Make the API URLs relative (#72)

* Removed unused code detected by staticcheck.

* Make the default URL relative 

This is so that any paths in the API prefix URL are preserved. E.g. `url.Parse("http://127.0.0.1:9090/foo").Parse("bar")` gives `"http://127.0.0.1:9090/foo/bar"`

* Made the metadata API url relative

This is so that any paths in the API prefix URL are preserved. E.g. `url.Parse("http://127.0.0.1:9090/foo").Parse("bar")` gives `"http://127.0.0.1:9090/foo/bar"`

Author: jkohen

metadata/cache.go

@@ -44,7 +44,7 @@ type Cache struct {
 
 // DefaultEndpointPath is the default HTTP path on which Prometheus serves
 // the target metadata endpoint.
-const DefaultEndpointPath = "/api/v1/targets/metadata"
+const DefaultEndpointPath = "api/v1/targets/metadata"
 
 // The old metric type value for textparse.MetricTypeUnknown that is used in
 // Prometheus 2.4 and earlier.

targets/cache.go

@@ -27,7 +27,7 @@ import (
 	"github.com/prometheus/prometheus/pkg/labels"
 )
 
-const DefaultAPIEndpoint = "/api/v1/targets"
+const DefaultAPIEndpoint = "api/v1/targets"
 
 func cacheKey(job, instance string) string {
 	return job + "\xff" + instance