From de264ba0575f62d04a5ada4cde0fd40990136bc6 Mon Sep 17 00:00:00 2001
From: EwenQuim <ewen.quimerch@gmail.com>
Date: Wed, 3 Jul 2024 22:39:35 +0200
Subject: [PATCH] Multi-return

---
 ctx.go                                      |  57 ++------
 examples/full-app-gourmet/views/partials.go |   4 +-
 examples/full-app-gourmet/views/recipe.go   |  27 ++--
 html.go                                     |  64 ++++++++-
 html_test.go                                |  10 +-
 multi_return.go                             |  61 +++++++++
 multi_return_test.go                        | 106 +++++++++++++++
 options.go                                  |  16 ++-
 options_test.go                             |  29 +++-
 serialization.go                            | 143 +++++++++++++++++++-
 serialization_test.go                       |  27 ++++
 serve.go                                    | 107 +++++++--------
 serve_test.go                               |  28 +++-
 13 files changed, 537 insertions(+), 142 deletions(-)
 create mode 100644 multi_return.go
 create mode 100644 multi_return_test.go

diff --git a/ctx.go b/ctx.go
index a0826086..9c008152 100644
--- a/ctx.go
+++ b/ctx.go
@@ -64,7 +64,7 @@ type ctx[B any] interface {
 	// and you want to override one above the other, you can do:
 	//   c.Render("admin.page.html", recipes, "partials/aaa/nav.partial.html")
 	// By default, [templateToExecute] is added to the list of templates to override.
-	Render(templateToExecute string, data any, templateGlobsToOverride ...string) (HTML, error)
+	Render(templateToExecute string, data any, templateGlobsToOverride ...string) (CtxRenderer, error)
 
 	Cookie(name string) (*http.Cookie, error) // Get request cookie
 	SetCookie(cookie http.Cookie)             // Sets response cookie
@@ -222,51 +222,14 @@ func (c ContextNoBody) SetCookie(cookie http.Cookie) {
 // that the templates will be parsed only once, removing
 // the need to parse the templates on each request but also preventing
 // to dynamically use new templates.
-func (c ContextNoBody) Render(templateToExecute string, data any, layoutsGlobs ...string) (HTML, error) {
-	if strings.Contains(templateToExecute, "/") || strings.Contains(templateToExecute, "*") {
-
-		layoutsGlobs = append(layoutsGlobs, templateToExecute) // To override all blocks defined in the main template
-		cloned := template.Must(c.templates.Clone())
-		tmpl, err := cloned.ParseFS(c.fs, layoutsGlobs...)
-		if err != nil {
-			return "", HTTPError{
-				Err:    err,
-				Status: http.StatusInternalServerError,
-				Title:  "Error parsing template",
-				Detail: fmt.Errorf("error parsing template '%s': %w", layoutsGlobs, err).Error(),
-				Errors: []ErrorItem{
-					{
-						Name:   "templates",
-						Reason: "Check that the template exists and have the correct extension. Globs: " + strings.Join(layoutsGlobs, ", "),
-					},
-				},
-			}
-		}
-		c.templates = template.Must(tmpl.Clone())
-	}
-
-	// Get only last template name (for example, with partials/nav/main/nav.partial.html, get nav.partial.html)
-	myTemplate := strings.Split(templateToExecute, "/")
-	templateToExecute = myTemplate[len(myTemplate)-1]
-
-	c.Res.Header().Set("Content-Type", "text/html; charset=utf-8")
-	err := c.templates.ExecuteTemplate(c.Res, templateToExecute, data)
-	if err != nil {
-		return "", HTTPError{
-			Err:    err,
-			Status: http.StatusInternalServerError,
-			Title:  "Error rendering template",
-			Detail: fmt.Errorf("error executing template '%s': %w", templateToExecute, err).Error(),
-			Errors: []ErrorItem{
-				{
-					Name:   "templates",
-					Reason: "Check that the template exists and have the correct extension. Template: " + templateToExecute,
-				},
-			},
-		}
-	}
-
-	return "", err
+func (c ContextNoBody) Render(templateToExecute string, data any, layoutsGlobs ...string) (CtxRenderer, error) {
+	return &StdRenderer{
+		templateToExecute: templateToExecute,
+		templates:         c.templates,
+		layoutsGlobs:      layoutsGlobs,
+		fs:                c.fs,
+		data:              data,
+	}, nil
 }
 
 // PathParams returns the path parameters of the request.
@@ -427,7 +390,7 @@ func body[B any](c ContextNoBody) (B, error) {
 		body, err = readURLEncoded[B](c.Req, c.readOptions)
 	case "application/xml":
 		body, err = readXML[B](c.Req.Context(), c.Req.Body, c.readOptions)
-	case "application/x-yaml":
+	case "application/x-yaml", "text/yaml; charset=utf-8", "application/yaml": // https://www.rfc-editor.org/rfc/rfc9512.html
 		body, err = readYAML[B](c.Req.Context(), c.Req.Body, c.readOptions)
 	case "application/octet-stream":
 		// Read c.Req Body to bytes
diff --git a/examples/full-app-gourmet/views/partials.go b/examples/full-app-gourmet/views/partials.go
index 5a92efa4..0ddd2dca 100644
--- a/examples/full-app-gourmet/views/partials.go
+++ b/examples/full-app-gourmet/views/partials.go
@@ -5,12 +5,12 @@ import (
 	"github.com/go-fuego/fuego/examples/full-app-gourmet/store/types"
 )
 
