easyjson 源码调试学习

golangLeetcode

发布于 2022-08-02 18:57:32

4320

发布于 2022-08-02 18:57:32

json解析逻辑一直很繁琐，是go项目可能遇到的性能瓶颈之一。easyjson的解决思路很直观，代码量也不大，整体思路是根据源码中的结构体生成定制化的marshal和unmarshal方法，由于是定制化的，解析的时候没有反射，性能可以做到很好，下面通过调试学习了一下定制化的marshal和unmarshal方法是如何生成的。

我们可以在Edit Configuration中进行配置然后我们在这个窗口去配置当前Go程序的参数配置好之后点击Debug即可。

我们从main函数入口开始找到了如下关键路径，首先是输入文件的解析

err := p.Parse(fname, fInfo.IsDir());

会解析我们输入的文件example.go

 package example 
 type AutoGenerated struct { 
 Name string json:"name" 
 Value int json:"value" 
 }

解析过程中会调用

f, err := parser.ParseFile(fset, fname, nil, parser.ParseComments)

获取ast

然后获取语法树中我们感兴趣的部分

 ast.Walk(&visitor{Parser: p}, f)

重点是

func (v *visitor) Visit(n ast.Node) (w ast.Visitor) {
 switch n := n.(type) { 
 case *ast.Package: 
 return v 
 case *ast.File: 
 v.PkgName = n.Name.String() 
 return v 
 case *ast.GenDecl:
  v.explicit = v.needType(n.Doc.Text()) 
  if !v.explicit && !v.AllStructs { 
  return nil
   } 
   return v
    case *ast.TypeSpec: 
    v.name = n.Name.String() // Allow to specify non-structs explicitly independent of '-all' flag. 
    if v.explicit { 
    v.StructNames = append(v.StructNames, v.name) 
    return nil 
    } 
    return v 
    case *ast.StructType: 
    v.StructNames = append(v.StructNames, v.name) 
    return nil 
    } 
    return nil 
    }

解析我们感兴趣的包，结构体声明等信息

g.writeStub();

生成文件 /Users/didi/goLang/src/github.com/xiazemin/go-json/json2go/example_easyjson.go

// TEMPORARY AUTOGENERATED FILE: easyjson stub code to make the package 
// compilable during generation. 
package example 
import ( 
“github.com/mailru/easyjson/jwriter” 
“github.com/mailru/easyjson/jlexer” 
) 
func ( AutoGenerated ) MarshalJSON() ([]byte, error) { 
return nil, nil 
} 
func (* AutoGenerated ) UnmarshalJSON([]byte) error {
 return nil 
 } 
 func ( AutoGenerated ) MarshalEasyJSON(w jwriter.Writer) {
 } 
 func ( AutoGenerated ) UnmarshalEasyJSON(l *jlexer.Lexer) {
 } 
 type EasyJSON_exporter_AutoGenerated *AutoGenerated g.writeMain()

生成临时文件 /Users/didi/goLang/src/github.com/xiazemin/go-json/json2go/easyjson-bootstrap501241316.go

// +build ignore 
// TEMPORARY AUTOGENERATED FILE: easyjson bootstapping code to launch 
// the actual generator. 
package main 
import ( 
“fmt” 
“os” 
“github.com/mailru/easyjson/gen” 
pkg “github.com/xiazemin/go-json/json2go” 
) 
func main() { 
g := gen.NewGenerator(“example_easyjson.go”) 
g.SetPkg(“example”, “github.com/xiazemin/go-json/json2go”) 
g.Add(pkg.EasyJSON_exporter_AutoGenerated(nil)) 
if err := g.Run(os.Stdout); 
err != nil { 
fmt.Fprintln(os.Stderr, err) 
os.Exit(1) 
}
}

创建另一个临时文件 /Users/didi/goLang/src/github.com/xiazemin/go-json/json2go/example_easyjson.go.tmp

执行命令

go run -tags “” easyjson-bootstrap501241316.go

将std out 指定为example_easyjson.go.tmp 内容为

// Code generated by easyjson for marshaling/unmarshaling. DO NOT EDIT.

package example

import (
  json "encoding/json"
  easyjson "github.com/mailru/easyjson"
  jlexer "github.com/mailru/easyjson/jlexer"
  jwriter "github.com/mailru/easyjson/jwriter"
)

// suppress unused package warning
var (
  _ *json.RawMessage
  _ *jlexer.Lexer
  _ *jwriter.Writer
  _ easyjson.Marshaler
)

func easyjsonEeca4a30DecodeGithubComXiazeminGoJsonJson2go(in *jlexer.Lexer, out *AutoGenerated) {
  isTopLevel := in.IsStart()
  if in.IsNull() {
    if isTopLevel {
      in.Consumed()
    }
    in.Skip()
    return
  }
  in.Delim('{')
  for !in.IsDelim('}') {
    key := in.UnsafeString()
    in.WantColon()
    if in.IsNull() {
      in.Skip()
      in.WantComma()
      continue
    }
    switch key {
    case "name":
      out.Name = string(in.String())
    case "value":
      out.Value = int(in.Int())
    default:
      in.SkipRecursive()
    }
    in.WantComma()
  }
  in.Delim('}')
  if isTopLevel {
    in.Consumed()
  }
}
func easyjsonEeca4a30EncodeGithubComXiazeminGoJsonJson2go(out *jwriter.Writer, in AutoGenerated) {
  out.RawByte('{')
  first := true
  _ = first
  {
    const prefix string = ",\"name\":"
    out.RawString(prefix[1:])
    out.String(string(in.Name))
  }
  {
    const prefix string = ",\"value\":"
    out.RawString(prefix)
    out.Int(int(in.Value))
  }
  out.RawByte('}')
}

// MarshalJSON supports json.Marshaler interface
func (v AutoGenerated) MarshalJSON() ([]byte, error) {
  w := jwriter.Writer{}
  easyjsonEeca4a30EncodeGithubComXiazeminGoJsonJson2go(&w, v)
  return w.Buffer.BuildBytes(), w.Error
}

// MarshalEasyJSON supports easyjson.Marshaler interface
func (v AutoGenerated) MarshalEasyJSON(w *jwriter.Writer) {
  easyjsonEeca4a30EncodeGithubComXiazeminGoJsonJson2go(w, v)
}

// UnmarshalJSON supports json.Unmarshaler interface
func (v *AutoGenerated) UnmarshalJSON(data []byte) error {
  r := jlexer.Lexer{Data: data}
  easyjsonEeca4a30DecodeGithubComXiazeminGoJsonJson2go(&r, v)
  return r.Error()
}

// UnmarshalEasyJSON supports easyjson.Unmarshaler interface
func (v *AutoGenerated) UnmarshalEasyJSON(l *jlexer.Lexer) {
  easyjsonEeca4a30DecodeGithubComXiazeminGoJsonJson2go(l, v)
}

重命名，流程结束

关键代码如下：