feat(activesync): force Sync TruncationSize override

doc/clients.md

@@ -77,9 +77,9 @@ and a `BodyPreference` **without** `TruncationSize` (full body). Horde
 responds with the complete body and no `Truncated` flag.
 
 **Implication:** Nine already limits Sync payload itself and can repair
-truncation on demand. A server-side maximum truncation cap is unnecessary for
-Nine; if one were applied, Nine would still recover via the button (provided
-ItemOperations Fetch remains uncapped).
+truncation on demand. A server-side forced Sync truncation size is
+unnecessary for Nine when left at 0; when set, Nine can still recover via
+ItemOperations Fetch (which remains uncapped).
 
 ## iOS Mail
 
@@ -110,7 +110,9 @@ rather than a single byte count.
 
 - Prefer leaving Sync body size to the client unless you have a measured
   bandwidth reason and understand which devices you serve.
-- Capping Sync truncation helps bandwidth only for clients that request large
-  bodies; it permanently harms Gmail users; Nine and iOS can recover.
+- Forcing a low Sync truncation size saves bandwidth for clients that
+  re-fetch (Nine, iOS); forcing a high value can reduce permanent clipping
+  on Gmail, which never re-fetches. See forcetruncationsize in Horde
+  configuration.
 - Full-body-on-demand paths (ItemOperations mailbox Fetch) should stay
   uncapped so well-behaved clients can complete truncated messages.

lib/Horde/ActiveSync.php

@@ -1,3 +1,3 @@
 <?php
 
 /**
@@ -789,7 +789,7 @@
 
         // Autodiscovery handles authentication on it's own.
         if ($cmd == 'Autodiscover') {
             $request = new Horde_ActiveSync_Request_Autodiscover($this, new Horde_ActiveSync_Device($this->_state));
 
             if (!empty(self::$_logger)) {
                 $request->setLogger(self::$_logger);
@@ -1127,7 +1127,7 @@
      */
     public function getSupportedCommands()
     {
         switch ($this->_maxVersion) {
             case self::VERSION_TWOFIVE:
                 return 'Sync,SendMail,SmartForward,SmartReply,GetAttachment,GetHierarchy,CreateCollection,DeleteCollection,MoveCollection,FolderSync,FolderCreate,FolderDelete,FolderUpdate,MoveItems,GetItemEstimate,MeetingResponse,ResolveRecipients,ValidateCert,Provision,Search,Ping';
 
@@ -1357,4 +1357,104 @@
         }
     }
 
+    /**
+     * Resolve activesync/sync forcetruncationsize from sync config.
+     *
+     * Falls back to deprecated maximumtruncationsize when the renamed key
+     * is not present (horde/base#143 installs).
+     *
+     * @author Torben Dannhauer <torben@dannhauer.de>
+     *
+     * @param array $syncConfig  activesync/sync settings from Horde config.
+     *
+     * @return integer  Forced TruncationSize in bytes; 0 = honor client.
+     */
+    public static function getForcedTruncationSize(array $syncConfig)
+    {
+        if (array_key_exists('forcetruncationsize', $syncConfig)) {
+            return (int)$syncConfig['forcetruncationsize'];
+        }
+
+        return (int)($syncConfig['maximumtruncationsize'] ?? 0);
+    }
+
+    /**
+     * Apply a server-forced truncation size, overriding the client value.
+     *
+     * When $forced is positive, the client-requested size is replaced
+     * whether it is larger or smaller. A value of 0 (or less) leaves the
+     * client value unchanged.
+     *
+     * @author Torben Dannhauer <torben@dannhauer.de>
+     *
+     * @param integer|false|null $size    Client size in bytes, or false/null
+     *                                    for unlimited / no truncation.
+     * @param integer $forced              Server override in bytes; 0 = off.
+     *
+     * @return integer|false|null  The effective truncation size.
+     */
+    public static function forceTruncationSize($size, $forced)
+    {
+        $forced = (int)$forced;
+        if ($forced <= 0) {
+            return $size;
+        }
+
+        return $forced;
+    }
+
+    /**
+     * Apply activesync/sync/forcetruncationsize to collection/options data.
+     *
+     * Mutates bodyprefs, bodypartprefs, truncation, and mimetruncation in
+     * place when a positive forced size is configured. ItemOperations Fetch
+     * is not affected.
+     *
+     * @author Torben Dannhauer <torben@dannhauer.de>
+     *
+     * @param array $options   Sync/collection options (by reference).
+     * @param integer $forced  Forced TruncationSize in bytes; 0 = honor client.
+     */
+    public static function applyForcedTruncationSize(array &$options, $forced)
+    {
+        $forced = (int)$forced;
+        if ($forced <= 0) {
+            return;
+        }
+
+        if (!empty($options['bodyprefs']) && is_array($options['bodyprefs'])) {
+            foreach ($options['bodyprefs'] as &$pref) {
+                if (!is_array($pref)) {
+                    continue;
+                }
+                $pref['truncationsize'] = self::forceTruncationSize(
+                    $pref['truncationsize'] ?? 0,
+                    $forced
+                );
+            }
+            unset($pref);
+        }
+
+        if (!empty($options['bodypartprefs']) && is_array($options['bodypartprefs'])) {
+            $options['bodypartprefs']['truncationsize'] = self::forceTruncationSize(
+                $options['bodypartprefs']['truncationsize'] ?? 0,
+                $forced
+            );
+        }
+
+        if (array_key_exists('mimetruncation', $options)) {
+            $options['mimetruncation'] = self::forceTruncationSize(
+                $options['mimetruncation'],
+                $forced
+            );
+        }
+
+        if (array_key_exists('truncation', $options)) {
+            $options['truncation'] = self::forceTruncationSize(
+                $options['truncation'],
+                $forced
+            );
+        }
+    }
+
 }

lib/Horde/ActiveSync/Request/Sync.php

@@ -1,3 +1,3 @@
 <?php
 
 /**
@@ -431,6 +431,13 @@
             $changecount = 0;
             $forceChanges = false;
 
