ioutil.ReadFile

// ReadFile reads the file named by filename and returns the contents.
// A successful call returns err == nil, not err == EOF. Because ReadFile
// reads the whole file, it does not treat an EOF from Read as an error
// to be reported.
func ReadFile(filename string) ([]byte, error) {
    f, err := os.Open(filename)
    if err != nil {
        return nil, err
    }
    defer f.Close()
    // It's a good but not certain bet that FileInfo will tell us exactly how much to
    // read, so let's try it but be prepared for the answer to be wrong.
    var n int64 = bytes.MinRead

    if fi, err := f.Stat(); err == nil {
        // As initial capacity for readAll, use Size + a little extra in case Size
        // is zero, and to avoid another allocation after Read has filled the
        // buffer. The readAll call will read into its allocated internal buffer
        // cheaply. If the size was wrong, we'll either waste some space off the end
        // or reallocate as needed, but in the overwhelmingly common case we'll get
        // it just right.
        if size := fi.Size() + bytes.MinRead; size > n {
            n = size
        }
    }
    return readAll(f, n)
}