Golang Bytes Buffer Code anatomy

This is a creation in Article, where the information may have evolved or changed.

Data structure, bytes buffertype buffer struct {buf       [] Byte            // byte slicing off        int                //  Write Data Runebytes [utf8 from &buf[off] address read data,  from &buf[len (BUF)] address. Utfmax]byte // avoid allocation of slice on each writebyte or  runebootstrap [64]byte          // memory  to hold first slice; helps small buffers  (Printf)  avoid  allocation.lastread  readop            / / last read operation, so that unread* can work correctly.}

Let's see how write is implemented in bytes buffer.

Func (b *buffer) writestring (s string) (n int, err error) {B.lastread = opinvalid//Non-read operation does not require read flag equals 0m: = b . Grow (Len (s))//growth size (accurately adjusted data in buf position, does not necessarily grow), M is of course old data end return copy (B.buf[m:], s), nil//copy data, starting from M}

The most important thing to see.

func  (B *buffer)  grow (n int)  int {m := b.len ()  //func  (b  *buffer)  len ()  int { return len (B.BUF)  - b.off }//  M is buf len  minus (-)  b.off (read start position) if m == 0 && b.off != 0  {b.truncate (0)  //below gives display} //resizing and positioning If len (B.BUF) +n > cap (B.BUF)  {var  buf []byteif b.buf == nil && n <= len (B.bootstrap)  {buf = b.bootstrap[0:] //This bootstrap caches buf slices, which is said to prevent heavy allocation} else if m+n  <= cap (B.BUF)/2 { //  twice times the principle of applying for a new slice copy (B.buf[:], b.buf[b.off:]) buf =  b.buf[:m]} else {// not enough space anywherebuf = makeslice ( Cap (B.BUF)  + n) copy (Buf, b.buf[b.off:])}b.buf = bufb.off = 0}b.buf =  b.buf[0 : b.off+m+n] //Assignment Return b.off + m} 

And look at the function truncate it used, cut the slices.

Func (b *buffer) Truncate (n int) {B.lastread = Opinvalidswitch {case N < 0 | | n > B.len ():p anic ("bytes. Buffer:truncation out of a range ") case n = = 0://Reuse buffer Space.b.off = 0}B.BUF = B.buf[0:b.off+n]}

Makeslice function

Func makeslice (n int) []byte {//If the make fails, give a known error.defer func () {If recover ()! = nil {Panic (errtoolarg e)}} () return make ([]byte, N)//actually call this make}

Finally take a look at a usage example

Package Mainimport ("bytes" "FMT" "StrConv" "Time") Func main () {var buffer bytes. Bufferttime: = time. Now (). Unixnano () for I: = 0; i < 10000000; i++ {buffer. WriteString (StrConv. Itoa (i))}ttime1: = time. Now (). Unixnano ()//take content buffer. Bytes () or buffer. String () fmt. Printf ("Time Cal%f%d\n", Float64 (ttime1-ttime)/float64 (1*time. Second), Len (buffer. String ()))}

Summary: Bytes Buffer: A container that writes a byte or string of strings