BufferWriter.go

package main

import (
	"log"
	"os"
	"bufio"
)

func main() {
	// Open file for writing
	file, err := os.OpenFile("test.txt", os.O_WRONLY, 0666)
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()

	// Create a buffered writer from the file
	bufferedWriter := bufio.NewWriter(file)

	// Write bytes to buffer
	bytesWritten, err := bufferedWriter.Write(
		[]byte{65, 66, 67},
	)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Bytes written: %d\n", bytesWritten)

	// Write string to buffer
	// Also available are WriteRune() and WriteByte()
	bytesWritten, err = bufferedWriter.WriteString(
		"Buffered string\n",
	)
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Bytes written: %d\n", bytesWritten)

	// Check how much is stored in buffer waiting
	unflushedBufferSize := bufferedWriter.Buffered()
	log.Printf("Bytes buffered: %d\n", unflushedBufferSize)

	// See how much buffer is available
	bytesAvailable := bufferedWriter.Available()
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Available buffer: %d\n", bytesAvailable)

	// Write memory buffer to disk
	bufferedWriter.Flush()

	// Revert any changes done to buffer that have
	// not yet been written to file with Flush()
	// We just flushed, so there are no changes to revert
	// The writer that you pass as an argument
	// is where the buffer will output to, if you want
	// to change to a new writer
	bufferedWriter.Reset(bufferedWriter)

	// See how much buffer is available
	bytesAvailable = bufferedWriter.Available()
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Available buffer: %d\n", bytesAvailable)

	// Resize buffer. The first argument is a writer
	// where the buffer should output to. In this case
	// we are using the same buffer. If we chose a number
	// that was smaller than the existing buffer, like 10
	// we would not get back a buffer of size 10, we will
	// get back a buffer the size of the original since
	// it was already large enough (default 4096)
	bufferedWriter = bufio.NewWriterSize(
		bufferedWriter,
		8000,
	)

	// Check available buffer size after resizing
	bytesAvailable = bufferedWriter.Available()
	if err != nil {
		log.Fatal(err)
	}
	log.Printf("Available buffer: %d\n", bytesAvailable)
}