Golang中二进制字节数组的终止指示符？

In Golang if I have a byte array of binary data how do I determine the termination of actual data if it is in a larger array. For example if I do the following, reading a file when it is plain text:

    chunk := make([]byte, 1024)
..read some data into the chunk but only 10 bytes are filled from the file...

I can then determine the actual size of the data by doing the following:

n := bytes.IndexByte(chunk, 0)

When it is plain text n will give me the end of the actual data - how do I do that if the data is binary?

io.Reader's Read function returns the number of bytes read.

You can then create a sub-slice of that size. For example:

data := make([]byte,1024)
n, err := reader.Read(arr)
if err != nil {
    // do something with error
} else {
    rightSized := data[:n] 
    // rightSized is []byte of N length now and shares the underlying 
    // backing array so it's both space and time efficient
    // this will contain whatever was read from the reader
}