Add support for client that uses GET as transport mechanism (#186)

Current implementation always uses POST as the transport mechanism. Adding GET support enables usage of GET queries for caching simply via URL.

Some notes:
- I left the existing API for creating a new client as is, but the implementation could be much cleaner by introducing some sort of configuration struct when creating a new client
- The construction of the query parameters follows the logic from Apollo's client implementation, which can be found here https://github.com/apollographql/apollo-client/blob/8beb4820edc6352996e08f7f73bde3573f1eb666/src/link/http/rewriteURIForGET.ts
- Updated integration tests to use both sets of clients. Updating the tests to use a test suite would be cleaner

internal/integration/generated.go

@@ -598,6 +598,13 @@ type MoreUserFieldsHair struct {
 // GetColor returns MoreUserFieldsHair.Color, and is useful for accessing the field via an interface.
 func (v *MoreUserFieldsHair) GetColor() string { return v.Color }
 
+type NewUser struct {
+	Name string `json:"name"`
+}
+
+// GetName returns NewUser.Name, and is useful for accessing the field via an interface.
+func (v *NewUser) GetName() string { return v.Name }
+
 // QueryFragment includes the GraphQL fields of Query requested by the fragment QueryFragment.
 type QueryFragment struct {
 	Beings []QueryFragmentBeingsBeing `json:"-"`
@@ -991,6 +998,14 @@ func (v *UserFields) __premarshalJSON() (*__premarshalUserFields, error) {
 	return &retval, nil
 }
 
+// __createUserInput is used internally by genqlient
+type __createUserInput struct {
+	User NewUser `json:"user"`
+}
+
+// GetUser returns __createUserInput.User, and is useful for accessing the field via an interface.
+func (v *__createUserInput) GetUser() NewUser { return v.User }
+
 // __queryWithCustomMarshalInput is used internally by genqlient
 type __queryWithCustomMarshalInput struct {
 	Date time.Time `json:"-"`
@@ -1290,6 +1305,26 @@ type __queryWithVariablesInput struct {
 // GetId returns __queryWithVariablesInput.Id, and is useful for accessing the field via an interface.
 func (v *__queryWithVariablesInput) GetId() string { return v.Id }
 
+// createUserCreateUser includes the requested fields of the GraphQL type User.
+type createUserCreateUser struct {
+	Id   string `json:"id"`
+	Name string `json:"name"`
+}
+
+// GetId returns createUserCreateUser.Id, and is useful for accessing the field via an interface.
+func (v *createUserCreateUser) GetId() string { return v.Id }
+
+// GetName returns createUserCreateUser.Name, and is useful for accessing the field via an interface.
+func (v *createUserCreateUser) GetName() string { return v.Name }
+
+// createUserResponse is returned by createUser on success.
+type createUserResponse struct {
+	CreateUser createUserCreateUser `json:"createUser"`
+}
+
+// GetCreateUser returns createUserResponse.CreateUser, and is useful for accessing the field via an interface.
+func (v *createUserResponse) GetCreateUser() createUserCreateUser { return v.CreateUser }
+
 // failingQueryMeUser includes the requested fields of the GraphQL type User.
 type failingQueryMeUser struct {
 	Id string `json:"id"`
@@ -3043,6 +3078,39 @@ type simpleQueryResponse struct {
 // GetMe returns simpleQueryResponse.Me, and is useful for accessing the field via an interface.
 func (v *simpleQueryResponse) GetMe() simpleQueryMeUser { return v.Me }
 
+func createUser(
+	ctx context.Context,
+	client graphql.Client,
+	user NewUser,
+) (*createUserResponse, map[string]interface{}, error) {
+	req := &graphql.Request{
+		OpName: "createUser",
+		Query: `
+mutation createUser ($user: NewUser!) {
+	createUser(input: $user) {
+		id
+		name
+	}
+}
+`,
+		Variables: &__createUserInput{
+			User: user,
+		},
+	}
+	var err error
+
+	var data createUserResponse
+	resp := &graphql.Response{Data: &data}
+
+	err = client.MakeRequest(
+		ctx,
+		req,
+		resp,
+	)
+
+	return &data, resp.Extensions, err
+}
+
 func failingQuery(
 	ctx context.Context,
 	client graphql.Client,

internal/integration/integration_test.go

@@ -25,14 +25,35 @@ func TestSimpleQuery(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := simpleQuery(ctx, client)
+	for _, client := range clients {
+		resp, _, err := simpleQuery(ctx, client)
+		require.NoError(t, err)
+
+		assert.Equal(t, "1", resp.Me.Id)
+		assert.Equal(t, "Yours Truly", resp.Me.Name)
+		assert.Equal(t, 17, resp.Me.LuckyNumber)
+	}
+}
+
+func TestMutation(t *testing.T) {
+	_ = `# @genqlient
+	mutation createUser($user: NewUser!) { createUser(input: $user) { id name } }`
+
+	ctx := context.Background()
+	server := server.RunServer()
+	defer server.Close()
+	postClient := newRoundtripClient(t, server.URL)
+	getClient := newRoundtripGetClient(t, server.URL)
+
+	resp, _, err := createUser(ctx, postClient, NewUser{Name: "Jack"})
 	require.NoError(t, err)
+	assert.Equal(t, "5", resp.CreateUser.Id)
+	assert.Equal(t, "Jack", resp.CreateUser.Name)
 
-	assert.Equal(t, "1", resp.Me.Id)
-	assert.Equal(t, "Yours Truly", resp.Me.Name)
-	assert.Equal(t, 17, resp.Me.LuckyNumber)
+	_, _, err = createUser(ctx, getClient, NewUser{Name: "Jill"})
+	require.Errorf(t, err, "client does not support mutations")
 }
 
 func TestServerError(t *testing.T) {
@@ -42,30 +63,34 @@ func TestServerError(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := failingQuery(ctx, client)
-	// As long as we get some response back, we should still return a full
-	// response -- and indeed in this case it should even have another field
-	// (which didn't err) set.
-	assert.Error(t, err)
-	assert.NotNil(t, resp)
-	assert.Equal(t, "1", resp.Me.Id)
+	for _, client := range clients {
+		resp, _, err := failingQuery(ctx, client)
+		// As long as we get some response back, we should still return a full
+		// response -- and indeed in this case it should even have another field
+		// (which didn't err) set.
+		assert.Error(t, err)
+		assert.NotNil(t, resp)
+		assert.Equal(t, "1", resp.Me.Id)
+	}
 }
 
 func TestNetworkError(t *testing.T) {
 	ctx := context.Background()
-	client := newRoundtripClient(t, "https://nothing.invalid/graphql")
+	clients := newRoundtripClients(t, "https://nothing.invalid/graphql")
 
