Reading specific number of bytes from a buffered r

Question

I am aware of the specific function in golang from the bufio package.

func (b *Reader) Peek(n int) ([]byte, error)

Peek returns the next n bytes without advancing the reader. The bytes stop being valid at the next read call. If Peek returns fewer than n bytes, it also returns an error explaining why the read is short. The error is ErrBufferFull if n is larger than b's buffer size.

I need to be able to read a specific number of bytes from a Reader that will advance the reader. Basically, identical to the function above, but it advances the reader. Does anybody know how to accomplish this?

Answer 1

To do this you just need to create a byte slice and read the data into this slice with

n := 512
buff := make([]byte, n)
fs.Read(buff)  // fs is your reader. Can be like this fs, _ := os.Open('file')

---

func (b *Reader) Read(p []byte) (n int, err error)

Read reads data into p. It returns the number of bytes read into p. The bytes are taken from at most one Read on the underlying Reader, hence n may be less than len(p)

Answer 2

Note that the bufio.Read method calls the underlying io.Read at most once, meaning that it can return n < len(p), without reaching EOF. If you want to read exactly len(p) bytes or fail with an error, you can use io.ReadFull like this:

n, err := io.ReadFull(reader, p)

This works even if the reader is buffered.

Answer 3

I am prefering Read() especially if you are going to read any type of files and it could be also useful in sending data in chunks, below is an example to show how it is used

fs, err := os.Open("fileName"); 

if err != nil{
    fmt.Println("error reading file")
    return
}

defer fs.Close()

reader := bufio.NewReader(fs)

buf := make([]byte, 1024)

for{
    v, _ := reader.Read(buf) //ReadString and ReadLine() also applicable or alternative

    if v == 0{
        return
    }
    //in case it is a string file, you could check its content here...
    fmt.Print(string(buf))
}

Answer 4

Pass a n-bytes sized buffer to the reader.

Answer 5

func (b *Reader) Read(p []byte) (n int, err error)

http://golang.org/pkg/bufio/#Reader.Read

The number of bytes read will be limited to len(p)