feat: readiness check (#1839)

* feat: readiness check

* fix: no need for query param

* docs: add a note

* chore: move the readyness check to its own endpoint

* docs(cr): add godoc

Co-authored-by: Joel Speed <Joel.speed@hotmail.co.uk>

pkg/middleware/readynesscheck_test.go

@@ -0,0 +1,84 @@
+package middleware
+
+import (
+	"context"
+	"errors"
+	"net/http"
+	"net/http/httptest"
+
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/ginkgo/extensions/table"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("ReadynessCheck suite", func() {
+	type requestTableInput struct {
+		readyPath        string
+		healthVerifiable Verifiable
+		requestString    string
+		expectedStatus   int
+		expectedBody     string
+	}
+
+	DescribeTable("when serving a request",
+		func(in *requestTableInput) {
+			req := httptest.NewRequest("", in.requestString, nil)
+
+			rw := httptest.NewRecorder()
+
+			handler := NewReadynessCheck(in.readyPath, in.healthVerifiable)(http.NotFoundHandler())
+			handler.ServeHTTP(rw, req)
+
+			Expect(rw.Code).To(Equal(in.expectedStatus))
+			Expect(rw.Body.String()).To(Equal(in.expectedBody))
+		},
+		Entry("when requesting the readyness check path", &requestTableInput{
+			readyPath:        "/ready",
+			healthVerifiable: &fakeVerifiable{nil},
+			requestString:    "http://example.com/ready",
+			expectedStatus:   200,
+			expectedBody:     "OK",
+		}),
+		Entry("when requesting a different path", &requestTableInput{
+			readyPath:        "/ready",
+			healthVerifiable: &fakeVerifiable{nil},
+			requestString:    "http://example.com/different",
+			expectedStatus:   404,
+			expectedBody:     "404 page not found\n",
+		}),
+		Entry("when a blank string is configured as a readyness check path and the request has no specific path", &requestTableInput{
+			readyPath:        "",
+			healthVerifiable: &fakeVerifiable{nil},
+			requestString:    "http://example.com",
+			expectedStatus:   404,
+			expectedBody:     "404 page not found\n",
+		}),
+		Entry("with full health check and without an underlying error", &requestTableInput{
+			readyPath:        "/ready",
+			healthVerifiable: &fakeVerifiable{nil},
+			requestString:    "http://example.com/ready",
+			expectedStatus:   200,
+			expectedBody:     "OK",
+		}),
+		Entry("with full health check and with an underlying error", &requestTableInput{
+			readyPath:        "/ready",
+			healthVerifiable: &fakeVerifiable{func(ctx context.Context) error { return errors.New("failed to check") }},
+			requestString:    "http://example.com/ready",
+			expectedStatus:   500,
+			expectedBody:     "error: failed to check",
+		}),
+	)
+})
+
+type fakeVerifiable struct {
+	mock func(context.Context) error
+}
+
+func (v *fakeVerifiable) VerifyConnection(ctx context.Context) error {
+	if v.mock != nil {
+		return v.mock(ctx)
+	}
+	return nil
+}
+
+var _ Verifiable = (*fakeVerifiable)(nil)