+            // Force Sync body truncation only (not ItemOperations Fetch).
+            // Covers partial Sync where Options were restored from SyncCache.
+            Horde_ActiveSync::applyForcedTruncationSize(
+                $collection,
+                Horde_ActiveSync::getForcedTruncationSize($syncSettings)
+            );
+
             if ($over_window || $cnt_global > $this->_collections->getDefaultWindowSize()) {
                 // Client-sent commands must still be imported (matching the
                 // non-streaming flow, where imports happen during parsing
@@ -1232,7 +1239,6 @@
         ));
     }
 
-
     /**
      * Import client-sent Sync commands that were queued during request
      * parsing (streaming only).
@@ -1314,6 +1320,7 @@
             $count += count($deferred['removes']);
             $keepAlives += $this->_emitKeepAlive();
         }
+
         // Orphans may have been queued without a ServerEntryId; resolve them
         // against a single successful co-batched Add before importing.
         if (!empty($deferred['orphan_instanceid_removes'])) {
@@ -2069,6 +2076,12 @@
             return;
         }
 
+        // Optional server override for BodyPreference / MIMETruncation (0 = off).
+        Horde_ActiveSync::applyForcedTruncationSize(
+            $options,
+            Horde_ActiveSync::getForcedTruncationSize($this->_driver->getSyncConfig())
+        );
+
         $collection = array_merge($collection, $options);
     }
 

test/unit/Horde/ActiveSync/TruncationCapTest.php

@@ -0,0 +1,95 @@
+<?php
+
+/**
+ * Copyright 2026 The Horde Project (http://www.horde.org/)
+ *
+ * @author Torben Dannhauer <torben@dannhauer.de>
+ * @category Horde
+ * @copyright 2026 The Horde Project
+ * @license http://www.horde.org/licenses/lgpl21 LGPL 2.1
+ * @package ActiveSync
+ */
+
+namespace Horde\ActiveSync;
+
+use Horde_ActiveSync;
+use PHPUnit\Framework\Attributes\CoversNothing;
+use PHPUnit\Framework\TestCase;
+
+#[CoversNothing]
+class TruncationCapTest extends TestCase
+{
+    public function testForceDisabledLeavesClientValue()
+    {
+        $this->assertSame(200000, Horde_ActiveSync::forceTruncationSize(200000, 0));
+        $this->assertSame(false, Horde_ActiveSync::forceTruncationSize(false, 0));
+        $this->assertSame(500, Horde_ActiveSync::forceTruncationSize(500, 0));
+    }
+
+    public function testForceOverridesLargerClientBodyPreference()
+    {
+        $this->assertSame(5000, Horde_ActiveSync::forceTruncationSize(200000, 5000));
+    }
+
+    public function testForceOverridesSmallerClientBodyPreference()
+    {
+        $this->assertSame(5000, Horde_ActiveSync::forceTruncationSize(500, 5000));
+    }
+
+    public function testForceOverridesUnlimitedClientBodyPreference()
+    {
+        $this->assertSame(5000, Horde_ActiveSync::forceTruncationSize(0, 5000));
+        $this->assertSame(5000, Horde_ActiveSync::forceTruncationSize(null, 5000));
+        $this->assertSame(5000, Horde_ActiveSync::forceTruncationSize(false, 5000));
+    }
+
+    public function testGetForcedTruncationSizePrefersNewKey()
+    {
+        $this->assertSame(
+            5000,
+            Horde_ActiveSync::getForcedTruncationSize([
+                'forcetruncationsize' => 5000,
+                'maximumtruncationsize' => 500,
+            ])
+        );
+    }
+
+    public function testGetForcedTruncationSizeFallsBackToDeprecatedKey()
+    {
+        $this->assertSame(
+            500,
+            Horde_ActiveSync::getForcedTruncationSize([
+                'maximumtruncationsize' => 500,
+            ])
+        );
+    }
+
+    public function testApplyForcedTruncationSizeToOptions()
+    {
+        $options = [
+            'bodyprefs' => [
+                Horde_ActiveSync::BODYPREF_TYPE_HTML => [
+                    'type' => Horde_ActiveSync::BODYPREF_TYPE_HTML,
+                    'truncationsize' => 200000,
+                ],
+                Horde_ActiveSync::BODYPREF_TYPE_PLAIN => [
+                    'type' => Horde_ActiveSync::BODYPREF_TYPE_PLAIN,
+                    'truncationsize' => 500,
+                ],
+            ],
+            'mimetruncation' => false,
+            'truncation' => 51200,
+        ];
+
+        Horde_ActiveSync::applyForcedTruncationSize($options, 0);
+        $this->assertSame(200000, $options['bodyprefs'][Horde_ActiveSync::BODYPREF_TYPE_HTML]['truncationsize']);
+        $this->assertSame(500, $options['bodyprefs'][Horde_ActiveSync::BODYPREF_TYPE_PLAIN]['truncationsize']);
+        $this->assertSame(false, $options['mimetruncation']);
+
+        Horde_ActiveSync::applyForcedTruncationSize($options, 5000);
+        $this->assertSame(5000, $options['bodyprefs'][Horde_ActiveSync::BODYPREF_TYPE_HTML]['truncationsize']);
+        $this->assertSame(5000, $options['bodyprefs'][Horde_ActiveSync::BODYPREF_TYPE_PLAIN]['truncationsize']);
+        $this->assertSame(5000, $options['mimetruncation']);
+        $this->assertSame(5000, $options['truncation']);
+    }
+}