CDRIVER-1447 logic bug with tag_sets

Author: ajdavis

src/mongoc/mongoc-server-description.c

@@ -32,6 +32,9 @@ static uint8_t kMongocEmptyBson[] = { 5, 0, 0, 0, 0 };
 
 static bson_oid_t kObjectIdZero = { {0} };
 
+static bool _match_tag_set (const mongoc_server_description_t *sd,
+                            bson_iter_t                       *tag_set_iter);
+
 /* Destroy allocated resources within @description, but don't free it */
 void
 mongoc_server_description_cleanup (mongoc_server_description_t *sd)
@@ -734,10 +737,10 @@ mongoc_server_description_filter_stale (mongoc_server_description_t **sds,
  *
  * mongoc_server_description_filter_tags --
  *
- *       Given a set of server descriptions, determine have the correct tags
- *       as per the Server Selection spec. Determines the number of
- *       eligible servers, and sets any servers that are NOT eligible to
- *       NULL in the descriptions set.
+ * Given a set of server descriptions, set to NULL any that don't
+ * match the the read preference's tag sets.
+ *
+ * https://github.com/mongodb/specifications/blob/master/source/server-selection/server-selection.rst#tag-set
  *
  *-------------------------------------------------------------------------
  */
@@ -749,14 +752,9 @@ mongoc_server_description_filter_tags (mongoc_server_description_t **description
 {
    const bson_t *rp_tags;
    bson_iter_t rp_tagset_iter;
-   bson_iter_t rp_iter;
-   bson_iter_t sd_iter;
-   uint32_t rp_len;
-   uint32_t sd_len;
-   const char *rp_val;
-   const char *sd_val;
+   bson_iter_t tag_set_iter;
    bool *sd_matched = NULL;
-   size_t found;
+   bool found;
    size_t i;
 
    if (!read_prefs) {
@@ -777,7 +775,7 @@ mongoc_server_description_filter_tags (mongoc_server_description_t **description
 
    /* for each read preference tag set */
    while (bson_iter_next (&rp_tagset_iter)) {
-      found = description_len;
+      found = false;
 
       for (i = 0; i < description_len; i++) {
          if (!descriptions[i]) {
@@ -786,29 +784,10 @@ mongoc_server_description_filter_tags (mongoc_server_description_t **description
             continue;
          }
 
-         sd_matched[i] = true;
-
-         bson_iter_recurse (&rp_tagset_iter, &rp_iter);
-
-         while (bson_iter_next (&rp_iter)) {
-            rp_val = bson_iter_utf8 (&rp_iter, &rp_len);
-
-            if (bson_iter_init_find (&sd_iter, &descriptions[i]->tags, bson_iter_key (&rp_iter))) {
-
-               /* If the server description has that key */
-               sd_val = bson_iter_utf8 (&sd_iter, &sd_len);
-
-               if (! (sd_len == rp_len && (0 == memcmp(rp_val, sd_val, rp_len)))) {
-                  /* If the key value doesn't match, no match */
-                  sd_matched[i] = false;
-                  found--;
-               }
-            } else {
-               /* If the server description doesn't have that key, no match */
-               sd_matched[i] = false;
-               found--;
-               break;
-            }
+         bson_iter_recurse (&rp_tagset_iter, &tag_set_iter);
+         sd_matched[i] = _match_tag_set (descriptions[i], &tag_set_iter);
+         if (sd_matched[i]) {
+            found = true;
          }
       }
 
@@ -823,6 +802,7 @@ mongoc_server_description_filter_tags (mongoc_server_description_t **description
       }
    }
 
+   /* tried each */
    for (i = 0; i < description_len; i++) {
       if (! sd_matched[i]) {
          descriptions[i] = NULL;
@@ -832,3 +812,46 @@ mongoc_server_description_filter_tags (mongoc_server_description_t **description
 CLEANUP:
    bson_free (sd_matched);
 }
+
+
+/*
+ *-------------------------------------------------------------------------
+ *
+ * _match_tag_set --
+ *
+ *       Check if a server's tags match one tag set, like
+ *       {'tag1': 'value1', 'tag2': 'value2'}.
+ *
+ *-------------------------------------------------------------------------
+ */
+static bool _match_tag_set (const mongoc_server_description_t *sd,
+                            bson_iter_t                       *tag_set_iter)
+{
+   bson_iter_t sd_iter;
+   uint32_t read_pref_tag_len;
+   uint32_t sd_len;
+   const char *read_pref_tag;
+   const char *read_pref_val;
+   const char *server_val;
+
+   while (bson_iter_next (tag_set_iter)) {
+      /* one {'tag': 'value'} pair from the read preference's tag set */
+      read_pref_tag = bson_iter_key (tag_set_iter);
+      read_pref_val = bson_iter_utf8 (tag_set_iter, &read_pref_tag_len);
+
+      if (bson_iter_init_find (&sd_iter, &sd->tags, read_pref_tag)) {
+         /* The server has this tag - does it have the right value? */
+         server_val = bson_iter_utf8 (&sd_iter, &sd_len);
+         if (sd_len != read_pref_tag_len ||
+             memcmp(read_pref_val, server_val, read_pref_tag_len)) {
+            /* If the values don't match, no match */
+            return false;
+         }
+      } else {
+         /* If the server description doesn't have that key, no match */
+         return false;
+      }
+   }
+
+   return true;
+}