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result_type.go
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result_type.go
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package dsl
import (
"fmt"
"mime"
"strings"
"goa.design/goa/eval"
"goa.design/goa/expr"
)
// Counter used to create unique result type names for identifier-less result
// types.
var resultTypeCount int
// ResultType defines a result type used to describe a method response.
//
// Result types have a unique identifier as described in RFC 6838. The
// identifier defines the default value for the Content-Type header of HTTP
// responses. Result types may also define a type name used to override the
// default Go type name generated from the identifier.
//
// The result type expression includes a listing of all the response attributes.
// Views specify which of the attributes are actually rendered so that the same
// result type expression may represent multiple rendering of a given response.
//
// All result types have a view named "default". This view is used to render the
// result type in responses when no other view is specified. If the default view
// is not explicitly described in the DSL then one is created that lists all the
// result type attributes.
//
// Note: it is not required to use a ResultType to describe the type of a method
// result, Type can also be used and is preferred if there is no need to define
// multiple views.
//
// ResultType is a top level DSL.
//
// ResultType accepts two or three arguments: the result type identifier, an
// optional type name and the defining DSL.
//
// Example:
//
// var BottleMT = ResultType("application/vnd.goa.example.bottle", "BottleResult", func() {
// Description("A bottle of wine")
// ContentType("application/json") // Override Content-Type header
//
// Attributes(func() {
// Attribute("id", Int, "ID of bottle")
// Attribute("href", String, "API href of bottle")
// Attribute("account", Account, "Owner account")
// Attribute("origin", Origin, "Details on wine origin")
// Required("id", "href")
// })
//
// View("default", func() { // Explicitly define default view
// Attribute("id")
// Attribute("href")
// })
//
// View("extended", func() { // Define "extended" view
// Attribute("id")
// Attribute("href")
// Attribute("account")
// Attribute("origin")
// })
// })
//
func ResultType(identifier string, args ...interface{}) *expr.ResultTypeExpr {
if _, ok := eval.Current().(eval.TopExpr); !ok {
eval.IncompatibleDSL()
return nil
}
var (
typeName string
fn func()
)
{
var err error
identifier, typeName, err = mediaTypeToResultType(identifier)
if err != nil {
eval.ReportError("invalid result type identifier %#v: %s", identifier, err)
// We don't return so that other errors may be captured
}
if len(args) > 0 {
switch a := args[0].(type) {
case func():
fn = a
case string:
typeName = a
default:
eval.InvalidArgError("function or string", args[0])
}
if len(args) > 1 {
if fn != nil {
eval.ReportError("DSL function must be last argument")
}
if f, ok := args[1].(func()); ok {
fn = f
} else {
eval.InvalidArgError("function", args[1])
}
if len(args) > 2 {
eval.ReportError("too many arguments")
}
}
}
}
canonicalID := expr.CanonicalIdentifier(identifier)
// Validate that result type identifier doesn't clash
for _, rt := range expr.Root.ResultTypes {
if re := rt.(*expr.ResultTypeExpr); re.Identifier == canonicalID {
eval.ReportError(
"result type %#v with canonical identifier %#v is defined twice",
identifier, canonicalID)
return nil
}
}
// Now save the type in the API result types map
mt := expr.NewResultTypeExpr(typeName, identifier, fn)
expr.Root.ResultTypes = append(expr.Root.ResultTypes, mt)
return mt
}
// TypeName makes it possible to set the Go struct name for a type or result
// type in the generated code. By default goa uses the name (type) or identifier
// (result type) given in the DSL and computes a valid Go identifier from it.
// This function makes it possible to override that and provide a custom name.
// name must be a valid Go identifier.
//
// TypeName must appear in a Type or ResultType expression.
func TypeName(name string) {
switch e := eval.Current().(type) {
case expr.UserType:
e.Rename(name)
case *expr.AttributeExpr:
e.AddMeta("struct:type:name", name)
default:
eval.IncompatibleDSL()
}
}
// View has two usages:
//
// - when used inside a ResultType DSL function it defines a view for the result
// type. A view lists a subset of the result type attributes that are used when
// marshalling responses.
//
// - when used inside a Result DSL function it defines the view used to marshal
// the result type returned by the method.
//
// Note that the view used to render a response can also be set dynamically by
// the method code in which case the result function should not specify a view
// in the design. The attribute names listed in a view must be identical to
// existing attributes in the result type on which the view is defined. If an
// attribute is itself a result type then the view may specify which view to use
// when marshaling the attribute using the View function recursively, see
// example below. All result types must have a view called "default" which is
// the view used to marshal results when no specific view is specified.
//
// View must appear in a ResultType or a Result expression.
//
// View accepts two arguments for the first usage: the view name and its
// defining DSL. View accepts a single argument for the second usage: the view
// name used to render the result.
//
// Examples:
//
// // MyResultType defines 2 views.
