Openmetrics label truncation

[Daniel Sabotta]

Hello,

I'm using dovecot 2.3.18 and want to collect metrics with prometheus via 
openmetrics.

I need to label the metrics with the destination host name.
The configuration works fine, but the label value is truncated after 32 chars 
(and a '...' is added).

My config:

service stats {
  inet_listener http {
    port = 9323
  }
}

metric my_metric {
  filter = event=smtp_client_transaction_finished
  group_by = dest_host status_code
}

I wrote a simple patch, that fixes that for me:

diff --git a/src/stats/stats-metrics.c b/src/stats/stats-metrics.c
index 877c142546..30126563ff 100644
--- a/src/stats/stats-metrics.c
+++ b/src/stats/stats-metrics.c
@@ -357,7 +357,7 @@ stats_metric_sub_metric_alloc(struct metric *metric, const 
char *name, pool_t po
        array_append_zero(&fields);
        sub_metric = stats_metric_alloc(pool, metric->name, metric->set,
                                        array_idx(&fields, 0));
-       sub_metric->sub_name = p_strdup(pool, str_sanitize_utf8(name, 32));
+       sub_metric->sub_name = p_strdup(pool, str_sanitize_utf8(name, 63));
        array_append(&metric->sub_metrics, &sub_metric, 1);
        return sub_metric;
 }


Why are labels truncated after 32?
Is there a reason I do not see?
I found no reasons in the openmetrics specification [1].


Thanks in advance

Daniel