feat: add unix socket support to deltachat-rpc-server

deltachat-rpc-server/README.md

@@ -1,7 +1,7 @@
 # Delta Chat RPC server
 
 This program provides a [JSON-RPC 2.0](https://www.jsonrpc.org/specification) interface to DeltaChat
-over standard I/O.
+over standard I/O or UNIX sockets.
 
 ## Install
 
@@ -35,3 +35,25 @@ languages other than Rust, for example:
 
 Run `deltachat-rpc-server --version` to check the version of the server.
 Run `deltachat-rpc-server --openrpc` to get [OpenRPC](https://open-rpc.org/) specification of the provided JSON-RPC API.
+
+### Usage over unix sockets
+
+> At this time this does not work on windows because rust does not support unix sockets on windows, yet (<https://github.com/rust-lang/rust/issues/150487>).
+
+Standard I/O is the default option, but you can also tell `deltachat-rpc-server` to use a unix socket instead.
+
+```
+deltachat-rpc-server --unix ./chatmail-core.sock
+```
+
+While this technically allows multiple processes to communicate with the same rpc server instance,
+please note that there is still only event queue, so only one of these processed should read the events at a time.
+
+You can test it with socat:
+```sh
+socat - UNIX-CONNECT:./chatmail-core.sock
+```
+Then paste the following jsonrpc command and press enter:
+```json
+{"method": "get_system_info","id": 1,"params": []}
+```