routerlist: Split the node checks into their own function

Split the node choosing checks into their own function, so we can call
it independently of iterating through the nodelist.

Part of 34200.

2 files changed, 71 insertions, 57 deletions

diff --git a/src/feature/nodelist/routerlist.c b/src/feature/nodelist/routerlist.c
index 72ea48898b..f606e3c18f 100644
--- a/src/feature/nodelist/routerlist.c
+++ b/src/feature/nodelist/routerlist.c
@@ -511,35 +511,34 @@ routers_have_same_or_addrs(const routerinfo_t *r1, const routerinfo_t *r2)
     r1->ipv6_orport == r2->ipv6_orport;
 }
 
-/** Add every suitable node from our nodelist to <b>sl</b>, so that
- * we can pick a node for a circuit.
+/* Returns true if <b>node</b> can be chosen based on <b>flags</b>.
+ *
+ * The following conditions are applied to all nodes:
+ *  - is running;
+ *  - is valid;
+ *  - has a general-purpose routerinfo;
+ *  - supports EXTEND2 cells;
+ *  - has an ntor circuit crypto key; and
+ *  - does not allow single-hop exits.
  *
- * If the following <b>flags</b> are set:
- *  - <b>CRN_NEED_UPTIME</b>: if any router has more than a minimum uptime,
- *                            return one of those;
- *  - <b>CRN_NEED_CAPACITY</b>: weight your choice by the advertised capacity
- *                              of each router;
- *  - <b>CRN_NEED_GUARD</b>: only consider Guard routers;
- *  - <b>CRN_WEIGHT_AS_EXIT</b>: we weight bandwidths as if picking an exit
- *                               node, otherwise we weight bandwidths for
- *                               picking a relay node (that is, possibly
- *                               discounting exit nodes);
- *  - <b>CRN_NEED_DESC</b>: only consider nodes that have a routerinfo or
- *                          microdescriptor -- that is, enough info to be
- *                          used to build a circuit;
- *  - <b>CRN_DIRECT_CONN</b>: only consider nodes that are suitable for direct
- *                            connections. Check ReachableAddresses,
- *                            ClientUseIPv4 0, and
+ * The <b>flags</b> chech that <b>node</b>:
+ *  - <b>CRN_NEED_UPTIME</b>: has more than a minimum uptime;
+ *  - <b>CRN_NEED_CAPACITY</b>: has more than a minimum capacity;
+ *  - <b>CRN_NEED_GUARD</b>: is a Guard;
+ *  - <b>CRN_NEED_DESC</b>: has a routerinfo or microdescriptor -- that is,
+ *                          enough info to be used to build a circuit;
+ *  - <b>CRN_DIRECT_CONN</b>: is suitable for direct connections. Checks
+ *                            for the relevant descriptors. Checks the address
+ *                            against ReachableAddresses, ClientUseIPv4 0, and
  *                            fascist_firewall_use_ipv6() == 0);
- *  - <b>CRN_PREF_ADDR</b>: only consider nodes that have an address that is
- *                          preferred by the ClientPreferIPv6ORPort setting.
- *  - <b>CRN_RENDEZVOUS_V3</b>: only consider nodes that can become v3 onion
- *                              service rendezvous points.
- *  - <b>CRN_INITIATE_IPV6_EXTEND</b>: only consider routers than can initiate
- *                                     IPv6 extends.
+ *  - <b>CRN_PREF_ADDR</b>: if we are connecting directly to the node, it has
+ *                          an address that is preferred by the
+ *                          ClientPreferIPv6ORPort setting;
+ *  - <b>CRN_RENDEZVOUS_V3</b>: can become a v3 onion service rendezvous point;
+ *  - <b>CRN_INITIATE_IPV6_EXTEND</b>: can initiate IPv6 extends.
  */
-void
-router_add_running_nodes_to_smartlist(smartlist_t *sl, int flags)
+bool
+router_can_choose_node(const node_t *node, int flags)
 {
   /* The full set of flags used for node selection. */
   const bool need_uptime = (flags & CRN_NEED_UPTIME) != 0;
@@ -555,38 +554,52 @@ router_add_running_nodes_to_smartlist(smartlist_t *sl, int flags)
     !router_or_conn_should_skip_reachable_address_check(get_options(),
                                                         pref_addr);
 
