Add support for passing URL query params to pod metric endpoints (#109)

Adds a new metric-config option named `rawQuery`. The value of
this option will be appended to the metric `path` as URL query
parameters to be used by the pod's application. E.g.,:
```
metric-config.pods.requests-per-second.json-path/rawQuery: "foo=bar&baz=bop"
```
will apppend `?foo=bar&baz=bop` to the URL.

Signed-off-by: Abe Friesen <2319792+doyshinda@users.noreply.github.com>

README.md

@@ -155,6 +155,17 @@ values of JSONPath expressions that evaluate to arrays/slices of numbers.
 It's optional but when the expression evaluates to an array/slice, it's absence will
 produce an error. The supported aggregation functions are `avg`, `max`, `min` and `sum`.
 
+The `raw-query` configuration option specifies the query params to send along to the endpoint:
+```yaml
+  metric-config.pods.requests-per-second.json-path/path: /metrics
+  metric-config.pods.requests-per-second.json-path/port: "9090"
+  metric-config.pods.requests-per-second.json-path/raw-query: "foo=bar&baz=bop"
+```
+will create a URL like this:
+```
+http://<podIP>:9090/metrics?foo=bar&baz=bop
+```
+
 ## Prometheus collector
 
 The Prometheus collector is a generic collector which can map Prometheus

pkg/collector/json_path_collector.go

@@ -25,6 +25,7 @@ type JSONPathMetricsGetter struct {
 	port       int
 	aggregator string
 	client     *http.Client
+	rawQuery   string
 }
 
 // NewJSONPathMetricsGetter initializes a new JSONPathMetricsGetter.
@@ -49,6 +50,10 @@ func NewJSONPathMetricsGetter(config map[string]string) (*JSONPathMetricsGetter,
 		getter.path = v
 	}
 
+	if v, ok := config["raw-query"]; ok {
+		getter.rawQuery = v
+	}
+
 	if v, ok := config["port"]; ok {
 		n, err := strconv.Atoi(v)
 		if err != nil {
@@ -83,7 +88,7 @@ func defaultHTTPClient() *http.Client {
 // endpoint and extracting the desired value using the specified json path
 // query.
 func (g *JSONPathMetricsGetter) GetMetric(pod *corev1.Pod) (float64, error) {
-	data, err := g.getPodMetrics(pod, g.scheme, g.path, g.port)
+	data, err := g.getPodMetrics(pod)
 	if err != nil {
 		return 0, err
 	}
@@ -140,20 +145,12 @@ func castSlice(in []interface{}) ([]float64, error) {
 }
 
 // getPodMetrics returns the content of the pods metrics endpoint.
-func (g *JSONPathMetricsGetter) getPodMetrics(pod *corev1.Pod, scheme, path string, port int) ([]byte, error) {
+func (g *JSONPathMetricsGetter) getPodMetrics(pod *corev1.Pod) ([]byte, error) {
 	if pod.Status.PodIP == "" {
 		return nil, fmt.Errorf("pod %s/%s does not have a pod IP", pod.Namespace, pod.Namespace)
 	}
 
-	if scheme == "" {
-		scheme = "http"
-	}
-
-	metricsURL := url.URL{
-		Scheme: scheme,
-		Host:   fmt.Sprintf("%s:%d", pod.Status.PodIP, port),
-		Path:   path,
-	}
+	metricsURL := g.buildMetricsURL(pod.Status.PodIP)
 
 	request, err := http.NewRequest(http.MethodGet, metricsURL.String(), nil)
 	if err != nil {
@@ -178,6 +175,22 @@ func (g *JSONPathMetricsGetter) getPodMetrics(pod *corev1.Pod, scheme, path stri
 	return data, nil
 }
 