-func (rs Ressource) unitPreselected(c fuego.ContextNoBody) (fuego.HTML, error) {
+func (rs Ressource) unitPreselected(c fuego.ContextNoBody) (fuego.CtxRenderer, error) {
 	id := c.QueryParam("IngredientID")
 
 	ingredient, err := rs.IngredientsQueries.GetIngredient(c.Context(), id)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	return c.Render("preselected-unit.partial.html", fuego.H{
diff --git a/examples/full-app-gourmet/views/recipe.go b/examples/full-app-gourmet/views/recipe.go
index f2a93666..97d29665 100644
--- a/examples/full-app-gourmet/views/recipe.go
+++ b/examples/full-app-gourmet/views/recipe.go
@@ -104,15 +104,18 @@ func (rs Ressource) showIndex(c fuego.ContextNoBody) (fuego.Templ, error) {
 	}), nil
 }
 
-func (rs Ressource) showRecipes(c fuego.ContextNoBody) (fuego.Templ, error) {
+func (rs Ressource) showRecipes(c fuego.ContextNoBody) (*fuego.DataOrTemplate[[]store.Recipe], error) {
 	recipes, err := rs.RecipesQueries.GetRecipes(c.Context())
 	if err != nil {
 		return nil, err
 	}
 
-	return templa.SearchPage(templa.SearchProps{
-		Recipes: recipes,
-	}), nil
+	return fuego.DataOrHTML(
+		recipes,
+		templa.SearchPage(templa.SearchProps{
+			Recipes: recipes,
+		}),
+	), nil
 }
 
 func (rs Ressource) relatedRecipes(c fuego.ContextNoBody) (fuego.Templ, error) {
@@ -220,7 +223,7 @@ func (rs Ressource) healthyRecipes(c fuego.ContextNoBody) (fuego.Templ, error) {
 	}), nil
 }
 
-func (rs Ressource) showRecipesList(c fuego.ContextNoBody) (fuego.HTML, error) {
+func (rs Ressource) showRecipesList(c fuego.ContextNoBody) (fuego.CtxRenderer, error) {
 	search := c.QueryParam("search")
 	recipes, err := rs.RecipesQueries.SearchRecipes(c.Context(), store.SearchRecipesParams{
 		Search: sql.NullString{
@@ -229,28 +232,28 @@ func (rs Ressource) showRecipesList(c fuego.ContextNoBody) (fuego.HTML, error) {
 		},
 	})
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	return c.Render("partials/recipes-list.partial.html", recipes)
 }
 
-func (rs Ressource) addRecipe(c *fuego.ContextWithBody[store.CreateRecipeParams]) (fuego.HTML, error) {
+func (rs Ressource) addRecipe(c *fuego.ContextWithBody[store.CreateRecipeParams]) (fuego.CtxRenderer, error) {
 	body, err := c.Body()
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	body.ID = uuid.NewString()
 
 	_, err = rs.RecipesQueries.CreateRecipe(c.Context(), body)
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	recipes, err := rs.RecipesQueries.GetRecipes(c.Context())
 	if err != nil {
-		return "", err
+		return nil, err
 	}
 
 	return c.Render("pages/admin.page.html", fuego.H{
@@ -258,12 +261,12 @@ func (rs Ressource) addRecipe(c *fuego.ContextWithBody[store.CreateRecipeParams]
 	})
 }
 
-func (rs Ressource) RecipePage(c fuego.ContextNoBody) (fuego.HTML, error) {
+func (rs Ressource) RecipePage(c fuego.ContextNoBody) (fuego.CtxRenderer, error) {
 	id := c.PathParam("id")
 
 	recipe, err := rs.RecipesQueries.GetRecipe(c.Context(), id)
 	if err != nil {
-		return "", fmt.Errorf("error getting recipe %s: %w", id, err)
+		return nil, fmt.Errorf("error getting recipe %s: %w", id, err)
 	}
 
 	ingredients, err := rs.IngredientsQueries.GetIngredientsOfRecipe(c.Context(), id)
diff --git a/html.go b/html.go
index fdffa571..802aeaf2 100644
--- a/html.go
+++ b/html.go
@@ -5,9 +5,14 @@ import (
 	"fmt"
 	"html/template"
 	"io"
+	"io/fs"
+	"net/http"
+	"strings"
 )
 
-// CtxRenderer can be used with [github.com/a-h/templ]
+// CtxRenderer is an interface that can be used to render a response.
+// It is used with standard library templating engine, by using fuego.ContextXXX.Render
+// It is compatible with [github.com/a-h/templ] out of the box.
 // Example:
 //
 //	func getRecipes(ctx fuego.ContextNoBody) (fuego.CtxRenderer, error) {
@@ -50,6 +55,63 @@ type HTML string
 // H is a shortcut for map[string]any
 type H map[string]any
 
