metrics: add METRIC_FAMILY_TYPE_OBJECT type

We will need a way to send journal entries as metrics. Those are already
json objects. So Lennart suggested to introduce a new type
METRIC_FAMILY_TYPE_OBJECT that does this. This commit implements
his suggestion.

src/shared/metrics.c

@@ -58,6 +58,7 @@ static const char * const metric_family_type_table[_METRIC_FAMILY_TYPE_MAX] = {
         [METRIC_FAMILY_TYPE_COUNTER] = "counter",
         [METRIC_FAMILY_TYPE_GAUGE]   = "gauge",
         [METRIC_FAMILY_TYPE_STRING]  = "string",
+        [METRIC_FAMILY_TYPE_OBJECT]  = "object",
 };
 
 DEFINE_STRING_TABLE_LOOKUP_TO_STRING(metric_family_type, MetricFamilyType);
@@ -229,3 +230,18 @@ int metric_build_send_double(
 
         return metric_build_send(mf, link, object, v, fields);
 }
+
+int metric_build_send_object(
+                const MetricFamily *mf,
+                sd_varlink *link,
+                const char *object,
+                sd_json_variant *value,
+                sd_json_variant *fields) {
+
+        assert(mf);
+        assert(link);
+        assert(value);
+        assert(sd_json_variant_is_object(value));
+
+        return metric_build_send(mf, link, object, value, fields);
+}

src/shared/metrics.h

@@ -7,6 +7,7 @@ typedef enum MetricFamilyType {
         METRIC_FAMILY_TYPE_COUNTER,
         METRIC_FAMILY_TYPE_GAUGE,
         METRIC_FAMILY_TYPE_STRING,
+        METRIC_FAMILY_TYPE_OBJECT,
         _METRIC_FAMILY_TYPE_MAX,
         _METRIC_FAMILY_TYPE_INVALID = -EINVAL,
 } MetricFamilyType;
@@ -39,3 +40,4 @@ int metrics_method_list(const MetricFamily mfs[], sd_varlink *link, sd_json_vari
 int metric_build_send_string(const MetricFamily* mf, sd_varlink *link, const char *object, const char *value, sd_json_variant *fields);
 int metric_build_send_unsigned(const MetricFamily* mf, sd_varlink *link, const char *object, uint64_t value, sd_json_variant *fields);
 int metric_build_send_double(const MetricFamily* mf, sd_varlink *link, const char *object, double value, sd_json_variant *fields);
+int metric_build_send_object(const MetricFamily* mf, sd_varlink *link, const char *object, sd_json_variant *value, sd_json_variant *fields);

src/shared/varlink-io.systemd.Metrics.c

@@ -9,7 +9,9 @@ static SD_VARLINK_DEFINE_ENUM_TYPE(
                 SD_VARLINK_FIELD_COMMENT("A gauge metric family type which is a value that can go up and down"),
                 SD_VARLINK_DEFINE_ENUM_VALUE(gauge),
                 SD_VARLINK_FIELD_COMMENT("A string metric family type"),
-                SD_VARLINK_DEFINE_ENUM_VALUE(string));
+                SD_VARLINK_DEFINE_ENUM_VALUE(string),
+                SD_VARLINK_FIELD_COMMENT("An object metric family type whose value is an arbitrary JSON object"),
+                SD_VARLINK_DEFINE_ENUM_VALUE(object));
 
 static SD_VARLINK_DEFINE_ERROR(NoSuchMetric);