fix: ESPIPE "illegal seek" error while seeding (#3137)

* fix: ESPIPE "illegal seek" error while seeding

The root cause is createSocket returning `{}` instead of `TR_BAD_SOCKET`
when we have too many peers in use. This defaulted to fd 0, which wound
up closing stdin.

Commit also includes some const-correctness changes made while tracking
the problem down.

libtransmission/net.cc

@@ -313,7 +313,7 @@ static tr_socket_t createSocket(tr_session* session, int domain, int type)
     if ((evutil_make_socket_nonblocking(sockfd) == -1) || !session->incPeerCount())
     {
         tr_netClose(session, sockfd);
-        return {};
+        return TR_BAD_SOCKET;
     }
 
     if (static bool buf_logged = false; !buf_logged)
@@ -474,7 +474,7 @@ static tr_socket_t tr_netBindTCPImpl(tr_address const* addr, tr_port port, bool
     static int const domains[NUM_TR_AF_INET_TYPES] = { AF_INET, AF_INET6 };
     struct sockaddr_storage sock;
 
-    tr_socket_t const fd = socket(domains[addr->type], SOCK_STREAM, 0);
+    auto const fd = socket(domains[addr->type], SOCK_STREAM, 0);
     if (fd == TR_BAD_SOCKET)
     {
         *errOut = sockerrno;
@@ -573,7 +573,7 @@ bool tr_net_hasIPv6(tr_port port)
     if (!alreadyDone)
     {
         int err = 0;
-        tr_socket_t fd = tr_netBindTCPImpl(&tr_in6addr_any, port, true, &err);
+        auto const fd = tr_netBindTCPImpl(&tr_in6addr_any, port, true, &err);
 
         if (fd != TR_BAD_SOCKET || err != EAFNOSUPPORT) /* we support ipv6 */
         {
@@ -600,7 +600,7 @@ tr_socket_t tr_netAccept(tr_session* session, tr_socket_t listening_sockfd, tr_a
     // accept the incoming connection
     struct sockaddr_storage sock;
     socklen_t len = sizeof(struct sockaddr_storage);
-    auto sockfd = accept(listening_sockfd, (struct sockaddr*)&sock, &len);
+    auto const sockfd = accept(listening_sockfd, (struct sockaddr*)&sock, &len);
     if (sockfd == TR_BAD_SOCKET)
     {
         return TR_BAD_SOCKET;
@@ -655,7 +655,7 @@ static int get_source_address(struct sockaddr const* dst, socklen_t dst_len, str
         return 0;
     }
 
-    int save = errno;
+    auto const save = errno;
     evutil_closesocket(s);
     errno = save;
     return -1;

libtransmission/peer-socket.h

@@ -26,7 +26,7 @@ union tr_peer_socket_handle
 
 struct tr_peer_socket
 {
-    enum tr_peer_socket_type type;
+    enum tr_peer_socket_type type = TR_PEER_SOCKET_TYPE_NONE;
     union tr_peer_socket_handle handle;
 };
 

libtransmission/session.h

@@ -59,9 +59,9 @@ struct tr_fdInfo;
 
 struct tr_bindinfo
 {
-    int socket;
-    tr_address addr;
-    struct event* ev;
+    tr_socket_t socket = TR_BAD_SOCKET;
+    tr_address addr = {};
+    struct event* ev = nullptr;
 };
 
 struct tr_turtle_info
@@ -343,8 +343,8 @@ public:
 
     /* The UDP sockets used for the DHT and uTP. */
     tr_port udp_port;
-    tr_socket_t udp_socket;
-    tr_socket_t udp6_socket;
+    tr_socket_t udp_socket = TR_BAD_SOCKET;
+    tr_socket_t udp6_socket = TR_BAD_SOCKET;
     unsigned char* udp6_bound;
     struct event* udp_event;
     struct event* udp6_event;

libtransmission/tr-lpd.cc

@@ -14,7 +14,6 @@
 using in_port_t = uint16_t; /* all missing */
 #else
 #include <ctime>
-#include <unistd.h> /* close() */
 #include <sys/types.h>
 #include <sys/socket.h> /* socket(), bind() */
 #include <netinet/in.h> /* sockaddr_in */

libtransmission/tr-udp.cc

@@ -118,7 +118,6 @@ static void rebind_ipv6(tr_session* ss, bool force)
 {
     struct sockaddr_in6 sin6;
     unsigned char const* ipv6 = tr_globalIPv6(ss);
-    tr_socket_t s = TR_BAD_SOCKET;
     int rc = -1;
     int one = 1;
 
@@ -140,7 +139,7 @@ static void rebind_ipv6(tr_session* ss, bool force)
         return;
     }
 
-    s = socket(PF_INET6, SOCK_DGRAM, 0);
+    auto const s = socket(PF_INET6, SOCK_DGRAM, 0);
 
     if (s == TR_BAD_SOCKET)
     {