Define /unix

protocols.csv

@@ -13,7 +13,7 @@ code,	size,	name,	comment
 132,	16,	sctp,
 301,	0,	udt,
 302,	0,	utp,
-400,	V,	unix,
+400,	V,	unix,	Percent-encoded path to a Unix domain socket
 421,	V,	p2p,	preferred over /ipfs
 421,	V,	ipfs,	backwards compatibility; equivalent to /p2p
 444,	96,	onion,
@@ -39,4 +39,4 @@ code,	size,	name,	comment
 280,	0,	webrtc-direct, ICE-lite webrtc transport with SDP munging during connection establishment and without use of a STUN server
 281, 	0,	webrtc, webrtc transport where connection establishment is according to w3c spec
 290,	0,	p2p-circuit,
-777,	V, memory, in memory transport for self-dialing and testing; arbitrary 
+777,	V, memory, in memory transport for self-dialing and testing; arbitrary

protocols/unix.md

@@ -0,0 +1,36 @@
+# `unix`
+
+This protocol encodes a Unix domain socket path to a resource. In the string
+representation, the path is encoded in a way consistent with a single URI Path
+segment per [RFC 3986 Section 3.3](https://datatracker.ietf.org/doc/html/rfc3986#autoid-23).
+
+Specifically following the grammar of a single `segment-nz`. In the binary
+representation, no encoding is needed as the value is length prefixed.
+
+When comparing multiaddrs, implementations should compare their binary
+representation to avoid ambiguities over which characters were escaped.
+
+## Examples
+
+The following is a table of examples converting some common Unix paths to their
+Multiaddr string form.
+
+| Unix Path                   | Multiaddr string form                   |
+| --------------------------- | --------------------------------------- |
+| /                           | `/unix/%2F`                             |
+| /file.socket                | `/unix/file.socket`                     |
+| /dir/file.socket            | `/unix/dir%2Ffile.socket`               |
+| /dir/file.socket/p2p/12D... | `/unix/dir%2Ffile.socket/p2p/12D...`    |
+| /tmp/foo/../bar             | `/unix/tmp%2Ffoo%2F..%2Fbar`            |
+| /%2F                        | `/unix/%252F`                           |
+| a%20space                   | `/unix/a%2520space`                     |
+| a%2Fslash                   | `/unix/a%252Fslash`                     |
+
+## Usage
+
+`/unix` would typically be found at the start of a multiaddr, however it may
+appear anywhere, for example in the case where we route through some sort of
+proxy server or SSH tunnel.
+
+The leading `/` character of the path can be omitted, unless it is the only
+character in the path, in which case it must be escaped as normal.