support P2PAnnex in connectPeer

This is probably enough to support accessing remotes using p2p-annex:: urls.
Not tested yet of course since there is not yet support for serving the
other side of such a connection, or for setting up such a connection.

P2P.Generic has an implementation of the whole interface to the
git-annex-p2p-<netname> commands.

P2P/Generic.hs

@@ -0,0 +1,57 @@
+{- P2P protocol, generic transports.
+ -
+ - See doc/design/generic_p2p_transport.mdwn
+ -
+ - Copyright 2025 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module P2P.Generic where
+
+import Common
+import P2P.Address
+
+genericP2PCommand :: P2PNetName -> String
+genericP2PCommand (P2PNetName netname) = "git-annex-p2p-" ++ netname
+
+connectGenericP2P :: P2PNetName -> UnderlyingP2PAddress -> CreateProcess
+connectGenericP2P netname (UnderlyingP2PAddress address) =
+	(proc (genericP2PCommand netname) [address])
+		{ std_in = CreatePipe
+		, std_out = CreatePipe
+		}
+
+socketGenericP2P :: P2PNetName -> UnderlyingP2PAddress -> CreateProcess
+socketGenericP2P netname (UnderlyingP2PAddress address) =
+	(proc (genericP2PCommand netname) ["socket", address])
+		{ std_in = CreatePipe
+		}
+
+addressGenericP2P :: P2PNetName -> CreateProcess
+addressGenericP2P netname =
+	(proc (genericP2PCommand netname) ["address"])
+		{ std_in = CreatePipe
+		}
+
+getSocketGenericP2P :: P2PNetName -> UnderlyingP2PAddress -> IO (Maybe (OsPath, ProcessHandle))
+getSocketGenericP2P netname address = do
+	(Just hin, Nothing, Nothing, pid) <- createProcess $
+		socketGenericP2P netname address
+	hGetLineUntilExitOrEOF pid hin >>= \case
+		Just l | not (null l) -> return $ Just (toOsPath l, pid)
+		_ -> return Nothing
+
+getAddressGenericP2P :: P2PNetName -> IO [P2PAddress]
+getAddressGenericP2P netname = do
+	(Just hin, Nothing, Nothing, pid) <- createProcess $
+		addressGenericP2P netname
+	go [] hin pid
+  where
+	go addrs hin pid = hGetLineUntilExitOrEOF pid hin >>= \case
+		Just l
+			| not (null l) -> 
+				let addr = P2PAnnex netname (UnderlyingP2PAddress l)
+				in go (addr:addrs) hin pid
+			| otherwise -> go addrs hin pid
+		Nothing -> return addrs

P2P/IO.hs

@@ -1,6 +1,6 @@
 {- P2P protocol, IO implementation
  -
- - Copyright 2016-2024 Joey Hess <id@joeyh.name>
+ - Copyright 2016-2025 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -20,7 +20,6 @@ module P2P.IO
 	, connectPeer
 	, closeConnection
 	, serveUnixSocket
-	, setupHandle
 	, ProtoFailure(..)
 	, describeProtoFailure
 	, runNetProto
@@ -31,6 +30,7 @@ module P2P.IO
 import Common
 import P2P.Protocol
 import P2P.Address
+import P2P.Generic
 import Git
 import Git.Command
 import Utility.AuthToken
@@ -138,7 +138,7 @@ stdioP2PConnectionDupped g = do
 -- Opens a connection to a peer. Does not authenticate with it.
 connectPeer :: Maybe Git.Repo -> P2PAddress -> IO P2PConnection
 connectPeer g (TorAnnex onionaddress onionport) = do
-	h <- setupHandle =<< connectHiddenService onionaddress onionport
+	h <- setupHandleFromSocket =<< connectHiddenService onionaddress onionport
 	return $ P2PConnection
 		{ connRepo = g
 		, connCheckAuth = const False
@@ -147,6 +147,17 @@ connectPeer g (TorAnnex onionaddress onionport) = do
 		, connProcess = Nothing
 		, connIdent = ConnIdent Nothing
 		}
+connectPeer g (P2PAnnex netname address) = do
+	(Just hin, Just hout, Nothing, pid) <- createProcess $
+		connectGenericP2P netname address
+	return $ P2PConnection
+		{ connRepo = g
+		, connCheckAuth = const False
+		, connIhdl = P2PHandle hout
+		, connOhdl = P2PHandle hin
+		, connProcess = Just pid
+		, connIdent = ConnIdent Nothing
+		}
 
 closeConnection :: P2PConnection -> IO ()
 closeConnection conn = do
@@ -185,10 +196,10 @@ serveUnixSocket unixsocket serveconn = do
 	S.listen soc 2
 	forever $ do
 		(conn, _) <- S.accept soc
-		setupHandle conn >>= serveconn
+		setupHandleFromSocket conn >>= serveconn
 
-setupHandle :: Socket -> IO Handle
-setupHandle s = do
+setupHandleFromSocket :: Socket -> IO Handle
+setupHandleFromSocket s = do
 	h <- socketToHandle s ReadWriteMode
 	hSetBuffering h LineBuffering
 	hSetBinaryMode h False

doc/design/generic_p2p_transport.mdwn

@@ -33,9 +33,9 @@ to convert the P2P network's own equivilant into a unix socket file.
 To configure `git-annex remotedaemon` to listen on a given P2P network,
 the user runs `git-annex p2p --enable <netname>`. That also
 runs `git-annex-p2p-<netname>`, this time with the parameter "address".
-That should output a single line, the P2P network address that can be used
-by peers to connect to the repository. It can first do whatever it needs to
-do to set up the P2P network.
+That should output one or more lines, the P2P network address (or addresses) 
+that can be used by peers to connect to the repository. It can first do
+whatever it needs to do to set up the P2P network.
 
 The program [[git-remote-p2p-annex]] is included in git-annex as a git
 remote helper program. git will use that program to handle `pull` and

git-annex.cabal

@@ -923,6 +923,7 @@ Executable git-annex
     P2P.Address
     P2P.Annex
     P2P.Auth
+    P2P.Generic
     P2P.Http.Types
     P2P.Http.Client
     P2P.Http.Url