Allow structs to be self-verifying.

main.go

@@ -32,6 +32,7 @@ var (
 	tags                []string
 	structNameFromTitle bool
 	minSizedInts        bool
+	structVerify        bool
 
 	errFlagFormat = errors.New("flag must be in the format URI=PACKAGE")
 
@@ -77,6 +78,7 @@ var (
 				Tags:                tags,
 				OnlyModels:          onlyModels,
 				MinSizedInts:        minSizedInts,
+				StructVerify:        structVerify,
 			}
 			for _, id := range allKeys(schemaPackageMap, schemaOutputMap, schemaRootTypeMap) {
 				mapping := generator.SchemaMapping{SchemaID: id}
@@ -174,6 +176,12 @@ also look for foo.json if --resolve-extension json is provided.`)
 		false,
 		"Uses sized int and uint values based on the min and max values for the field")
 
+	rootCmd.PersistentFlags().BoolVar(
+		&structVerify,
+		"struct-verify",
+		false,
+		"Add a Verify method to the generated struct that validates the struct against the schema")
+
 	abortWithErr(rootCmd.Execute())
 }
 

pkg/generator/config.go

@@ -16,6 +16,7 @@ type Config struct {
 	OnlyModels          bool
 	MinSizedInts        bool
 	Loader              schemas.Loader
+	StructVerify        bool
 }
 
 type SchemaMapping struct {

pkg/generator/generate.go

@@ -53,6 +53,10 @@ func New(config Config) (*Generator, error) {
 		formatters = append(formatters, &yamlFormatter{})
 	}
 
+	if config.StructVerify {
+		formatters = append(formatters, &verifyFormatter{})
+	}
+
 	generator := &Generator{
 		caser:      text.NewCaser(config.Capitalizations, config.ResolveExtensions),
 		config:     config,

pkg/generator/json_formatter.go

@@ -105,10 +105,7 @@ func (jf *jsonFormatter) enumUnmarshal(
 		enumType.Generate(out)
 		out.Newline()
 
-		varName := "v"
-		if wrapInStruct {
-			varName += ".Value"
-		}
+		varName := enumVarName(wrapInStruct)
 
 		out.Printlnf("if err := json.Unmarshal(b, &%s); err != nil { return err }", varName)
 		out.Printlnf("var ok bool")

pkg/generator/utils.go

@@ -45,3 +45,13 @@ func isNamedType(t codegen.Type) bool {
 
 	return false
 }
+
+func enumVarName(wrapInStruct bool) string {
+	varName := "v"
+
+	if wrapInStruct {
+		varName += ".Value"
+	}
+
+	return varName
+}

