Adding first version of HealthCheck

Added a expvar style handler for the debug http server to allow health checks (/debug/health).

Signed-off-by: Diogo Monica <diogo@docker.com>

health/api/api_test.go

@@ -0,0 +1,86 @@
+package api
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/docker/distribution/health"
+)
+
+// TestGETDownHandlerDoesNotChangeStatus ensures that calling the endpoint
+// /debug/health/down with METHOD GET returns a 404
+func TestGETDownHandlerDoesNotChangeStatus(t *testing.T) {
+	recorder := httptest.NewRecorder()
+
+	req, err := http.NewRequest("GET", "https://fakeurl.com/debug/health/down", nil)
+	if err != nil {
+		t.Errorf("Failed to create request.")
+	}
+
+	DownHandler(recorder, req)
+
+	if recorder.Code != 404 {
+		t.Errorf("Did not get a 404.")
+	}
+}
+
+// TestGETUpHandlerDoesNotChangeStatus ensures that calling the endpoint
+// /debug/health/down with METHOD GET returns a 404
+func TestGETUpHandlerDoesNotChangeStatus(t *testing.T) {
+	recorder := httptest.NewRecorder()
+
+	req, err := http.NewRequest("GET", "https://fakeurl.com/debug/health/up", nil)
+	if err != nil {
+		t.Errorf("Failed to create request.")
+	}
+
+	DownHandler(recorder, req)
+
+	if recorder.Code != 404 {
+		t.Errorf("Did not get a 404.")
+	}
+}
+
+// TestPOSTDownHandlerChangeStatus ensures the endpoint /debug/health/down changes
+// the status code of the response to 503
+// This test is order dependent, and should come before TestPOSTUpHandlerChangeStatus
+func TestPOSTDownHandlerChangeStatus(t *testing.T) {
+	recorder := httptest.NewRecorder()
+
+	req, err := http.NewRequest("POST", "https://fakeurl.com/debug/health/down", nil)
+	if err != nil {
+		t.Errorf("Failed to create request.")
+	}
+
+	DownHandler(recorder, req)
+
+	if recorder.Code != 200 {
+		t.Errorf("Did not get a 200.")
+	}
+
+	if len(health.CheckStatus()) != 1 {
+		t.Errorf("DownHandler didn't add an error check.")
+	}
+}
+
+// TestPOSTUpHandlerChangeStatus ensures the endpoint /debug/health/up changes
+// the status code of the response to 200
+func TestPOSTUpHandlerChangeStatus(t *testing.T) {
+	recorder := httptest.NewRecorder()
+
+	req, err := http.NewRequest("POST", "https://fakeurl.com/debug/health/up", nil)
+	if err != nil {
+		t.Errorf("Failed to create request.")
+	}
+
+	UpHandler(recorder, req)
+
+	if recorder.Code != 200 {
+		t.Errorf("Did not get a 200.")
+	}
+
+	if len(health.CheckStatus()) != 0 {
+		t.Errorf("UpHandler didn't remove the error check.")
+	}
+}