-	resp, _, err := failingQuery(ctx, client)
-	// As we guarantee in the README, even on network error you always get a
-	// non-nil response; this is so you can write e.g.
-	//	resp, err := failingQuery(ctx)
-	//	return resp.Me.Id, err
-	// without a bunch of extra ceremony.
-	assert.Error(t, err)
-	assert.NotNil(t, resp)
-	assert.Equal(t, new(failingQueryResponse), resp)
+	for _, client := range clients {
+		resp, _, err := failingQuery(ctx, client)
+		// As we guarantee in the README, even on network error you always get a
+		// non-nil response; this is so you can write e.g.
+		//	resp, err := failingQuery(ctx)
+		//	return resp.Me.Id, err
+		// without a bunch of extra ceremony.
+		assert.Error(t, err)
+		assert.NotNil(t, resp)
+		assert.Equal(t, new(failingQueryResponse), resp)
+	}
 }
 
 func TestVariables(t *testing.T) {
@@ -80,19 +105,24 @@ func TestVariables(t *testing.T) {
 	// this right in Go (without adding `pointer: true` just for this purpose),
 	// and unmarshal(marshal(resp)) == resp should still hold, so we don't
 	// worry about it.
-	client := graphql.NewClient(server.URL, http.DefaultClient)
+	clients := []graphql.Client{
+		graphql.NewClient(server.URL, http.DefaultClient),
+		graphql.NewClientUsingGet(server.URL, http.DefaultClient),
+	}
 
-	resp, _, err := queryWithVariables(ctx, client, "2")
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithVariables(ctx, client, "2")
+		require.NoError(t, err)
 
-	assert.Equal(t, "2", resp.User.Id)
-	assert.Equal(t, "Raven", resp.User.Name)
-	assert.Equal(t, -1, resp.User.LuckyNumber)
+		assert.Equal(t, "2", resp.User.Id)
+		assert.Equal(t, "Raven", resp.User.Name)
+		assert.Equal(t, -1, resp.User.LuckyNumber)
 
-	resp, _, err = queryWithVariables(ctx, client, "374892379482379")
-	require.NoError(t, err)
+		resp, _, err = queryWithVariables(ctx, client, "374892379482379")
+		require.NoError(t, err)
 
-	assert.Zero(t, resp.User)
+		assert.Zero(t, resp.User)
+	}
 }
 
 func TestExtensions(t *testing.T) {
@@ -102,12 +132,14 @@ func TestExtensions(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	_, extensions, err := simpleQueryExt(ctx, client)
-	require.NoError(t, err)
-	assert.NotNil(t, extensions)
-	assert.Equal(t, extensions["foobar"], "test")
+	for _, client := range clients {
+		_, extensions, err := simpleQueryExt(ctx, client)
+		require.NoError(t, err)
+		assert.NotNil(t, extensions)
+		assert.Equal(t, extensions["foobar"], "test")
+	}
 }
 
 func TestOmitempty(t *testing.T) {
@@ -119,22 +151,24 @@ func TestOmitempty(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithOmitempty(ctx, client, "2")
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithOmitempty(ctx, client, "2")
+		require.NoError(t, err)
 
-	assert.Equal(t, "2", resp.User.Id)
-	assert.Equal(t, "Raven", resp.User.Name)
-	assert.Equal(t, -1, resp.User.LuckyNumber)
+		assert.Equal(t, "2", resp.User.Id)
+		assert.Equal(t, "Raven", resp.User.Name)
+		assert.Equal(t, -1, resp.User.LuckyNumber)
 
-	// should return default user, not the user with ID ""
-	resp, _, err = queryWithOmitempty(ctx, client, "")
-	require.NoError(t, err)
+		// should return default user, not the user with ID ""
+		resp, _, err = queryWithOmitempty(ctx, client, "")
+		require.NoError(t, err)
 
-	assert.Equal(t, "1", resp.User.Id)
-	assert.Equal(t, "Yours Truly", resp.User.Name)
-	assert.Equal(t, 17, resp.User.LuckyNumber)
+		assert.Equal(t, "1", resp.User.Id)
+		assert.Equal(t, "Yours Truly", resp.User.Name)
+		assert.Equal(t, 17, resp.User.LuckyNumber)
+	}
 }
 
 func TestCustomMarshal(t *testing.T) {
@@ -146,24 +180,26 @@ func TestCustomMarshal(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithCustomMarshal(ctx, client,
-		time.Date(2025, time.January, 1, 12, 34, 56, 789, time.UTC))
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithCustomMarshal(ctx, client,
+			time.Date(2025, time.January, 1, 12, 34, 56, 789, time.UTC))
+		require.NoError(t, err)
 
-	assert.Len(t, resp.UsersBornOn, 1)
-	user := resp.UsersBornOn[0]
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
-	assert.Equal(t,
-		time.Date(2025, time.January, 1, 0, 0, 0, 0, time.UTC),
-		user.Birthdate)
+		assert.Len(t, resp.UsersBornOn, 1)
+		user := resp.UsersBornOn[0]
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
+		assert.Equal(t,
+			time.Date(2025, time.January, 1, 0, 0, 0, 0, time.UTC),
+			user.Birthdate)
 
-	resp, _, err = queryWithCustomMarshal(ctx, client,
-		time.Date(2021, time.January, 1, 12, 34, 56, 789, time.UTC))
-	require.NoError(t, err)
-	assert.Len(t, resp.UsersBornOn, 0)
+		resp, _, err = queryWithCustomMarshal(ctx, client,
+			time.Date(2021, time.January, 1, 12, 34, 56, 789, time.UTC))
+		require.NoError(t, err)
+		assert.Len(t, resp.UsersBornOn, 0)
+	}
 }
 
 func TestCustomMarshalSlice(t *testing.T) {
@@ -175,24 +211,26 @@ func TestCustomMarshalSlice(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithCustomMarshalSlice(ctx, client,
-		[]time.Time{time.Date(2025, time.January, 1, 12, 34, 56, 789, time.UTC)})
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithCustomMarshalSlice(ctx, client,
+			[]time.Time{time.Date(2025, time.January, 1, 12, 34, 56, 789, time.UTC)})
+		require.NoError(t, err)
 
-	assert.Len(t, resp.UsersBornOnDates, 1)
-	user := resp.UsersBornOnDates[0]
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
-	assert.Equal(t,
-		time.Date(2025, time.January, 1, 0, 0, 0, 0, time.UTC),
-		user.Birthdate)
+		assert.Len(t, resp.UsersBornOnDates, 1)
+		user := resp.UsersBornOnDates[0]
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
+		assert.Equal(t,
+			time.Date(2025, time.January, 1, 0, 0, 0, 0, time.UTC),
+			user.Birthdate)
 
