[BUGFIX] allow multiple parallel connections by default

Use the original method of tracking connections by CIDs by default.
If zero-sized CID support is turned on, connections are tracked by
the address.  A new connection is not created if another connection
is using the same network address.

src/liblsquic/lsquic_conn_hash.c

@@ -26,7 +26,7 @@
 
 
 static const unsigned char *
-conn2hash_server (const struct lsquic_conn *lconn, unsigned char *buf,
+conn2hash_by_cid (const struct lsquic_conn *lconn, unsigned char *buf,
                                                                 size_t *sz)
 {
     *sz = sizeof(lconn->cn_cid);
@@ -63,7 +63,7 @@ sockaddr2hash (const struct sockaddr *sa, unsigned char *buf, size_t *sz)
 
 
 static const unsigned char *
-conn2hash_client (const struct lsquic_conn *lconn, unsigned char *buf,
+conn2hash_by_addr (const struct lsquic_conn *lconn, unsigned char *buf,
                                                                 size_t *sz)
 {
     sockaddr2hash((struct sockaddr *) &lconn->cn_local_addr, buf, sz);
@@ -72,7 +72,7 @@ conn2hash_client (const struct lsquic_conn *lconn, unsigned char *buf,
 
 
 int
-conn_hash_init (struct conn_hash *conn_hash, int server)
+conn_hash_init (struct conn_hash *conn_hash, enum conn_hash_flags flags)
 {
     unsigned n;
 
@@ -84,10 +84,11 @@ conn_hash_init (struct conn_hash *conn_hash, int server)
         return -1;
     for (n = 0; n < n_buckets(conn_hash->ch_nbits); ++n)
         TAILQ_INIT(&conn_hash->ch_buckets[n]);
-    if (server)
-        conn_hash->ch_conn2hash = conn2hash_server;
+    conn_hash->ch_flags = flags;
+    if (flags & CHF_USE_ADDR)
+        conn_hash->ch_conn2hash = conn2hash_by_addr;
     else
-        conn_hash->ch_conn2hash = conn2hash_client;
+        conn_hash->ch_conn2hash = conn2hash_by_cid;
     LSQ_INFO("initialized");
     return 0;
 }

src/liblsquic/lsquic_conn_hash.h

@@ -20,6 +20,12 @@ struct sockaddr;
 
 TAILQ_HEAD(lsquic_conn_head, lsquic_conn);
 
+enum conn_hash_flags
+{
+    CHF_USE_ADDR    = 1 << 0,
+};
+
+
 struct conn_hash
 {
     struct lsquic_conn_head *ch_buckets;
@@ -29,6 +35,7 @@ struct conn_hash
     }                        ch_iter;
     unsigned                 ch_count;
     unsigned                 ch_nbits;
+    enum conn_hash_flags     ch_flags;
     const unsigned char *  (*ch_conn2hash)(const struct lsquic_conn *,
                                             unsigned char *, size_t *);
 };
@@ -37,7 +44,7 @@ struct conn_hash
 
 /* Returns -1 if malloc fails */
 int
-conn_hash_init (struct conn_hash *, int server);
+conn_hash_init (struct conn_hash *, enum conn_hash_flags);
 
 void
 conn_hash_cleanup (struct conn_hash *);
@@ -76,4 +83,6 @@ conn_hash_first (struct conn_hash *);
 struct lsquic_conn *
 conn_hash_next (struct conn_hash *);
 
+#define conn_hash_using_addr(h) ((h)->ch_flags & CHF_USE_ADDR)
+
 #endif

src/liblsquic/lsquic_engine.c

@@ -323,7 +323,9 @@ lsquic_engine_new (unsigned flags,
         engine->pub.enp_pmi_ctx  = NULL;
     }
     engine->pub.enp_engine = engine;
-    conn_hash_init(&engine->conns_hash, flags & ENG_SERVER);
+    conn_hash_init(&engine->conns_hash,
+        !(flags & ENG_SERVER) && engine->pub.enp_settings.es_support_tcid0 ?
+        CHF_USE_ADDR : 0);
     engine->attq = attq_create();
     eng_hist_init(&engine->history);
     engine->batch_size = INITIAL_OUT_BATCH_SIZE;
@@ -419,7 +421,17 @@ find_conn (lsquic_engine_t *engine, lsquic_packet_in_t *packet_in,
 {
     lsquic_conn_t *conn;
 
-    conn = conn_hash_find_by_addr(&engine->conns_hash, sa_local);
+    if (conn_hash_using_addr(&engine->conns_hash))
+        conn = conn_hash_find_by_addr(&engine->conns_hash, sa_local);
+    else if (packet_in->pi_flags & PI_CONN_ID)
+        conn = conn_hash_find_by_cid(&engine->conns_hash,
+                                                    packet_in->pi_conn_id);
+    else
+    {
+        LSQ_DEBUG("packet header does not have connection ID: discarding");
+        return NULL;
+    }
+
     if (!conn)
         return NULL;
 
@@ -568,6 +580,13 @@ lsquic_engine_connect (lsquic_engine_t *engine, const struct sockaddr *local_sa,
         goto err;
     }
 
+    if (conn_hash_using_addr(&engine->conns_hash)
+                && conn_hash_find_by_addr(&engine->conns_hash, local_sa))
+    {
+        LSQ_ERROR("cannot have more than one connection on the same port");
+        goto err;
+    }
+
     if (0 == max_packet_size)
     {
         switch (peer_sa->sa_family)