+// StdRenderer renders a template using the standard library templating engine.
+type StdRenderer struct {
+	templateToExecute string
+	templates         *template.Template
+	layoutsGlobs      []string
+	fs                fs.FS
+	data              any
+}
+
+var _ CtxRenderer = StdRenderer{}
+
+func (s StdRenderer) Render(ctx context.Context, w io.Writer) error {
+	if strings.Contains(s.templateToExecute, "/") || strings.Contains(s.templateToExecute, "*") {
+
+		s.layoutsGlobs = append(s.layoutsGlobs, s.templateToExecute) // To override all blocks defined in the main template
+		cloned := template.Must(s.templates.Clone())
+		tmpl, err := cloned.ParseFS(s.fs, s.layoutsGlobs...)
+		if err != nil {
+			return HTTPError{
+				Err:    err,
+				Status: http.StatusInternalServerError,
+				Title:  "Error parsing template",
+				Detail: fmt.Errorf("error parsing template '%s': %w", s.layoutsGlobs, err).Error(),
+				Errors: []ErrorItem{
+					{
+						Name:   "templates",
+						Reason: "Check that the template exists and have the correct extension. Globs: " + strings.Join(s.layoutsGlobs, ", "),
+					},
+				},
+			}
+		}
+		s.templates = template.Must(tmpl.Clone())
+	}
+
+	// Get only last template name (for example, with partials/nav/main/nav.partial.html, get nav.partial.html)
+	myTemplate := strings.Split(s.templateToExecute, "/")
+	s.templateToExecute = myTemplate[len(myTemplate)-1]
+
+	err := s.templates.ExecuteTemplate(w, s.templateToExecute, s.data)
+	if err != nil {
+		return HTTPError{
+			Err:    err,
+			Status: http.StatusInternalServerError,
+			Title:  "Error rendering template",
+			Detail: fmt.Errorf("error executing template '%s': %w", s.templateToExecute, err).Error(),
+			Errors: []ErrorItem{
+				{
+					Name:   "templates",
+					Reason: "Check that the template exists and have the correct extension. Template: " + s.templateToExecute,
+				},
+			},
+		}
+	}
+
+	return err
+}
+
 // loadTemplates
 func (s *Server) loadTemplates(patterns ...string) error {
 	tmpl, err := template.ParseFS(s.fs, patterns...)
diff --git a/html_test.go b/html_test.go
index 990c5be8..7e07f37f 100644
--- a/html_test.go
+++ b/html_test.go
@@ -18,7 +18,7 @@ func TestRender(t *testing.T) {
 		WithTemplateGlobs("testdata/*.html"),
 	)
 
-	Get(s, "/test", func(ctx *ContextNoBody) (HTML, error) {
+	Get(s, "/test", func(ctx *ContextNoBody) (CtxRenderer, error) {
 		return ctx.Render("testdata/test.html", H{"Name": "test"})
 	})
 
@@ -43,7 +43,7 @@ func TestRender(t *testing.T) {
 	})
 
 	t.Run("cannot parse unexisting file", func(t *testing.T) {
-		Get(s, "/file-not-found", func(ctx ContextNoBody) (HTML, error) {
+		Get(s, "/file-not-found", func(ctx ContextNoBody) (CtxRenderer, error) {
 			return ctx.Render("testdata/not-found.html", H{"Name": "test"})
 		})
 
@@ -56,7 +56,7 @@ func TestRender(t *testing.T) {
 	})
 
 	t.Run("can execute template with missing variable in map", func(t *testing.T) {
-		Get(s, "/impossible", func(ctx ContextNoBody) (HTML, error) {
+		Get(s, "/impossible", func(ctx ContextNoBody) (CtxRenderer, error) {
 			return ctx.Render("testdata/test.html", H{"NotName": "test"})
 		})
 
@@ -71,7 +71,7 @@ func TestRender(t *testing.T) {
 	})
 
 	t.Run("cannot execute template with missing variable in struct", func(t *testing.T) {
-		Get(s, "/impossible-struct", func(ctx ContextNoBody) (HTML, error) {
+		Get(s, "/impossible-struct", func(ctx ContextNoBody) (CtxRenderer, error) {
 			return ctx.Render("testdata/test.html", struct{}{})
 		})
 
@@ -93,7 +93,7 @@ func BenchmarkRender(b *testing.B) {
 		WithTemplateGlobs("testdata/*.html"),
 	)
 
-	Get(s, "/test", func(ctx ContextNoBody) (HTML, error) {
+	Get(s, "/test", func(ctx ContextNoBody) (CtxRenderer, error) {
 		return ctx.Render("testdata/test.html", H{"Name": "test"})
 	})
 
