Bug 328755 - Assigning a zero-length string should not alloc a buffer. r=bsmedberg

xpcom/io/Base64.cpp

@@ -209,7 +209,10 @@ EncodeInputStream(nsIInputStream *aInputStream,
   if (state.charsOnStack)
     Encode(state.c, state.charsOnStack, state.buffer);
 
-  *aDest.EndWriting() = '\0';
+  if (aDest.Length())
+    // May belong to an nsCString with an unallocated buffer, so only null
+    // terminate if there is a need to.
+    *aDest.EndWriting() = '\0';
 
   return NS_OK;
 }

xpcom/io/nsEscape.cpp

@@ -153,6 +153,13 @@ int32_t nsUnescapeCount(char * str)
     char* const pc1 = c1;
     char* const pc2 = c2;
 
+    if (!*src) {
+      // A null string was passed in.  Nothing to escape.
+      // Returns early as the string might not actually be mutable with
+      // length 0.
+      return 0;
+    }
+
     while (*src)
     {
         c1[0] = *(src+1);

xpcom/string/public/nsCharTraits.h

@@ -100,7 +100,7 @@ struct nsCharTraits<char16_t>
     typedef uint16_t  unsigned_char_type;
     typedef char      incompatible_char_type;
 
-    static char_type *sEmptyBuffer;
+    static char_type* const sEmptyBuffer;
 
     static
     void
@@ -326,7 +326,7 @@ struct nsCharTraits<char>
     typedef unsigned char  unsigned_char_type;
     typedef char16_t      incompatible_char_type;
 
-    static char_type *sEmptyBuffer;
+    static char_type* const sEmptyBuffer;
 
     static
     void

xpcom/string/src/nsSubstring.cpp

@@ -40,10 +40,12 @@ using mozilla::Atomic;
 
 // ---------------------------------------------------------------------------
 
-static char16_t gNullChar = 0;
+static const char16_t gNullChar = 0;
 
-char*      nsCharTraits<char>     ::sEmptyBuffer = (char*) &gNullChar;
-char16_t* nsCharTraits<char16_t>::sEmptyBuffer =         &gNullChar;
+char* const nsCharTraits<char>::sEmptyBuffer =
+  (char*) const_cast<char16_t*>(&gNullChar);
+char16_t* const nsCharTraits<char16_t>::sEmptyBuffer =
+  const_cast<char16_t*>(&gNullChar);
 
 // ---------------------------------------------------------------------------
 

xpcom/string/src/nsTSubstring.cpp

@@ -304,7 +304,7 @@ nsTSubstring_CharT::Assign( const char_type* data, size_type length )
 bool
 nsTSubstring_CharT::Assign( const char_type* data, size_type length, const fallible_t& )
   {
-    if (!data)
+    if (!data || length == 0)
       {
         Truncate();
         return true;