-	resp, _, err = queryWithCustomMarshalSlice(ctx, client,
-		[]time.Time{time.Date(2021, time.January, 1, 12, 34, 56, 789, time.UTC)})
-	require.NoError(t, err)
-	assert.Len(t, resp.UsersBornOnDates, 0)
+		resp, _, err = queryWithCustomMarshalSlice(ctx, client,
+			[]time.Time{time.Date(2021, time.January, 1, 12, 34, 56, 789, time.UTC)})
+		require.NoError(t, err)
+		assert.Len(t, resp.UsersBornOnDates, 0)
+	}
 }
 
 func TestCustomMarshalOptional(t *testing.T) {
@@ -209,28 +247,30 @@ func TestCustomMarshalOptional(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	date := time.Date(2025, time.January, 1, 12, 34, 56, 789, time.UTC)
-	resp, _, err := queryWithCustomMarshalOptional(ctx, client, &date, nil)
-	require.NoError(t, err)
+	for _, client := range clients {
+		date := time.Date(2025, time.January, 1, 12, 34, 56, 789, time.UTC)
+		resp, _, err := queryWithCustomMarshalOptional(ctx, client, &date, nil)
+		require.NoError(t, err)
 
-	assert.Len(t, resp.UserSearch, 1)
-	user := resp.UserSearch[0]
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
-	assert.Equal(t,
-		time.Date(2025, time.January, 1, 0, 0, 0, 0, time.UTC),
-		user.Birthdate)
+		assert.Len(t, resp.UserSearch, 1)
+		user := resp.UserSearch[0]
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
+		assert.Equal(t,
+			time.Date(2025, time.January, 1, 0, 0, 0, 0, time.UTC),
+			user.Birthdate)
 
-	id := "2"
-	resp, _, err = queryWithCustomMarshalOptional(ctx, client, nil, &id)
-	require.NoError(t, err)
-	assert.Len(t, resp.UserSearch, 1)
-	user = resp.UserSearch[0]
-	assert.Equal(t, "2", user.Id)
-	assert.Equal(t, "Raven", user.Name)
-	assert.Zero(t, user.Birthdate)
+		id := "2"
+		resp, _, err = queryWithCustomMarshalOptional(ctx, client, nil, &id)
+		require.NoError(t, err)
+		assert.Len(t, resp.UserSearch, 1)
+		user = resp.UserSearch[0]
+		assert.Equal(t, "2", user.Id)
+		assert.Equal(t, "Raven", user.Name)
+		assert.Zero(t, user.Birthdate)
+	}
 }
 
 func TestInterfaceNoFragments(t *testing.T) {
@@ -243,58 +283,60 @@ func TestInterfaceNoFragments(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithInterfaceNoFragments(ctx, client, "1")
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithInterfaceNoFragments(ctx, client, "1")
+		require.NoError(t, err)
 
-	// We should get the following response:
-	//	me: User{Id: 1, Name: "Yours Truly"},
-	//	being: User{Id: 1, Name: "Yours Truly"},
+		// We should get the following response:
+		//	me: User{Id: 1, Name: "Yours Truly"},
+		//	being: User{Id: 1, Name: "Yours Truly"},
 
-	assert.Equal(t, "1", resp.Me.Id)
-	assert.Equal(t, "Yours Truly", resp.Me.Name)
+		assert.Equal(t, "1", resp.Me.Id)
+		assert.Equal(t, "Yours Truly", resp.Me.Name)
 
-	// Check fields both via interface and via type-assertion:
-	assert.Equal(t, "User", resp.Being.GetTypename())
-	assert.Equal(t, "1", resp.Being.GetId())
-	assert.Equal(t, "Yours Truly", resp.Being.GetName())
+		// Check fields both via interface and via type-assertion:
+		assert.Equal(t, "User", resp.Being.GetTypename())
+		assert.Equal(t, "1", resp.Being.GetId())
+		assert.Equal(t, "Yours Truly", resp.Being.GetName())
 
-	user, ok := resp.Being.(*queryWithInterfaceNoFragmentsBeingUser)
-	require.Truef(t, ok, "got %T, not User", resp.Being)
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
+		user, ok := resp.Being.(*queryWithInterfaceNoFragmentsBeingUser)
+		require.Truef(t, ok, "got %T, not User", resp.Being)
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
 
-	resp, _, err = queryWithInterfaceNoFragments(ctx, client, "3")
-	require.NoError(t, err)
+		resp, _, err = queryWithInterfaceNoFragments(ctx, client, "3")
+		require.NoError(t, err)
 
-	// We should get the following response:
-	//	me: User{Id: 1, Name: "Yours Truly"},
-	//	being: Animal{Id: 3, Name: "Fido"},
+		// We should get the following response:
+		//	me: User{Id: 1, Name: "Yours Truly"},
+		//	being: Animal{Id: 3, Name: "Fido"},
 
-	assert.Equal(t, "1", resp.Me.Id)
-	assert.Equal(t, "Yours Truly", resp.Me.Name)
+		assert.Equal(t, "1", resp.Me.Id)
+		assert.Equal(t, "Yours Truly", resp.Me.Name)
 
-	assert.Equal(t, "Animal", resp.Being.GetTypename())
-	assert.Equal(t, "3", resp.Being.GetId())
-	assert.Equal(t, "Fido", resp.Being.GetName())
+		assert.Equal(t, "Animal", resp.Being.GetTypename())
+		assert.Equal(t, "3", resp.Being.GetId())
+		assert.Equal(t, "Fido", resp.Being.GetName())
 
-	animal, ok := resp.Being.(*queryWithInterfaceNoFragmentsBeingAnimal)
-	require.Truef(t, ok, "got %T, not Animal", resp.Being)
-	assert.Equal(t, "3", animal.Id)
-	assert.Equal(t, "Fido", animal.Name)
+		animal, ok := resp.Being.(*queryWithInterfaceNoFragmentsBeingAnimal)
+		require.Truef(t, ok, "got %T, not Animal", resp.Being)
+		assert.Equal(t, "3", animal.Id)
+		assert.Equal(t, "Fido", animal.Name)
 
-	resp, _, err = queryWithInterfaceNoFragments(ctx, client, "4757233945723")
-	require.NoError(t, err)
+		resp, _, err = queryWithInterfaceNoFragments(ctx, client, "4757233945723")
+		require.NoError(t, err)
 
-	// We should get the following response:
-	//	me: User{Id: 1, Name: "Yours Truly"},
-	//	being: null
+		// We should get the following response:
+		//	me: User{Id: 1, Name: "Yours Truly"},
+		//	being: null
 
-	assert.Equal(t, "1", resp.Me.Id)
-	assert.Equal(t, "Yours Truly", resp.Me.Name)
+		assert.Equal(t, "1", resp.Me.Id)
+		assert.Equal(t, "Yours Truly", resp.Me.Name)
 
-	assert.Nil(t, resp.Being)
+		assert.Nil(t, resp.Being)
+	}
 }
 
 func TestInterfaceListField(t *testing.T) {
@@ -306,39 +348,41 @@ func TestInterfaceListField(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithInterfaceListField(ctx, client,
-		[]string{"1", "3", "12847394823"})
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithInterfaceListField(ctx, client,
+			[]string{"1", "3", "12847394823"})
+		require.NoError(t, err)
 
-	require.Len(t, resp.Beings, 3)
+		require.Len(t, resp.Beings, 3)
 
