//比如要解析resp.Body(io.ReadCloser)，我们可以这样处理 body,err:=IoUtil.ReadAll(resp.Body)
接着，我们继续分析分析函数
funcReadAll(rio.Reader)([]byte,error){
returnreadAll(r,bytes.MinRead)//constMinRead=512
}
//
funcreadAll(rio.Reader,capacityint64)(b[]byte,errerror){
buf:=bytes.NewBuffer(make([]byte,capacity))
//funcNewBuffer(buf[]byte)*Buffer{return&Buffer{buf:buf}}一个新的buffer实例
deferfunc(){
e:=recover()
ife==nil{
return
}
//buf太大会返回相应错误
ifpanicErr,ok:=e.(error);ok&&panicErr==bytes.ErrTooLarge{
err=panicErr
}else{
panic(e)
}
}()
_,err=buf.ReadFrom(r)//关键就是这个家伙
returnbuf.Bytes(),err
}
来继续看看 buf.ReadFrom的实现吧：
//先看一下Buffer的定义，有帮助下面理解
typeBufferstruct{
buf[]byte//最新数据存放在buf[off:len(buf)]
offint//从&buf[off]开始读,从&buf[len(buf)]开始写
runeBytes[utf8.UTFMax]byte//avoidallocationofsliceoneachWriteByteorRune
bootstrap[64]byte
//memorytoholdfirstslice;helpssmallbuffers(Printf)avoidallocation.
lastReadreadOp//lastreadoperation,sothatUnread*canworkcorrectly.
}
func(b*Buffer)ReadFrom(rio.Reader)(nint64,errerror){
b.lastRead=opInvalid//0
ifb.off>=len(b.buf){
b.Truncate(0)//还没有写就想读，清空buf
}
for{
iffree:=cap(b.buf)-len(b.buf);free<MinRead{
//free的大小是总容量-现在占有长度
newBuf:=b.buf
ifb.off+free<MinRead{
//分配更大空间，分配失败会报错
newBuf=makeSlice(2*cap(b.buf)+MinRead)
}
//把读的内容b.buf[b.off:]拷贝到newbuf前面去
copy(newBuf,b.buf[b.off:])
//读写之间的差距就是应该读的buf
b.buf=newBuf[:len(b.buf)-b.off]
b.off=0
}
//把io.Reader内容写到buf的free中去
m,e:=r.Read(b.buf[len(b.buf):cap(b.buf)])
//重新调整buf的大小
b.buf=b.buf[0:len(b.buf)+m]
n+=int64(m)
//读到尾部就返回
ife==io.EOF{
break
}
ife!=nil{
returnn,e
}
}
returnn,nil//erriSEOF,soreturnnilexplicitly
}
接下来再来看看是怎么Read进buf里面去的吧：
func(b*Buffer)Read(p[]byte)(nint,errerror){
b.lastRead=opInvalid
ifb.off>=len(b.buf){
//Bufferisempty,resettorecoverspace.
b.Truncate(0)
iflen(p)==0{
return
}
return0,io.EOF
}
//就是这里咯，把b.buf[b.off:]的值写到p中去，记住copy(s1,s2)是s2写到s1中去，不要弄反咯
//而且此Buffer其实是io.ReadCloser接口转化的类型
n=copy(p,b.buf[b.off:])
b.off+=n
ifn>0{
b.lastRead=opRead
}
return
}
