plantuml_serverに渡す文字列を生成する。

plantuml_cli.go

package main

import (
	"fmt"
	"bytes"
	"strings"
	"compress/zlib"
	"math"
)

const encodeStr = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz-_"

func encode64(str string) (string, error) {
	var b bytes.Buffer
	w, err := zlib.NewWriterLevel(&b, zlib.BestCompression)
	if err != nil {
		return "", err
	}
	defer w.Close()
	w.Write([]byte(str))
	w.Flush()

	bytesData := b.Bytes()
	bytesData = bytesData[2:len(bytesData)-4]
	bytesData[0] += 1

	var l int
	outputLength := int((math.Ceil(float64(len(bytesData)) / 3)) * 4)
	code := make([]string, outputLength)
	codeIndex := 0
	for i := 0; i < len(bytesData); i += 3 {
		var result [4]string
		l = len(bytesData[i:])
		switch {
		case l >= 3:
			fmt.Printf("%02x %02x %02x || ", int(bytesData[i]), int(bytesData[i+1]), int(bytesData[i+2]))
			result, err = append3bytes(int(bytesData[i]), int(bytesData[i+1]), int(bytesData[i+2]))
		case l == 2:
			fmt.Printf("%02x %02x %02x || ", int(bytesData[i]), int(bytesData[i+1]), 0)
			result, err = append3bytes(int(bytesData[i]), int(bytesData[i+1]), 0)

		case l == 1:
			fmt.Printf("%02x %02x %02x || ", int(bytesData[i]), 0, 0)
			result, err = append3bytes(int(bytesData[i]), 0, 0)
		}
		if err != nil {
			return "", err
		}
		for _, r := range result {
			code[codeIndex] = r
			codeIndex += 1
		}
	}

	return strings.Join(code, ""), nil
}

func append3bytes(b1, b2, b3 int) ([4]string, error) {
	c1 := int((b1 >> 2) & 0x3F)
	c2 := int((((b1 & 0x3) << 4) | (b2 >> 4)) & 0x3F)
	c3 := int((((b2 & 0xF) << 2) | (b3 >> 6)) & 0x3F)
	c4 := int(b3 & 0x3F)
	fmt.Printf("%02d %02d %02d %02d || %06b %06b %06b %06b\n", c1, c2, c3, c4, c1, c2, c3, c4)
	return [4]string{string(encodeStr[c1]), string(encodeStr[c2]), string(encodeStr[c3]), string(encodeStr[c4])}, nil
}

func main() {
	var stdin string
	fmt.Scan(&stdin)

// 	fmt.Println(stdin)
	result, err := encode64(stdin)
	if err != nil {
		fmt.Println(err)
	}
	fmt.Println(result[:])
}