-	// We should get the following three beings:
-	//	User{Id: 1, Name: "Yours Truly"},
-	//	Animal{Id: 3, Name: "Fido"},
-	//	null
+		// We should get the following three beings:
+		//	User{Id: 1, Name: "Yours Truly"},
+		//	Animal{Id: 3, Name: "Fido"},
+		//	null
 
-	// Check fields both via interface and via type-assertion:
-	assert.Equal(t, "User", resp.Beings[0].GetTypename())
-	assert.Equal(t, "1", resp.Beings[0].GetId())
-	assert.Equal(t, "Yours Truly", resp.Beings[0].GetName())
+		// Check fields both via interface and via type-assertion:
+		assert.Equal(t, "User", resp.Beings[0].GetTypename())
+		assert.Equal(t, "1", resp.Beings[0].GetId())
+		assert.Equal(t, "Yours Truly", resp.Beings[0].GetName())
 
-	user, ok := resp.Beings[0].(*queryWithInterfaceListFieldBeingsUser)
-	require.Truef(t, ok, "got %T, not User", resp.Beings[0])
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
+		user, ok := resp.Beings[0].(*queryWithInterfaceListFieldBeingsUser)
+		require.Truef(t, ok, "got %T, not User", resp.Beings[0])
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
 
-	assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
-	assert.Equal(t, "3", resp.Beings[1].GetId())
-	assert.Equal(t, "Fido", resp.Beings[1].GetName())
+		assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
+		assert.Equal(t, "3", resp.Beings[1].GetId())
+		assert.Equal(t, "Fido", resp.Beings[1].GetName())
 
-	animal, ok := resp.Beings[1].(*queryWithInterfaceListFieldBeingsAnimal)
-	require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
-	assert.Equal(t, "3", animal.Id)
-	assert.Equal(t, "Fido", animal.Name)
+		animal, ok := resp.Beings[1].(*queryWithInterfaceListFieldBeingsAnimal)
+		require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
+		assert.Equal(t, "3", animal.Id)
+		assert.Equal(t, "Fido", animal.Name)
 
-	assert.Nil(t, resp.Beings[2])
+		assert.Nil(t, resp.Beings[2])
+	}
 }
 
 func TestInterfaceListPointerField(t *testing.T) {
@@ -353,34 +397,36 @@ func TestInterfaceListPointerField(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithInterfaceListPointerField(ctx, client,
-		[]string{"1", "3", "12847394823"})
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithInterfaceListPointerField(ctx, client,
+			[]string{"1", "3", "12847394823"})
+		require.NoError(t, err)
 
-	require.Len(t, resp.Beings, 3)
+		require.Len(t, resp.Beings, 3)
 
-	// Check fields both via interface and via type-assertion:
-	assert.Equal(t, "User", (*resp.Beings[0]).GetTypename())
-	assert.Equal(t, "1", (*resp.Beings[0]).GetId())
-	assert.Equal(t, "Yours Truly", (*resp.Beings[0]).GetName())
+		// Check fields both via interface and via type-assertion:
+		assert.Equal(t, "User", (*resp.Beings[0]).GetTypename())
+		assert.Equal(t, "1", (*resp.Beings[0]).GetId())
+		assert.Equal(t, "Yours Truly", (*resp.Beings[0]).GetName())
 
-	user, ok := (*resp.Beings[0]).(*queryWithInterfaceListPointerFieldBeingsUser)
-	require.Truef(t, ok, "got %T, not User", *resp.Beings[0])
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
+		user, ok := (*resp.Beings[0]).(*queryWithInterfaceListPointerFieldBeingsUser)
+		require.Truef(t, ok, "got %T, not User", *resp.Beings[0])
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
 
-	assert.Equal(t, "Animal", (*resp.Beings[1]).GetTypename())
-	assert.Equal(t, "3", (*resp.Beings[1]).GetId())
-	assert.Equal(t, "Fido", (*resp.Beings[1]).GetName())
+		assert.Equal(t, "Animal", (*resp.Beings[1]).GetTypename())
+		assert.Equal(t, "3", (*resp.Beings[1]).GetId())
+		assert.Equal(t, "Fido", (*resp.Beings[1]).GetName())
 
-	animal, ok := (*resp.Beings[1]).(*queryWithInterfaceListPointerFieldBeingsAnimal)
-	require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
-	assert.Equal(t, "3", animal.Id)
-	assert.Equal(t, "Fido", animal.Name)
+		animal, ok := (*resp.Beings[1]).(*queryWithInterfaceListPointerFieldBeingsAnimal)
+		require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
+		assert.Equal(t, "3", animal.Id)
+		assert.Equal(t, "Fido", animal.Name)
 
-	assert.Nil(t, resp.Beings[2])
+		assert.Nil(t, resp.Beings[2])
+	}
 }
 
 func TestFragments(t *testing.T) {
@@ -407,62 +453,64 @@ func TestFragments(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithFragments(ctx, client, []string{"1", "3", "12847394823"})
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithFragments(ctx, client, []string{"1", "3", "12847394823"})
+		require.NoError(t, err)
 
-	require.Len(t, resp.Beings, 3)
+		require.Len(t, resp.Beings, 3)
 
-	// We should get the following three beings:
-	//	User{Id: 1, Name: "Yours Truly"},
-	//	Animal{Id: 3, Name: "Fido"},
-	//	null
+		// We should get the following three beings:
+		//	User{Id: 1, Name: "Yours Truly"},
+		//	Animal{Id: 3, Name: "Fido"},
+		//	null
 
-	// Check fields both via interface and via type-assertion when possible
-	// User has, in total, the fields: __typename id name luckyNumber.
-	assert.Equal(t, "User", resp.Beings[0].GetTypename())
-	assert.Equal(t, "1", resp.Beings[0].GetId())
-	assert.Equal(t, "Yours Truly", resp.Beings[0].GetName())
-	// (hair and luckyNumber we need to cast for)
+		// Check fields both via interface and via type-assertion when possible
+		// User has, in total, the fields: __typename id name luckyNumber.
+		assert.Equal(t, "User", resp.Beings[0].GetTypename())
+		assert.Equal(t, "1", resp.Beings[0].GetId())
+		assert.Equal(t, "Yours Truly", resp.Beings[0].GetName())
+		// (hair and luckyNumber we need to cast for)
 
-	user, ok := resp.Beings[0].(*queryWithFragmentsBeingsUser)
-	require.Truef(t, ok, "got %T, not User", resp.Beings[0])
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "Yours Truly", user.Name)
-	assert.Equal(t, "Black", user.Hair.Color)
-	assert.Equal(t, 17, user.LuckyNumber)
+		user, ok := resp.Beings[0].(*queryWithFragmentsBeingsUser)
+		require.Truef(t, ok, "got %T, not User", resp.Beings[0])
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "Yours Truly", user.Name)
+		assert.Equal(t, "Black", user.Hair.Color)
+		assert.Equal(t, 17, user.LuckyNumber)
 
