From f9e411dda80a39143502fc102604cc24a5f99c06 Mon Sep 17 00:00:00 2001
From: unknown <kate522@88.com>
Date: Thu, 27 Aug 2026 03:49:56 +0800
Subject: [PATCH] =?UTF-8?q?=E8=BF=9B=E8=A1=8C=E4=BA=86=E4=B8=80=E4=BA=9B?=
 =?UTF-8?q?=E4=BC=98=E5=8C=96?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 src/Content/Download.php | 138 +++++++++++++++++++++++----------------
 1 file changed, 82 insertions(+), 56 deletions(-)

diff --git a/src/Content/Download.php b/src/Content/Download.php
index 2f99e604..36d09d57 100644
--- a/src/Content/Download.php
+++ b/src/Content/Download.php
@@ -329,18 +329,21 @@ class Download {
         $idx = (int) $row['source_index'];
         if (empty($meta['downloads'][$idx]['url'])) $this->fail_410();
 
-        // HEAD probes validate the link but must never consume it.
-        $is_head = strtoupper((string) ($_SERVER['REQUEST_METHOD'] ?? 'GET')) === 'HEAD';
+        // Probes (HEAD requests and Speculative-Loading prefetches) validate
+        // availability but must never consume a use nor waste bandwidth.
+        $is_probe = $this->is_probe_request();
 
         $target_url = esc_url_raw((string) $meta['downloads'][$idx]['url']);
 
         // Local attachment / uploads file: stream without artificial throttling.
         $local_path = $this->resolve_local_download_path($target_url);
         if ($local_path !== '' && is_readable($local_path)) {
-            $delivered = $this->stream_local_file($local_path);
-            // Count only fully delivered bodies; aborted transfers stay reusable.
-            if ($delivered && !$is_head) {
-                $this->consume_token($row, $token);
+            $this->send_download_headers($local_path);
+            if (!$is_probe) {
+                // Count only fully delivered bodies; aborted transfers stay reusable.
+                if ($this->stream_body($local_path)) {
+                    $this->consume_token($row, $token);
+                }
             }
             exit;
         }
@@ -348,13 +351,84 @@ class Download {
         nocache_headers();
         wp_redirect($target_url, 302);
         // Remote hosts give no completion signal, so the redirect hand-off
-        // counts as delivery; HEAD probes still never consume.
-        if (!$is_head) {
+        // counts as delivery; probes still never consume.
+        if (!$is_probe) {
             $this->consume_token($row, $token);
         }
         exit;
     }
 
+    /**
+     * Requests that inspect the link instead of taking the download: plain
+     * HEAD plus browser speculative prefetches (Sec-Purpose: prefetch).
+     */
+    private function is_probe_request(): bool {
+        if (strtoupper((string) ($_SERVER['REQUEST_METHOD'] ?? 'GET')) === 'HEAD') {
+            return true;
+        }
+        $purpose = strtolower((string) ($_SERVER['HTTP_SEC_PURPOSE'] ?? ($_SERVER['HTTP_PURPOSE'] ?? '')));
+        return $purpose !== '' && str_contains($purpose, 'prefetch');
+    }
+
+    /**
+     * Emit the attachment headers for a local download.
+     */
+    private function send_download_headers(string $path): void {
+        $filename = basename($path);
+        $size = filesize($path);
+        if ($size === false) {
+            $this->fail_410();
+        }
+
+        nocache_headers();
+        header('Content-Description: File Transfer');
+        header('Content-Type: application/octet-stream');
+        header('Content-Disposition: attachment; filename="' . rawurlencode($filename) . '"');
+        header('Content-Transfer-Encoding: binary');
+        header('Content-Length: ' . (string) $size);
+    }
+
+    /**
+     * Stream the local file body after its headers. Returns true only when
+     * every byte was flushed to the client.
+     */
+    private function stream_body(string $path): bool {
+        $size = filesize($path);
+        if ($size === false) {
+            $this->fail_410();
+        }
+
+        $chunk = 1024 * 64; // 64KB
+
+        $fh = fopen($path, 'rb');
+        if (!$fh) {
+            $this->fail_410();
+        }
+        // Disable output compression so Content-Length remains accurate.
+        if (function_exists('apache_setenv')) {
+            @apache_setenv('no-gzip', '1');
+        }
+        @ini_set('zlib.output_compression', 'Off');
+        while (!feof($fh)) {
+            if (connection_aborted()) {
+                fclose($fh);
+                return false;
+            }
+            $buf = fread($fh, $chunk);
+            if ($buf === false) {
+                fclose($fh);
+                return false;
+            }
+            echo $buf;
+            if (function_exists('flush')) {
+                flush();
+            }
+        }
+        fclose($fh);
+
+        return !connection_aborted();
+    }
+
     /**
      * Map a site-local URL to a filesystem path under uploads (or ABSPATH).
      */
@@ -388,54 +462,6 @@ class Download {
         return '';
     }
 
-    /**
-     * Stream a local file. Returns true only when the body was sent in full.
-     */
-    private function stream_local_file(string $path): bool {
-        $filename = basename($path);
-        $size = filesize($path);
-        if ($size === false) {
-            $this->fail_410();
-        }
-
-        nocache_headers();
-        header('Content-Description: File Transfer');
-        header('Content-Type: application/octet-stream');
-        header('Content-Disposition: attachment; filename="' . rawurlencode($filename) . '"');
-        header('Content-Transfer-Encoding: binary');
-        header('Content-Length: ' . (string) $size);
-
-        $chunk = 1024 * 64; // 64KB
-
-        $fh = fopen($path, 'rb');
-        if (!$fh) {
-            $this->fail_410();
-        }
-        // Disable output compression so Content-Length remains accurate.
-        if (function_exists('apache_setenv')) {
-            @apache_setenv('no-gzip', '1');
-        }
-        @ini_set('zlib.output_compression', 'Off');
-        while (!feof($fh)) {
-            if (connection_aborted()) {
-                fclose($fh);
-                return false;
-            }
-            $buf = fread($fh, $chunk);
-            if ($buf === false) {
-                fclose($fh);
-                return false;
-            }
-            echo $buf;
-            if (function_exists('flush')) {
-                flush();
-            }
-        }
-        fclose($fh);
-
-        return !connection_aborted();
-    }
-
     /**
      * Count a delivered download. The guard caps concurrent finishers at
      * max_uses instead of overshooting the counter.