redis.go

package main

/**
 * This is a little too permissive (and hacked together), but it illustrates
 * the point of encoding a bufio.Scanner that is stateful, so that it can
 * parse the redis protocol.
 */

import (
	"bufio"
	"bytes"
	"fmt"
	"strconv"
)

const (
	Marker = iota
	Int
	Content
)

func newScanFunc() bufio.SplitFunc {
	expected := Marker
	var tmp int64 = -1
	size := -1
	dollar := false
	return func(data []byte, atEOF bool) (advance int, token []byte, err error) {
		switch expected {
		case Marker:
			fmt.Println("parsing marker")
			advance, token, err = bufio.ScanBytes(data, atEOF)
			expected = Int
			dollar = !atEOF && data[0] == '$'
		case Int:
			fmt.Println("parsing int")
			advance, token, err = bufio.ScanWords(data, atEOF)
			advance += 1
			if dollar {
				tmp, err = strconv.ParseInt(string(token), 10, 32)
				size = int(tmp)
				expected = Content
			} else {
				expected = Marker
			}
		case Content:
			fmt.Println("parsing content")
			if len(data) < size {
				if atEOF {
					return 0, nil, fmt.Errorf("incomplete message at EOF")
				} else {
					return 0, nil, nil // ask to try again with more data
				}
			} else {
				advance = size + 2
				token = data[:size]
				expected = Marker
			}
		}

		return
	}
}

func main() {
	reader := bytes.NewBufferString("*1\r\n$11\r\nhello world\r\n*1\r\n$13\r\ngoodbye world\r\n")
	scanner := bufio.NewScanner(reader)
	scanner.Split(newScanFunc())
	for scanner.Scan() {
		fmt.Println(scanner.Text())
	}
}