How to encode and decode data with variable-length encoding (e.g., varint) in Go?

In Go, you can encode and decode data with variable-length encoding, such as varint, using the encoding/binary package.

To encode an integer using varint encoding, you can use binary.Write function with a binary.VarintWriter:

package main

import (
	"encoding/binary"
	"fmt"
	"os"
)

func main() {
	num := 150

	// Encode the number using varint encoding
	buff := make([]byte, binary.MaxVarintLen64)
	n := binary.PutVarint(buff, int64(num))

	// Write the encoded bytes to a file
	file, err := os.Create("encoded_data")
	if err != nil {
		fmt.Println("Error creating file:", err)
		return
	}
	defer file.Close()

	file.Write(buff[:n])
	fmt.Println("Number encoded and written to file")
}

To decode the encoded data back to the original integer, you can use binary.Read function with a binary.VarintReader:

package main

import (
	"encoding/binary"
	"fmt"
	"os"
)

func main() {
	// Read the encoded varint bytes from file
	file, err := os.Open("encoded_data")
	if err != nil {
		fmt.Println("Error opening file:", err)
		return
	}
	defer file.Close()

	buff := make([]byte, binary.MaxVarintLen64)
	_, err = file.Read(buff)
	if err != nil {
		fmt.Println("Error reading file:", err)
		return
	}

	// Decode the varint bytes back to the original number
	num, bytesRead := binary.Varint(buff)
	if bytesRead <= 0 {
		fmt.Println("Error decoding varint")
		return
	}

	fmt.Println("Decoded number:", num)
}

Make sure to change the file name in both code snippets to match the file where you want to read/write the encoded varint data.