improve unix sockets support

[keenser]

Hi, please add support for socket only listeners
Currently 'socket' configuration option takes effect only with enabled 'port' or 'tls_port' and if there is no socket file already exists in filesystem
POC patch:

+++ b/src/server.c
@@ -407,6 +407,10 @@ static int dm_bind_and_listen(int sock, struct sockaddr *saddr, socklen_t len, i
                err = errno;
                TRACE(TRACE_EMERG, "setsockopt::error [%s]", strerror(err));
        }
+       if (setsockopt(sock, SOL_SOCKET, SO_REUSEPORT, &so_reuseaddress, sizeof(so_reuseaddress)) == -1) {
+               err = errno;
+               TRACE(TRACE_EMERG, "setsockopt::error [%s]", strerror(err));
+       }
        /* bind the address */
        if ((bind(sock, saddr, len)) == -1) {
                err = errno;
@@ -442,6 +446,7 @@ static int create_unix_socket(ServerConfig_T * conf)
 
        TRACE(TRACE_DEBUG, "create socket [%s] backlog [%d]", conf->socket, conf->backlog);
 
+       unlink(conf->socket);
        // any error in dm_bind_and_listen is fatal
        dm_bind_and_listen(sock, (struct sockaddr *)&un, sizeof(un), conf->backlog, FALSE);
        
@@ -796,7 +801,7 @@ int server_run(ServerConfig_T *conf)
        if (server_setup(conf))
                return -1;
 
-       if (strlen(conf->port) || strlen(conf->ssl_port)) {
+       if (strlen(conf->port) || strlen(conf->ssl_port) || strlen(conf->socket)) {
 
                if (MATCH(conf->service_name, "HTTP")) {
                        int port = atoi(conf->port);

[alan-hicks]

Hi Keenser,

I'm confused as to your use case and what you are trying to accomplish. Clients using DBMail services expect ip:port based connections.

Although your patch doesn't apply using the current branch, setsockopt (@@ -407,6 +407,10) appears to duplicate the same four lines, and unlink (@@ -442,6 +446,7) is already in server_close_sockets so I'm unsure why you would add it to create_unix_socket.

[keenser]

Hi Alan-hicks,
I'm trying to use socket-only setup for dbmail-lmtpd service togehter with postfix (mailbox_transport = lmtp:unix:/dbmail/lmtp.sock) running on the same host. Listening inet port via dbmail-lmtpd is not required in this sittuation))

As I can see current implementation of dm_bind_and_listen uses setsockopt only for SO_REUSEADDR
and (@@ -407,6 +407,10) adds SO_REUSEPORT property

You are right that server_close_sockets already has unlink, but problem still appers if effective_user and effective_group used in configuration
socket file created with uid 0, while server_close_sockets executes with unprivilated user configured in effective_user and unlink failes to remove socket file in my setup
We can change uid/gid just after file creation in tail of create_unix_socket but this will not cover some scenarios when server_close_sockets can't be executed (killall -9 dbmail-lmtpd, server power failure , etc)

[alan-hicks]

Thanks for the clear use case and issues you are facing. This is a useful enhancement.