MXS-1249: Add function for getting the "version" of a service

The behaviour of the query classifier needs to change depending
on the version of the servers of a service. With this function
"some" version of the service can be obtained.

include/maxscale/service.h

@@ -355,4 +355,29 @@ static inline uint64_t service_get_capabilities(const SERVICE *service)
     return service->capabilities;
 }
 
+typedef enum service_version_which_t
+{
+    SERVICE_VERSION_ANY,  /*< Any version of the servers of a service. */
+    SERVICE_VERSION_MIN,  /*< The minimum version. */
+    SERVICE_VERSION_MAX,  /*< The maximum version. */
+} service_version_which_t;
+
+/**
+ * Return the version of the service. The returned version can be
+ *
+ * - the version of any (in practice the first) server associated
+ *   with the service,
+ * - the smallest version of any of the servers associated with
+ *   the service, or
+ * - the largest version of any of the servers associated with
+ *   the service.
+ *
+ * @param service  The service.
+ * @param which    Which version.
+ * @param version  On output contains the version of the service.
+ */
+void service_get_version(const SERVICE *service,
+                         service_version_which_t which,
+                         SERVER_VERSION* version);
+
 MXS_END_DECLS

server/core/service.cc

@@ -2673,3 +2673,90 @@ json_t* service_relations_to_server(const SERVER* server, const char* host)
 
     return rel;
 }
+
+void service_get_version(const SERVICE *service,
+                         service_version_which_t which,
+                         SERVER_VERSION* version)
+{
+    if (which == SERVICE_VERSION_ANY)
+    {
+        SERVER_REF* sref = service->dbref;
+
+        while (sref && !sref->active)
+        {
+            sref = sref->next;
+        }
+
+        if (sref)
+        {
+            *version = sref->server->version;
+        }
+        else
+        {
+            version->major = version->minor = version->patch = 0;
+        }
+    }
+    else
+    {
+        size_t n = 0;
+
+        SERVER_VERSION v;
+
+        if (which == SERVICE_VERSION_MIN)
+        {
+            v.major = UINT32_MAX;
+            v.minor = UINT32_MAX;
+            v.patch = UINT32_MAX;
+        }
+        else
+        {
+            ss_dassert(which == SERVICE_VERSION_MAX);
+
+            v.major = 0;
+            v.minor = 0;
+            v.patch = 0;
+        }
+
+        SERVER_REF* sref = service->dbref;
+
+        while (sref)
+        {
+            if (sref->active)
+            {
+                ++n;
+
+                SERVER* s = sref->server;
+
+                if (which == SERVICE_VERSION_MIN)
+                {
+                    if ((s->version.major < v.major) ||
+                        ((s->version.major == v.major) && (s->version.minor < v.minor)) ||
+                        ((s->version.major == v.major) && (s->version.minor == v.minor) &&
+                         (s->version.patch < v.patch)))
+                    {
+                        v = s->version;
+                    }
+                }
+                else
+                {
+                    if ((s->version.major > v.major) ||
+                        ((s->version.major == v.major) && (s->version.minor > v.minor)) ||
+                        ((s->version.major == v.major) && (s->version.minor == v.minor) &&
+                         (s->version.patch > v.patch)))
+                    {
+                        v = s->version;
+                    }
+                }
+            }
+
+            sref = sref->next;
+        }
+
+        if (n == 0)
+        {
+            v.major = v.minor = v.patch = 0;
+        }
+
+        *version = v;
+    }
+}