diff --git a/multi_return.go b/multi_return.go
new file mode 100644
index 00000000..38def6d1
--- /dev/null
+++ b/multi_return.go
@@ -0,0 +1,61 @@
+package fuego
+
+import (
+	"context"
+	"encoding/json"
+	"encoding/xml"
+	"fmt"
+	"io"
+
+	"gopkg.in/yaml.v3"
+)
+
+// DataOrTemplate is a struct that can return either data or a template
+// depending on the asked type.
+type DataOrTemplate[T any] struct {
+	Data     T
+	Template any
+}
+
+var (
+	_ CtxRenderer    = DataOrTemplate[any]{} // Can render HTML (template)
+	_ json.Marshaler = DataOrTemplate[any]{} // Can render JSON (data)
+	_ xml.Marshaler  = DataOrTemplate[any]{} // Can render XML (data)
+	_ yaml.Marshaler = DataOrTemplate[any]{} // Can render YAML (data)
+	_ fmt.Stringer   = DataOrTemplate[any]{} // Can render string (data)
+)
+
+func (m DataOrTemplate[T]) MarshalJSON() ([]byte, error) {
+	return json.Marshal(m.Data)
+}
+
+func (m DataOrTemplate[T]) MarshalXML(e *xml.Encoder, _ xml.StartElement) error {
+	return e.Encode(m.Data)
+}
+
+func (m DataOrTemplate[T]) MarshalYAML() (interface{}, error) {
+	return m.Data, nil
+}
+
+func (m DataOrTemplate[T]) String() string {
+	return fmt.Sprintf("%v", m.Data)
+}
+
+func (m DataOrTemplate[T]) Render(c context.Context, w io.Writer) error {
+	switch m.Template.(type) {
+	case CtxRenderer:
+		return m.Template.(CtxRenderer).Render(c, w)
+	case Renderer:
+		return m.Template.(Renderer).Render(w)
+	default:
+		panic("template must be either CtxRenderer or Renderer")
+	}
+}
+
+// Helper function to create a DataOrTemplate return item without specifying the type.
+func DataOrHTML[T any](data T, template any) *DataOrTemplate[T] {
+	return &DataOrTemplate[T]{
+		Data:     data,
+		Template: template,
+	}
+}
diff --git a/multi_return_test.go b/multi_return_test.go
new file mode 100644
index 00000000..83240b43
--- /dev/null
+++ b/multi_return_test.go
@@ -0,0 +1,106 @@
+package fuego
+
+import (
+	"context"
+	"errors"
+	"io"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+type MockCtxRenderer struct {
+	RenderFunc func(context.Context, io.Writer) error
+}
+
+func RenderString(s string) MockCtxRenderer {
+	return MockCtxRenderer{
+		RenderFunc: func(c context.Context, w io.Writer) error {
+			_, err := w.Write([]byte(s))
+			return err
+		},
+	}
+}
+
+var _ CtxRenderer = MockCtxRenderer{}
+
+func (m MockCtxRenderer) Render(c context.Context, w io.Writer) error {
+	if m.RenderFunc == nil {
+		return errors.New("RenderFunc is nil")
+	}
+	return m.RenderFunc(c, w)
+}
+
+type MyType struct {
+	Name string
+}
+
+func TestMultiReturn(t *testing.T) {
+	s := NewServer()
+
+	Get(s, "/data", func(c ContextNoBody) (DataOrTemplate[MyType], error) {
+		entity := MyType{Name: "Ewen"}
+
+		return DataOrTemplate[MyType]{
+			Data:     entity,
+			Template: RenderString(`<div>` + entity.Name + `</div>`),
+		}, nil
+	})
+
+	Get(s, "/other", func(c ContextNoBody) (*DataOrTemplate[MyType], error) {
+		entity := MyType{Name: "Ewen"}
+
+		return DataOrHTML(
+			entity,
+			RenderString(`<div>`+entity.Name+`</div>`),
+		), nil
+	})
+
+	t.Run("requests HTML by default", func(t *testing.T) {
+		recorder := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/data", nil)
+
+		s.Mux.ServeHTTP(recorder, req)
+
+		require.Equal(t, 200, recorder.Code)
+		require.Equal(t, "text/html; charset=utf-8", recorder.Header().Get("Content-Type"))
+		require.Equal(t, `<div>Ewen</div>`, recorder.Body.String())
+	})
+
+	t.Run("requests JSON", func(t *testing.T) {
+		recorder := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/data", nil)
+		req.Header.Set("Accept", "application/json")
+
+		s.Mux.ServeHTTP(recorder, req)
+
+		require.Equal(t, 200, recorder.Code)
+		require.Equal(t, "application/json", recorder.Header().Get("Content-Type"))
+		require.Equal(t, crlf(`{"Name":"Ewen"}`), recorder.Body.String())
+	})
+
+	t.Run("requests XML", func(t *testing.T) {
+		recorder := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/data", nil)
+		req.Header.Set("Accept", "application/xml")
+
+		s.Mux.ServeHTTP(recorder, req)
+
+		require.Equal(t, 200, recorder.Code)
+		require.Equal(t, "application/xml", recorder.Header().Get("Content-Type"))
+		require.Equal(t, `<MyType><Name>Ewen</Name></MyType>`, recorder.Body.String())
+	})
+
+	t.Run("requests HTML", func(t *testing.T) {
+		recorder := httptest.NewRecorder()
+		req := httptest.NewRequest("GET", "/data", nil)
+		req.Header.Set("Accept", "text/html")
+
+		s.Mux.ServeHTTP(recorder, req)
+
+		require.Equal(t, 200, recorder.Code)
+		require.Contains(t, recorder.Header().Get("Content-Type"), "text/html")
+		require.Equal(t, `<div>Ewen</div>`, recorder.Body.String())
+	})
+}
diff --git a/options.go b/options.go
index f6d43c18..58d29efc 100644
--- a/options.go
+++ b/options.go
@@ -70,10 +70,12 @@ type Server struct {
 	DisallowUnknownFields bool // If true, the server will return an error if the request body contains unknown fields. Useful for quick debugging in development.
 	DisableOpenapi        bool // If true, the routes within the server will not generate an openapi spec.
 	maxBodySize           int64
-	Serialize             func(w http.ResponseWriter, ans any)   // Used to serialize the response. Defaults to [SendJSON].
-	SerializeError        func(w http.ResponseWriter, err error) // Used to serialize the error response. Defaults to [SendJSONError].
-	ErrorHandler          func(err error) error                  // Used to transform any error into a unified error type structure with status code. Defaults to [ErrorHandler]
-	startTime             time.Time
+
+	// Custom serializer that overrides the default one.
+	Serialize      func(w http.ResponseWriter, ans any)
+	SerializeError func(w http.ResponseWriter, err error) // Used to serialize the error response. Defaults to [SendJSONError].
+	ErrorHandler   func(err error) error                  // Used to transform any error into a unified error type structure with status code. Defaults to [ErrorHandler]
+	startTime      time.Time
 
