golang BufferIO

测试一下golang库函数里面bufio模块代码,Readline根据'\n'切分数据

packagemain

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

typeReaderstruct{
	buf[]byte
	rdio.Reader//readerprovidedbytheclient
	r,wint//bufreadandwritepositions
	errerror
	lastByteint
	lastRuneSizeint
}

constminReadBufferSize=16
constmaxConsecutiveEmptyReads=100

varerrNegativeRead=errors.New("bufio:readerreturnednegativecountfromRead")
varErrBufferFull=errors.New("bufio:bufferfull")

func(b*Reader)readErr()error{
	err:=b.err
	b.err=nil
	returnerr
}

//fillreadsanewchunkintothebuffer.
func(b*Reader)fill(){
	//Slideexistingdatatobeginning.
	//fmt.Printf("readerr%v\n",b.r)
	ifb.r>0{
		copy(b.buf,b.buf[b.r:b.w])
		b.w-=b.r
		b.r=0
	}

	ifb.w>=len(b.buf){
		panic("bufio:triedtofillfullbuffer")
	}

	//Readnewdata:tryalimitednumberoftimes.
	//如果一直读取失败,则最多读取100次
	fori:=maxConsecutiveEmptyReads;i>0;i--{
		n,err:=b.rd.Read(b.buf[b.w:])
		//fmt.Printf("count%v\n",n)
		ifn<0{
			panic(errNegativeRead)
		}
		b.w+=n
		iferr!=nil{
			b.err=err
			return
		}
		ifn>0{
			return
		}
	}
	b.err=io.ErrNoProgress
}

func(b*Reader)Buffered()int{returnb.w-b.r}

func(b*Reader)ReadSlice(delimbyte)(line[]byte,errerror){
	for{
		//Searchbuffer.
		//fmt.Printf("bytesindex%verr%v\n",bytes.IndexByte(b.buf[b.r:b.w],delim),b.err)
		ifi:=bytes.IndexByte(b.buf[b.r:b.w],delim);i>=0{
			line=b.buf[b.r:b.r+i+1]
			//fmt.Printf("lineis%v\n",string(line))
			b.r+=i+1
			break
		}

		//Pendingerror?
		ifb.err!=nil{
			line=b.buf[b.r:b.w]
			b.r=b.w
			err=b.readErr()
			break
		}

		//Bufferfull?
		//fmt.Printf("bufiobuffered%vlenbuf%v\n",b.Buffered(),len(b.buf))

		ifb.Buffered()>=len(b.buf){
			b.r=b.w
			line=b.buf
			err=ErrBufferFull
			break
		}

		b.fill()//bufferisnotfull
	}

	//Handlelastbyte,ifany.
	ifi:=len(line)-1;i>=0{
		b.lastByte=int(line[i])
		b.lastRuneSize=-1
	}

	return
}

func(b*Reader)ReadLine()(line[]byte,isPrefixbool,errerror){
	line,err=b.ReadSlice('\n')
	iferr==ErrBufferFull{
		//Handlethecasewhere"\r\n"straddlesthebuffer.
		iflen(line)>0&&line[len(line)-1]=='\r'{
			//Putthe'\r'backonbufanddropitfromline.
			//LetthenextcalltoReadLinecheckfor"\r\n".
			ifb.r==0{
				//shouldbeunreachable
				panic("bufio:triedtorewindpaststartofbuffer")
			}
			b.r--
			line=line[:len(line)-1]
		}
		returnline,true,nil
	}

	iflen(line)==0{
		iferr!=nil{
			line=nil
		}
		return
	}
	err=nil

	ifline[len(line)-1]=='\n'{
		drop:=1
		iflen(line)>1&&line[len(line)-2]=='\r'{
			drop=2
		}
		line=line[:len(line)-drop]
	}
	return
}

funcmain(){
	reader:=bytes.NewReader([]byte("absc\r\nddd\n"))

	b:=&Reader{
		buf:make([]byte,100),rd:reader,lastByte:-1,lastRuneSize:-1,}
	for{
		line,isPrefix,err:=b.ReadLine()
		fmt.Printf("line%v/prefix%v/err%v\n",string(line),err)

		iferr==io.EOF{
			break
		}

		time.Sleep(1*time.Second)
	}

}

输出结果：

lineabsc/prefixfalse/err<nil>
lineddd/prefixfalse/err<nil>
line/prefixfalse/errEOF