promdump: custom metrics are broken

The error handling changes made so that the tool aborts if none of the metrics were dumped successfully did not consider custom metrics, so custom metric export would always fail.

This fix moves the skipped, successful, and failed metrics counts to the global scope and increments these counts appropriately during custom metric export.

The summary line was updated to use a calculated total that includes the custom metric if specified.

This commit also makes failure to export a custom metric (if specified) non-fatal.

promdump/promdump.go

@@ -116,6 +116,10 @@ var (
 	customMetricCount uint // Holds custom metric file counts
 	logger            *log.Logger
 
+	skippedMetrics    = 0
+	successfulMetrics = 0
+	failedMetrics     = 0
+
 	// We'll refer to time.Now using this variable so that we can swap it out for a static time in the test suite
 	// as needed.
 	now = time.Now
@@ -1331,18 +1335,22 @@ func main() {
 			v.dumpSuccessful = true
 		}
 	}
+
+	totalMetrics := len(collectMetrics)
+
 	if *metric != "" {
+		totalMetrics += 1
 		customMetricCount, err = exportMetric(ctx, promApi, *metric, beginTS, endTS, *periodDur, *batchDur, *batchesPerFile, *out)
-		if err != nil {
-			logger.Fatalln("exportMetric:", err)
+		if err == nil {
+			successfulMetrics += 1
+		} else {
+			logger.Printf("exportMetric: export of custom metric '%v' failed with error %v", *metric, err)
+			failedMetrics += 1
 		}
 	}
 	logger.Println("main: Finished with Prometheus connection")
 
 	// TODO: Put this in a func?
-	skippedMetrics := 0
-	successfulMetrics := 0
-	failedMetrics := 0
 	for _, v := range collectMetrics {
 		if v.collect {
 			if v.dumpSuccessful {
@@ -1354,7 +1362,7 @@ func main() {
 			skippedMetrics += 1
 		}
 	}
-	logger.Printf("main: summary: %v metrics processed (skipped: %v dumped: %v failed: %v)", len(collectMetrics), skippedMetrics, successfulMetrics, failedMetrics)
+	logger.Printf("main: summary: %v metrics processed (skipped: %v dumped: %v failed: %v)", totalMetrics, skippedMetrics, successfulMetrics, failedMetrics)
 	if successfulMetrics < 1 {
 		logger.Fatalf("main: no metrics were dumped successfully; aborting")
 	} else if failedMetrics > 0 {