tree: don't set error on failure, this is the caller's responsibility

src/port.c

@@ -321,15 +321,22 @@ int ep_port_ctl(ep_port_t* port_info,
 int ep_port_add_socket(ep_port_t* port_info,
                        ep_sock_t* sock_info,
                        SOCKET socket) {
-  return tree_add(&port_info->sock_tree, &sock_info->tree_node, socket);
+  if (tree_add(&port_info->sock_tree, &sock_info->tree_node, socket) < 0)
+    return_error(-1, ERROR_ALREADY_EXISTS);
+  return 0;
 }
 
 int ep_port_del_socket(ep_port_t* port_info, ep_sock_t* sock_info) {
-  return tree_del(&port_info->sock_tree, &sock_info->tree_node);
+  if (tree_del(&port_info->sock_tree, &sock_info->tree_node) < 0)
+    return_error(-1, ERROR_NOT_FOUND);
+  return 0;
 }
 
 ep_sock_t* ep_port_find_socket(ep_port_t* port_info, SOCKET socket) {
-  return ep_sock_find_in_tree(&port_info->sock_tree, socket);
+  ep_sock_t* sock_info = ep_sock_find_in_tree(&port_info->sock_tree, socket);
+  if (sock_info == NULL)
+    return_error(NULL, ERROR_NOT_FOUND);
+  return sock_info;
 }
 
 static poll_group_allocator_t* _ep_port_get_poll_group_allocator(

src/tree.c

@@ -30,7 +30,7 @@ int tree_add(tree_t* tree, tree_node_t* node, uintptr_t key) {
   existing_node = RB_INSERT(tree, tree, node);
 
   if (existing_node != NULL)
-    return_error(-1, ERROR_ALREADY_EXISTS);
+    return -1;
 
   return 0;
 }
@@ -41,7 +41,7 @@ int tree_del(tree_t* tree, tree_node_t* node) {
   removed_node = RB_REMOVE(tree, tree, node);
 
   if (removed_node == NULL)
-    return_error(-1, ERROR_NOT_FOUND);
+    return -1;
   else
     assert(removed_node == node);
 
@@ -49,17 +49,12 @@ int tree_del(tree_t* tree, tree_node_t* node) {
 }
 
 tree_node_t* tree_find(tree_t* tree, uintptr_t key) {
-  tree_node_t* node;
   tree_node_t lookup;
 
   memset(&lookup, 0, sizeof lookup);
   lookup.key = key;
 
-  node = RB_FIND(tree, tree, &lookup);
-  if (node == NULL)
-    return_error(NULL, ERROR_NOT_FOUND);
-
-  return node;
+  return RB_FIND(tree, tree, &lookup);
 }
 
 tree_node_t* tree_root(tree_t* tree) {

src/tree.h

@@ -4,6 +4,11 @@
 #include "internal.h"
 #include "rb.h"
 
+/* NB: the tree functions do not set errno or LastError when they fail. Each of
+ * the API functions has at most one failure mode. It is up to the caller to
+ * set an appropriate error code when necessary.
+ */
+
 typedef RB_HEAD(tree, tree_node) tree_t;
 
 typedef struct tree_node {