 	OpenAPIConfig OpenAPIConfig
 
@@ -109,7 +111,6 @@ func NewServer(options ...func(*Server)) *Server {
 	defaultOptions := [...]func(*Server){
 		WithAddr("localhost:9999"),
 		WithDisallowUnknownFields(true),
-		WithSerializer(SendJSON),
 		WithErrorSerializer(SendJSONError),
 		WithErrorHandler(ErrorHandler),
 	}
@@ -258,6 +259,9 @@ func WithAddr(addr string) func(*Server) {
 	return func(c *Server) { c.Server.Addr = addr }
 }
 
+// WithXML sets the serializer to XML
+//
+// Deprecated: fuego supports automatic XML serialization when using the header "Accept: application/xml".
 func WithXML() func(*Server) {
 	return func(c *Server) {
 		c.Serialize = SendXML
@@ -274,6 +278,8 @@ func WithLogHandler(handler slog.Handler) func(*Server) {
 	}
 }
 
+// WithSerializer sets a custom serializer that overrides the default one.
+// Please send a PR if you think the default serializer should be improved, instead of jumping to this option.
 func WithSerializer(serializer func(w http.ResponseWriter, ans any)) func(*Server) {
 	return func(c *Server) { c.Serialize = serializer }
 }
diff --git a/options_test.go b/options_test.go
index 16e1788f..e0d186f6 100644
--- a/options_test.go
+++ b/options_test.go
@@ -5,6 +5,7 @@ import (
 	"html/template"
 	"io"
 	"log/slog"
+	"net/http"
 	"net/http/httptest"
 	"testing"
 
@@ -37,15 +38,14 @@ func TestNewServer(t *testing.T) {
 }
 
 func TestWithXML(t *testing.T) {
-	s := NewServer(
-		WithXML(),
-	)
+	s := NewServer()
 	Get(s, "/", controller)
 	Get(s, "/error", controllerWithError)
 
 	t.Run("response is XML", func(t *testing.T) {
 		recorder := httptest.NewRecorder()
 		req := httptest.NewRequest("GET", "/", nil)
+		req.Header.Set("Accept", "application/xml")
 
 		s.Mux.ServeHTTP(recorder, req)
 
@@ -57,12 +57,13 @@ func TestWithXML(t *testing.T) {
 	t.Run("error response is XML", func(t *testing.T) {
 		recorder := httptest.NewRecorder()
 		req := httptest.NewRequest("GET", "/error", nil)
+		req.Header.Set("Accept", "application/xml")
 
 		s.Mux.ServeHTTP(recorder, req)
 
 		require.Equal(t, 500, recorder.Code)
-		require.Equal(t, "application/xml", recorder.Header().Get("Content-Type"))
 		require.Equal(t, "<HTTPError><title>Internal Server Error</title><status>500</status></HTTPError>", recorder.Body.String())
+		require.Equal(t, "application/xml", recorder.Header().Get("Content-Type"))
 	})
 }
 
@@ -373,3 +374,23 @@ func TestServerTags(t *testing.T) {
 		require.Equal(t, subGroup.tags, []string{"my-server-tag"})
 	})
 }
+
+func TestCustomSerialization(t *testing.T) {
+	s := NewServer(
+		WithSerializer(func(w http.ResponseWriter, a any) {
+			w.WriteHeader(202)
+			w.Write([]byte("custom serialization"))
+		}),
+	)
+
+	Get(s, "/", func(c *ContextNoBody) (ans, error) {
+		return ans{Ans: "Hello World"}, nil
+	})
+
+	req := httptest.NewRequest("GET", "/", nil)
+	w := httptest.NewRecorder()
+	s.Mux.ServeHTTP(w, req)
+
+	require.Equal(t, 202, w.Code)
+	require.Equal(t, "custom serialization", w.Body.String())
+}
diff --git a/serialization.go b/serialization.go
index 7fda640d..1880840b 100644
--- a/serialization.go
+++ b/serialization.go
@@ -5,9 +5,12 @@ import (
 	"encoding/json"
 	"encoding/xml"
 	"errors"
+	"fmt"
 	"log/slog"
 	"net/http"
 	"reflect"
+
+	"gopkg.in/yaml.v3"
 )
 
 // OutTransformer is an interface for entities that can be transformed.
@@ -76,8 +79,22 @@ func Send(w http.ResponseWriter, text string) {
 	_, _ = w.Write([]byte(text))
 }
 