// var MyResultType = ResultType("application/vnd.goa.my", func() {
// Attributes(func() {
// Attribute("id", String)
// Attribute("name", String)
// Attribute("origin", OriginResult)
// })
//
// View("default", func() {
// // "id" and "name" must be result type attributes
// Attribute("id")
// Attribute("name")
// })
//
// View("extended", func() {
// Attribute("id")
// Attribute("name")
// Attribute("origin", func() {
// // Use view "extended" to render attribute "origin"
// View("extended")
// })
// })
// })
//
// // MyMethod uses the extended view of MyResultType to marshal the
// // response.
// var _ = Service("MyService", func() {
// Method("MyMethod", func() {
// Result(MyResultType, func() { View("extended") })
// GRPC(func() {})
// })
// })
//
func View(name string, adsl ...func()) {
switch e := eval.Current().(type) {
case *expr.ResultTypeExpr:
mt := e
if mt.View(name) != nil {
eval.ReportError("multiple expressions for view %#v in result type %#v", name, mt.TypeName)
return
}
at := &expr.AttributeExpr{}
ok := false
if len(adsl) > 0 {
ok = eval.Execute(adsl[0], at)
} else if a, ok := mt.Type.(*expr.Array); ok {
// inherit view from collection element if present
elem := a.ElemType
if elem != nil {
if pa, ok2 := elem.Type.(*expr.ResultTypeExpr); ok2 {
if v := pa.View(name); v != nil {
at = v.AttributeExpr
ok = true
} else {
eval.ReportError("unknown view %#v", name)
return
}
}
}
}
if ok {
view, err := buildView(name, mt, at)
if err != nil {
eval.ReportError(err.Error())
return
}
mt.Views = append(mt.Views, view)
}
case *expr.AttributeExpr:
e.AddMeta("view", name)
default:
eval.IncompatibleDSL()
}
}
// CollectionOf creates a collection result type from its element result type. A
// collection result type represents the content of responses that return a
// collection of values such as listings. The expression accepts an optional DSL
// as second argument that allows specifying which view(s) of the original result
// type apply.
//
// The resulting result type identifier is built from the element result type by
// appending the result type parameter "type" with value "collection".
//
// CollectionOf must appear wherever ResultType can.
//
// CollectionOf takes the element result type as first argument and an optional
// DSL as second argument.
//
// Example:
//
// var DivisionResult = ResultType("application/vnd.goa.divresult", func() {
// Attributes(func() {
// Attribute("value", Float64)
// Attribute("remainder", Int)
// })
// View("default", func() {
// Attribute("value")
// Attribute("remainder")
// })
// View("tiny", func() {
// Attribute("value")
// })
// })
//
// var MultiResults = CollectionOf(DivisionResult)
//
// var TinyMultiResults = CollectionOf(DivisionResult, func() {
// View("tiny") // use "tiny" view to render the collection elements
// })
//
func CollectionOf(v interface{}, adsl ...func()) *expr.ResultTypeExpr {
var m *expr.ResultTypeExpr
var ok bool
m, ok = v.(*expr.ResultTypeExpr)
if !ok {
if id, ok := v.(string); ok {
// Check if a result type exists with the given type name
if dt := expr.Root.UserType(id); dt != nil {
if mt, ok := dt.(*expr.ResultTypeExpr); ok {
m = mt
}
} else {
// Check if a result type exists with the given identifier
id, typeName, err := mediaTypeToResultType(id)
if dt := expr.Root.UserType(typeName); dt != nil {
if mt, ok := dt.(*expr.ResultTypeExpr); ok {
m = mt
}
}
if err != nil {
eval.ReportError("invalid result type identifier %#v in CollectionOf: %s", id, err)
}
}
}
}
if m == nil {
eval.ReportError("invalid CollectionOf argument: not a result type and not a known result type identifier")
// don't return nil to avoid panics, the error will get reported at the end
return expr.NewResultTypeExpr("InvalidCollection", "text/plain", nil)
}
id := m.Identifier
rtype, params, err := mime.ParseMediaType(id)
if err != nil {
eval.ReportError("invalid result type identifier %#v: %s", id, err)
// don't return nil to avoid panics, the error will get reported at the end
return expr.NewResultTypeExpr("InvalidCollection", "text/plain", nil)
}
hasType := false
for param := range params {
if param == "type" {
hasType = true
break
}
}
if !hasType {
params["type"] = "collection"
}
id = mime.FormatMediaType(rtype, params)
canonical := expr.CanonicalIdentifier(id)
if mt := expr.Root.GeneratedResultType(canonical); mt != nil {
// Already have a type for this collection, reuse it.
return mt
}
mt := expr.NewResultTypeExpr("", id, func() {
rt, ok := eval.Current().(*expr.ResultTypeExpr)
if !ok {
eval.IncompatibleDSL()
return
}
// Cannot compute collection type name before element result type
// DSL has executed since the DSL may modify element type name
// via the TypeName function.
rt.TypeName = m.TypeName + "Collection"
rt.AttributeExpr = &expr.AttributeExpr{Type: ArrayOf(m)}
if len(adsl) > 0 {
eval.Execute(adsl[0], rt)
}
if rt.Views == nil {
// If the DSL didn't create any view (or there is no DSL
// at all) then inherit the views from the collection
// element.
rt.Views = make([]*expr.ViewExpr, len(m.Views))
for i, v := range m.Views {
v := v
rt.Views[i] = v
}
}
})
// do not execute the DSL right away, will be done last to make sure
// the element DSL has run first.
