SSE Transport must be inserted before POST, so add convenience for using the DefaultServer

graphql/handler.go

@@ -93,6 +93,7 @@ type (
 	Transport interface {
 		Supports(r *http.Request) bool
 		Do(w http.ResponseWriter, r *http.Request, exec GraphExecutor)
+		String() string
 	}
 )
 

graphql/handler/server.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"slices"
 	"time"
 
 	"github.com/vektah/gqlparser/v2/ast"
@@ -39,6 +40,8 @@ func NewDefaultServer(es graphql.ExecutableSchema) *Server {
 	})
 	srv.AddTransport(transport.Options{})
 	srv.AddTransport(transport.GET{})
+	// To enable Server-Sent-Events, must insert here:
+	// srv.AddTransport(transport.SSE{})
 	srv.AddTransport(transport.POST{})
 	srv.AddTransport(transport.MultipartForm{})
 
@@ -56,6 +59,22 @@ func (s *Server) AddTransport(transport graphql.Transport) {
 	s.transports = append(s.transports, transport)
 }
 
+func (s *Server) PrependTransport(transport graphql.Transport) {
+	s.transports = append([]graphql.Transport{transport}, s.transports...)
+}
+
+// AddPrePostTransport is primarily for adding experimental transports like
+// SSE so that the usual POST transport doesn't respond
+func (s *Server) AddPrePostTransport(transport graphql.Transport) {
+	postIndex := slices.IndexFunc(s.transports, func(n graphql.Transport) bool {
+		return n.String() == "POST"
+	})
+
+	if postIndex != -1 {
+		s.transports = slices.Insert(s.transports, postIndex, transport)
+	}
+}
+
 func (s *Server) SetErrorPresenter(f graphql.ErrorPresenterFunc) {
 	s.exec.SetErrorPresenter(f)
 }
@@ -96,6 +115,7 @@ func (s *Server) AroundResponses(f graphql.ResponseMiddleware) {
 	s.exec.AroundResponses(f)
 }
 
+// Transport choice is first acceptable
 func (s *Server) getTransport(r *http.Request) graphql.Transport {
 	for _, t := range s.transports {
 		if t.Supports(r) {
@@ -119,13 +139,13 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	r = r.WithContext(graphql.StartOperationTrace(r.Context()))
 
-	transport := s.getTransport(r)
-	if transport == nil {
+	gqlTransport := s.getTransport(r)
+	if gqlTransport == nil {
 		sendErrorf(w, http.StatusBadRequest, "transport not supported")
 		return
 	}
 
-	transport.Do(w, r, s.exec)
+	gqlTransport.Do(w, r, s.exec)
 }
 
 func sendError(w http.ResponseWriter, code int, errors ...*gqlerror.Error) {

graphql/handler/server_test.go

@@ -166,6 +166,12 @@ func TestErrorServer(t *testing.T) {
 
 type panicTransport struct{}
 
+var _ graphql.Transport = panicTransport{}
+
+func (t panicTransport) String() string {
+	return "panicTransport"
+}
+
 func (t panicTransport) Supports(r *http.Request) bool {
 	return true
 }

graphql/handler/transport/http_form_multipart.go

@@ -28,6 +28,10 @@ type MultipartForm struct {
 
 var _ graphql.Transport = MultipartForm{}
 
+func (f MultipartForm) String() string {
+	return "MultipartForm"
+}
+
 func (f MultipartForm) Supports(r *http.Request) bool {
 	if r.Header.Get("Upgrade") != "" {
 		return false

graphql/handler/transport/http_form_urlencoded.go

@@ -21,6 +21,10 @@ type UrlEncodedForm struct {
 
 var _ graphql.Transport = UrlEncodedForm{}
 
+func (h UrlEncodedForm) String() string {
+	return "UrlEncodedForm"
+}
+
 func (h UrlEncodedForm) Supports(r *http.Request) bool {
 	if r.Header.Get("Upgrade") != "" {
 		return false

graphql/handler/transport/http_get.go

@@ -24,6 +24,10 @@ type GET struct {
 
 var _ graphql.Transport = GET{}
 
+func (h GET) String() string {
+	return "GET"
+}
+
 func (h GET) Supports(r *http.Request) bool {
 	if r.Header.Get("Upgrade") != "" {
 		return false

graphql/handler/transport/http_graphql.go

@@ -23,6 +23,10 @@ type GRAPHQL struct {
 
 var _ graphql.Transport = GRAPHQL{}
 
+func (h GRAPHQL) String() string {
+	return "GRAPHQL"
+}
+
 func (h GRAPHQL) Supports(r *http.Request) bool {
 	if r.Header.Get("Upgrade") != "" {
 		return false

graphql/handler/transport/http_post.go

@@ -22,6 +22,10 @@ type POST struct {
 
 var _ graphql.Transport = POST{}
 
+func (h POST) String() string {
+	return "POST"
+}
+
 func (h POST) Supports(r *http.Request) bool {
 	if r.Header.Get("Upgrade") != "" {
 		return false

graphql/handler/transport/options.go

@@ -15,6 +15,10 @@ type Options struct {
 
 var _ graphql.Transport = Options{}
 
+func (o Options) String() string {
+	return "Options"
+}
+
 func (o Options) Supports(r *http.Request) bool {
 	return r.Method == "HEAD" || r.Method == "OPTIONS"
 }

graphql/handler/transport/sse.go

@@ -18,6 +18,10 @@ type SSE struct{}
 
 var _ graphql.Transport = SSE{}
 
+func (t SSE) String() string {
+	return "SSE"
+}
+
 func (t SSE) Supports(r *http.Request) bool {
 	if !strings.Contains(r.Header.Get("Accept"), "text/event-stream") {
 		return false

graphql/handler/transport/websocket.go

@@ -86,6 +86,10 @@ var (
 	_ error             = WebsocketError{}
 )
 
+func (t Websocket) String() string {
+	return "Websocket"
+}
+
 func (t Websocket) Supports(r *http.Request) bool {
 	return r.Header.Get("Upgrade") != ""
 }