api: Begin implementing an API

internal/config/http.go

@@ -2,9 +2,12 @@ package config
 
 import (
 	"fmt"
+	"net/http"
 	"net/url"
 	"strings"
 
+	"github.com/FAU-CDI/wisski-distillery/internal/config/validators"
+	"github.com/tkw1536/pkglib/httpx"
 	"golang.org/x/net/idna"
 )
 
@@ -22,6 +25,30 @@ type HTTPConfig struct {
 	// It can be enabled by setting an email for certbot certificates.
 	// This email address can be configured here.
 	CertbotEmail string `yaml:"certbot_email" validate:"email"`
+
+	// API determines if the API is enabled.
+	// In a future version of the distillery, it will be enabled by default.
+	API validators.NullableBool `yaml:"api" validate:"bool" default:"false"`
+}
+
+var apiNotEnabled = httpx.Response{
+	StatusCode: http.StatusForbidden,
+	Body:       []byte(`{"message":"API is not enabled"}`),
+}
+
+func (hcfg HTTPConfig) APIDecorator(methods ...string) func(http.Handler) http.Handler {
+	methods = append(methods, "OPTIONS") // always permit the options method!
+
+	if !hcfg.API.Value {
+		return func(http.Handler) http.Handler {
+			return httpx.PermitMethods(apiNotEnabled, methods...)
+		}
+	}
+
+	// permit only the specified methods
+	return func(h http.Handler) http.Handler {
+		return httpx.PermitMethods(h, methods...)
+	}
 }
 
 // JoinPath returns the root public url joined with the provided parts.