[bugfix] Set Vary header correctly on cache-control (#1988)

* [bugfix] Set Vary header correctly on cache-control

* Prefer activitypub types on AP endpoints

* use immutable on file server, vary by range

* vary auth on Accept

internal/middleware/cachecontrol.go

@@ -23,12 +23,53 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-// CacheControl returns a new gin middleware which allows callers to control cache settings on response headers.
-//
-// For directives, see https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
-func CacheControl(directives ...string) gin.HandlerFunc {
-	ccHeader := strings.Join(directives, ", ")
+type CacheControlConfig struct {
+	// Slice of Cache-Control directives, which will be
+	// joined comma-separated and served as the value of
+	// the Cache-Control header.
+	//
+	// If no directives are set, the Cache-Control header
+	// will not be sent in the response at all.
+	//
+	// For possible Cache-Control directive values, see:
+	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Cache-Control
+	Directives []string
+
+	// Slice of Vary header values, which will be joined
+	// comma-separated and served as the value of the Vary
+	// header in the response.
+	//
+	// If no Vary header values are supplied, then the
+	// Vary header will be omitted in the response.
+	//
+	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Vary
+	Vary []string
+}
+
+// CacheControl returns a new gin middleware which allows
+// routes to control cache settings on response headers.
+func CacheControl(config CacheControlConfig) gin.HandlerFunc {
+	if len(config.Directives) == 0 {
+		// No Cache-Control directives provided,
+		// return empty/stub function.
+		return func(c *gin.Context) {}
+	}
+
+	// Cache control is usually done on hot paths so
+	// parse vars outside of the returned function.
+	var (
+		ccHeader   = strings.Join(config.Directives, ", ")
+		varyHeader = strings.Join(config.Vary, ", ")
+	)
+
+	if varyHeader == "" {
+		return func(c *gin.Context) {
+			c.Header("Cache-Control", ccHeader)
+		}
+	}
+
 	return func(c *gin.Context) {
 		c.Header("Cache-Control", ccHeader)
+		c.Header("Vary", varyHeader)
 	}
 }