sheriff
go get github.com/liip/sheriff
Package sheriff marshals structs conditionally based on tags on the fields.
A typical use is an API which marshals structs into JSON and maintains different API versions. Using sheriff, struct fields can be annotated with API version and group tags.
By invoking sheriff with specific options, those tags determine whether a field will be added to the output map or not. It can then be marshalled using "encoding/json".
NOTE: This package is tested only on Go 1.7+, it might work on Go 1.6 too, but no support is given.
Implemented tags
Groups
Groups can be used for limiting the output based on freely defined parameters. For example: restrict marshalling the email
address of a user to the user itself by just adding the group personal if the user fetches his profile.
Multiple groups can be separated by comma.
Example:
type GroupsExample struct {
Username string `json:"username" groups:"api"`
Email string `json:"email" groups:"personal"`
SomethingElse string `json:"something_else" groups:"api,personal"`
}Anonymous fields
Tags added to a struct’s anonymous field propagates to the inner-fields if no other tags are specified.
Example:
type UserInfo struct {
UserPrivateInfo `groups:"private"`
UserPublicInfo `groups:"public"`
}
type UserPrivateInfo struct {
Age string
}
type UserPublicInfo struct {
ID string
Email string
}Since
Since specifies the version since that field is available. It's inclusive and SemVer compatible using
github.com/hashicorp/go-version.
If you specify version 2 in a tag, this version will be output in case you specify version >=2.0.0 as the API version.
Example:
type SinceExample struct {
Username string `json:"username" since:"2.1.0"`
Email string `json:"email" since:"2"`
}Until
Until specifies the version until that field is available. It's the opposite of since, inclusive and SemVer
compatible using github.com/hashicorp/go-version.
If you specify version 2 in a tag, this version will be output in case you specify version <=2.0.0 as the API version.
Example:
type UntilExample struct {
Username string `json:"username" until:"2.1.0"`
Email string `json:"email" until:"2"`
}Example
package main
import (
"encoding/json"
"fmt"
"log"
"github.com/hashicorp/go-version"
"github.com/liip/sheriff"
)
type User struct {
Username string `json:"username" groups:"api"`
Email string `json:"email" groups:"personal"`
Name string `json:"name" groups:"api"`
Roles []string `json:"roles" groups:"api" since:"2"`
}
type UserList []User
func MarshalUsers(version *version.Version, groups []string, users UserList) ([]byte, error) {
o := &sheriff.Options{
Groups: groups,
ApiVersion: version,
}
data, err := sheriff.Marshal(o, users)
if err != nil {
return nil, err
}
return json.MarshalIndent(data, "", " ")
}
func main() {
users := UserList{
User{
Username: "alice",
Email: "alice@example.org",
Name: "Alice",
Roles: []string{"user", "admin"},
},
User{
Username: "bob",
Email: "bob@example.org",
Name: "Bob",
Roles: []string{"user"},
},
}
v1, err := version.NewVersion("1.0.0")
if err != nil {
log.Panic(err)
}
v2, err := version.NewVersion("2.0.0")
output, err := MarshalUsers(v1, []string{"api"}, users)
if err != nil {
log.Panic(err)
}
fmt.Println("Version 1 output:")
fmt.Printf("%s\n\n", output)
output, err = MarshalUsers(v2, []string{"api"}, users)
if err != nil {
log.Panic(err)
}
fmt.Println("Version 2 output:")
fmt.Printf("%s\n\n", output)
output, err = MarshalUsers(v2, []string{"api", "personal"}, users)
if err != nil {
log.Panic(err)
}
fmt.Println("Version 2 output with personal group too:")
fmt.Printf("%s\n\n", output)
}
// Output:
// Version 1 output:
// [
// {
// "name": "Alice",
// "username": "alice"
// },
// {
// "name": "Bob",
// "username": "bob"
// }
// ]
//
// Version 2 output:
// [
// {
// "name": "Alice",
// "roles": [
// "user",
// "admin"
// ],
// "username": "alice"
// },
// {
// "name": "Bob",
// "roles": [
// "user"
// ],
// "username": "bob"
// }
// ]
//
// Version 2 output with personal group too:
// [
// {
// "email": "alice@example.org",
// "name": "Alice",
// "roles": [
// "user",
// "admin"
// ],
// "username": "alice"
// },
// {
// "email": "bob@example.org",
// "name": "Bob",
// "roles": [
// "user"
// ],
// "username": "bob"
// }
// ]Benchmarks
There's a simple benchmark in bench_test.go which compares running sheriff -> JSON versus just marshalling into JSON
and runs on every build. Just marshalling JSON itself takes usually between 3 and 5 times less nanoseconds per operation
compared to running sheriff and JSON.
Want to make sheriff faster? Please send us your pull request or open an issue discussing a possible improvement
Acknowledgements
- This idea and code has been created partially during a Liip hackday.
- Thanks to @basgys for reviews & improvements.
Related projects
mweibel/php-to-go is a code generator translating PHP models (using JMS serializer) to Go structs with sheriff tags. The two projects were initially developed together and just recently php-to-go has been split out and published too.
