Golang Reader from Byte Array

Introduction

In Go, a reader is an interface that allows reading a sequence of bytes. It is used extensively in I/O operations, such as reading data from files, sockets, or HTTP responses. In this tutorial, we will learn how to create a reader from a byte array, and use it to read data in memory.

Creating a Reader from Byte Array

To create a reader from a byte array, we can use the bytes.NewReader() function. This function takes a byte slice as a parameter, and returns a *bytes.Reader value which implements the io.Reader interface.

package main

import (
    "bytes"
    "fmt"
    "io"
)

func main() {
    data := []byte("Hello, World!")
    reader := bytes.NewReader(data)

    buffer := make([]byte, 5)
    for {
        n, err := reader.Read(buffer)
        if err != nil {
            if err == io.EOF {
                break
            }
            panic(err)
        }
        fmt.Print(string(buffer[:n]))
    }
}

In the example above, we have created a byte array containing the string "Hello, World!", and created a *bytes.Reader from it using the bytes.NewReader() function. We then created a buffer of length 5, and used a for loop to read data from the reader in chunks of at most 5 bytes, until we reach the end of the reader.

Conclusion

In this tutorial, we have learned how to create a reader from a byte array, and use it to read data in memory. This technique can be useful in situations where we need to manipulate data before writing it to a file or sending it over a network, or when we need to read data from a non-standard source, such as a memory-mapped file or a buffer in shared memory.