1 files changed, 53 insertions, 1 deletions

diff --git a/src/vdbemem.c b/src/vdbemem.c
index 1250eea77..07fb8feee 100644
--- a/src/vdbemem.c
+++ b/src/vdbemem.c
@@ -315,6 +315,37 @@ int sqlite3VdbeMemClearAndResize(Mem *pMem, int szNew){
 }
 
 /*
+** If pMem is already a string, detect if it is a zero-terminated
+** string, or make it into one if possible, and mark it as such.
+**
+** This is an optimization.  Correct operation continues even if
+** this routine is a no-op.
+*/
+void sqlite3VdbeMemZeroTerminateIfAble(Mem *pMem){
+  if( (pMem->flags & (MEM_Str|MEM_Term))!=MEM_Str ) return;
+  if( pMem->enc!=SQLITE_UTF8 ) return;
+  if( NEVER(pMem->z==0) ) return;
+  if( pMem->flags & MEM_Dyn ){
+    if( pMem->xDel==sqlite3_free
+     && sqlite3_msize(pMem->z) >= (u64)(pMem->n+1)
+    ){
+      pMem->z[pMem->n] = 0;
+      pMem->flags |= MEM_Term;
+      return;
+    }
+    if( pMem->xDel==(void(*)(void*))sqlite3RCStrUnref ){
+      /* Blindly assume that all RCStr objects are zero-terminated */
+      pMem->flags |= MEM_Term;
+      return;
+    }
+  }else if( pMem->szMalloc>0 && pMem->szMalloc >= pMem->n+1 ){
+    pMem->z[pMem->n] = 0;
+    pMem->flags |= MEM_Term;
+    return;
+  }
+}
+
+/*
 ** It is already known that pMem contains an unterminated string.
 ** Add the zero terminator.
 **
@@ -803,6 +834,7 @@ int sqlite3VdbeMemCast(Mem *pMem, u8 aff, u8 encoding){
       break;
     }
     default: {
+      int rc;
       assert( aff==SQLITE_AFF_TEXT );
       assert( MEM_Str==(MEM_Blob>>3) );
       pMem->flags |= (pMem->flags&MEM_Blob)>>3;
@@ -810,7 +842,9 @@ int sqlite3VdbeMemCast(Mem *pMem, u8 aff, u8 encoding){
       assert( pMem->flags & MEM_Str || pMem->db->mallocFailed );
       pMem->flags &= ~(MEM_Int|MEM_Real|MEM_IntReal|MEM_Blob|MEM_Zero);
       if( encoding!=SQLITE_UTF8 ) pMem->n &= ~1;
-      return sqlite3VdbeChangeEncoding(pMem, encoding);
+      rc = sqlite3VdbeChangeEncoding(pMem, encoding);
+      if( rc ) return rc;
+      sqlite3VdbeMemZeroTerminateIfAble(pMem);
     }
   }
   return SQLITE_OK;
@@ -1334,6 +1368,24 @@ const void *sqlite3ValueText(sqlite3_value* pVal, u8 enc){
   return valueToText(pVal, enc);
 }
 
+/* Return true if sqlit3_value object pVal is a string or blob value
+** that uses the destructor specified in the second argument.
+**
+** TODO:  Maybe someday promote this interface into a published API so
+** that third-party extensions can get access to it?
+*/
+int sqlite3ValueIsOfClass(const sqlite3_value *pVal, void(*xFree)(void*)){
+  if( ALWAYS(pVal!=0)
+   && ALWAYS((pVal->flags & (MEM_Str|MEM_Blob))!=0)
+   && (pVal->flags & MEM_Dyn)!=0
+   && pVal->xDel==xFree
+  ){
+    return 1;
+  }else{
+    return 0;
+  }
+}
+
 /*
 ** Create a new sqlite3_value object.
 */