*expr.Root.GeneratedTypes = append(*expr.Root.GeneratedTypes, mt)
return mt
}
// Reference sets a type or result type reference. The value itself can be a
// type or a result type. The reference type attributes define the default
// properties for attributes with the same name in the type using the reference.
//
// Reference may be used in Type or ResultType, it may appear multiple times in
// which case attributes are looked up in each reference in order of appearance
// in the DSL.
//
// Reference accepts a single argument: the type or result type containing the
// attributes that define the default properties of the attributes of the type
// or result type that uses Reference.
//
// Example:
//
// var Bottle = Type("bottle", func() {
// Attribute("name", String, func() {
// MinLength(3)
// })
// Attribute("vintage", Int32, func() {
// Minimum(1970)
// })
// Attribute("somethingelse", String)
// })
//
// var BottleResult = ResultType("vnd.goa.bottle", func() {
// Reference(Bottle)
// Attributes(func() {
// Attribute("id", UInt64, "ID is the bottle identifier")
//
// // The type and validation of "name" and "vintage" are
// // inherited from the Bottle type "name" and "vintage"
// // attributes.
// Attribute("name")
// Attribute("vintage")
// })
// })
//
func Reference(t expr.DataType) {
if !expr.IsObject(t) {
eval.ReportError("argument of Reference must be an object, got %s", t.Name())
return
}
switch def := eval.Current().(type) {
case *expr.ResultTypeExpr:
def.References = append(def.References, t)
case *expr.AttributeExpr:
def.References = append(def.References, t)
default:
eval.IncompatibleDSL()
}
}
// Extend adds the parameter type attributes to the type using Extend. The
// parameter type must be an object.
//
// Extend may be used in Type or ResultType. Extend accepts a single argument:
// the type or result type containing the attributes to be copied.
//
// Example:
//
// var CreateBottlePayload = Type("CreateBottlePayload", func() {
// Attribute("name", String, func() {
// MinLength(3)
// })
// Attribute("vintage", Int32, func() {
// Minimum(1970)
// })
// })
//
// var UpdateBottlePayload = Type("UpatePayload", func() {
// Attribute("id", String, "ID of bottle to update")
// Extend(CreateBottlePayload) // Adds attributes "name" and "vintage"
// })
//
func Extend(t expr.DataType) {
if !expr.IsObject(t) {
eval.ReportError("argument of Extend must be an object, got %s", t.Name())
return
}
switch def := eval.Current().(type) {
case *expr.ResultTypeExpr:
def.Bases = append(def.Bases, t)
case *expr.AttributeExpr:
def.Bases = append(def.Bases, t)
default:
eval.IncompatibleDSL()
}
}
// Attributes implements the result type Attributes DSL. See ResultType.
func Attributes(fn func()) {
mt, ok := eval.Current().(*expr.ResultTypeExpr)
if !ok {
eval.IncompatibleDSL()
return
}
eval.Execute(fn, mt.AttributeExpr)
}
// mediaTypeToResultType returns the formatted identifier and the result type
// name from the given identifier string. If the given identifier is invalid it
// returns text/plain as the identifier and an error.
func mediaTypeToResultType(identifier string) (string, string, error) {
identifier, params, err := mime.ParseMediaType(identifier)
if err != nil {
identifier = "text/plain"
}
identifier = mime.FormatMediaType(identifier, params)
lastPart := identifier
lastPartIndex := strings.LastIndex(identifier, "/")
if lastPartIndex > -1 {
lastPart = identifier[lastPartIndex+1:]
}
plusIndex := strings.Index(lastPart, "+")
if plusIndex > 0 {
lastPart = lastPart[:plusIndex]
}
lastPart = strings.TrimPrefix(lastPart, "vnd.")
elems := strings.Split(lastPart, ".")
for i, e := range elems {
elems[i] = strings.Title(e)
}
typeName := strings.Join(elems, "")
if typeName == "" {
resultTypeCount++
typeName = fmt.Sprintf("ResultType%d", resultTypeCount)
}
return identifier, typeName, err
}
// buildView builds a view expression given an attribute and a corresponding
// result type. The attribute must be an object listing the child attributes
// that make up the view.
func buildView(name string, mt *expr.ResultTypeExpr, at *expr.AttributeExpr) (*expr.ViewExpr, error) {
if at.Type == nil {
return nil, fmt.Errorf("invalid view DSL")
}
o := expr.AsObject(at.Type)
if o == nil {
return nil, fmt.Errorf("invalid view DSL")
}
for _, nat := range *o {
n := nat.Name
cat := nat.Attribute
if existing := mt.Find(n); existing != nil {
dup := expr.DupAtt(existing)
if _, ok := cat.Meta["view"]; ok {
dup.AddMeta("view", cat.Meta["view"]...)
}
o.Set(n, dup)
} else if n != "links" {
return nil, fmt.Errorf("unknown attribute %#v", n)
}
}
return &expr.ViewExpr{
AttributeExpr: at,
Name: name,
Parent: mt,
}, nil
}