Add documentation

protocols/autonat/src/v2.rs

@@ -1,3 +1,23 @@
+//! The second version of the autonat protocol.
+//!
+//! The implementation follows the [libp2p spec](https://github.com/libp2p/specs/blob/03718ef0f2dea4a756a85ba716ee33f97e4a6d6c/autonat/autonat-v2.md).
+//!
+//! The new version fixes the issues of the first version:
+//! - The server now always dials back over a newly allocated port. This greatly reduces the risk of
+//!     false positives that often occured in the first version, when the clinet-server connection
+//!     occured over a hole-punched port.
+//! - The server protects against DoS attacks by requiring the client to send more data to the
+//!     server then the dial back puts on the client, thus making the protocol unatractive for an
+//!     attacker.
+//!
+//! The protocol is seperated into two parts:
+//! - The client part, which is implemented in the `client` module. (The client is the party that
+//!     wants to check if it is reachable from the outside.)
+//! - The server part, which is implemented in the `server` module. (The server is the party
+//!     performing reachability checks on behalf of the client.)
+//!
+//! The two can be used together.
+
 use libp2p_swarm::StreamProtocol;
 
 pub mod client;