expire files on access

S3 can use lifecycle rules to delete files, but:
* files might not disappear instantly on expiration, which is fine as long
  as we can ensure that client-side they do expire on time
* it is rule-based, which might not be granular enough for our use case
  some files in a collection will expire at a set date that can be
  modified afterwards. So we can't set a rule to expire after x days
  without working around the limitation of the rules by (ab)using tags

might change my mind later, for now this fixes the files being
accessible way past their supposed expiration date.

server/files.go

@@ -152,14 +152,22 @@ func Download(ctx context.Context, input *DownloadInput) (*huma.StreamResponse,
 	if err != nil {
 		return nil, err
 	}
+	stat, err := obj.Stat()
+	if err != nil {
+		return nil, err
+	}
+
+	if stat.Expires.Unix() != 0 && stat.Expires.Before(time.Now()) {
+		go DeleteObject(ctx, input.Filename)
+		return nil, huma.Error410Gone("File expired")
+	}
 
 	return &huma.StreamResponse{
 		Body: func(ctx huma.Context) {
 			defer obj.Close()
 
 			writer := ctx.BodyWriter()
 
-			stat, err := obj.Stat()
 			filename := url.PathEscape(stat.UserMetadata["Filename"])
 			content_type := stat.UserMetadata["Type"]
 

server/s3.go

@@ -53,3 +53,13 @@ func GetFileObject(ctx context.Context, filename string) (*minio.Object, error)
 	obj, err := client.GetObject(ctx, CONFIG.S3.BucketName, filename, minio.GetObjectOptions{})
 	return obj, err
 }
+
+func DeleteObject(ctx context.Context, filename string) error {
+	client, err := getS3Client()
+	if err != nil {
+		return err
+	}
+
+	err = client.RemoveObject(ctx, CONFIG.S3.BucketName, filename, minio.RemoveObjectOptions{})
+	return err
+}