net.server_epoll: Add support for systemd socket activation

Allows creating listening sockets and accepting client connections
before Prosody starts.
This is unlike normal Prosody dynamic resource management, where ports
may added and removed at any time, and the ports defined by the config.

Weird things happen if these are closed (e.g. due to reload) so here we
prevent closing and ensure sockets are reused when opened again.

2 files changed, 41 insertions, 0 deletions

diff --git a/CHANGES b/CHANGES
index 70aa13c3..4938f013 100644
--- a/CHANGES
+++ b/CHANGES
@@ -68,6 +68,7 @@ TRUNK
 - Arguments to `prosodyctl shell` that start with ':' are now turned into method calls
 - Support for Type=notify and notify-reload systemd service type added
 - Support for the roster *group* access_model in mod_pep
+- Support for systemd socket activation in server_epoll
 
 ## Removed
 
diff --git a/net/server_epoll.lua b/net/server_epoll.lua
index c946a751..6c110241 100644
--- a/net/server_epoll.lua
+++ b/net/server_epoll.lua
@@ -35,6 +35,38 @@ local poller = require "prosody.util.poll"
 local EEXIST = poller.EEXIST;
 local ENOENT = poller.ENOENT;
 
+-- systemd socket activation
+local SD_LISTEN_FDS_START = 3;
+local SD_LISTEN_FDS = tonumber(os.getenv("LISTEN_FDS")) or 0;
+
+local inherited_sockets = setmetatable({}, {
+	__index = function(t, k)
+		local serv_mt = debug.getregistry()["tcp{server}"];
+		for i = 1, SD_LISTEN_FDS do
+			local serv = socket.tcp();
+			if serv:getfd() ~= _SOCKETINVALID then
+				-- If LuaSocket allocated a FD for then we can't really close it and it would leak.
+				log("error", "LuaSocket not compatible with socket activation. Upgrade LuaSocket or disable socket activation.");
+				setmetatable(t, nil);
+				break
+			end
+			serv:setfd(SD_LISTEN_FDS_START + i - 1);
+			debug.setmetatable(serv, serv_mt);
+			serv:settimeout(0);
+			local ip, port = serv:getsockname();
+			t[ip .. ":" .. port] = serv;
+			if ip == "0.0.0.0" then
+				-- LuaSocket treats '*' as an alias for '0.0.0.0'
+				t["*:" .. port] = serv;
+			end
+		end
+
+		-- Disable lazy-loading mechanism once performed
+		setmetatable(t, nil);
+		return t[k];
+	end;
+});
+
 local poll = assert(poller.new());
 
 local _ENV = nil;
@@ -944,6 +976,14 @@ local function wrapserver(conn, addr, port, listeners, config)
 end
 
 local function listen(addr, port, listeners, config)
+	local inherited = inherited_sockets[addr .. ":" .. port];
+	if inherited then
+		local conn = wrapserver(inherited, addr, port, listeners, config);
+		-- sockets created by systemd must not be :close() since we may not have
+		-- privileges to create them
+		conn.destroy = interface.del;
+		return conn;
+	end
 	local conn, err = socket.bind(addr, port, cfg.tcp_backlog);
 	if not conn then return conn, err; end
 	conn:settimeout(0);