a minimal implementation of RESP/Redis client

encoder.go

package main

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

const (
	SimpleString = byte('+')
	Error        = byte('-')
	Integer      = byte(':')
	BulkString   = byte('$')
	Array        = byte('*')
)

var Terminator = []byte{'\r', '\n'}

var (
	ErrNull     = errors.New("null value")
	ErrNotArray = errors.New("not an array")
)

type ValueEncoder interface {
	Encode(value interface{}, w io.Writer) error
}

type SimpleStringEncoder struct{}

func (*SimpleStringEncoder) Encode(value interface{}, w io.Writer) error {
	if value == nil {
		return ErrNull
	}

	message := []byte{SimpleString}
	message = append(message, []byte(fmt.Sprint(value))...)
	message = append(message, Terminator...)
	_, err := w.Write(message)

	return err
}

type BulkStringEncoder struct{}

func (*BulkStringEncoder) Encode(value interface{}, w io.Writer) error {
	if value == nil {
		return ErrNull
	}

	v := fmt.Sprint(value)
	message := []byte{BulkString}
	message = append(message, []byte(fmt.Sprintf("%d%s", len(v), Terminator))...)
	message = append(message, []byte(v)...)
	message = append(message, Terminator...)
	_, err := w.Write(message)

	return err
}

type ArrayEncoder struct{}

func (*ArrayEncoder) Encode(value interface{}, w io.Writer) error {
	if value == nil {
		return ErrNull
	}

	array := value.([]interface{})
	message := []byte{Array}
	message = append(message, []byte(fmt.Sprintf("%d%s", len(array), Terminator))...)

  // todo: interpret these better
	encoder := BulkStringEncoder{}
	for _, v := range array {
		w := bytes.NewBuffer([]byte{})
		encoder.Encode(v, w)
		message = append(message, w.Bytes()...)
	}

	_, err := w.Write(message)
	return err
}

redis.go

package main

import (
	"log"
	"net"
)

type Client struct {
	conn net.Conn
}

func (c *Client) SendCommand(args ...interface{}) {
	encoder := ArrayEncoder{}

	encoder.Encode(args, c.conn)

}

func main() {
	conn, err := net.Dial("tcp", ":6379")
	if err != nil {
		log.Fatalln(err)
	}

	c := Client{conn}

	c.SendCommand(  "PUBLISH", "test", "Hello, World"  )
}