debugging parser.go

parser.go

package main

import (
	"fmt"
	"io"
	"strings"
	"time"
)

const (
	defaultBufSize = 32
)

type parser struct {
	//buffer is a slice of bigBuffer
	bigBuffer, buffer []byte
	reader            io.Reader
	lastRead          time.Time
}

func newParser(reader io.Reader) *parser {
	return &parser{reader: reader}
}

func (p *parser) readMore() (int, error) {
	if len(p.buffer) == cap(p.buffer) {
		var newBuffer []byte
		switch {
		//initialize the parser
		case len(p.bigBuffer) == 0:
			fmt.Println("------------------------ 0")
			fmt.Println(p.bigBuffer)
			fmt.Println(p.buffer)
			p.bigBuffer = make([]byte, defaultBufSize)
			newBuffer = p.bigBuffer[0:0]

		//shift buffer back to the start of bigBuffer
		case 2*len(p.buffer) <= len(p.bigBuffer):
			fmt.Println("------------------------ 1")
			fmt.Println(p.bigBuffer)
			fmt.Println(p.buffer)

			newBuffer = p.bigBuffer[0:len(p.buffer)]

		//reallocate big buffer with enough space to shift buffer
		default:
			fmt.Println("------------------------ 3")
			fmt.Println(p.bigBuffer)
			fmt.Println(p.buffer)

			p.bigBuffer = make([]byte, 2*len(p.buffer))
			newBuffer = p.bigBuffer[0:len(p.buffer)]
		}

		copy(newBuffer, p.buffer)
		fmt.Println("------------------------ 4")
		fmt.Println(p.bigBuffer)
		fmt.Println(p.buffer)

		p.buffer = newBuffer
		fmt.Println("------------------------ 5")
		fmt.Println(p.bigBuffer)
		fmt.Println(p.buffer)

	}

	n, e := p.reader.Read(p.buffer[len(p.buffer):cap(p.buffer)])
	p.lastRead = time.Now()
	p.buffer = p.buffer[:len(p.buffer)+n]
	return n, e
}

func main() {
	reader := strings.NewReader("Hello, Reader! 123456789abcdefghijklmnopqrstuABCDEFGHIJKLMNOPQRSTUVWXYZ")
	parser := newParser(reader)
	var newBuffer []byte
	parser.bigBuffer = make([]byte, defaultBufSize)
	newBuffer = parser.bigBuffer[0:0]
	fmt.Println("------------------------ 0")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))
	copy(newBuffer, parser.buffer)
	fmt.Println("------------------------ 1")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	parser.buffer = newBuffer
	fmt.Println("------------------------ 2")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	n, _ := parser.reader.Read(parser.buffer[len(parser.buffer):cap(parser.buffer)])

	fmt.Println("------------------------ 3")
	fmt.Println(n)

	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	parser.lastRead = time.Now()
	parser.buffer = parser.buffer[:len(parser.buffer)+n]

	// -------------------------------------------------------------------

	newBuffer = parser.bigBuffer[0:len(parser.buffer)]

	fmt.Println("------------------------ 4")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))
	copy(newBuffer, parser.buffer)
	fmt.Println("------------------------ 5")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	parser.buffer = newBuffer
	fmt.Println("------------------------ 6")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	n, _ = parser.reader.Read(parser.buffer[len(parser.buffer):cap(parser.buffer)])

	fmt.Println("------------------------ 7")
	fmt.Println(n)

	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	parser.lastRead = time.Now()
	parser.buffer = parser.buffer[:len(parser.buffer)+n]

	// -------------------------------------------------------------------

	parser.bigBuffer = make([]byte, 2*len(parser.buffer))
	newBuffer = parser.bigBuffer[0:len(parser.buffer)]

	fmt.Println("------------------------ 8")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))
	copy(newBuffer, parser.buffer)
	fmt.Println("------------------------ 9")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	parser.buffer = newBuffer
	fmt.Println("------------------------ 10")
	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	n, _ = parser.reader.Read(parser.buffer[len(parser.buffer):cap(parser.buffer)])

	fmt.Println("------------------------ 11")
	fmt.Println(n)

	fmt.Println(parser.bigBuffer)
	fmt.Println(parser.buffer)
	fmt.Println(string(parser.bigBuffer))
	fmt.Println(string(parser.buffer))

	parser.lastRead = time.Now()
	parser.buffer = parser.buffer[:len(parser.buffer)+n]
}