feat: const validation support

fixes #472

Author: perher

pkg/generator/schema_generator.go

@@ -392,10 +392,19 @@ func (g *schemaGenerator) structFieldValidators(
 case codegen.PrimitiveType:
 if v.Type == schemas.TypeNameString {
 hasPattern := len(f.SchemaType.Pattern) != 0
-if f.SchemaType.MinLength != 0 || f.SchemaType.MaxLength != 0 || hasPattern {
+if f.SchemaType.MinLength != 0 || f.SchemaType.MaxLength != 0 || hasPattern || f.SchemaType.Const != nil {
 // Double escape the escape characters so we don't effectively parse the escapes within the value.
 escapedPattern := f.SchemaType.Pattern
 
+var constVal *string
+if f.SchemaType.Const != nil {
+if s, ok := f.SchemaType.Const.(string); ok {
+constVal = &s
+} else {
+g.warner(fmt.Sprintf("Ignoring non string const value: %v", f.SchemaType.Const))
+}
+}
+
 replaceJSONCharactersBy := []string{"\\b", "\\f", "\\n", "\\r", "\\t"}
 
 replaceJSONCharacters := []string{"\b", "\f", "\n", "\r", "\t"}
@@ -410,6 +419,7 @@ func (g *schemaGenerator) structFieldValidators(
 minLength: f.SchemaType.MinLength,
 maxLength: f.SchemaType.MaxLength,
 pattern: escapedPattern,
+constVal: constVal,
 isNillable: isNillable,
 })
 }
@@ -422,7 +432,8 @@ func (g *schemaGenerator) structFieldValidators(
 f.SchemaType.Maximum != nil ||
 f.SchemaType.ExclusiveMaximum != nil ||
 f.SchemaType.Minimum != nil ||
-f.SchemaType.ExclusiveMinimum != nil {
+f.SchemaType.ExclusiveMinimum != nil ||
+f.SchemaType.Const != nil {
 validators = append(validators, &numericValidator{
 jsonName: f.JSONName,
 fieldName: f.Name,
@@ -432,13 +443,31 @@ func (g *schemaGenerator) structFieldValidators(
 exclusiveMaximum: f.SchemaType.ExclusiveMaximum,
 minimum: f.SchemaType.Minimum,
 exclusiveMinimum: f.SchemaType.ExclusiveMinimum,
+constVal: f.SchemaType.Const,
 roundToInt: strings.Contains(v.Type, "int"),
 })
 }
 
 if f.SchemaType.MultipleOf != nil && v.Type == float64Type {
 g.output.file.Package.AddImport("math", "")
 }
+} else if v.Type == "bool" {
+if f.SchemaType.Const != nil {
+var constVal *bool
+if f.SchemaType.Const != nil {
+if b, ok := f.SchemaType.Const.(bool); ok {
+constVal = &b
+} else {
+g.warner(fmt.Sprintf("Ignoring non boolean const value: %v", f.SchemaType.Const))
+}
+}
+validators = append(validators, &booleanValidator{
+jsonName: f.JSONName,
+fieldName: f.Name,
+isNillable: isNillable,
+constVal: constVal,
+})
+}
 }
 
 case *codegen.ArrayType:

pkg/generator/validator.go

@@ -348,6 +348,7 @@ type stringValidator struct {
 maxLength int
 isNillable bool
 pattern string
+constVal *string
 }
 
 func (v *stringValidator) generate(out *codegen.Emitter, unmarshalTemplate string) error {
@@ -385,6 +386,14 @@ func (v *stringValidator) generate(out *codegen.Emitter, unmarshalTemplate strin
 }
 }
 
+if v.constVal != nil {
+out.Printlnf(`if %s%s%s != "%s" {`, checkPointer, pointerPrefix, value, *v.constVal)
+out.Indent(1)
+out.Printlnf(`return fmt.Errorf("field %%s: must be equal to %%s", "%s", "%s")`, fieldName, *v.constVal)
+out.Indent(-1)
+out.Printlnf("}")
+}
+
 if v.minLength == 0 && v.maxLength == 0 {
 return nil
 }
@@ -424,6 +433,7 @@ type numericValidator struct {
 exclusiveMaximum *any
 minimum *float64
 exclusiveMinimum *any
+constVal any
 roundToInt bool
 }
 
