From ae02f0961141bbf7678219d638dcd6be29675116 Mon Sep 17 00:00:00 2001
From: Andras Timar <andras.timar@collabora.com>
Date: Tue, 8 Sep 2026 21:11:34 +0200
Subject: [PATCH] feat(wopi): report the file's SHA-256 in CheckFileInfo

After an upload that gets no answer, the editor has to work out whether
what is in storage is what it just sent. Without a hash to compare it
falls back on the byte count, which cannot tell our own document from
another editor's of the same length: the wrong answer either loses the
other writer's work or puts a needless conflict in front of the user.

Report the file's SHA-256 in the CheckFileInfo SHA256 field so there is
something better to compare. The field is only present when a hash is on
record; CheckFileInfo is on the document-open path and must not read a
whole file to compute one.

For it to be on record when it matters, hash the body of PutFile as it
streams past and store the result, the way the DAV endpoint stores the
checksums a sync client sends. Wrapping the stream costs no extra read,
since the bytes pass through us in any case. The scanner clears the
checksum whenever a file changes, so what we hand out is never stale: it
either describes the current contents or is absent, and setting it after
putContent() keeps it that way.

Files written by other means, or before this change, simply carry no
SHA-256 and the editor falls back as it does today.

Signed-off-by: Andras Timar <andras.timar@collabora.com>
---
 lib/Controller/WopiController.php | 76 +++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)

diff --git a/lib/Controller/WopiController.php b/lib/Controller/WopiController.php
index 77cb84e517..b9952aa425 100644
--- a/lib/Controller/WopiController.php
+++ b/lib/Controller/WopiController.php
@@ -7,6 +7,7 @@
 
 namespace OCA\Richdocuments\Controller;
 
+use OC\Files\Stream\HashWrapper;
 use OCA\Files_Versions\Versions\IVersionManager;
 use OCA\Richdocuments\AppConfig;
 use OCA\Richdocuments\AppInfo\Application;
@@ -215,6 +216,13 @@ public function checkFileInfo(
 			'ServerPrivateInfo' => [],
 		];
 
+		// Only reported when we already know it. Never hash here: CheckFileInfo
+		// is on the document-open path and the files can be large.
+		$sha256 = $this->getStoredSha256($file);
+		if ($sha256 !== null) {
+			$response['SHA256'] = $sha256;
+		}
+
 		if ($this->capabilitiesService->hasSettingIframeSupport()) {
 			$token = $this->generateSettingToken($userId);
 			if (!$isPublic) {
@@ -653,6 +661,14 @@ public function putFile(
 
 			$content = fopen('php://input', 'rb');
 
+			// Hash the body as it streams past, so the editor can later tell
+			// whether what is in storage is what it uploaded. This costs no
+			// extra read: the bytes are going through us anyway.
+			$sha256 = null;
+			$content = HashWrapper::wrap($content, 'sha256', function (string $hash) use (&$sha256): void {
+				$sha256 = $hash;
+			});
+
 			$freespace = (int)$file->getStorage()->free_space($file->getInternalPath());
 			$contentLength = (int)$this->request->getHeader('Content-Length');
 
@@ -666,6 +682,8 @@ public function putFile(
 				return new JSONResponse(['message' => 'File locked'], Http::STATUS_INTERNAL_SERVER_ERROR);
 			}
 
+			$this->storeSha256($file, $sha256);
+
 			if ($wopi->hasTemplateId()) {
 				$wopi->setTemplateId(null);
 				$this->wopiMapper->update($wopi);
@@ -898,6 +916,64 @@ private function getLock(Wopi $wopi, string $lock): JSONResponse {
 		return new JSONResponse();
 	}
 
+	/**
+	 * Remember the SHA-256 of the contents we have just written, in the same
+	 * cache field the DAV endpoint uses for the checksums a sync client sends.
+	 *
+	 * The scanner clears that field whenever a file changes, so a stored value
+	 * is never stale: it either describes the current contents or is absent.
+	 * That is what lets us hand it out again without re-reading the file.
+	 */
+	private function storeSha256(File $file, ?string $sha256): void {
+		if ($sha256 === null || $sha256 === '') {
+			return;
+		}
+
+		try {
+			// After putContent(), so the rescan that clears the field has run.
+			$file->getStorage()->getCache()->update($file->getId(), [
+				'checksum' => 'SHA256:' . $sha256,
+			]);
+		} catch (\Throwable $e) {
+			// A checksum we fail to record only costs the editor a hint.
+			$this->logger->debug('Could not store the SHA-256 of the uploaded file', ['exception' => $e]);
+		}
+	}
+
+	/**
+	 * The stored SHA-256 of this file, Base64-encoded for the WOPI SHA256
+	 * field, or null when none is on record.
+	 *
+	 * Checksums are stored as space-separated TYPE:HEX pairs, so a file may
+	 * carry an MD5 or SHA1 from a sync client and no SHA-256 at all.
+	 */
+	private function getStoredSha256(File $file): ?string {
+		try {
+			$checksums = $file->getChecksum();
+		} catch (\Throwable $e) {
+			return null;
+		}
+
+		if (!is_string($checksums) || $checksums === '') {
+			return null;
+		}
+
+		foreach (explode(' ', $checksums) as $checksum) {
+			if (stripos($checksum, 'SHA256:') !== 0) {
+				continue;
+			}
+
+			$raw = @hex2bin(substr($checksum, strlen('SHA256:')));
+			if ($raw === false || strlen($raw) !== 32) {
+				return null;
+			}
+
+			return base64_encode($raw);
+		}
+
+		return null;
+	}
+
 	/**
 	 * @throws NotFoundException
 	 * @throws GenericFileException