+// buildMetricsURL will build the full URL needed to hit the pod metric endpoint.
+func (g *JSONPathMetricsGetter) buildMetricsURL(podIP string) url.URL {
+	var scheme = g.scheme
+
+	if scheme == "" {
+		scheme = "http"
+	}
+
+	return url.URL{
+		Scheme:   scheme,
+		Host:     fmt.Sprintf("%s:%d", podIP, g.port),
+		Path:     g.path,
+		RawQuery: g.rawQuery,
+	}
+}
+
 // reduce will reduce a slice of numbers given a aggregator function's name. If it's empty or not recognized, an error is returned.
 func reduce(values []float64, aggregator string) (float64, error) {
 	switch aggregator {

pkg/collector/json_path_collector_test.go

@@ -1,6 +1,7 @@
 package collector
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/oliveagle/jsonpath"
@@ -70,6 +71,25 @@ func TestNewJSONPathMetricsGetter(t *testing.T) {
 
 	_, err4 := NewJSONPathMetricsGetter(configErrorPort)
 	require.Error(t, err4)
+
+	configWithRawQuery := map[string]string{
+		"json-key":  "$.values",
+		"scheme":    "http",
+		"path":      "/metrics",
+		"port":      "9090",
+		"raw-query": "foo=bar&baz=bop",
+	}
+	jpath5, _ := jsonpath.Compile(configWithRawQuery["json-key"])
+	getterWithRawQuery, err5 := NewJSONPathMetricsGetter(configWithRawQuery)
+
+	require.NoError(t, err5)
+	compareMetricsGetter(t, &JSONPathMetricsGetter{
+		jsonPath: jpath5,
+		scheme:   "http",
+		path:     "/metrics",
+		port:     9090,
+		rawQuery: "foo=bar&baz=bop",
+	}, getterWithRawQuery)
 }
 
 func TestCastSlice(t *testing.T) {
@@ -110,3 +130,44 @@ func TestReduce(t *testing.T) {
 	_, err5 := reduce([]float64{1, 2, 3}, "inexistent_function")
 	require.Errorf(t, err5, "slice of numbers was returned by JSONPath, but no valid aggregator function was specified: %v", "inexistent_function")
 }
+
+func TestBuildMetricsURL(t *testing.T) {
+	scheme := "http"
+	ip := "1.2.3.4"
+	port := "9090"
+	path := "/v1/test/"
+	rawQuery := "foo=bar&baz=bop"
+
+	// Test building URL with rawQuery
+	configWithRawQuery := map[string]string{
+		"json-key":  "$.value",
+		"scheme":    scheme,
+		"path":      path,
+		"port":      port,
+		"raw-query": rawQuery,
+	}
+	_, err := jsonpath.Compile(configWithRawQuery["json-key"])
+	require.NoError(t, err)
+	getterWithRawQuery, err1 := NewJSONPathMetricsGetter(configWithRawQuery)
+	require.NoError(t, err1)
+
+	expectedURLWithQuery := fmt.Sprintf("%s://%s:%s%s?%s", scheme, ip, port, path, rawQuery)
+	receivedURLWithQuery := getterWithRawQuery.buildMetricsURL(ip)
+	require.Equal(t, receivedURLWithQuery.String(), expectedURLWithQuery)
+
+	// Test building URL without rawQuery
+	configWithNoQuery := map[string]string{
+		"json-key": "$.value",
+		"scheme":   scheme,
+		"path":     path,
+		"port":     port,
+	}
+	_, err2 := jsonpath.Compile(configWithNoQuery["json-key"])
+	require.NoError(t, err2)
+	getterWithNoQuery, err3 := NewJSONPathMetricsGetter(configWithNoQuery)
+	require.NoError(t, err3)
+
+	expectedURLNoQuery := fmt.Sprintf("%s://%s:%s%s", scheme, ip, port, path)
+	receivedURLNoQuery := getterWithNoQuery.buildMetricsURL(ip)
+	require.Equal(t, receivedURLNoQuery.String(), expectedURLNoQuery)
+}