-	// Animal has, in total, the fields:
-	//	__typename
-	//	id
-	//	species
-	//	owner {
-	//		id
-	//		name
-	//		... on User { luckyNumber }
-	//	}
-	assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
-	assert.Equal(t, "3", resp.Beings[1].GetId())
-	// (hair, species, and owner.* we have to cast for)
+		// Animal has, in total, the fields:
+		//	__typename
+		//	id
+		//	species
+		//	owner {
+		//		id
+		//		name
+		//		... on User { luckyNumber }
+		//	}
+		assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
+		assert.Equal(t, "3", resp.Beings[1].GetId())
+		// (hair, species, and owner.* we have to cast for)
 
-	animal, ok := resp.Beings[1].(*queryWithFragmentsBeingsAnimal)
-	require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
-	assert.Equal(t, "3", animal.Id)
-	assert.Equal(t, SpeciesDog, animal.Species)
-	assert.True(t, animal.Hair.HasHair)
+		animal, ok := resp.Beings[1].(*queryWithFragmentsBeingsAnimal)
+		require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
+		assert.Equal(t, "3", animal.Id)
+		assert.Equal(t, SpeciesDog, animal.Species)
+		assert.True(t, animal.Hair.HasHair)
 
-	assert.Equal(t, "1", animal.Owner.GetId())
-	assert.Equal(t, "Yours Truly", animal.Owner.GetName())
-	// (luckyNumber we have to cast for, again)
+		assert.Equal(t, "1", animal.Owner.GetId())
+		assert.Equal(t, "Yours Truly", animal.Owner.GetName())
+		// (luckyNumber we have to cast for, again)
 
-	owner, ok := animal.Owner.(*queryWithFragmentsBeingsAnimalOwnerUser)
-	require.Truef(t, ok, "got %T, not User", animal.Owner)
-	assert.Equal(t, "1", owner.Id)
-	assert.Equal(t, "Yours Truly", owner.Name)
-	assert.Equal(t, 17, owner.LuckyNumber)
+		owner, ok := animal.Owner.(*queryWithFragmentsBeingsAnimalOwnerUser)
+		require.Truef(t, ok, "got %T, not User", animal.Owner)
+		assert.Equal(t, "1", owner.Id)
+		assert.Equal(t, "Yours Truly", owner.Name)
+		assert.Equal(t, 17, owner.LuckyNumber)
 
-	assert.Nil(t, resp.Beings[2])
+		assert.Nil(t, resp.Beings[2])
+	}
 }
 
 func TestNamedFragments(t *testing.T) {
@@ -500,73 +548,75 @@ func TestNamedFragments(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithNamedFragments(ctx, client, []string{"1", "3", "12847394823"})
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithNamedFragments(ctx, client, []string{"1", "3", "12847394823"})
+		require.NoError(t, err)
 
-	require.Len(t, resp.Beings, 3)
+		require.Len(t, resp.Beings, 3)
 
-	// We should get the following three beings:
-	//	User{Id: 1, Name: "Yours Truly"},
-	//	Animal{Id: 3, Name: "Fido"},
-	//	null
+		// We should get the following three beings:
+		//	User{Id: 1, Name: "Yours Truly"},
+		//	Animal{Id: 3, Name: "Fido"},
+		//	null
 
-	// Check fields both via interface and via type-assertion when possible
-	// User has, in total, the fields: __typename id luckyNumber.
-	assert.Equal(t, "User", resp.Beings[0].GetTypename())
-	assert.Equal(t, "1", resp.Beings[0].GetId())
-	// (luckyNumber, hair we need to cast for)
+		// Check fields both via interface and via type-assertion when possible
+		// User has, in total, the fields: __typename id luckyNumber.
+		assert.Equal(t, "User", resp.Beings[0].GetTypename())
+		assert.Equal(t, "1", resp.Beings[0].GetId())
+		// (luckyNumber, hair we need to cast for)
 
-	user, ok := resp.Beings[0].(*queryWithNamedFragmentsBeingsUser)
-	require.Truef(t, ok, "got %T, not User", resp.Beings[0])
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, "1", user.UserFields.Id)
-	assert.Equal(t, "1", user.UserFields.MoreUserFields.Id)
-	assert.Equal(t, "1", user.UserFields.LuckyFieldsUser.MoreUserFields.Id)
-	// on UserFields, but we should be able to access directly via embedding:
-	assert.Equal(t, 17, user.LuckyNumber)
-	assert.Equal(t, "Black", user.Hair.Color)
-	assert.Equal(t, "Black", user.UserFields.MoreUserFields.Hair.Color)
-	assert.Equal(t, "Black", user.UserFields.LuckyFieldsUser.MoreUserFields.Hair.Color)
+		user, ok := resp.Beings[0].(*queryWithNamedFragmentsBeingsUser)
+		require.Truef(t, ok, "got %T, not User", resp.Beings[0])
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, "1", user.UserFields.Id)
+		assert.Equal(t, "1", user.UserFields.MoreUserFields.Id)
+		assert.Equal(t, "1", user.UserFields.LuckyFieldsUser.MoreUserFields.Id)
+		// on UserFields, but we should be able to access directly via embedding:
+		assert.Equal(t, 17, user.LuckyNumber)
+		assert.Equal(t, "Black", user.Hair.Color)
+		assert.Equal(t, "Black", user.UserFields.MoreUserFields.Hair.Color)
+		assert.Equal(t, "Black", user.UserFields.LuckyFieldsUser.MoreUserFields.Hair.Color)
 
-	// Animal has, in total, the fields:
-	//	__typename
-	//	id
-	//	hair { hasHair }
-	//	owner { id luckyNumber }
-	assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
-	assert.Equal(t, "3", resp.Beings[1].GetId())
-	// (hair.* and owner.* we have to cast for)
+		// Animal has, in total, the fields:
+		//	__typename
+		//	id
+		//	hair { hasHair }
+		//	owner { id luckyNumber }
+		assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
+		assert.Equal(t, "3", resp.Beings[1].GetId())
+		// (hair.* and owner.* we have to cast for)
 
-	animal, ok := resp.Beings[1].(*queryWithNamedFragmentsBeingsAnimal)
-	require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
-	// Check that we filled in *both* ID fields:
-	assert.Equal(t, "3", animal.Id)
-	assert.Equal(t, "3", animal.AnimalFields.Id)
-	// on AnimalFields:
-	assert.True(t, animal.Hair.HasHair)
-	assert.Equal(t, "1", animal.Owner.GetId())
-	// (luckyNumber we have to cast for, again)
+		animal, ok := resp.Beings[1].(*queryWithNamedFragmentsBeingsAnimal)
+		require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
+		// Check that we filled in *both* ID fields:
+		assert.Equal(t, "3", animal.Id)
+		assert.Equal(t, "3", animal.AnimalFields.Id)
+		// on AnimalFields:
+		assert.True(t, animal.Hair.HasHair)
+		assert.Equal(t, "1", animal.Owner.GetId())
+		// (luckyNumber we have to cast for, again)
 
