I want to remove a base64 header from a base64 data URI, for example given:

data:video/mp4;base64,TWFuIGlzIGRpc3Rpbmd1aXNoZWQsIG5vdCBvbmx5IGJ5IGhpcyByZWFzb24sIGJ1dCBieSB0aGlz

I want to remove the prefix:

data:video/mp4;base64,

The problem is that I receive different types of video, so I don't know how to reliably remove this header in any form it may present itself. Can someone help?

CodePudding user response：

Cut the string at the comma to get the base64 data:

func decode(uri string) ([]byte, error) {
  if !strings.HasPrefix(uri, "data:") {
    return nil, errors.New("not a data uri")
  }
  _, data, ok := strings.Cut(uri, ",")
  if !ok {
    return nil, errors.New("not a data uri")
  }
  return base64.URLEncoding.DecodeString(data)
}

The strings.Cut function was added in Go 1.18. Use strings.Index to cut on comma in earlier versions of Go:

func decode(uri string) ([]byte, error) {
    if !strings.HasPrefix(uri, "data:") {
        return nil, errors.New("not a data uri")
    }
    i := strings.Index(uri, ",")
    if i < 0 {
        return nil, errors.New("not a data uri")
    }
    return base64.URLEncoding.DecodeString(uri[i 1:])
}