+- webfuse provider
+
+### Webfuse Service
+
+A `webfuse service` is both,
+- a [websocket](https://en.wikipedia.org/wiki/WebSocket) service providing the `webfuse` protocol
+- a [fuse](https://github.com/libfuse/libfuse) filesystem attached to a local mountpoint
+
+The `webfuse service` awaits incoming connections from a `webfuse provider`. Once connected, it communicates all the filesystem requests originated by the `libfuse` to the connected `webfuse provider` using the `websocket`-based `webfuse protocol`.
+
+By doing so, `webfuse` allows to inject a filesystem to a remote device.
+
+### Webfuse Provider
+
+A `webfuse provider` provides a filesystem to a remote device using the `websocket`-based `webfuse protocol`. Therefore, a `webfuse provider` implements a `websocket` client.
+
+
+## Similar Projects
+
+### Davfs2
+
+[davfs2](http://savannah.nongnu.org/projects/davfs2) is a Linux file system driver that allows to mount a [WebDAV](https://wiki.archlinux.org/index.php/WebDAV) resource. WebDAV is an extension to HTTP/1.1 that allows remote collaborative authoring of Web resources.
+
+Unlike webfuse, davfs2 mounts a remote filesystem locally, that is provided by a WebDAV server. In contrast, webfuse starts a server awaiting client connections to attach the remote file system.
+
+## Further Documentation
+
+-   [Build instructions](doc/build.md)
+-   [Webfuse Protocol](doc/protocol.md)
+
+## webfuse legacy
+
+`webfuse2` is a complete re-implementation of the original idea behind `webfuse`. In contrast to the original `webfuse` implementation, `webfuse2` provides also write access to the filesystem and allows to use all standard options of a fuse filesystem.
+
+But `webfuse2` marks also some breaking changes:
+
+- `webfuse2` uses a new, binary protocol which is not compatible to the JSON-based protocol of legacy `webfuse`
+- `webfuse` does not provide an API nor a library to program against  
+  _(if you are interested in an API or a library for webfuse2 feel free to create an issue)_
+
+When you are interested in the original `webfuse` implementation take a look at it [branch](https://github.com/falk-werner/webfuse/tree/master).