+  if (!node->is_running || !node->is_valid)
+    return false;
+  if (need_desc && !node_has_preferred_descriptor(node, direct_conn))
+    return false;
+  if (node->ri && node->ri->purpose != ROUTER_PURPOSE_GENERAL)
+    return false;
+  if (node_is_unreliable(node, need_uptime, need_capacity, need_guard))
+    return false;
+  /* Don't choose nodes if we are certain they can't do EXTEND2 cells */
+  if (node->rs && !routerstatus_version_supports_extend2_cells(node->rs, 1))
+    return false;
+  /* Don't choose nodes if we are certain they can't do ntor. */
+  if ((node->ri || node->md) && !node_has_curve25519_onion_key(node))
+    return false;
+  /* Exclude relays that allow single hop exit circuits. This is an
+   * obsolete option since 0.2.9.2-alpha and done by default in
+   * 0.3.1.0-alpha. */
+  if (node_allows_single_hop_exits(node))
+    return false;
+  /* Exclude relays that can not become a rendezvous for a hidden service
+   * version 3. */
+  if (rendezvous_v3 &&
+      !node_supports_v3_rendezvous_point(node))
+    return false;
+  /* Choose a node with an OR address that matches the firewall rules */
+  if (direct_conn && check_reach &&
+      !fascist_firewall_allows_node(node,
+                                    FIREWALL_OR_CONNECTION,
+                                    pref_addr))
+    return false;
+  if (initiate_ipv6_extend && !node_supports_initiating_ipv6_extends(node))
+    return false;
+
+  return true;
+}
+
+/** Add every suitable node from our nodelist to <b>sl</b>, so that
+ * we can pick a node for a circuit based on <b>flags</b>.
+ *
+ * See router_can_choose_node() for details of <b>flags</b>.
+ */
+void
+router_add_running_nodes_to_smartlist(smartlist_t *sl, int flags)
+{
   SMARTLIST_FOREACH_BEGIN(nodelist_get_list(), const node_t *, node) {
-    if (!node->is_running || !node->is_valid)
-      continue;
-    if (need_desc && !node_has_preferred_descriptor(node, direct_conn))
-      continue;
-    if (node->ri && node->ri->purpose != ROUTER_PURPOSE_GENERAL)
-      continue;
-    if (node_is_unreliable(node, need_uptime, need_capacity, need_guard))
-      continue;
-    /* Don't choose nodes if we are certain they can't do EXTEND2 cells */
-    if (node->rs && !routerstatus_version_supports_extend2_cells(node->rs, 1))
-      continue;
-    /* Don't choose nodes if we are certain they can't do ntor. */
-    if ((node->ri || node->md) && !node_has_curve25519_onion_key(node))
-      continue;
-    /* Exclude relays that allow single hop exit circuits. This is an
-     * obsolete option since 0.2.9.2-alpha and done by default in
-     * 0.3.1.0-alpha. */
-    if (node_allows_single_hop_exits(node))
-      continue;
-    /* Exclude relays that can not become a rendezvous for a hidden service
-     * version 3. */
-    if (rendezvous_v3 &&
-        !node_supports_v3_rendezvous_point(node))
-      continue;
-    /* Choose a node with an OR address that matches the firewall rules */
-    if (direct_conn && check_reach &&
-        !fascist_firewall_allows_node(node,
-                                      FIREWALL_OR_CONNECTION,
-                                      pref_addr))
-      continue;
-    if (initiate_ipv6_extend && !node_supports_initiating_ipv6_extends(node))
+    if (!router_can_choose_node(node, flags))
       continue;
     smartlist_add(sl, (void *)node);
   } SMARTLIST_FOREACH_END(node);
diff --git a/src/feature/nodelist/routerlist.h b/src/feature/nodelist/routerlist.h
index 7d0788bacb..98472b2771 100644
--- a/src/feature/nodelist/routerlist.h
+++ b/src/feature/nodelist/routerlist.h
@@ -58,6 +58,7 @@ int router_dir_conn_should_skip_reachable_address_check(
                                        int try_ip_pref);
 void router_reset_status_download_failures(void);
 int routers_have_same_or_addrs(const routerinfo_t *r1, const routerinfo_t *r2);
+bool router_can_choose_node(const node_t *node, int flags);
 void router_add_running_nodes_to_smartlist(smartlist_t *sl, int flags);
 
 const routerinfo_t *routerlist_find_my_routerinfo(void);