kensniper/go-tagexpr

An interesting go struct tag expression syntax for field validation, etc.

go-tagexpr

An interesting go struct tag expression syntax for field validation, etc.

Usage

• Validator: A powerful validator that supports struct tag expression

• Binding: A powerful HTTP request parameters binder that supports struct tag expression

Feature

• Support for a variety of common operator
• Support for accessing arrays, slices, members of the dictionary
• Support access to any field in the current structure
• Support access to nested fields, non-exported fields, etc.
• Support registers function expression
• Built-in len, sprintf, regexp functions
• Support single mode and multiple mode to define expression
• Parameter check subpackage
• Use offset pointers to directly take values, better performance
• Required go version ≥1.9

Example

package tagexpr_test

import (
	"fmt"

	tagexpr "github.com/bytedance/go-tagexpr/v2"
)

func Example() {
	type T struct {
		A  int             `tagexpr:"$<0||$>=100"`
		B  string          `tagexpr:"len($)>1 && regexp('^\\w*$')"`
		C  bool            `tagexpr:"expr1:(f.g)$>0 && $; expr2:'C must be true when T.f.g>0'"`
		d  []string        `tagexpr:"@:len($)>0 && $[0]=='D'; msg:sprintf('invalid d: %v',$)"`
		e  map[string]int  `tagexpr:"len($)==$['len']"`
		e2 map[string]*int `tagexpr:"len($)==$['len']"`
		f  struct {
			g int `tagexpr:"$"`
		}
	}

	vm := tagexpr.New("tagexpr")
	t := &T{
		A:  107,
		B:  "abc",
		C:  true,
		d:  []string{"x", "y"},
		e:  map[string]int{"len": 1},
		e2: map[string]*int{"len": new(int)},
		f: struct {
			g int `tagexpr:"$"`
		}{1},
	}

	tagExpr, err := vm.Run(t)
	if err != nil {
		panic(err)
	}

	fmt.Println(tagExpr.Eval("A"))
	fmt.Println(tagExpr.Eval("B"))
	fmt.Println(tagExpr.Eval("C@expr1"))
	fmt.Println(tagExpr.Eval("C@expr2"))
	if !tagExpr.Eval("d").(bool) {
		fmt.Println(tagExpr.Eval("d@msg"))
	}
	fmt.Println(tagExpr.Eval("e"))
	fmt.Println(tagExpr.Eval("e2"))
	fmt.Println(tagExpr.Eval("f.g"))

	// Output:
	// true
	// true
	// true
	// C must be true when T.f.g>0
	// invalid d: [x y]
	// true
	// false
	// 1
}

Syntax

Struct tag syntax spec:

type T struct {
	// Single model
    Field1 T1 `tagName:"expression"`
	// Multiple model
    Field2 T2 `tagName:"exprName:expression; [exprName2:expression2;]..."`
	// Omit it
    Field3 T3 `tagName:"-"`
    // Omit it when it is nil
    Field4 T4 `tagName:"?"`
    ...
}

NOTE: The exprName under the same struct field cannot be the same！

Operator or Operand	Explain
true false	boolean
0 0.0	float64 "0"
''	String
\\'	Escape ' delims in string
\"	Escape " delims in string
nil	nil, undefined
!	not
+	Digital addition or string splicing
-	Digital subtraction or negative
*	Digital multiplication
/	Digital division
%	division remainder, as: float64(int64(a)%int64(b))
==	eq
!=	ne
>	gt
>=	ge
<	lt
<=	le
&&	Logic and
||	Logic or
()	Expression group
(X)$	Struct field value named X
(X.Y)$	Struct field value named X.Y
$	Shorthand for (X)$, omit (X) to indicate current struct field value
(X)$['A']	Map value with key A or struct A sub-field in the struct field X
(X)$[0]	The 0th element or sub-field of the struct field X(type: map, slice, array, struct)
len((X)$)	Built-in function len, the length of struct field X
mblen((X)$)	the length of string field X (character number)
regexp('^\\w*$', (X)$)	Regular match the struct field X, return boolean
regexp('^\\w*$')	Regular match the current struct field, return boolean
sprintf('X value: %v', (X)$)	fmt.Sprintf, format the value of struct field X
range(KvExpr, forEachExpr)	Iterate over an array, slice, or dictionary - #k is the element key var - #v is the element value var - ## is the number of elements - e.g. example

Operator priority(high -> low):

• () ! bool float64 string nil
• * / %
• + -
• < <= > >=
• == !=
• &&
• ||

Field Selector

field_lv1.field_lv2...field_lvn

Expression Selector

• If expression is single model or exprName is @:

field_lv1.field_lv2...field_lvn

• If expression is multiple model and exprName is not @:

field_lv1.field_lv2...field_lvn@exprName

Benchmark

goos: darwin
goarch: amd64
pkg: github.com/bytedance/go-tagexpr
BenchmarkTagExpr-4   	10000000	       148 ns/op	      32 B/op	       3 allocs/op
BenchmarkReflect-4   	10000000	       182 ns/op	      16 B/op	       2 allocs/op
PASS

Go to test code