Fix metrics filter with colon : in query value

Example of a metric filter affected by this:
```
cloudsql.googleapis.com/database:resource.labels.database_id="project-id:database-name"
```

+ Added/updated tests
+ Updated README with this example and a note about quoting special characters

Signed-off-by: Daniel Kontsek <[email protected]>

Author: dn0

README.md

@@ -165,16 +165,18 @@ Example: \
 
 The `filter_query` will be applied to a final metrics API query when querying for metric data. You can read more about the metric API filter options in GCPs documentation https://cloud.google.com/monitoring/api/v3/filters
 
-The final query sent to the metrics API already includes filters for project and metric type. Each applicable `filter_query` will be appended to the query with an AND
+The final query sent to the metrics API already includes filters for project and metric type. Each applicable `filter_query` will be appended to the query with an `AND`. String filter values that contain special characters (e.g. `:` colon) must be quoted with quotation marks `"`. Please always check logs for potential syntax errors from GCP.
 
 Full example
 ```
 stackdriver_exporter \
  --google.project-ids=my-test-project \
  --monitoring.metrics-prefixes='pubsub.googleapis.com/subscription' \
  --monitoring.metrics-prefixes='compute.googleapis.com/instance/cpu' \
+ --monitoring.metrics-prefixes='cloudsql.googleapis.com/database' \
  --monitoring.filters='pubsub.googleapis.com/subscription:resource.labels.subscription_id=monitoring.regex.full_match("us-west4.*my-team-subs.*")' \
- --monitoring.filters='compute.googleapis.com/instance/cpu:resource.labels.instance=monitoring.regex.full_match("us-west4.*my-team-subs.*")'
+ --monitoring.filters='compute.googleapis.com/instance/cpu:resource.labels.instance=monitoring.regex.full_match("us-west4.*my-team-subs.*")' \
+ --monitoring.filters='cloudsql.googleapis.com/database:resource.labels.database_id="my-test-project:my-database-name"'
 ```
 
 Using projects filter:

utils/utils.go

@@ -42,11 +42,11 @@ func NormalizeMetricName(metricName string) string {
 }
 
 func SplitExtraFilter(extraFilter string, separator string) (string, string) {
-	mPrefix := strings.Split(extraFilter, separator)
-	if mPrefix[0] == extraFilter {
+	mPrefix := strings.SplitN(extraFilter, separator, 2)
+	if len(mPrefix) != 2 {
 		return "", ""
 	}
-	return mPrefix[0], strings.Join(mPrefix[1:], "")
+	return mPrefix[0], mPrefix[1]
 }
 
 func ProjectResource(projectID string) string {

utils/utils_test.go

@@ -31,3 +31,23 @@ var _ = Describe("ProjectResource", func() {
 		Expect(ProjectResource("fake-project-1")).To(Equal("projects/fake-project-1"))
 	})
 })
+
+var _ = Describe("SplitExtraFilter", func() {
+	It("returns an empty string from incomplete filter", func() {
+		metricPrefix, filterQuery := SplitExtraFilter("This_is__a-MetricName.Example/with/no/filter", ":")
+		Expect(metricPrefix).To(Equal(""))
+		Expect(filterQuery).To(Equal(""))
+	})
+
+	It("returns a metric prefix and filter query from basic filter", func() {
+		metricPrefix, filterQuery := SplitExtraFilter("This_is__a-MetricName.Example/with:filter.name=filter_value", ":")
+		Expect(metricPrefix).To(Equal("This_is__a-MetricName.Example/with"))
+		Expect(filterQuery).To(Equal("filter.name=filter_value"))
+	})
+
+	It("returns a metric prefix and filter query filter with colon", func() {
+		metricPrefix, filterQuery := SplitExtraFilter(`This_is__a-MetricName.Example/with:filter.name="filter:value"`, ":")
+		Expect(metricPrefix).To(Equal("This_is__a-MetricName.Example/with"))
+		Expect(filterQuery).To(Equal("filter.name=\"filter:value\""))
+	})
+})