Marshal - HackMD

Marshal ===   不給你的,自己來!!! :dizzy: > [name=郭學聰 Hsueh-Tsung Kuo] [time=Sun, 06 Aug 2017] [color=red] ---  ## who am I? ![fieliapm](https://pbs.twimg.com/profile_images/591670980021387264/aZAYLRUe_400x400.png) ----  * programmer from Rayark, a game company in Taiwan * backend engineer * usually develop something related to my work in Python, Ruby, Golang, C# * built almost entire VOEZ game server by myself only ---  ## conclusion #### Too Long; Didn't Read ----  ```go= type UnixTime struct { //anonymous field time.Time `bson:",inline" json:",inline"` } func (unixTime UnixTime) MarshalJSON() ([]byte, error) { return json.Marshal(unixTime.Time.Unix()) } func (unixTime *UnixTime) UnmarshalJSON(data []byte) error { var unixTimeInt int64 err := json.Unmarshal(data, &unixTimeInt) if err != nil { return err } unixTime.Time = time.Unix(unixTimeInt, 0) return nil } ``` ----  #### is this it? ----  #### there seems to be much behind all this! ---  ## outline ----  3. conclusion 4. outline 5. preface: type system 6. origin: json package 1. json marshal/unmarshal package 2. usage 3. implementation & example 7. customization 1. requirement 2. try it 3. result 4. solution ----  8. new coming problem 1. case 2. try it 3. reason 4. dirty solution 9. better way 10. summary 1. slogan 2. special thanks 11. appendix: code to test marshal/unmarshal 12. Q&A ---  ## preface: type system ----  ```go= // struct type Person struct { Name string Age int } // interface type Reader interface { Read(p []byte) (n int, err error) } ``` ---  ## origin: json package ----  ### json marshal/unmarshal package * https://golang.org/pkg/encoding/json/ ----  ### usage ```go= // encode b, err := json.Marshal(&fromData) enc := json.NewEncoder(writer) err := enc.Encode(&fromData) // decode err := json.Unmarshal(b, &toData) dec := json.NewDecoder(reader) err := dec.Decode(&toData) ``` ----  ### implementation ```go= // encoder will call this method type Marshaler interface { MarshalJSON() ([]byte, error) } // decoder will call this method type Unmarshaler interface { UnmarshalJSON([]byte) error } ``` ----  ### example ```go= // can be value or pointer receiver func (variable Type) MarshalJSON() ([]byte, error) // must be pointer receiver (need to overwrite variable) func (variable *Type) UnmarshalJSON([]byte) error ``` ---  ## customization ----  ### requirement * time.Time.MarshalJSON() -> 2017-08-06T13:40:00+08:00 * prefer to use UNIX epoch time -> 1501998000 ----  ### try it ----  ```go= type AccountCoreData struct { Name string UUID string CreatedAt time.Time UpdatedAt time.Time } ``` ----  ```go= // AccountCoreData reflection redefinition type _AuxAccountCoreData struct { *AccountCoreData `bson:",inline" json:",inline"` CreatedAt int64 UpdatedAt int64 } ``` ----  ```go= func (accountCoreData AccountCoreData) MarshalJSON() ([]byte, error) { return json.Marshal(_AuxAccountCoreData{ AccountCoreData: &accountCoreData, CreatedAt: accountCoreData.CreatedAt.Unix(), UpdatedAt: accountCoreData.UpdatedAt.Unix(), }) } ``` ----  ```go= func (accountCoreData *AccountCoreData) UnmarshalJSON(data []byte) error { aux := &_AuxAccountCoreData{ AccountCoreData: accountCoreData, } err := json.Unmarshal(data, aux) if err != nil { return err } accountCoreData.CreatedAt = time.Unix(aux.CreatedAt, 0) accountCoreData.UpdatedAt = time.Unix(aux.UpdatedAt, 0) return nil } ``` ----  ### result #### 然後它就死掉了 * infinite call -> stack overflow! * MarshalJSON() -> json.Marshal() -> MarshalJSON() -> json.Marshal() -> ... * UnmarshalJSON() -> json.Unmarshal() -> UnmarshalJSON() -> json.Unmarshal() -> ... ----  ### solution #### avoid inheritance ----  ```go= // avoid inheritance!!! type _AccountCoreDataAlias AccountCoreData // AccountCoreData reflection redefinition type _AuxAccountCoreData struct { *_AccountCoreDataAlias `bson:",inline" json:",inline"` CreatedAt int64 UpdatedAt int64 } ``` ----  ```go= func (accountCoreData AccountCoreData) MarshalJSON() ([]byte, error) { return json.Marshal(_AuxAccountCoreData{ _AccountCoreDataAlias: (*_AccountCoreDataAlias)(&accountCoreData), CreatedAt: accountCoreData.CreatedAt.Unix(), UpdatedAt: accountCoreData.UpdatedAt.Unix(), }) } ``` ----  ```go= func (accountCoreData *AccountCoreData) UnmarshalJSON(data []byte) error { aux := &_AuxAccountCoreData{ _AccountCoreDataAlias: (*_AccountCoreDataAlias)(accountCoreData), } err := json.Unmarshal(data, aux) if err != nil { return err } accountCoreData.CreatedAt = time.Unix(aux.CreatedAt, 0) accountCoreData.UpdatedAt = time.Unix(aux.UpdatedAt, 0) return nil } ``` ---  ## new coming problem ---- ### case  ```go= type AccountInfo struct { AccountCoreData `bson:",inline" json:",inline"` BirthYear int64 Description string } ``` ----  ### try it call json.Marshal() or json.Unmarshal() ... * BirthYear and Description are gone ----  ### reason #### why? ----  #### receiver fallback * AccountInfo.MarshalJSON() = AccountCoreData.MarshalJSON() * AccountInfo.UnmarshalJSON() = AccountCoreData.UnmarshalJSON() ----  ### dirty solution ----  ```go= // AccountInfo reflection redefinition type _AuxAccountInfo struct { *_AuxAccountCoreData `bson:",inline" json:",inline"` BirthYear *int64 Description *string } ``` ----  ```go= func (accountInfo AccountInfo) MarshalJSON() ([]byte, error) { return json.Marshal(_AuxAccountInfo{ _AuxAccountCoreData: &_AuxAccountCoreData{ _AccountCoreDataAlias: (*_AccountCoreDataAlias)(&accountInfo.AccountCoreData), CreatedAt: accountInfo.AccountCoreData.CreatedAt.Unix(), UpdatedAt: accountInfo.AccountCoreData.UpdatedAt.Unix(), }, BirthYear: &accountInfo.BirthYear, Description: &accountInfo.Description, }) } ``` ----  ```go= func (accountInfo *AccountInfo) UnmarshalJSON(data []byte) error { aux := &_AuxAccountInfo{ _AuxAccountCoreData: &_AuxAccountCoreData{ _AccountCoreDataAlias: (*_AccountCoreDataAlias)(&accountInfo.AccountCoreData), }, BirthYear: &accountInfo.BirthYear, Description: &accountInfo.Description, } err := json.Unmarshal(data, aux) if err != nil { return err } accountInfo.AccountCoreData.CreatedAt = time.Unix(aux._AuxAccountCoreData.CreatedAt, 0) accountInfo.AccountCoreData.UpdatedAt = time.Unix(aux._AuxAccountCoreData.UpdatedAt, 0) return nil } ``` ----  #### code is like a sh*t!!! ---  ## better way ----  ```go= type UnixTime time.Time // MarshalJSON() and UnmarshalJSON() is gone ``` ----  ```go= type UnixTime struct { //anonymous field time.Time `bson:",inline" json:",inline"` } // 1. MarshalJSON() and UnmarshalJSON() is inherited // 2. keep