From cff2580bc6b540ff1bb9b890d9cf79c1bcc563a5 Mon Sep 17 00:00:00 2001
From: David P <daparks@mozilla.com>
Date: Fri, 16 May 2025 19:08:45 +0000
Subject: [PATCH] Bug 1966443: Use proper length for Windows clipboard elements
 r=win-reviewers,emilio,gstoll

NULLs are expected in the clipboard data.  Clipboard code tries to use
spans in a lot of places but there is a lot of old string stuff remaining
as well.

Differential Revision: https://phabricator.services.mozilla.com/D249702
---
 widget/windows/nsClipboard.cpp | 50 +++++++++++++++++++---------------
 1 file changed, 28 insertions(+), 22 deletions(-)

diff --git a/widget/windows/nsClipboard.cpp b/widget/windows/nsClipboard.cpp
index 8c53b0ae3cb6..575be7accd43 100644
--- a/widget/windows/nsClipboard.cpp
+++ b/widget/windows/nsClipboard.cpp
@@ -578,6 +578,7 @@ NS_IMETHODIMP nsClipboard::SetNativeClipboardData(
 }
 
 //-------------------------------------------------------------------------
+/* static */
 nsresult nsClipboard::GetGlobalData(HGLOBAL aHGBL, void** aData,
                                     uint32_t* aLen) {
   MOZ_CLIPBOARD_LOG("%s", __FUNCTION__);
@@ -700,6 +701,29 @@ HRESULT nsClipboard::FillSTGMedium(IDataObject* aDataObject, UINT aFormat,
 }
 
 //-------------------------------------------------------------------------
+// Get the data out of the global data handle. The size we
+// return should be the size returned from GetGlobalData(), since the
+// string returned from Windows may have nulls inserted -- it may not
+// even be null-terminated.  GetGlobalData adds bytes for null
+// termination to the buffer but they are not considered in the returned
+// byte count.  We check and skip the last counted byte if it is a null
+// since Windows also appears to add null termination.  See GetGlobalData.
+template <typename CharType>
+static nsresult GetCharDataFromGlobalData(STGMEDIUM& aStm, CharType** aData,
+                                   uint32_t* aLen) {
+  uint32_t nBytes = 0;
+  MOZ_TRY(nsClipboard::GetGlobalData(aStm.hGlobal,
+                                     reinterpret_cast<void**>(aData), &nBytes));
+  auto nChars = nBytes / sizeof(CharType);
+  if (nChars < 1) {
+    *aLen = 0;
+    return NS_OK;
+  }
+  bool hasNullTerminator = (*aData)[nChars - 1] == CharType(0);
+  *aLen = hasNullTerminator ? nBytes - sizeof(CharType) : nBytes;
+  return NS_OK;
+}
+
 // If aFormat is CF_DIBV5, aMIMEImageFormat must be a type for which we have
 // an image encoder (e.g. image/png).
 // For other values of aFormat, it is OK to pass null for aMIMEImageFormat.
@@ -764,31 +788,13 @@ nsresult nsClipboard::GetNativeDataOffClipboard(IDataObject* aDataObject,
   // compile-time-constant format indicators:
   switch (fe.cfFormat) {
     case CF_TEXT: {
-      // Get the data out of the global data handle. The size we
-      // return should not include the null because the other
-      // platforms don't use nulls, so just return the length we get
-      // back from strlen(), since we know CF_TEXT is null
-      // terminated. Recall that GetGlobalData() returns the size of
-      // the allocated buffer, not the size of the data (on 98, these
-      // are not the same) so we can't use that.
-      uint32_t allocLen = 0;
-      MOZ_TRY(GetGlobalData(stm.hGlobal, aData, &allocLen));
-      *aLen = strlen(reinterpret_cast<char*>(*aData));
-      return NS_OK;
+      return GetCharDataFromGlobalData(stm, reinterpret_cast<char**>(aData),
+                                       aLen);
     }
 
     case CF_UNICODETEXT: {
-      // Get the data out of the global data handle. The size we
-      // return should not include the null because the other
-      // platforms don't use nulls, so just return the length we get
-      // back from strlen(), since we know CF_UNICODETEXT is null
-      // terminated. Recall that GetGlobalData() returns the size of
-      // the allocated buffer, not the size of the data (on 98, these
-      // are not the same) so we can't use that.
-      uint32_t allocLen = 0;
-      MOZ_TRY(GetGlobalData(stm.hGlobal, aData, &allocLen));
-      *aLen = NS_strlen(reinterpret_cast<char16_t*>(*aData)) * 2;
-      return NS_OK;
+      return GetCharDataFromGlobalData(stm, reinterpret_cast<char16_t**>(aData),
+                                       aLen);
     }
 
     case CF_DIBV5: {