pkg/generator/verify_formatter.go

@@ -0,0 +1,195 @@
+package generator
+
+import (
+	"strings"
+
+	"github.com/atombender/go-jsonschema/pkg/codegen"
+)
+
+type verifyFormatter struct{}
+
+func (v verifyFormatter) addImport(_ *codegen.File) {}
+
+func (v verifyFormatter) generate(declType codegen.TypeDecl, validators []validator) func(*codegen.Emitter) {
+	return func(out *codegen.Emitter) {
+		var prefix string
+		switch declType.Type.(type) {
+		// No need to dereference the struct just to verify it.
+		case *codegen.StructType:
+			prefix = "*"
+
+		default:
+			prefix = ""
+		}
+
+		out.Comment("Verify checks all fields on the struct match the schema.")
+		out.Printlnf("func (%s %s%s) Verify() error {", varNamePlainStruct, prefix, declType.Name)
+		out.Indent(1)
+
+		for _, va := range validators {
+			desc := va.desc()
+			if desc.beforeJSONUnmarshal || desc.requiresRawAfter || !desc.hasError {
+				continue
+			}
+
+			va.generate(out)
+		}
+
+		if stct, ok := declType.Type.(*codegen.StructType); ok {
+			for _, field := range stct.Fields {
+				name := strings.ToLower(field.Name[0:1]) + field.Name[1:]
+				if verifyEmit := v.verifyType(field.Type, name); verifyEmit != nil {
+					out.Printlnf("%s := %s", name, getPlainName(field.Name))
+					verifyEmit(out)
+				}
+			}
+		}
+
+		out.Printlnf("return nil")
+		out.Indent(-1)
+		out.Printlnf("}")
+	}
+}
+
+func (v verifyFormatter) verifyType(tpe codegen.Type, access string) func(*codegen.Emitter) {
+	// For some types, pointers are sometimes used and sometime not.
+	switch utpe := tpe.(type) {
+	case *codegen.ArrayType:
+		return v.verifyArray(*utpe, access)
+
+	case codegen.ArrayType:
+		return v.verifyArray(utpe, access)
+
+	case codegen.CustomNameType, *codegen.CustomNameType, codegen.NamedType, *codegen.NamedType, *codegen.StructType:
+		return func(out *codegen.Emitter) {
+			out.Printlnf("if err := %s.Verify(); err != nil {", access)
+			out.Indent(1)
+			out.Printlnf("return err")
+			out.Indent(-1)
+			out.Printlnf("}")
+		}
+
+	case *codegen.MapType:
+		return v.verifyMap(*utpe, access)
+
+	case codegen.MapType:
+		return v.verifyMap(utpe, access)
+
+	case *codegen.PointerType:
+		return v.verifyPointer(*utpe, access)
+
+	case codegen.PointerType:
+		return v.verifyPointer(utpe, access)
+
+	default:
+		return nil
+	}
+}
+
+func (v verifyFormatter) enumMarshal(_ codegen.TypeDecl) func(*codegen.Emitter) {
+	return func(out *codegen.Emitter) {}
+}
+
+func (v verifyFormatter) enumUnmarshal(
+	declType codegen.TypeDecl,
+	_ codegen.Type,
+	valueConstant *codegen.Var,
+	wrapInStruct bool,
+) func(*codegen.Emitter) {
+	return func(out *codegen.Emitter) {
+		varName := enumVarName(wrapInStruct)
+
+		out.Comment("Verify checks all fields on the struct match the schema.")
+		out.Printlnf("func (%s %s) Verify() error {", varNamePlainStruct, declType.Name)
+		out.Indent(1)
+		out.Printlnf("for _, expected := range %s {", valueConstant.Name)
+		out.Indent(1)
+		out.Printlnf("if reflect.DeepEqual(%s, expected) { return nil }", varName)
+		out.Indent(-1)
+		out.Printlnf("}")
+		out.Printlnf(`return fmt.Errorf("invalid value (expected one of %%#v): %%#v", %s, %s)`,
+			valueConstant.Name, varName)
+		out.Indent(-1)
+		out.Printlnf("}")
+	}
+}
+
+func (v verifyFormatter) verifyArray(tpe codegen.ArrayType, access string) func(*codegen.Emitter) {
+	aaccess := "a" + access
+
+	verifyFn := v.verifyType(tpe.Type, aaccess)
+	if verifyFn == nil {
+		return nil
+	}
+
+	return func(out *codegen.Emitter) {
+		out.Printlnf("for _, %s := range %s {", aaccess, access)
+		out.Indent(1)
+		verifyFn(out)
+		out.Indent(-1)
+		out.Printlnf("}")
+	}
+}
+
+func (v verifyFormatter) verifyMap(tpe codegen.MapType, access string) func(*codegen.Emitter) {
+	keyAccess := "k" + access
+	valueAccess := "v" + access
+	verifyKeyFn := v.verifyType(tpe.KeyType, keyAccess)
+	verifyValueFn := v.verifyType(tpe.ValueType, valueAccess)
+
+	if verifyKeyFn == nil && verifyValueFn == nil {
+		return nil
+	}
+
+	if verifyKeyFn == nil {
+		keyAccess = "_"
+	}
+
+	if verifyValueFn == nil {
+		valueAccess = "_"
+	}
+
+	return func(out *codegen.Emitter) {
+		out.Printlnf("for %s, %s := range %s {", keyAccess, valueAccess, access)
+		out.Indent(1)
+
+		if verifyKeyFn != nil {
+			verifyKeyFn(out)
+		}
+
+		if verifyValueFn != nil {
+			verifyValueFn(out)
+		}
+
+		out.Indent(-1)
+		out.Printlnf("}")
+	}
+}
+
+func (v verifyFormatter) verifyPointer(tpe codegen.PointerType, access string) func(*codegen.Emitter) {
+	var prefix string
+	switch tpe.Type.(type) {
+	// Access the verify and fields without copying it.
+	case codegen.CustomNameType, *codegen.CustomNameType, codegen.NamedType, *codegen.NamedType:
+		prefix = ""
+
+	default:
+		prefix = "*"
+	}
+
+	paccess := "p" + access
+
+	verifyFn := v.verifyType(tpe.Type, paccess)
+	if verifyFn == nil {
+		return nil
+	}
+
+	return func(out *codegen.Emitter) {
+		out.Printlnf("if %s != nil {", access)
+		out.Printlnf("%s := %s%s", paccess, prefix, access)
+		out.Indent(1)
+		verifyFn(out)
+		out.Indent(-1)
+		out.Printlnf("}")
+	}
+}

pkg/generator/yaml_formatter.go

@@ -108,10 +108,7 @@ func (yf *yamlFormatter) enumUnmarshal(
 		enumType.Generate(out)
 		out.Newline()
 
-		varName := "v"
-		if wrapInStruct {
-			varName += ".Value"
-		}
+		varName := enumVarName(wrapInStruct)
 
 		out.Printlnf("if err := value.Decode(&%s); err != nil { return err }", varName)
 		out.Printlnf("var ok bool")