Safely error if "pgo df" does not find any clusters

In this case previously, "pgo df" would actually time out and return an error that read like a Go debug message. Issue: [ch9202]

Author: Jonathan S. Katz

docs/content/releases/4.5.0.md

@@ -143,6 +143,7 @@ To remove an annotation, one follows the format:
 - The pgBackRest URI style defaults to `host` if it is not set.
 - pgBackRest commands can now be executed even if there are multiple pgBackRest Pods available in a Deployment, so long as there is only one "running" pgBackRest Pod.
 - Ensure pgBackRest S3 Secrets can be upgraded from PostgreSQL Operator 4.3.
+- Return an error if a cluster is not found when using `pgo df` instead of timing out.
 - pgBadger now has a default memory limit of 64Mi, which should help avoid a visit from the OOM killer.
 - Fix `pgo label` when applying multiple labels at once.
 - Fix `pgo create pgorole` so that the expression `--permissions=*` works.

internal/apiserver/dfservice/dfimpl.go

@@ -57,7 +57,18 @@ func DfCluster(request msgs.DfRequest) msgs.DfResponse {
 return CreateErrorResponse(err.Error())
 }
 
-log.Debugf("df clusters found len is %d", len(clusterList.Items))
+totalClusters := len(clusterList.Items)
+
+log.Debugf("df clusters found len is %d", totalClusters)
+
+// if there are no clusters found, exit early
+if totalClusters == 0 {
+response.Status = msgs.Status{
+Code: msgs.Error,
+Msg: fmt.Sprintf("no clusters found for selector %q in namespace %q", selector, namespace),
+}
+return response
+}
 
 // iterate through each cluster and get the information about the disk
 // utilization. As there could be a lot of clusters doing this, we opt for
@@ -76,7 +87,6 @@ func DfCluster(request msgs.DfRequest) msgs.DfResponse {
 
 // track the progress / completion, so we know when to exit
 processed := 0
-totalClusters := len(clusterList.Items)
 
 loop:
 for {