+// SendYAML sends a YAML response.
+// Declared as a variable to be able to override it for clients that need to customize serialization.
+var SendYAML = func(w http.ResponseWriter, ans any) {
+	w.Header().Set("Content-Type", "application/x-yaml")
+	err := yaml.NewEncoder(w).Encode(ans)
+	if err != nil {
+		w.WriteHeader(http.StatusInternalServerError)
+		slog.Error("Cannot serialize YAML", "error", err)
+		_, _ = w.Write([]byte(`{"error":"Cannot serialize YAML"}`))
+		return
+	}
+}
+
 // SendJSON sends a JSON response.
-func SendJSON(w http.ResponseWriter, ans any) {
+// Declared as a variable to be able to override it for clients that need to customize serialization.
+var SendJSON = func(w http.ResponseWriter, ans any) {
 	w.Header().Set("Content-Type", "application/json")
 	err := json.NewEncoder(w).Encode(ans)
 	if err != nil {
@@ -88,6 +105,28 @@ func SendJSON(w http.ResponseWriter, ans any) {
 	}
 }
 
+// SendError sends an error.
+// Declared as a variable to be able to override it for clients that need to customize serialization.
+var SendError = func(w http.ResponseWriter, r *http.Request, err error) {
+	accept := parseAcceptHeader(r.Header.Get("Accept"), nil)
+	if accept == "" {
+		accept = "application/json"
+	}
+
+	switch accept {
+	case "application/xml":
+		SendXMLError(w, err)
+	case "text/html":
+		_ = SendHTMLError(r.Context(), w, err)
+	case "text/plain":
+		_ = SendText(w, err)
+	case "application/json":
+		SendJSONError(w, err)
+	default:
+		SendJSONError(w, err)
+	}
+}
+
 // SendJSONError sends a JSON error response.
 // If the error implements ErrorWithStatus, the status code will be set.
 func SendJSONError(w http.ResponseWriter, err error) {
@@ -109,7 +148,8 @@ func SendJSONError(w http.ResponseWriter, err error) {
 }
 
 // SendXML sends a XML response.
-func SendXML(w http.ResponseWriter, ans any) {
+// Declared as a variable to be able to override it for clients that need to customize serialization.
+var SendXML = func(w http.ResponseWriter, ans any) {
 	w.Header().Set("Content-Type", "application/xml")
 	err := xml.NewEncoder(w).Encode(ans)
 	if err != nil {
@@ -132,3 +172,102 @@ func SendXMLError(w http.ResponseWriter, err error) {
 	w.WriteHeader(status)
 	SendXML(w, err)
 }
+
+func SendHTMLError(ctx context.Context, w http.ResponseWriter, err error) error {
+	status := http.StatusInternalServerError
+	var errorStatus ErrorWithStatus
+	if errors.As(err, &errorStatus) {
+		status = errorStatus.StatusCode()
+	}
+
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+	w.WriteHeader(status)
+	return SendHTML(ctx, w, err.Error())
+}
+
+// SendHTML sends a HTML response.
+// Declared as a variable to be able to override it for clients that need to customize serialization.
+var SendHTML = func(ctx context.Context, w http.ResponseWriter, ans any) error {
+	w.Header().Set("Content-Type", "text/html; charset=utf-8")
+
+	ctxRenderer, ok := any(ans).(CtxRenderer)
+	if ok {
+		return ctxRenderer.Render(ctx, w)
+	}
+
+	renderer, ok := any(ans).(Renderer)
+	if ok {
+		return renderer.Render(w)
+	}
+
+	html, ok := any(ans).(HTML)
+	if ok {
+		_, err := w.Write([]byte(html))
+		return err
+	}
+
+	htmlString, ok := any(ans).(string)
+	if ok {
+		_, err := w.Write([]byte(htmlString))
+		return err
+	}
+
+	// The type cannot be converted to HTML
+	return fmt.Errorf("cannot serialize HTML from type %T (not string, fuego.HTML and does not implement fuego.CtxRenderer or fuego.Renderer)", ans)
+}
+
+func SendText(w http.ResponseWriter, ans any) error {
+	var err error
+	w.Header().Set("Content-Type", "text/plain; charset=utf-8")
+	stringToWrite, ok := any(ans).(string)
+	if !ok {
+		stringToWritePtr, okPtr := any(ans).(*string)
+		if okPtr {
+			stringToWrite = *stringToWritePtr
+		} else {
+			stringToWrite = fmt.Sprintf("%v", ans)
+		}
+	}
+	_, err = w.Write([]byte(stringToWrite))
+
+	return err
+}
+
+func InferAcceptHeaderFromType(ans any) string {
+	_, ok := any(ans).(string)
+	if ok {
+		return "text/plain"
+	}
+
+	_, ok = any(ans).(*string)
+	if ok {
+		return "text/plain"
+	}
+
+	_, ok = any(ans).(HTML)
+	if ok {
+		return "text/html"
+	}
+
+	_, ok = any(ans).(CtxRenderer)
+	if ok {
+		return "text/html"
+	}
+
+	_, ok = any(&ans).(*CtxRenderer)
+	if ok {
+		return "text/html"
+	}
+
+	_, ok = any(ans).(Renderer)
+	if ok {
+		return "text/html"
+	}
+
+	_, ok = any(&ans).(*Renderer)
+	if ok {
+		return "text/html"
+	}
+
+	return "application/json"
+}
diff --git a/serialization_test.go b/serialization_test.go
index be9f21d7..e894d25c 100644
--- a/serialization_test.go
+++ b/serialization_test.go
@@ -2,6 +2,7 @@ package fuego
 
 import (
 	"context"
+	"io"
 	"net/http/httptest"
 	"testing"
 