-	owner, ok := animal.Owner.(*AnimalFieldsOwnerUser)
-	require.Truef(t, ok, "got %T, not User", animal.Owner)
-	// Check that we filled in *both* ID fields:
-	assert.Equal(t, "1", owner.Id)
-	assert.Equal(t, "1", owner.UserFields.Id)
-	assert.Equal(t, "1", owner.UserFields.MoreUserFields.Id)
-	assert.Equal(t, "1", owner.UserFields.LuckyFieldsUser.MoreUserFields.Id)
-	// on UserFields:
-	assert.Equal(t, 17, owner.LuckyNumber)
-	assert.Equal(t, "Black", owner.UserFields.MoreUserFields.Hair.Color)
-	assert.Equal(t, "Black", owner.UserFields.LuckyFieldsUser.MoreUserFields.Hair.Color)
+		owner, ok := animal.Owner.(*AnimalFieldsOwnerUser)
+		require.Truef(t, ok, "got %T, not User", animal.Owner)
+		// Check that we filled in *both* ID fields:
+		assert.Equal(t, "1", owner.Id)
+		assert.Equal(t, "1", owner.UserFields.Id)
+		assert.Equal(t, "1", owner.UserFields.MoreUserFields.Id)
+		assert.Equal(t, "1", owner.UserFields.LuckyFieldsUser.MoreUserFields.Id)
+		// on UserFields:
+		assert.Equal(t, 17, owner.LuckyNumber)
+		assert.Equal(t, "Black", owner.UserFields.MoreUserFields.Hair.Color)
+		assert.Equal(t, "Black", owner.UserFields.LuckyFieldsUser.MoreUserFields.Hair.Color)
 
-	// Lucky-based fields we can also get by casting to the fragment-interface.
-	luckyOwner, ok := animal.Owner.(LuckyFields)
-	require.Truef(t, ok, "got %T, not Lucky", animal.Owner)
-	assert.Equal(t, 17, luckyOwner.GetLuckyNumber())
+		// Lucky-based fields we can also get by casting to the fragment-interface.
+		luckyOwner, ok := animal.Owner.(LuckyFields)
+		require.Truef(t, ok, "got %T, not Lucky", animal.Owner)
+		assert.Equal(t, 17, luckyOwner.GetLuckyNumber())
 
-	assert.Nil(t, resp.Beings[2])
+		assert.Nil(t, resp.Beings[2])
+	}
 }
 
 func TestFlatten(t *testing.T) {
@@ -629,54 +679,56 @@ func TestFlatten(t *testing.T) {
 	ctx := context.Background()
 	server := server.RunServer()
 	defer server.Close()
-	client := newRoundtripClient(t, server.URL)
+	clients := newRoundtripClients(t, server.URL)
 
-	resp, _, err := queryWithFlatten(ctx, client, []string{"1", "3", "12847394823"})
-	require.NoError(t, err)
+	for _, client := range clients {
+		resp, _, err := queryWithFlatten(ctx, client, []string{"1", "3", "12847394823"})
+		require.NoError(t, err)
 
-	require.Len(t, resp.Beings, 3)
+		require.Len(t, resp.Beings, 3)
 
-	// We should get the following three beings:
-	//	User{Id: 1, Name: "Yours Truly"},
-	//	Animal{Id: 3, Name: "Fido"},
-	//	null
+		// We should get the following three beings:
+		//	User{Id: 1, Name: "Yours Truly"},
+		//	Animal{Id: 3, Name: "Fido"},
+		//	null
 
-	// Check fields both via interface and via type-assertion when possible
-	// User has, in total, the fields: __typename id luckyNumber.
-	assert.Equal(t, "User", resp.Beings[0].GetTypename())
-	assert.Equal(t, "1", resp.Beings[0].GetId())
-	// (luckyNumber we need to cast for)
+		// Check fields both via interface and via type-assertion when possible
+		// User has, in total, the fields: __typename id luckyNumber.
+		assert.Equal(t, "User", resp.Beings[0].GetTypename())
+		assert.Equal(t, "1", resp.Beings[0].GetId())
+		// (luckyNumber we need to cast for)
 
-	user, ok := resp.Beings[0].(*QueryFragmentBeingsUser)
-	require.Truef(t, ok, "got %T, not User", resp.Beings[0])
-	assert.Equal(t, "1", user.Id)
-	assert.Equal(t, 17, user.InnerLuckyFieldsUser.LuckyNumber)
+		user, ok := resp.Beings[0].(*QueryFragmentBeingsUser)
+		require.Truef(t, ok, "got %T, not User", resp.Beings[0])
+		assert.Equal(t, "1", user.Id)
+		assert.Equal(t, 17, user.InnerLuckyFieldsUser.LuckyNumber)
 
-	// Animal has, in total, the fields:
-	//	__typename
-	//	id
-	//	owner { id name ... on User { friends { id name } } }
-	assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
-	assert.Equal(t, "3", resp.Beings[1].GetId())
-	// (owner.* we have to cast for)
+		// Animal has, in total, the fields:
+		//	__typename
+		//	id
+		//	owner { id name ... on User { friends { id name } } }
+		assert.Equal(t, "Animal", resp.Beings[1].GetTypename())
+		assert.Equal(t, "3", resp.Beings[1].GetId())
+		// (owner.* we have to cast for)
 
-	animal, ok := resp.Beings[1].(*QueryFragmentBeingsAnimal)
-	require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
-	assert.Equal(t, "3", animal.Id)
-	// on AnimalFields:
-	assert.Equal(t, "1", animal.Owner.GetId())
-	assert.Equal(t, "Yours Truly", animal.Owner.GetName())
-	// (friends.* we have to cast for, again)
+		animal, ok := resp.Beings[1].(*QueryFragmentBeingsAnimal)
+		require.Truef(t, ok, "got %T, not Animal", resp.Beings[1])
+		assert.Equal(t, "3", animal.Id)
+		// on AnimalFields:
+		assert.Equal(t, "1", animal.Owner.GetId())
+		assert.Equal(t, "Yours Truly", animal.Owner.GetName())
+		// (friends.* we have to cast for, again)
 
-	owner, ok := animal.Owner.(*InnerBeingFieldsUser)
-	require.Truef(t, ok, "got %T, not User", animal.Owner)
-	assert.Equal(t, "1", owner.Id)
-	assert.Equal(t, "Yours Truly", owner.Name)
-	assert.Len(t, owner.Friends, 1)
-	assert.Equal(t, "2", owner.Friends[0].Id)
-	assert.Equal(t, "Raven", owner.Friends[0].Name)
+		owner, ok := animal.Owner.(*InnerBeingFieldsUser)
+		require.Truef(t, ok, "got %T, not User", animal.Owner)
+		assert.Equal(t, "1", owner.Id)
+		assert.Equal(t, "Yours Truly", owner.Name)
+		assert.Len(t, owner.Friends, 1)
+		assert.Equal(t, "2", owner.Friends[0].Id)
+		assert.Equal(t, "Raven", owner.Friends[0].Name)
 
