Bug 409500. Compute the right output length for our base64 decoding. r=jduell

nsresult

NS_DeserializeObject(const nsCSubstring& str, nsISupports** obj)

{

  // Base64 maps 3 binary bytes -> 4 ASCII bytes, so this calculation gives us

  // the right size. Compare also the comment in plbase64.h.

  PRUint32 size = (str.Length() * 3) / 4;

  // Base64 maps 3 binary bytes -> 4 ASCII bytes.  If the original byte array

  // does not have length 0 mod 3, the input is padded with zeros and the

  // output is padded with a corresponding number of trailing '=' (which are

  // then sometimes dropped).  To compute the correct length of the original

  // byte array, we have to subtract the number of trailing '=' and then

  // multiply by 3 and then divide by 4 (making sure this is an integer

  // division).

  PRUint32 size = str.Length();

  if (size > 0 && str[size-1] == '=') {

    if (size > 1 && str[size-2] == '=') {

      size -= 2;

    } else {

      size -= 1;

    }

  }

  size = (size * 3) / 4;

  char* buf = PL_Base64Decode(str.BeginReading(), str.Length(), nsnull);

  if (!buf)

    return NS_ERROR_OUT_OF_MEMORY;