Apollo Federation Spec: Fetch service capabilities

example/apollo_federation/README.md

@@ -0,0 +1,35 @@
+# Apollo Federation
+
+A simple example of integration with apollo federation as subgraph. Tested with Go v1.18, Node.js v16.14.2 and yarn 1.22.18.
+
+To run this server
+
+`go run ./example/apollo_federation/subgraph_one/server.go`
+
+`go run ./example/apollo_federation/subgraph_two/server.go`
+
+`cd example/apollo_federation/gateway`
+
+`yarn start`
+
+and go to localhost:4000 to interact
+
+Execute the query:
+
+```
+query {
+  hello
+  hi
+}
+```
+
+and you should see a result similar to this:
+
+```json
+{
+  "data": {
+    "hello": "Hello from subgraph one!",
+    "hi": "Hi from subgraph two!"
+  }
+}
+```

example/apollo_federation/gateway/.gitignore

@@ -0,0 +1 @@
+/node_modules

example/apollo_federation/gateway/index.js

@@ -0,0 +1,20 @@
+const { ApolloServer }  = require('apollo-server')
+const { ApolloGateway, IntrospectAndCompose } = require('@apollo/gateway');
+
+const gateway = new ApolloGateway({
+    supergraphSdl: new IntrospectAndCompose({
+        subgraphs: [
+            { name: 'one', url: 'http://localhost:4001/query' },
+            { name: 'two', url: 'http://localhost:4002/query' },
+        ],
+    }),
+});
+
+const server = new ApolloServer({
+    gateway,
+    subscriptions: false,
+});
+
+server.listen().then(({ url }) => {
+    console.log(`Server ready at ${url}`);
+});

example/apollo_federation/gateway/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "apollo-federation-gateway",
+  "version": "1.0.0",
+  "description": "Graphql Federation",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js"
+  },
+  "dependencies": {
+    "@apollo/gateway": "^0.49.0",
+    "apollo-server": "^2.21.1",
+    "graphql": "^15.5.0"
+  }
+}

example/apollo_federation/subgraph_one/server.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/graph-gophers/graphql-go"
+	"github.com/graph-gophers/graphql-go/relay"
+)
+
+var schema = `
+	schema {
+		query: Query
+	}
+
+	type Query {
+		hello: String!
+	}
+`
+
+type resolver struct{}
+
+func (r *resolver) Hello() string {
+	return "Hello from subgraph one!"
+}
+
+func main() {
+	opts := []graphql.SchemaOpt{graphql.UseFieldResolvers(), graphql.MaxParallelism(20)}
+	schema := graphql.MustParseSchema(schema, &resolver{}, opts...)
+
+	http.Handle("/query", &relay.Handler{Schema: schema})
+
+	log.Fatal(http.ListenAndServe(":4001", nil))
+}

example/apollo_federation/subgraph_two/server.go

@@ -0,0 +1,34 @@
+package main
+
+import (
+	"log"
+	"net/http"
+
+	"github.com/graph-gophers/graphql-go"
+	"github.com/graph-gophers/graphql-go/relay"
+)
+
+var schema = `
+	schema {
+		query: Query
+	}
+
+	type Query {
+		hi: String!
+	}
+`
+
+type resolver struct{}
+
+func (r *resolver) Hi() string {
+	return "Hi from subgraph two!"
+}
+
+func main() {
+	opts := []graphql.SchemaOpt{graphql.UseFieldResolvers(), graphql.MaxParallelism(20)}
+	schema := graphql.MustParseSchema(schema, &resolver{}, opts...)
+
+	http.Handle("/query", &relay.Handler{Schema: schema})
+
+	log.Fatal(http.ListenAndServe(":4002", nil))
+}

example/social/introspect.json

@@ -589,6 +589,33 @@
         "name": "User",
         "possibleTypes": null
       },
+      {
+        "description": null,
+        "enumValues": null,
+        "fields": [
+          {
+            "args": [],
+            "deprecationReason": null,
+            "description": null,
+            "isDeprecated": false,
+            "name": "sdl",
+            "type": {
+              "kind": "NON_NULL",
+              "name": null,
+              "ofType": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              }
+            }
+          }
+        ],
+        "inputFields": null,
+        "interfaces": [],
+        "kind": "OBJECT",
+        "name": "_Service",
+        "possibleTypes": null
+      },
       {
         "description": "A Directive provides a way to describe alternate runtime execution and type validation behavior in a GraphQL document.\n\nIn some cases, you need to provide options to alter GraphQL's execution behavior\nin ways field arguments will not suffice, such as conditionally including or\nskipping a field. Directives provide this by describing additional information\nto the executor.",
         "enumValues": null,

example/starwars/introspect.json

@@ -1231,6 +1231,33 @@
         "name": "String",
         "possibleTypes": null
       },
+      {
+        "description": null,
+        "enumValues": null,
+        "fields": [
+          {
+            "args": [],
+            "deprecationReason": null,
+            "description": null,
+            "isDeprecated": false,
+            "name": "sdl",
+            "type": {
+              "kind": "NON_NULL",
+              "name": null,
+              "ofType": {
+                "kind": "SCALAR",
+                "name": "String",
+                "ofType": null
+              }
+            }
+          }
+        ],
+        "inputFields": null,
+        "interfaces": [],
+        "kind": "OBJECT",
+        "name": "_Service",
+        "possibleTypes": null
+      },
       {
         "description": "A Directive provides a way to describe alternate runtime execution and type validation behavior in a GraphQL document.\n\nIn some cases, you need to provide options to alter GraphQL's execution behavior\nin ways field arguments will not suffice, such as conditionally including or\nskipping a field. Directives provide this by describing additional information\nto the executor.",
         "enumValues": null,

