[Haskell] Finding the length of a String in bytes

Hi there. I recently needed to add a Content-Length header to my HTTP request forged with Network.HTTP [1]. However, this needs to be the length of the body content in bytes, not characters. Without assuming the characters will all be ASCII, is there an easy way of doing this? length seems to have the correct results, but I'm uneasy about relying on this. Any comments? -- -David House, dmhouse@gmail.com