bson or xml Marshal/Unmarshal ``` ----  ```go= func (unixTime UnixTime) MarshalJSON() ([]byte, error) { return json.Marshal(unixTime.Time.Unix()) } ``` ----  ```go= func (unixTime *UnixTime) UnmarshalJSON(data []byte) error { var unixTimeInt int64 err := json.Unmarshal(data, &unixTimeInt) if err != nil { return err } unixTime.Time = time.Unix(unixTimeInt, 0) return nil } ``` ----  #### Panacea? * :x: UnixTime as anonymous field of struct ---  ## summary ----  ### slogan ----  ![而是你要享受這個過程](http://i.imgur.com/SWwsRq3.jpg) http://i.imgur.com/SWwsRq3.jpg ----  ![不要太看重得與失, 而是你要享受這個過程](http://i.imgur.com/XDq9TWd.gif) http://i.imgur.com/XDq9TWd.gif ----  > :hash: "不要太看重得與失, 而是你要享受這個過程" > [name=田中謙介] [color=red] there are big stories in type, struct field, interface, and receiver ----  ### special thanks * Rayark Inc. * CTO & CIO * backend team * other teams ---  ## appendix ----  ### code to test marshal/unmarshal ----  ```go= package main import ( "encoding/json" "encoding/xml" "fmt" "time" ) type UnixTime struct { //anonymous field time.Time `bson:",inline" json:",inline"` } func (unixTime UnixTime) MarshalJSON() ([]byte, error) { return json.Marshal(unixTime.Time.Unix()) } func (unixTime *UnixTime) UnmarshalJSON(data []byte) error { var unixTimeInt int64 err := json.Unmarshal(data, &unixTimeInt) if err != nil { return err } unixTime.Time = time.Unix(unixTimeInt, 0) return nil } // AccountCoreData type AccountCoreData struct { Name string UUID string CreatedAt UnixTime UpdatedAt UnixTime //CreatedAt time.Time //UpdatedAt time.Time } /* // avoid inheritance!!! type _AccountCoreDataAlias AccountCoreData // AccountCoreData reflection redefinition type _AuxAccountCoreData struct { //*AccountCoreData `bson:",inline" json:",inline"` *_AccountCoreDataAlias `bson:",inline" json:",inline"` CreatedAt int64 UpdatedAt int64 } func (accountCoreData AccountCoreData) MarshalJSON() ([]byte, error) { return json.Marshal(_AuxAccountCoreData{ //AccountCoreData: &accountCoreData, _AccountCoreDataAlias: (*_AccountCoreDataAlias)(&accountCoreData), CreatedAt: accountCoreData.CreatedAt.Unix(), UpdatedAt: accountCoreData.UpdatedAt.Unix(), }) } func (accountCoreData *AccountCoreData) UnmarshalJSON(data []byte) error { aux := &_AuxAccountCoreData{ //AccountCoreData: accountCoreData, _AccountCoreDataAlias: (*_AccountCoreDataAlias)(accountCoreData), } err := json.Unmarshal(data, aux) if err != nil { return err } accountCoreData.CreatedAt = time.Unix(aux.CreatedAt, 0) accountCoreData.UpdatedAt = time.Unix(aux.UpdatedAt, 0) return nil } */ // AccountInfo type AccountInfo struct { AccountCoreData `bson:",inline" json:",inline"` BirthYear int64 Description string } /* // avoid inheritance!!! //type _AccountInfoAlias AccountInfo // AccountInfo reflection redefinition type _AuxAccountInfo struct { *_AuxAccountCoreData `bson:",inline" json:",inline"` BirthYear *int64 Description *string } func (accountInfo AccountInfo) MarshalJSON() ([]byte, error) { return json.Marshal(_AuxAccountInfo{ _AuxAccountCoreData: &_AuxAccountCoreData{ //AccountCoreData: &accountInfo.AccountCoreData, _AccountCoreDataAlias: (*_AccountCoreDataAlias)(&accountInfo.AccountCoreData), CreatedAt: accountInfo.AccountCoreData.CreatedAt.Unix(), UpdatedAt: accountInfo.AccountCoreData.UpdatedAt.Unix(), }, BirthYear: &accountInfo.BirthYear, Description: &accountInfo.Description, }) } func (accountInfo *AccountInfo) UnmarshalJSON(data []byte) error { aux := &_AuxAccountInfo{ _AuxAccountCoreData: &_AuxAccountCoreData{ //AccountCoreData: &accountInfo.AccountCoreData, _AccountCoreDataAlias: (*_AccountCoreDataAlias)(&accountInfo.AccountCoreData), }, BirthYear: &accountInfo.BirthYear, Description: &accountInfo.Description, } err := json.Unmarshal(data, aux) if err != nil { return err } accountInfo.AccountCoreData.CreatedAt = time.Unix(aux._AuxAccountCoreData.CreatedAt, 0) accountInfo.AccountCoreData.UpdatedAt = time.Unix(aux._AuxAccountCoreData.UpdatedAt, 0) return nil } */ func main() { accountCoreData := AccountCoreData{ Name: "Rasmus Faber", UUID: "123e4567-e89b-12d3-a456-426655440000", CreatedAt: UnixTime{Time: time.Now()}, UpdatedAt: UnixTime{Time: time.Unix(1501998000, 0)}, //CreatedAt: time.Now(), //UpdatedAt: time.Unix(1501998000, 0), } accountInfo := AccountInfo{ AccountCoreData: accountCoreData, BirthYear: 1979, Description: "Swedish pianist, DJ, remixer, composer, record producer, sound engineer, and founder of the record label Farplane Records.", } fmt.Println("account core data:") fmt.Println("original:") fmt.Println(accountCoreData) accountCoreDataJson, err := json.Marshal(accountCoreData) if err != nil { panic(err) } fmt.Println("JSON:") fmt.Println(string(accountCoreDataJson)) var accountCoreDataParsed AccountCoreData json.Unmarshal(accountCoreDataJson, &accountCoreDataParsed) fmt.Println("parsed:") fmt.Println(accountCoreDataParsed) accountCoreDataXML, err := xml.Marshal(accountCoreData) if err != nil { panic(err) } fmt.Println("XML:") fmt.Println(string(accountCoreDataXML)) fmt.Println("account info:") fmt.Println("original:") fmt.Println(accountInfo) accountInfoJson, err := json.Marshal(accountInfo) if err != nil { panic(err) } fmt.Println("JSON:") fmt.Println(string(accountInfoJson)) var accountInfoParsed AccountInfo json.Unmarshal(accountInfoJson, &accountInfoParsed) fmt.Println("parsed:") fmt.Println(accountInfoParsed) accountInfoXML, err := xml.Marshal(accountInfo) if err != nil { panic(err) } fmt.Println("XML:") fmt.Println(string(accountInfoXML)) } ``` ---  ## Q&A --- <style> .reveal code { font-size: 12px !important; line-height: 1.2; } body { background-color: Indigo; } .rightpart{ float:right; width:50%; } .leftpart{ margin-right: 50% !important; height:50%; } .reveal section img { background:none; border:none; box-shadow:none; } p.blo { font-size: 50px !important; background:#B6BDBB; border:1px solid silver; 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Syntax	Example	Reference
# Header	Header	基本排版
- Unordered List	Unordered List
1. Ordered List	Ordered List
- [ ] Todo List	Todo List
> Blockquote	Blockquote
Bold font	Bold font
Italics font	Italics font
~~Strikethrough~~	~~Strikethrough~~
19^th^	19^th
H~2~O	H₂O
++Inserted text++	Inserted text
==Marked text==	Marked text
[link text](https:// "title")	Link
![image alt](https:// "title")	Image
`Code`	`Code`	在筆記中貼入程式碼
```javascript var i = 0; ```	`var i = 0;`
:smile:		Emoji list
{%youtube youtube_id %}	Externals
$L^aT_eX$	L^aT_eX
:::info This is a alert area. :::	This is a alert area.