Add HealthCheck middleware

pkg/middleware/healthcheck.go

@@ -0,0 +1,48 @@
+package middleware
+
+import (
+	"fmt"
+	"net/http"
+
+	"github.com/justinas/alice"
+)
+
+func NewHealthCheck(paths, userAgents []string) alice.Constructor {
+	return func(next http.Handler) http.Handler {
+		return healthCheck(paths, userAgents, next)
+	}
+}
+
+func healthCheck(paths, userAgents []string, next http.Handler) http.Handler {
+	// Use a map as a set to check health check paths
+	pathSet := make(map[string]struct{})
+	for _, path := range paths {
+		pathSet[path] = struct{}{}
+	}
+
+	// Use a map as a set to check health check paths
+	userAgentSet := make(map[string]struct{})
+	for _, userAgent := range userAgents {
+		userAgentSet[userAgent] = struct{}{}
+	}
+
+	return http.HandlerFunc(func(rw http.ResponseWriter, req *http.Request) {
+		if isHealthCheckRequest(pathSet, userAgentSet, req) {
+			rw.WriteHeader(http.StatusOK)
+			fmt.Fprintf(rw, "OK")
+			return
+		}
+
+		next.ServeHTTP(rw, req)
+	})
+}
+
+func isHealthCheckRequest(paths, userAgents map[string]struct{}, req *http.Request) bool {
+	if _, ok := paths[req.URL.EscapedPath()]; ok {
+		return true
+	}
+	if _, ok := userAgents[req.Header.Get("User-Agent")]; ok {
+		return true
+	}
+	return false
+}