-	assert.Nil(t, resp.Beings[2])
+		assert.Nil(t, resp.Beings[2])
+	}
 }
 
 func TestGeneratedCode(t *testing.T) {

internal/integration/roundtrip.go

@@ -101,10 +101,25 @@ func (c *roundtripClient) MakeRequest(ctx context.Context, req *graphql.Request,
 	return nil
 }
 
+func newRoundtripClients(t *testing.T, endpoint string) []graphql.Client {
+	return []graphql.Client{newRoundtripClient(t, endpoint), newRoundtripGetClient(t, endpoint)}
+}
+
 func newRoundtripClient(t *testing.T, endpoint string) graphql.Client {
 	transport := &lastResponseTransport{wrapped: http.DefaultTransport}
+	httpClient := &http.Client{Transport: transport}
 	return &roundtripClient{
-		wrapped:   graphql.NewClient(endpoint, &http.Client{Transport: transport}),
+		wrapped:   graphql.NewClient(endpoint, httpClient),
+		transport: transport,
+		t:         t,
+	}
+}
+
+func newRoundtripGetClient(t *testing.T, endpoint string) graphql.Client {
+	transport := &lastResponseTransport{wrapped: http.DefaultTransport}
+	httpClient := &http.Client{Transport: transport}
+	return &roundtripClient{
+		wrapped:   graphql.NewClientUsingGet(endpoint, httpClient),
 		transport: transport,
 		t:         t,
 	}

internal/integration/schema.graphql

@@ -12,6 +12,10 @@ type Query {
   fail: Boolean
 }
 
+type Mutation {
+  createUser(input: NewUser!): User!
+}
+
 type User implements Being & Lucky {
   id: ID!
   name: String!
@@ -21,6 +25,10 @@ type User implements Being & Lucky {
   friends: [User!]!
 }
 
+input NewUser {
+    name: String!
+}
+
 type Hair { color: String }   # silly name to confuse the name-generator
 
 type Animal implements Being {

internal/integration/server/gqlgen_exec.go

@@ -35,6 +35,7 @@ type Config struct {
 }
 
 type ResolverRoot interface {
+	Mutation() MutationResolver
 	Query() QueryResolver
 }
 
@@ -58,6 +59,10 @@ type ComplexityRoot struct {
 		Color func(childComplexity int) int
 	}
 
+	Mutation struct {
+		CreateUser func(childComplexity int, input NewUser) int
+	}
+
 	Query struct {
 		Being            func(childComplexity int, id string) int
 		Beings           func(childComplexity int, ids []string) int
@@ -80,6 +85,9 @@ type ComplexityRoot struct {
 	}
 }
 
+type MutationResolver interface {
+	CreateUser(ctx context.Context, input NewUser) (*User, error)
+}
 type QueryResolver interface {
 	Me(ctx context.Context) (*User, error)
 	User(ctx context.Context, id *string) (*User, error)
@@ -156,6 +164,18 @@ func (e *executableSchema) Complexity(typeName, field string, childComplexity in
 
 		return e.complexity.Hair.Color(childComplexity), true
 
+	case "Mutation.createUser":
+		if e.complexity.Mutation.CreateUser == nil {
+			break
+		}
+
+		args, err := ec.field_Mutation_createUser_args(context.TODO(), rawArgs)
+		if err != nil {
+			return 0, false
+		}
+
+		return e.complexity.Mutation.CreateUser(childComplexity, args["input"].(NewUser)), true
+
 	case "Query.being":
 		if e.complexity.Query.Being == nil {
 			break
@@ -316,6 +336,20 @@ func (e *executableSchema) Exec(ctx context.Context) graphql.ResponseHandler {
 			var buf bytes.Buffer
 			data.MarshalGQL(&buf)
 
+			return &graphql.Response{
+				Data: buf.Bytes(),
+			}
+		}
+	case ast.Mutation:
+		return func(ctx context.Context) *graphql.Response {
+			if !first {
+				return nil
+			}
+			first = false
+			data := ec._Mutation(ctx, rc.Operation.SelectionSet)
+			var buf bytes.Buffer
+			data.MarshalGQL(&buf)
+
 			return &graphql.Response{
 				Data: buf.Bytes(),
 			}
@@ -360,6 +394,10 @@ type Query {
   fail: Boolean
 }
 
+type Mutation {
+  createUser(input: NewUser!): User!
+}
+
 type User implements Being & Lucky {
   id: ID!
   name: String!
@@ -369,6 +407,10 @@ type User implements Being & Lucky {
   friends: [User!]!
 }
 
+input NewUser {
+    name: String!
+}
+
 type Hair { color: String }   # silly name to confuse the name-generator
 
 type Animal implements Being {
@@ -402,6 +444,21 @@ var parsedSchema = gqlparser.MustLoadSchema(sources...)
 
 // region    ***************************** args.gotpl *****************************
 
+func (ec *executionContext) field_Mutation_createUser_args(ctx context.Context, rawArgs map[string]interface{}) (map[string]interface{}, error) {
+	var err error
+	args := map[string]interface{}{}
+	var arg0 NewUser
+	if tmp, ok := rawArgs["input"]; ok {
+		ctx := graphql.WithPathContext(ctx, graphql.NewPathWithField("input"))
+		arg0, err = ec.unmarshalNNewUser2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐNewUser(ctx, tmp)
+		if err != nil {
+			return nil, err
+		}
+	}
+	args["input"] = arg0
+	return args, nil
+}
+
 func (ec *executionContext) field_Query___type_args(ctx context.Context, rawArgs map[string]interface{}) (map[string]interface{}, error) {
 	var err error
 	args := map[string]interface{}{}
@@ -805,6 +862,48 @@ func (ec *executionContext) _Hair_color(ctx context.Context, field graphql.Colle
 	return ec.marshalOString2ᚖstring(ctx, field.Selections, res)
 }
 
+func (ec *executionContext) _Mutation_createUser(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
+	defer func() {
+		if r := recover(); r != nil {
+			ec.Error(ctx, ec.Recover(ctx, r))
+			ret = graphql.Null
+		}
+	}()
+	fc := &graphql.FieldContext{
+		Object:     "Mutation",
+		Field:      field,
+		Args:       nil,
+		IsMethod:   true,
+		IsResolver: true,
+	}
+
+	ctx = graphql.WithFieldContext(ctx, fc)
+	rawArgs := field.ArgumentMap(ec.Variables)
+	args, err := ec.field_Mutation_createUser_args(ctx, rawArgs)
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	fc.Args = args
+	resTmp, err := ec.ResolverMiddleware(ctx, func(rctx context.Context) (interface{}, error) {
+		ctx = rctx // use context from middleware stack in children
+		return ec.resolvers.Mutation().CreateUser(rctx, args["input"].(NewUser))
+	})
+	if err != nil {
+		ec.Error(ctx, err)
+		return graphql.Null
+	}
+	if resTmp == nil {
+		if !graphql.HasFieldError(ctx, fc) {
+			ec.Errorf(ctx, "must not be null")
+		}
+		return graphql.Null
+	}
+	res := resTmp.(*User)
+	fc.Result = res
+	return ec.marshalNUser2ᚖgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐUser(ctx, field.Selections, res)
+}
+
 func (ec *executionContext) _Query_me(ctx context.Context, field graphql.CollectedField) (ret graphql.Marshaler) {
 	defer func() {
 		if r := recover(); r != nil {
@@ -2609,6 +2708,29 @@ func (ec *executionContext) ___Type_specifiedByURL(ctx context.Context, field gr
 
