io.Reader 如果是实现了io.Seeker接口，想要重复读取则比较简单，直接调用Seek()方法把offset移到起始处即可，比如本地文件的IO，如果不支持Seek想要重复读取，则相对麻烦，这里我们可以借助一个buffer，从io.Reader读取数据的时候，同时把读出来的数据写到这个buffer中缓存起来，当要重新读取时，先从buffer里读，buffer读完再接着从原始的io.Reader里读，代码如下：
import (
"bytes"
"fmt"
"io"
"log"
"math/rand"
"net/http"
"time"
)
type MultiReadable struct {
originReader io.Reader
reader io.Reader
cache *bytes.Buffer
}
func NewMultiReadable(reader io.Reader) *MultiReadable {
return &MultiReadable{
originReader: reader,
reader: reader,
}
}
func (mr *MultiReadable) Read(p []byte) (int, error) {
n, err := mr.reader.Read(p)
// 如果 reader 不支持Seek，则把读取出来的内容同时写入到一个buffer中
if _, ok := mr.reader.(io.Seeker); !ok && n > 0 {
if mr.cache == nil {
mr.cache = &bytes.Buffer{}
}
mr.cache.Write(p[:n])
}
return n, err
}
func (mr *MultiReadable) Reset() error {
// 如果reader支持Seek，直接使用Seek即可
if seeker, ok := mr.reader.(io.Seeker); ok {
_, err := seeker.Seek(0, io.SeekStart)
return err
}
if mr.cache != nil && mr.cache.Len() > 0 {
mr.reader = io.MultiReader(mr.cache, mr.reader)
mr.cache = nil
}
return nil
}
func (mr *MultiReadable) Close() error {
if closer, ok := mr.originReader.(io.Closer); ok {
return closer.Close()
}
return nil
}
测试代码：
// getLongestValidUtf8Prefix get the longest valid utf8 string bytes from p
func getLongestValidUtf8Prefix(p []byte) []byte {
lastValid := 0
for lastValid < len(p) {
r, size := utf8.DecodeRune(p[lastValid:])
if r == utf8.RuneError {
return p[:lastValid]
}
lastValid += size
}
return p[:lastValid]
}
func main() {
resp, err := http.Get("http://www.baidu.com/")
if err != nil {
log.Fatal(err)
}
mr := NewMultiReadable(resp.Body)
defer func() {
if err := mr.Close(); err != nil {
log.Println(err)
}
}()
for i := 0; i < 10; i++ {
if err := mr.Reset(); err != nil {
log.Fatal(err)
}
buf, err := io.ReadAll(io.LimitReader(mr, int64(i)*60+100))
if err != nil {
log.Fatal(err)
}
fmt.Println(string(getLongestValidUtf8Prefix(buf)))
fmt.Println("------------------------------------")
}
}
输出：
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charse
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" co
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" content="全球领先的中文搜索引擎、致力于让网
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" content="全球领先的中文搜索引擎、致力于让网民更便捷地获取信息，找到所求。百度超过千
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" content="全球领先的中文搜索引擎、致力于让网民更便捷地获取信息，找到所求。百度超过千亿的中文网页数据库，可以瞬间找到相关的搜
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" content="全球领先的中文搜索引擎、致力于让网民更便捷地获取信息，找到所求。百度超过千亿的中文网页数据库，可以瞬间找到相关的搜索结果。"><link rel="shortcut icon" href="/favicon.ico" ty
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" content="全球领先的中文搜索引擎、致力于让网民更便捷地获取信息，找到所求。百度超过千亿的中文网页数据库，可以瞬间找到相关的搜索结果。"><link rel="shortcut icon" href="/favicon.ico" type="image/x-icon" /><link rel="search" type="application/ope
------------------------------------
<!DOCTYPE html><!--STATUS OK--><html><head><meta http-equiv="Content-Type" content="text/html;charset=utf-8"><meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1"><meta content="always" name="referrer"><meta name="theme-color" content="#ffffff"><meta name="description" content="全球领先的中文搜索引擎、致力于让网民更便捷地获取信息，找到所求。百度超过千亿的中文网页数据库，可以瞬间找到相关的搜索结果。"><link rel="shortcut icon" href="/favicon.ico" type="image/x-icon" /><link rel="search" type="application/opensearchdescription+xml" href="/content-search.xml" title="
------------------------------------
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