[bugfix] Set cache-control max-age dynamically for s3 (#1510)

* [bugfix] set cache-control max-age dynamically for s3

* woops

* double whoops

* time until, thank you linter, bless you, you're the best, no matter what kim says

* aa

internal/api/fileserver.go

@@ -31,31 +31,25 @@ type Fileserver struct {
 	fileserver *fileserver.Module
 }
 
-// maxAge returns an appropriate max-age value for the
-// storage method that's being used.
-//
-// The default max-age is very long to reflect that we
-// never host different files at the same URL (since
-// ULIDs are generated per piece of media), so we can
-// easily prevent clients having to fetch files repeatedly.
-//
-// If we're using non-proxying s3, however, the max age is
-// significantly shorter, to ensure that clients don't
-// cache redirect responses to expired pre-signed URLs.
-func maxAge() string {
-	if config.GetStorageBackend() == "s3" && !config.GetStorageS3Proxy() {
-		return "max-age=86400" // 24h
-	}
-
-	return "max-age=604800" // 7d
-}
-
 func (f *Fileserver) Route(r router.Router, m ...gin.HandlerFunc) {
 	fileserverGroup := r.AttachGroup("fileserver")
 
-	// attach middlewares appropriate for this group
+	// Attach middlewares appropriate for this group.
 	fileserverGroup.Use(m...)
-	fileserverGroup.Use(middleware.CacheControl("private", maxAge()))
+	// If we're using local storage or proxying s3, we can set a
+	// long max-age on all file requests to reflect that we
+	// never host different files at the same URL (since
+	// ULIDs are generated per piece of media), so we can
+	// easily prevent clients having to fetch files repeatedly.
+	//
+	// If we *are* using non-proxying s3, however, the max age
+	// must be set dynamically within the request handler,
+	// based on how long the signed URL has left to live before
+	// it expires. This ensures that clients won't cache expired
+	// links. This is done within fileserver/servefile.go.
+	if config.GetStorageBackend() == "local" || config.GetStorageS3Proxy() {
+		fileserverGroup.Use(middleware.CacheControl("private", "max-age=604800")) // 7d
+	}
 
 	f.fileserver.Route(fileserverGroup.Handle)
 }

internal/api/fileserver/servefile.go

@@ -24,6 +24,7 @@ import (
 	"net/http"
 	"strconv"
 	"strings"
+	"time"
 
 	"codeberg.org/gruf/go-fastcopy"
 	"github.com/gin-gonic/gin"
@@ -89,6 +90,10 @@ func (m *Module) ServeFile(c *gin.Context) {
 
 	if content.URL != nil {
 		// This is a non-local, non-proxied S3 file we're redirecting to.
+		// Derive the max-age value from how long the link has left until
+		// it expires.
+		maxAge := int(time.Until(content.URL.Expiry).Seconds())
+		c.Header("Cache-Control", "private,max-age="+strconv.Itoa(maxAge))
 		c.Redirect(http.StatusFound, content.URL.String())
 		return
 	}

internal/api/model/content.go

@@ -20,8 +20,9 @@ package model
 
 import (
 	"io"
-	"net/url"
 	"time"
+
+	"github.com/superseriousbusiness/gotosocial/internal/storage"
 )
 
 // Content wraps everything needed to serve a blob of content (some kind of media) through the API.
@@ -35,7 +36,7 @@ type Content struct {
 	// Actual content
 	Content io.ReadCloser
 	// Resource URL to forward to if the file can be fetched from the storage directly (e.g signed S3 URL)
-	URL *url.URL
+	URL *storage.PresignedURL
 }
 
 // GetContentRequestForm describes a piece of content desired by the caller of the fileserver API.

internal/storage/storage.go

@@ -41,6 +41,13 @@ const (
 	urlCacheExpiryFrequency = time.Minute * 5
 )
 
+// PresignedURL represents a pre signed S3 URL with
+// an expiry time.
+type PresignedURL struct {
+	*url.URL
+	Expiry time.Time // link expires at this time
+}
+
 // ErrAlreadyExists is a ptr to underlying storage.ErrAlreadyExists,
 // to put the related errors in the same package as our storage wrapper.
 var ErrAlreadyExists = storage.ErrAlreadyExists
@@ -54,11 +61,11 @@ type Driver struct {
 	// S3-only parameters
 	Proxy          bool
 	Bucket         string
-	PresignedCache *ttl.Cache[string, *url.URL]
+	PresignedCache *ttl.Cache[string, PresignedURL]
 }
 
 // URL will return a presigned GET object URL, but only if running on S3 storage with proxying disabled.
-func (d *Driver) URL(ctx context.Context, key string) *url.URL {
+func (d *Driver) URL(ctx context.Context, key string) *PresignedURL {
 	// Check whether S3 *without* proxying is enabled
 	s3, ok := d.Storage.(*storage.S3Storage)
 	if !ok || d.Proxy {
@@ -72,7 +79,7 @@ func (d *Driver) URL(ctx context.Context, key string) *url.URL {
 	d.PresignedCache.Unlock()
 
 	if ok {
-		return e.Value
+		return &e.Value
 	}
 
 	u, err := s3.Client().PresignedGetObject(ctx, d.Bucket, key, urlCacheTTL, url.Values{
@@ -82,8 +89,14 @@ func (d *Driver) URL(ctx context.Context, key string) *url.URL {
 		// If URL request fails, fallback is to fetch the file. So ignore the error here
 		return nil
 	}
-	d.PresignedCache.Set(key, u)
+
-	return u
+	psu := PresignedURL{
+		URL:    u,
+		Expiry: time.Now().Add(urlCacheTTL), // link expires in 24h time
+	}
+
+	d.PresignedCache.Set(key, psu)
+	return &psu
 }
 
 func AutoConfig() (*Driver, error) {
@@ -151,7 +164,7 @@ func NewS3Storage() (*Driver, error) {
 	}
 
 	// ttl should be lower than the expiry used by S3 to avoid serving invalid URLs
-	presignedCache := ttl.New[string, *url.URL](0, 1000, urlCacheTTL-urlCacheExpiryFrequency)
+	presignedCache := ttl.New[string, PresignedURL](0, 1000, urlCacheTTL-urlCacheExpiryFrequency)
 	presignedCache.Start(urlCacheExpiryFrequency)
 
 	return &Driver{