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server: correctly adjudicate collision bind() of specific port #82

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Aug 21, 2024
Merged

server: correctly adjudicate collision bind() of specific port #82

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48 changes: 29 additions & 19 deletions src/serverconn.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -408,18 +408,40 @@ ServIface::ServIface(const SockAddr &addr, server::Server::Pvt *server, bool fal
server->acceptor_loop.assertInLoop();
auto orig_port = bind_addr.port();

sock = evsocket(bind_addr.family(), SOCK_STREAM, 0);

if(evutil_make_listen_socket_reuseable(sock.sock))
log_warn_printf(connsetup, "Unable to make socket reusable%s", "\n");

// try to bind to requested port, then fallback to a random port
while(true) {

sock = evsocket(bind_addr.family(), SOCK_STREAM, 0);

if(evutil_make_listen_socket_reuseable(sock.sock))
log_warn_printf(connsetup, "Unable to make socket reusable%s", "\n");

try {
sock.bind(bind_addr);
// semantics of SO_REUSEADDR on *nix allow multiple bind() to success.
// however, only one listen() will succeed

// added in libevent 2.1.1
#ifndef LEV_OPT_DISABLED
# define LEV_OPT_DISABLED 0
#endif

const int backlog = 4;
auto list(evconnlistener_new(server->acceptor_loop.base, onConnS, this, LEV_OPT_DISABLED|LEV_OPT_CLOSE_ON_EXEC, backlog, sock.sock));
if(!list) {
int err = evutil_socket_geterror(sock);
throw std::system_error(err, std::system_category());
}
listener = evlisten(__FILE__, __LINE__, list);

if(!LEV_OPT_DISABLED)
evconnlistener_disable(listener.get());

} catch(std::system_error& e) {
if(fallback && e.code().value()==SOCK_EADDRINUSE) {
log_debug_printf(connsetup, "Address %s in use\n", bind_addr.tostring().c_str());
if(fallback && (e.code().value()==SOCK_EADDRINUSE || e.code().value()==SOCK_EACCES)) {
log_debug_printf(connsetup, "Address %s in use or not permitted: %s\n",
bind_addr.tostring().c_str(),
e.what());
bind_addr.setPort(0);
fallback = false;
continue;
Expand All @@ -438,18 +460,6 @@ ServIface::ServIface(const SockAddr &addr, server::Server::Pvt *server, bool fal
if(orig_port && bind_addr.port() != orig_port) {
log_warn_printf(connsetup, "Server unable to bind port %u, falling back to %s\n", orig_port, name.c_str());
}

// added in libevent 2.1.1
#ifndef LEV_OPT_DISABLED
# define LEV_OPT_DISABLED 0
#endif

const int backlog = 4;
listener = evlisten(__FILE__, __LINE__,
evconnlistener_new(server->acceptor_loop.base, onConnS, this, LEV_OPT_DISABLED|LEV_OPT_CLOSE_ON_EXEC, backlog, sock.sock));

if(!LEV_OPT_DISABLED)
evconnlistener_disable(listener.get());
}

void ServIface::onConnS(struct evconnlistener *listener, evutil_socket_t sock, struct sockaddr *peer, int socklen, void *raw)
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