graphql_test.go

@@ -2144,6 +2144,7 @@ func TestIntrospection(t *testing.T) {
 							{ "name": "SearchResult" },
 							{ "name": "Starship" },
 							{ "name": "String" },
+							{ "name": "_Service" },
 							{ "name": "__Directive" },
 							{ "name": "__DirectiveLocation" },
 							{ "name": "__EnumValue" },
@@ -4326,3 +4327,36 @@ func TestCircularFragmentMaxDepth(t *testing.T) {
 		},
 	})
 }
+
+func TestQueryService(t *testing.T) {
+	t.Parallel()
+
+	schemaString := `
+	schema {
+		query: Query
+	}
+
+	type Query {
+		hello: String!
+	}`
+
+	gqltesting.RunTests(t, []*gqltesting.Test{
+		{
+			Schema: graphql.MustParseSchema(schemaString, &helloWorldResolver1{}),
+			Query: `
+				{
+					_service{
+						sdl
+					}
+				}
+			`,
+			ExpectedResult: fmt.Sprintf(`
+				{
+					"_service": {
+						"sdl": "\n\tschema {\n\t\tquery: Query\n\t}\n\n\ttype Query {\n\t\thello: String!\n\t}"
+					}
+				}
+			`),
+		},
+	})
+}

internal/exec/resolvable/meta.go

@@ -12,8 +12,10 @@ type Meta struct {
 	FieldSchema   Field
 	FieldType     Field
 	FieldTypename Field
+	FieldService  Field
 	Schema        *Object
 	Type          *Object
+	Service       *Object
 }
 
 func newMeta(s *types.Schema) *Meta {
@@ -32,6 +34,12 @@ func newMeta(s *types.Schema) *Meta {
 		panic(err)
 	}
 
+	metaService := s.Types["_Service"].(*types.ObjectTypeDefinition)
+	sv, err := b.makeObjectExec(metaService.Name, metaService.Fields, nil, false, reflect.TypeOf(&introspection.Service{}))
+	if err != nil {
+		panic(err)
+	}
+
 	if err := b.finish(); err != nil {
 		panic(err)
 	}
@@ -60,11 +68,21 @@ func newMeta(s *types.Schema) *Meta {
 		TraceLabel: "GraphQL field: __type",
 	}
 
+	fieldService := Field{
+		FieldDefinition: types.FieldDefinition{
+			Name: "_service",
+			Type: s.Types["_Service"],
+		},
+		TraceLabel: "GraphQL field: _service",
+	}
+
 	return &Meta{
 		FieldSchema:   fieldSchema,
 		FieldTypename: fieldTypename,
 		FieldType:     fieldType,
+		FieldService:  fieldService,
 		Schema:        so,
 		Type:          t,
+		Service:       sv,
 	}
 }

internal/exec/selected/selected.go

@@ -121,6 +121,17 @@ func applySelectionSet(r *Request, s *resolvable.Schema, e *resolvable.Object, s
 					})
 				}
 
+			case "_service":
+				if !r.DisableIntrospection {
+					flattenedSels = append(flattenedSels, &SchemaField{
+						Field:       s.Meta.FieldService,
+						Alias:       field.Alias.Name,
+						Sels:        applySelectionSet(r, s, s.Meta.Service, field.SelectionSet),
+						Async:       true,
+						FixedResult: reflect.ValueOf(introspection.WrapService(r.Schema)),
+					})
+				}
+
 			default:
 				fe := e.Fields[field.Name.Name]
 

internal/schema/meta.go

@@ -200,4 +200,8 @@ var metaSrc = `
 		# Indicates this type is a non-null. ` + "`" + `ofType` + "`" + ` is a valid field.
 		NON_NULL
 	}
+
+	type _Service {
+		sdl: String!
+	}
 `

internal/schema/schema.go

@@ -161,6 +161,8 @@ func Parse(s *types.Schema, schemaString string, useStringDescriptions bool) err
 		}
 	}
 
+	s.SchemaString = schemaString
+
 	return nil
 }
 

internal/validation/validation.go

@@ -327,6 +327,11 @@ func validateSelection(c *opContext, sel types.Selection, t types.NamedType) {
 				},
 				Type: c.schema.Types["__Type"],
 			}
+		case "_service":
+			f = &types.FieldDefinition{
+				Name: "_service",
+				Type: c.schema.Types["_Service"],
+			}
 		default:
 			f = fields(t).Get(fieldName)
 			if f == nil && t != nil {

introspection/introspection.go

@@ -310,3 +310,16 @@ func (r *Directive) Args() []*InputValue {
 	}
 	return l
 }
+
+type Service struct {
+	schema *types.Schema
+}
+
+// WrapService is only used internally.
+func WrapService(schema *types.Schema) *Service {
+	return &Service{schema}
+}
+
+func (r *Service) SDL() string {
+	return r.schema.SchemaString
+}

types/schema.go

@@ -35,6 +35,7 @@ type Schema struct {
 	Unions          []*Union
 	Enums           []*EnumTypeDefinition
 	Extensions      []*Extension
+	SchemaString    string
 }
 
 func (s *Schema) Resolve(name string) Type {