CDRIVER-2809 topology listeners must cast away const

Author: ajdavis

src/libmongoc/doc/application-performance-monitoring.rst

@@ -84,6 +84,8 @@ This example program prints something like:
 
   topology opening
   topology changed: Unknown -> ReplicaSetNoPrimary
+    secondary UNAVAILABLE
+    primary UNAVAILABLE
   server opening: localhost:27017
   server opening: localhost:27018
   localhost:27017 heartbeat started
@@ -94,6 +96,8 @@ This example program prints something like:
   topology changed: ReplicaSetNoPrimary -> ReplicaSetWithPrimary
     new servers:
         RSPrimary localhost:27017
+    secondary UNAVAILABLE
+    primary AVAILABLE
   localhost:27019 heartbeat started
   localhost:27018 heartbeat succeeded: { ... reply ... }
   server changed: localhost:27018 Unknown -> RSSecondary
@@ -103,6 +107,8 @@ This example program prints something like:
     new servers:
         RSPrimary localhost:27017
         RSSecondary localhost:27018
+    secondary AVAILABLE
+    primary AVAILABLE
   localhost:27019 heartbeat succeeded: { ... reply ... }
   server changed: localhost:27019 Unknown -> RSSecondary
   topology changed: ReplicaSetWithPrimary -> ReplicaSetWithPrimary
@@ -113,6 +119,8 @@ This example program prints something like:
         RSPrimary localhost:27017
         RSSecondary localhost:27018
         RSSecondary localhost:27019
+    secondary AVAILABLE
+    primary AVAILABLE
   topology closed
 
   Events:
@@ -126,7 +134,7 @@ This example program prints something like:
      heartbeat succeeded: 3
      heartbeat failed: 0
 
-The driver discovers the third member, "localhost:27019", and adds it to the topology.
+The driver connects to the mongods on ports 27017 and 27018, which were specified in the URI, and determines which is primary. It also discovers the third member, "localhost:27019", and adds it to the topology.
 
 .. only:: html
 

src/libmongoc/doc/includes/cast-away-td-const.txt

@@ -0,0 +1 @@
+Use this function in a topology-changed callback registered with :symbol:`mongoc_apm_set_topology_changed_cb`. For historical reasons, the :symbol:`mongoc_topology_description_t` passed to the callback is a const pointer, you must cast away const to pass the pointer to |td-func|.

src/libmongoc/doc/mongoc_topology_description_has_readable_server.rst

@@ -16,6 +16,10 @@ Determines if the topology has a readable server available.
 Servers are filtered by the given read preferences only if the driver is connected to a replica set, otherwise the read preferences are ignored.
 This function uses the driver's current knowledge of the state of the MongoDB server or servers it is connected to; it does no I/O and it does not block.
 
+.. |td-func| replace:: ``mongoc_topology_description_has_readable_server``
+
+.. include:: includes/cast-away-td-const.txt
+
 Parameters
 ----------
 

src/libmongoc/doc/mongoc_topology_description_has_writable_server.rst

@@ -14,6 +14,10 @@ Synopsis
 
 Determines if the topology has a writable server available, such as a primary, mongos, or standalone. This function uses the driver's current knowledge of the state of the MongoDB server or servers it is connected to; it does no I/O and it does not block.
 
+.. |td-func| replace:: ``mongoc_topology_description_has_writable_server``
+
+.. include:: includes/cast-away-td-const.txt
+
 Parameters
 ----------
 

src/libmongoc/examples/example-sdam-monitoring.c

@@ -76,6 +76,7 @@ topology_changed (const mongoc_apm_topology_changed_t *event)
    mongoc_server_description_t **new_sds;
    size_t n_new_sds;
    size_t i;
+   mongoc_read_prefs_t *prefs;
 
    context = (stats_t *) mongoc_apm_topology_changed_get_context (event);
    context->topology_changed_events++;
@@ -107,6 +108,24 @@ topology_changed (const mongoc_apm_topology_changed_t *event)
       }
    }
 
+   prefs = mongoc_read_prefs_new (MONGOC_READ_SECONDARY);
+
+   /* it is safe, and unfortunately necessary, to cast away const here */
+   if (mongoc_topology_description_has_readable_server (
+          (mongoc_topology_description_t *) new_td, prefs)) {
+      printf ("  secondary AVAILABLE\n");
+   } else {
+      printf ("  secondary UNAVAILABLE\n");
+   }
+
+   if (mongoc_topology_description_has_writable_server (
+          (mongoc_topology_description_t *) new_td)) {
+      printf ("  primary AVAILABLE\n");
+   } else {
+      printf ("  primary UNAVAILABLE\n");
+   }
+
+   mongoc_read_prefs_destroy (prefs);
    mongoc_server_descriptions_destroy_all (prev_sds, n_prev_sds);
    mongoc_server_descriptions_destroy_all (new_sds, n_new_sds);
 }