@@ -239,3 +240,29 @@ func TestSend(t *testing.T) {
 
 	require.Equal(t, "Hello World", w.Body.String())
 }
+
+type templateMock struct{}
+
+func (t templateMock) Render(w io.Writer) error {
+	return nil
+}
+
+var _ Renderer = templateMock{}
+
+func TestInferAcceptHeaderFromType(t *testing.T) {
+	t.Run("can infer json", func(t *testing.T) {
+		accept := InferAcceptHeaderFromType(response{})
+		require.Equal(t, "application/json", accept)
+	})
+
+	t.Run("can infer that type is a template (implements Renderer)", func(t *testing.T) {
+		accept := InferAcceptHeaderFromType(templateMock{})
+		require.Equal(t, "text/html", accept)
+	})
+
+	t.Run("can infer that type is a template (implements CtxRenderer)", func(t *testing.T) {
+
+		accept := InferAcceptHeaderFromType(MockCtxRenderer{})
+		require.Equal(t, "text/html", accept)
+	})
+}
diff --git a/serve.go b/serve.go
index 219ff12c..275bc2e7 100644
--- a/serve.go
+++ b/serve.go
@@ -1,11 +1,13 @@
 package fuego
 
 import (
+	"errors"
 	"fmt"
 	"html/template"
 	"log/slog"
 	"net/http"
 	"reflect"
+	"strings"
 	"time"
 )
 
@@ -76,13 +78,7 @@ func initContext[Contextable ctx[Body], Body any](baseContext ContextNoBody) Con
 
 // HTTPHandler converts a Fuego controller into a http.HandlerFunc.
 func HTTPHandler[ReturnType, Body any, Contextable ctx[Body]](s *Server, controller func(c Contextable) (ReturnType, error)) http.HandlerFunc {
-	returnsHTML := reflect.TypeOf(controller).Out(0).Name() == "HTML"
-	var r ReturnType
-	_, returnsString := any(r).(*string)
-	if !returnsString {
-		_, returnsString = any(r).(string)
-	}
-
+	// Just a check, not used at request time
 	baseContext := *new(Contextable)
 	if reflect.TypeOf(baseContext) == nil {
 		slog.Info(fmt.Sprintf("context is nil: %v %T", baseContext, baseContext))
@@ -91,10 +87,10 @@ func HTTPHandler[ReturnType, Body any, Contextable ctx[Body]](s *Server, control
 
 	return func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("X-Powered-By", "Fuego")
-
 		w.Header().Set("Trailer", "Server-Timing")
-		timeCtxInit := time.Now()
 
+		// CONTEXT INITIALIZATION
+		timeCtxInit := time.Now()
 		var templates *template.Template
 		if s.template != nil {
 			templates = template.Must(s.template.Clone())
@@ -113,10 +109,11 @@ func HTTPHandler[ReturnType, Body any, Contextable ctx[Body]](s *Server, control
 		timeController := time.Now()
 		w.Header().Set("Server-Timing", Timing{"fuegoReqInit", timeController.Sub(timeCtxInit), ""}.String())
 
+		// CONTROLLER
 		ans, err := controller(ctx)
 		if err != nil {
 			err = s.ErrorHandler(err)
-			s.SerializeError(w, err)
+			SendError(w, r, err)
 			return
 		}
 		timeAfterController := time.Now()
@@ -126,66 +123,58 @@ func HTTPHandler[ReturnType, Body any, Contextable ctx[Body]](s *Server, control
 			return
 		}
 
-		ctxRenderer, ok := any(ans).(CtxRenderer)
-		if ok {
-			w.Header().Set("Content-Type", "text/html; charset=utf-8")
-			err = ctxRenderer.Render(r.Context(), w)
-			if err != nil {
-				err = s.ErrorHandler(err)
-				s.SerializeError(w, err)
-			}
-			w.Header().Set("Server-Timing", Timing{"render", time.Since(timeAfterController), ""}.String())
+		// TRANSFORM OUT
+		timeTransformOut := time.Now()
+		ans, err = transformOut(r.Context(), ans)
+		if err != nil {
+			err = s.ErrorHandler(err)
+			SendError(w, r, err)
 			return
 		}
+		timeAfterTransformOut := time.Now()
+		w.Header().Add("Server-Timing", Timing{"transformOut", timeAfterTransformOut.Sub(timeTransformOut), "transformOut"}.String())
 
-		renderer, ok := any(ans).(Renderer)
-		if ok {
-			w.Header().Set("Content-Type", "text/html; charset=utf-8")
-			err = renderer.Render(w)
-			if err != nil {
-				err = s.ErrorHandler(err)
-				s.SerializeError(w, err)
-			}
-			w.Header().Add("Server-Timing", Timing{"render", time.Since(timeAfterController), ""}.String())
+		// SERIALIZATION
+		// Custom serialization
+		if s.Serialize != nil {
+			s.Serialize(w, ans)
 			return
 		}
 
