尝试更改流中的字节进行解码，但遇到问题

在Golang实战开发的过程中，我们经常会遇到一些这样那样的问题，然后要卡好半天，等问题解决了才发现原来一些细节知识点还是没有掌握好。今天golang学习网就整理分享《尝试更改流中的字节进行解码，但遇到问题》，聊聊，希望可以帮助到正在努力赚钱的你。

我正在尝试使用可传递到 json 解码器的自定义读取器来包装 io.readercloser，它在生产中将来自请求处理程序。

我创建了以下内容

import (
    "io"
)

// removenull is a stream wrapper that should remove null bytes from the byte stream
type removenull struct {
    reader io.readcloser
}

// newremovenullstream creates a new removenull reader which passes the stream through a null check first
func newremovenullstream(reader io.readcloser) removenull {
    return removenull{
        reader: reader,
    }
}

// read wraps a reader to remove null bytes in the stream
func (null removenull) read(p []byte) (n int, err error) {
    n, err = null.reader.read(p)
    if err != nil {
        return n, err
    }

    nn := 0
    for i := range p {
        if p[i] != 0 {
            p[nn] = p[i]
            nn++

        }
    }
    p = p[:nn]
    // fmt.println(p) i can see the value of p changing and all the null bytes are removed
    return n, nil
}

// close closes the internal reader
func (null removenull) close() error {
    return null.close()
}

当我运行以下命令时，我可以从打印语句中看到，确实所有空字节都被删除，并且 len(p) == 所有预期好字节的大小。我编写了下面的测试来查看代码是否按我的预期工作，这就是我意识到它不是的地方。

这是完整的测试

import (
    "bytes"
    "encoding/json"
    "fmt"
    "io"
    "io/ioutil"
    "testing"

    "github.com/francoispqt/gojay" // can be replaced with the std json lib, code still doesn't work
)

func TestRemoveNull_Read(t *testing.T) {
    type fields struct {
        Reader io.ReadCloser
    }
    tests := []struct {
        name   string
        fields fields
        want   string
    }{
        {
            name: "should remove null bytes",
            fields: fields{
                Reader: ioutil.NopCloser(bytes.NewReader([]byte{123, 34, 98, 111, 100, 121, 34, 58, 34, 102, 101, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 109, 97, 108, 101, 34, 125})),
            },
            want: "female",
        },
    }
    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            reader := tt.fields.Reader
            reader = NewRemoveNullStream(tt.fields.Reader) // wrapper the reader above in the nullByte reader

            // passed the reader into this JSON unmarshaller
            decoder := gojay.BorrowDecoder(reader)
            defer decoder.Release()

            var v _testStruct
            err := decoder.DecodeObject(&v)
            if err != nil {
                t.Fatalf("ReadAll failed %v", err)
            }

            bb, _ := json.Marshal(v)
            fmt.Println(string(bb)) // all the null bytes are still present

            fmt.Println(len(v.Body), len(tt.want))
            if v.Body != tt.want {
                t.Fatalf("DecodeObject() unexpected value, got %s want %s", v.Body, tt.want)
            }
        })
    }
}

type _testStruct struct {
    Body string `json:"body"`
}

func (v *_testStruct) UnmarshalJSONObject(dec *gojay.Decoder, k string) error {

    switch k {
    case "body":
        err := dec.String(&v.Body)
        return err
    }
    return nil
}

// NKeys returns the number of keys to unmarshal
func (v *_testStruct) NKeys() int { return 0 }

从测试中我可以看到解码时所有空字节仍然存在，但在removenull阅读器中我可以看到所有空字节已从下划线数组中删除。关于出了什么问题以及如何实现从流中删除字节以避免让解码器解码空字节的目标有什么想法吗？

解决方案

您的 read 实现中存在错误。如果出现 io.eof，同时存在错误和数据，它会提前终止。它返回错误的读取字节数。分配切片的最后一部分也是没有意义的，因为它不会更新传递到函数中的切片。

试试这个：

func (null RemoveNull) Read(p []byte) (n int, err error) {
    n, err = null.Reader.Read(p)
    nn := 0
    for i:=0;i<n;i++ {
        if p[i] != 0 {
            p[nn] = p[i]
            nn++

        }
    }
    return nn, err
}

文中关于的知识介绍，希望对你的学习有所帮助！若是受益匪浅，那就动动鼠标收藏这篇《尝试更改流中的字节进行解码，但遇到问题》文章吧，也可关注golang学习网公众号了解相关技术文章。