Fix panic when setting only_counter for default relabelings (#279)

Deduplicate labels used in `Collection.init()` in the same way as in
`processSource`.
Side-Effect: When overriding `method` one needs to manually add the
split/whitelist config from `DefaultRelabelings` in their own config
file.
Resolve #216

features/issues.feature

@@ -92,6 +92,20 @@ Feature: Various issues reported in the bug tracker remain solved
     Then the exporter should report value 3 for metric http_parse_errors_total{vhost="test"}
     And the exporter should report value 2 for metric http_parse_errors_total{vhost="test2"}
 
+  Scenario: Issue 216: Cannot set only_counter for status, daemon panics
+    Given a running exporter listening with configuration file "test-config-issue216.hcl"
+    When the following HTTP request is logged to "access.log"
+      """
+      172.17.0.1 - - [23/Jun/2016:16:04:20 +0000] "GET / HTTP/1.1" 200 612 "-" "curl/7.29.0" "-" 10 10
+      172.17.0.1 - - [23/Jun/2016:16:04:20 +0000] "POST / HTTP/1.1" 200 612 "-" "curl/7.29.0" "-" 10 10
+      172.17.0.1 - - [23/Jun/2016:16:04:20 +0000] "GET / HTTP/1.1" 500 612 "-" "curl/7.29.0" "-" 10 10
+      172.17.0.1 - - [23/Jun/2016:16:04:20 +0000] "GET / HTTP/1.1" 418 612 "-" "curl/7.29.0" "-" 10 10
+      """
+    Then the process should be running
+    And the exporter should report value 1 for metric nginx_http_response_count_total{method="GET",status="200"}
+    And the exporter should report value 1 for metric nginx_http_response_count_total{method="other",status="200"}
+    And the exporter should report value 4 for metric nginx_http_response_time_seconds_hist_count
+
   Scenario: Issue 224: Missing float values
     Given a running exporter listening with configuration file "test-config-issue217.yaml"
     When the following HTTP request is logged to "access.log"
@@ -101,4 +115,3 @@ Feature: Various issues reported in the bug tracker remain solved
       """
     Then the exporter should report value 0 for metric test_parse_errors_total
     Then the exporter should report value 4 for metric test_http_upstream_time_seconds_sum{method="GET",status="200"}
-

features/steps/steps.py

@@ -98,3 +98,10 @@ def step_impl(context, val, metric, endpoint='/metrics'):
     if not "%s %s" % (metric, val) in lines:
         raise AssertionError(
             'expected metric "%s" could not be verified. Actual metrics:\n%s' % (metric, text))
+
+
+@then("the process should be running")
+def step_impl(context):
+    rc = context.process.poll()
+    if rc is not None:
+        raise AssertionError(f"The process has exited with return code {rc}")

features/test-config-issue216.hcl

@@ -0,0 +1,24 @@
+listen {
+  port = 4040
+}
+
+namespace "nginx" {
+  source = {
+    files = [
+      ".behave-sandbox/access.log"
+    ]
+  }
+
+  format = "$remote_addr - $remote_user [$time_local] \"$request\" $status $body_bytes_sent \"$http_referer\" \"$http_user_agent\" \"$http_x_forwarded_for\" $request_time $upstream_response_time"
+
+  relabel "status" {
+    from = "status"
+    only_counter = true
+  }
+  relabel "method" {
+    from = "request"
+    only_counter = true
+    split = 1
+    whitelist = [ "GET" ]
+  }
+}

pkg/metrics/collection_init.go

@@ -6,36 +6,22 @@ import (
 	"github.com/prometheus/client_golang/prometheus"
 )
 
-func inLabels(label string, labels []string) bool {
-	for _, l := range labels {
-		if label == l {
-			return true
-		}
-	}
-	return false
-}
-
 // Init initializes a metrics struct
 func (m *Collection) Init(cfg *config.NamespaceConfig) {
 	cfg.MustCompile()
 
 	labels := cfg.OrderedLabelNames
 	counterLabels := labels
 
-	for i := range cfg.RelabelConfigs {
-		if !cfg.RelabelConfigs[i].OnlyCounter {
-			labels = append(labels, cfg.RelabelConfigs[i].TargetLabel)
-		}
-		counterLabels = append(counterLabels, cfg.RelabelConfigs[i].TargetLabel)
-	}
+	relabelings := relabeling.NewRelabelings(cfg.RelabelConfigs)
+	relabelings = append(relabelings, relabeling.DefaultRelabelings...)
+	relabelings = relabeling.UniqueRelabelings(relabelings)
 
-	for _, r := range relabeling.DefaultRelabelings {
-		if !inLabels(r.TargetLabel, labels) {
+	for _, r := range relabelings {
+		if !r.OnlyCounter {
 			labels = append(labels, r.TargetLabel)
 		}
-		if !inLabels(r.TargetLabel, counterLabels) {
-			counterLabels = append(counterLabels, r.TargetLabel)
-		}
+		counterLabels = append(counterLabels, r.TargetLabel)
 	}
 
 	m.CountTotal = prometheus.NewCounterVec(prometheus.CounterOpts{