api: Begin implementing an API

internal/config/config.yml

@@ -39,6 +39,10 @@ http:
   # This email address can be configured here. 
   certbot_email: null
 
+  # Enable or Disable the HTTP API.
+  # In the future, it will be enabled by default, but at this point it is not.
+  api: null
+
 # Configuration for the (public) homepage of the distillery.
 home:
   # the title of the distillery to be set

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.

internal/config/validators/bool.go

@@ -8,13 +8,13 @@ import (
 
 // NullableBool represents a bool that can be null
 type NullableBool struct {
-	Null, Value bool
+	Set, Value bool
 }
 
 func (nb *NullableBool) UnmarshalYAML(value *yaml.Node) error {
-	nb.Null = false
+	nb.Set = true
 	if err := value.Decode(&nb.Value); err != nil {
-		nb.Null = true
+		nb.Set = false
 		nb.Value = false
 	}
 
@@ -22,19 +22,19 @@ func (nb *NullableBool) UnmarshalYAML(value *yaml.Node) error {
 }
 
 func (nb NullableBool) MarshalYAML() (interface{}, error) {
-	if nb.Null {
+	if !nb.Set {
 		return nil, nil
 	}
 	return nb.Value, nil
 }
 
 func ValidateBool(value *NullableBool, dflt string) (err error) {
-	if value.Null {
+	if !value.Set {
 		res, err := strconv.ParseBool(dflt)
 		if err != nil {
 			return err
 		}
-		value.Null = false
+		value.Set = true
 		value.Value = res
 	}
 	return err