@@ -437,6 +447,14 @@ func (v *numericValidator) generate(out *codegen.Emitter, unmarshalTemplate stri
 pointerPrefix = "*"
 }
 
+if v.constVal != nil {
+out.Printlnf(`if %s%s%s != %v {`, checkPointer, pointerPrefix, value, v.constVal)
+out.Indent(1)
+out.Printlnf(`return fmt.Errorf("field %%s: must be equal to %%v", "%s", %v)`, v.jsonName, v.constVal)
+out.Indent(-1)
+out.Printlnf("}")
+}
+
 if v.multipleOf != nil {
 if v.roundToInt {
 out.Printlnf(`if %s %s%s %% %v != 0 {`, checkPointer, pointerPrefix, value, v.valueOf(*v.multipleOf))
@@ -519,6 +537,42 @@ func (v *numericValidator) valueOf(val float64) any {
 return val
 }
 
+type booleanValidator struct {
+jsonName string
+fieldName string
+isNillable bool
+constVal *bool
+}
+
+func (v *booleanValidator) generate(out *codegen.Emitter, unmarshalTemplate string) error {
+value := getPlainName(v.fieldName)
+fieldName := v.jsonName
+checkPointer := ""
+pointerPrefix := ""
+
+if v.isNillable {
+checkPointer = fmt.Sprintf("%s != nil && ", value)
+pointerPrefix = "*"
+}
+
+if v.constVal != nil {
+out.Printlnf(`if %s%s%s != %t {`, checkPointer, pointerPrefix, value, *v.constVal)
+out.Indent(1)
+out.Printlnf(`return fmt.Errorf("field %%s: must be equal to %%t", "%s", %t)`, fieldName, *v.constVal)
+out.Indent(-1)
+out.Printlnf("}")
+}
+
+return nil
+}
+
+func (v *booleanValidator) desc() *validatorDesc {
+return &validatorDesc{
+hasError: true,
+beforeJSONUnmarshal: false,
+}
+}
+
 func getPlainName(fieldName string) string {
 if fieldName == "" {
 return varNamePlainStruct

pkg/schemas/model.go

@@ -170,6 +170,7 @@ type Type struct {
 AdditionalProperties *Type `json:"additionalProperties,omitempty"` // Section 5.18.
 Enum []interface{} `json:"enum,omitempty"` // Section 5.20.
 Type TypeList `json:"type,omitempty"` // Section 5.21.
+Const interface{} `json:"const,omitempty"`
 // RFC draft-bhutton-json-schema-01, section 10.
 AllOf []*Type `json:"allOf,omitempty"` // Section 10.2.1.1.
 AnyOf []*Type `json:"anyOf,omitempty"` // Section 10.2.1.2.

tests/data/core/const/const.go

@@ -0,0 +1,52 @@
+{
+ "$schema": "http://json-schema.org/draft-04/schema#",
+ "id": "https://example.com/primitives",
+ "type": "object",
+ "properties": {
+ "myString": {
+ "type": "string",
+ "const": "foo"
+ },
+ "myNumber": {
+ "type": "number",
+ "const": 4.2
+ },
+ "myInteger": {
+ "type": "integer",
+ "const": 42
+ },
+ "myBoolean": {
+ "type": "boolean",
+ "const": true
+ }
+ },
+ "$defs": {
+ "Required": {
+ "type": "object",
+ "properties": {
+ "myString": {
+ "type": "string",
+ "const": "foo"
+ },
+ "myNumber": {
+ "type": "number",
+ "const": 4.2
+ },
+ "myInteger": {
+ "type": "integer",
+ "const": 42
+ },
+ "myBoolean": {
+ "type": "boolean",
+ "const": true
+ }
+ },
+ "required": [
+ "myString",
+ "myNumber",
+ "myInteger",
+ "myBoolean"
+ ]
+ }
+ }
+}