Move initialization of the Port struct to the child process

In postmaster, use a more lightweight ClientSocket struct that
encapsulates just the socket itself and the remote endpoint's address
that you get from accept() call. ClientSocket is passed to the child
process, which initializes the bigger Port struct. This makes it more
clear what information postmaster initializes, and what is left to the
child process.

Rename the StreamServerPort and StreamConnection functions to make it
more clear what they do. Remove StreamClose, replacing it with plain
closesocket() calls.

Reviewed-by: Tristan Partin, Andres Freund
Discussion: https://www.postgresql.org/message-id/7a59b073-5b5b-151e-7ed3-8b01ff7ce9ef@iki.fi

Author: hlinnaka

src/backend/libpq/pqcomm.c

@@ -29,11 +29,10 @@
  * INTERFACE ROUTINES
  *
  * setup/teardown:
- *		StreamServerPort	- Open postmaster's server port
- *		StreamConnection	- Create new connection with client
- *		StreamClose			- Close a client/backend connection
+ *		ListenServerPort	- Open postmaster's server port
+ *		AcceptConnection	- Accept new connection with client
  *		TouchSocketFiles	- Protect socket files against /tmp cleaners
- *		pq_init			- initialize libpq at backend startup
+ *		pq_init				- initialize libpq at backend startup
  *		socket_comm_reset	- reset libpq during error recovery
  *		socket_close		- shutdown libpq at backend exit
  *
@@ -168,13 +167,18 @@ WaitEventSet *FeBeWaitSet;
  *		pq_init - initialize libpq at backend startup
  * --------------------------------
  */
-void
-pq_init(void)
+Port *
+pq_init(ClientSocket *client_sock)
 {
-	Port	   *port = MyProcPort;
+	Port	   *port;
 	int			socket_pos PG_USED_FOR_ASSERTS_ONLY;
 	int			latch_pos PG_USED_FOR_ASSERTS_ONLY;
 
+	/* allocate the Port struct and copy the ClientSocket contents to it */
+	port = palloc0(sizeof(Port));
+	port->sock = client_sock->sock;
+	port->raddr = client_sock->raddr;
+
 	/* fill in the server (local) address */
 	port->laddr.salen = sizeof(port->laddr.addr);
 	if (getsockname(port->sock,
@@ -310,6 +314,8 @@ pq_init(void)
 	 */
 	Assert(socket_pos == FeBeWaitSetSocketPos);
 	Assert(latch_pos == FeBeWaitSetLatchPos);
+
+	return port;
 }
 
 /* --------------------------------
@@ -384,16 +390,13 @@ socket_close(int code, Datum arg)
 
 
 
-/*
- * Streams -- wrapper around Unix socket system calls
- *
- *
- *		Stream functions are used for vanilla TCP connection protocol.
+/* --------------------------------
+ * Postmaster functions to handle sockets.
+ * --------------------------------
  */
 
-
 /*
- * StreamServerPort -- open a "listening" port to accept connections.
+ * ListenServerPort -- open a "listening" port to accept connections.
  *
  * family should be AF_UNIX or AF_UNSPEC; portNumber is the port number.
  * For AF_UNIX ports, hostName should be NULL and unixSocketDir must be
@@ -408,7 +411,7 @@ socket_close(int code, Datum arg)
  * RETURNS: STATUS_OK or STATUS_ERROR
  */
 int
-StreamServerPort(int family, const char *hostName, unsigned short portNumber,
+ListenServerPort(int family, const char *hostName, unsigned short portNumber,
 				 const char *unixSocketDir,
 				 pgsocket ListenSockets[], int *NumListenSockets, int MaxListen)
 {
@@ -774,22 +777,23 @@ Setup_AF_UNIX(const char *sock_path)
 
 
 /*
- * StreamConnection -- create a new connection with client using
- *		server port.  Set port->sock to the FD of the new connection.
+ * AcceptConnection -- accept a new connection with client using
+ *		server port.  Fills *client_sock with the FD and endpoint info
+ *		of the new connection.
  *
  * ASSUME: that this doesn't need to be non-blocking because
  *		the Postmaster waits for the socket to be ready to accept().
  *
  * RETURNS: STATUS_OK or STATUS_ERROR
  */
 int
-StreamConnection(pgsocket server_fd, Port *port)
+AcceptConnection(pgsocket server_fd, ClientSocket *client_sock)
 {
 	/* accept connection and fill in the client (remote) address */
-	port->raddr.salen = sizeof(port->raddr.addr);
-	if ((port->sock = accept(server_fd,
-							 (struct sockaddr *) &port->raddr.addr,
-							 &port->raddr.salen)) == PGINVALID_SOCKET)
+	client_sock->raddr.salen = sizeof(client_sock->raddr.addr);
+	if ((client_sock->sock = accept(server_fd,
+									(struct sockaddr *) &client_sock->raddr.addr,
+									&client_sock->raddr.salen)) == PGINVALID_SOCKET)
 	{
 		ereport(LOG,
 				(errcode_for_socket_access(),
@@ -809,23 +813,6 @@ StreamConnection(pgsocket server_fd, Port *port)
 	return STATUS_OK;
 }
 
-/*
- * StreamClose -- close a client/backend connection
- *
- * NOTE: this is NOT used to terminate a session; it is just used to release
- * the file descriptor in a process that should no longer have the socket
- * open.  (For example, the postmaster calls this after passing ownership
- * of the connection to a child process.)  It is expected that someone else
- * still has the socket open.  So, we only want to close the descriptor,
- * we do NOT want to send anything to the far end.
- */
-void
-StreamClose(pgsocket sock)
-{
-	if (closesocket(sock) != 0)
-		elog(LOG, "could not close client or listen socket: %m");
-}
-
 /*
  * TouchSocketFiles -- mark socket files as recently accessed
  *