 // region    **************************** input.gotpl *****************************
 
+func (ec *executionContext) unmarshalInputNewUser(ctx context.Context, obj interface{}) (NewUser, error) {
+	var it NewUser
+	asMap := map[string]interface{}{}
+	for k, v := range obj.(map[string]interface{}) {
+		asMap[k] = v
+	}
+
+	for k, v := range asMap {
+		switch k {
+		case "name":
+			var err error
+
+			ctx := graphql.WithPathContext(ctx, graphql.NewPathWithField("name"))
+			it.Name, err = ec.unmarshalNString2string(ctx, v)
+			if err != nil {
+				return it, err
+			}
+		}
+	}
+
+	return it, nil
+}
+
 // endregion **************************** input.gotpl *****************************
 
 // region    ************************** interface.gotpl ***************************
@@ -2780,6 +2902,46 @@ func (ec *executionContext) _Hair(ctx context.Context, sel ast.SelectionSet, obj
 	return out
 }
 
+var mutationImplementors = []string{"Mutation"}
+
+func (ec *executionContext) _Mutation(ctx context.Context, sel ast.SelectionSet) graphql.Marshaler {
+	fields := graphql.CollectFields(ec.OperationContext, sel, mutationImplementors)
+	ctx = graphql.WithFieldContext(ctx, &graphql.FieldContext{
+		Object: "Mutation",
+	})
+
+	out := graphql.NewFieldSet(fields)
+	var invalids uint32
+	for i, field := range fields {
+		innerCtx := graphql.WithRootFieldContext(ctx, &graphql.RootFieldContext{
+			Object: field.Name,
+			Field:  field,
+		})
+
+		switch field.Name {
+		case "__typename":
+			out.Values[i] = graphql.MarshalString("Mutation")
+		case "createUser":
+			innerFunc := func(ctx context.Context) (res graphql.Marshaler) {
+				return ec._Mutation_createUser(ctx, field)
+			}
+
+			out.Values[i] = ec.OperationContext.RootResolverMiddleware(innerCtx, innerFunc)
+
+			if out.Values[i] == graphql.Null {
+				invalids++
+			}
+		default:
+			panic("unknown field " + strconv.Quote(field.Name))
+		}
+	}
+	out.Dispatch()
+	if invalids > 0 {
+		return graphql.Null
+	}
+	return out
+}
+
 var queryImplementors = []string{"Query"}
 
 func (ec *executionContext) _Query(ctx context.Context, sel ast.SelectionSet) graphql.Marshaler {
@@ -3670,6 +3832,11 @@ func (ec *executionContext) marshalNInt2int(ctx context.Context, sel ast.Selecti
 	return res
 }
 
+func (ec *executionContext) unmarshalNNewUser2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐNewUser(ctx context.Context, v interface{}) (NewUser, error) {
+	res, err := ec.unmarshalInputNewUser(ctx, v)
+	return res, graphql.ErrorOnPath(ctx, err)
+}
+
 func (ec *executionContext) unmarshalNSpecies2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐSpecies(ctx context.Context, v interface{}) (Species, error) {
 	var res Species
 	err := res.UnmarshalGQL(v)
@@ -3695,6 +3862,10 @@ func (ec *executionContext) marshalNString2string(ctx context.Context, sel ast.S
 	return res
 }
 
+func (ec *executionContext) marshalNUser2githubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐUser(ctx context.Context, sel ast.SelectionSet, v User) graphql.Marshaler {
+	return ec._User(ctx, sel, &v)
+}
+
 func (ec *executionContext) marshalNUser2ᚕᚖgithubᚗcomᚋKhanᚋgenqlientᚋinternalᚋintegrationᚋserverᚐUserᚄ(ctx context.Context, sel ast.SelectionSet, v []*User) graphql.Marshaler {
 	ret := make(graphql.Array, len(v))
 	var wg sync.WaitGroup

internal/integration/server/gqlgen_models.go

@@ -34,6 +34,10 @@ type Hair struct {
 	Color *string `json:"color"`
 }
 
+type NewUser struct {
+	Name string `json:"name"`
+}
+
 type User struct {
 	ID          string  `json:"id"`
 	Name        string  `json:"name"`

internal/integration/server/server.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"fmt"
 	"net/http/httptest"
+	"strconv"
 
 	"github.com/99designs/gqlgen/graphql"
 	"github.com/99designs/gqlgen/graphql/handler"
@@ -73,6 +74,24 @@ func beingByID(id string) Being {
 	return nil
 }
 
+func getNewID() string {
+	maxID := 0
+	for _, user := range users {
+		intID, _ := strconv.Atoi(user.ID)
+		if intID > maxID {
+			maxID = intID
+		}
+	}
+	for _, animal := range animals {
+		intID, _ := strconv.Atoi(animal.ID)
+		if intID > maxID {
+			maxID = intID
+		}
+	}
+	newID := maxID + 1
+	return strconv.Itoa(newID)
+}
+
 func (r *queryResolver) Me(ctx context.Context) (*User, error) {
 	return userByID("1"), nil
 }
@@ -129,9 +148,16 @@ func (r *queryResolver) Fail(ctx context.Context) (*bool, error) {
 	return &f, fmt.Errorf("oh no")
 }
 
+func (m mutationResolver) CreateUser(ctx context.Context, input NewUser) (*User, error) {
+	newUser := User{ID: getNewID(), Name: input.Name, Friends: []*User{}}
+	users = append(users, &newUser)
+	return &newUser, nil
+}
+
 func RunServer() *httptest.Server {
 	gqlgenServer := handler.New(NewExecutableSchema(Config{Resolvers: &resolver{}}))
 	gqlgenServer.AddTransport(transport.POST{})
+	gqlgenServer.AddTransport(transport.GET{})
 	gqlgenServer.AroundResponses(func(ctx context.Context, next graphql.ResponseHandler) *graphql.Response {
 		graphql.RegisterExtension(ctx, "foobar", "test")
 		return next(ctx)
@@ -140,10 +166,15 @@ func RunServer() *httptest.Server {
 }
 
 type (
-	resolver      struct{}
-	queryResolver struct{}
+	resolver         struct{}
+	queryResolver    struct{}
+	mutationResolver struct{}
 )
 
+func (r *resolver) Mutation() MutationResolver {
+	return &mutationResolver{}
+}
+
 func (r *resolver) Query() QueryResolver { return &queryResolver{} }
 
 //go:generate go run github.com/99designs/gqlgen