-		if returnsHTML {
-			w.Header().Set("Content-Type", "text/html; charset=utf-8")
-			_, err = w.Write([]byte(any(ans).(HTML)))
-			if err != nil {
-				s.SerializeError(w, err)
-			}
-			w.Header().Add("Server-Timing", Timing{"render", time.Since(timeAfterController), ""}.String())
-			return
+		// Default serialization
+		switch parseAcceptHeader(r.Header.Get("Accept"), ans) {
+		case "application/xml":
+			SendXML(w, ans)
+		case "text/html":
+			err = SendHTML(r.Context(), w, ans)
+		case "text/plain":
+			err = SendText(w, ans)
+		case "application/json":
+			SendJSON(w, ans)
+		case "application/yaml":
+			SendYAML(w, ans)
+		default:
+			SendError(w, r, errors.New("unsupported Accept header"))
 		}
+		w.Header().Add("Server-Timing", Timing{"serialize", time.Since(timeAfterTransformOut), ""}.String())
 
-		timeTransformOut := time.Now()
-		ans, err = transformOut(r.Context(), ans)
+		// FINAL ERROR HANDLING
 		if err != nil {
 			err = s.ErrorHandler(err)
-			s.SerializeError(w, err)
-			return
+			SendError(w, r, err)
 		}
+	}
+}
 
-		if returnsString {
-			w.Header().Set("Content-Type", "text/plain; charset=utf-8")
-			stringToWrite, ok := any(ans).(string)
-			if !ok {
-				stringToWrite = *any(ans).(*string)
-			}
-			_, err = w.Write([]byte(stringToWrite))
-			if err != nil {
-				s.SerializeError(w, err)
-			}
-			w.Header().Add("Server-Timing", Timing{"write", time.Since(timeTransformOut), "transformOut"}.String())
-			return
-		}
-
-		timeAfterTransformOut := time.Now()
-		w.Header().Add("Server-Timing", Timing{"transformOut", timeAfterTransformOut.Sub(timeTransformOut), "transformOut"}.String())
-
-		s.Serialize(w, ans)
-		w.Header().Add("Server-Timing", Timing{"serialize", time.Since(timeAfterTransformOut), ""}.String())
+func parseAcceptHeader(accept string, ans any) string {
+	if strings.Index(accept, ",") > 0 {
+		accept = accept[:strings.Index(accept, ",")]
+	}
+	if accept == "*/*" {
+		accept = ""
+	}
+	if accept == "" {
+		accept = InferAcceptHeaderFromType(ans)
 	}
+	return accept
 }
diff --git a/serve_test.go b/serve_test.go
index 2e147d12..43e7fd1a 100644
--- a/serve_test.go
+++ b/serve_test.go
@@ -165,6 +165,7 @@ func TestHttpHandler(t *testing.T) {
 		handler := HTTPHandler(s, testControllerReturningPtrToString)
 
 		req := httptest.NewRequest("GET", "/testing", nil)
+		req.Header.Set("Accept", "text/plain")
 		w := httptest.NewRecorder()
 		handler(w, req)
 
@@ -266,7 +267,7 @@ func TestServeRenderer(t *testing.T) {
 			s.Mux.ServeHTTP(w, req)
 
 			require.Equal(t, 500, w.Code)
-			require.Equal(t, "<body><h1>error</h1></body>", w.Body.String())
+			require.Equal(t, crlf(`{"title":"Internal Server Error","status":500}`), w.Body.String())
 		})
 
 		t.Run("error in rendering", func(t *testing.T) {
@@ -275,7 +276,7 @@ func TestServeRenderer(t *testing.T) {
 			s.Mux.ServeHTTP(w, req)
 
 			require.Equal(t, 500, w.Code)
-			require.Equal(t, "<body><h1>error</h1></body>", w.Body.String())
+			require.Equal(t, crlf(`{"title":"Internal Server Error","status":500}`), w.Body.String())
 		})
 	})
 
@@ -305,7 +306,17 @@ func TestServeRenderer(t *testing.T) {
 			s.Mux.ServeHTTP(w, req)
 
 			require.Equal(t, 500, w.Code)
-			require.Equal(t, "<body><h1>error</h1></body>", w.Body.String())
+			require.Equal(t, crlf(`{"title":"Internal Server Error","status":500}`), w.Body.String())
+		})
+
+		t.Run("error return, asking for HTML", func(t *testing.T) {
+			req := httptest.NewRequest("GET", "/ctx/error-in-controller", nil)
+			req.Header.Set("Accept", "text/html")
+			w := httptest.NewRecorder()
+			s.Mux.ServeHTTP(w, req)
+
+			require.Equal(t, 500, w.Code)
+			require.Equal(t, "Internal Server Error (500): ", w.Body.String())
 		})
 
 		t.Run("error in rendering", func(t *testing.T) {
@@ -314,7 +325,7 @@ func TestServeRenderer(t *testing.T) {
 			s.Mux.ServeHTTP(w, req)
 
 			require.Equal(t, 500, w.Code)
-			require.Equal(t, "<body><h1>error</h1></body>", w.Body.String())
+			require.Equal(t, crlf(`{"title":"Internal Server Error","status":500}`), w.Body.String())
 		})
 	})
 }
@@ -483,7 +494,13 @@ func TestServer_RunTLS(t *testing.T) {
 			defer conn.Close()
 
 			client := &http.Client{Transport: &http.Transport{TLSClientConfig: &tls.Config{InsecureSkipVerify: true}}}
-			resp, err := client.Get(fmt.Sprintf("https://%s/test", s.Server.Addr))
+			req, err := http.NewRequest("GET", fmt.Sprintf("https://%s/test", s.Server.Addr), nil)
+			if err != nil {
+				t.Fatal(err)
+			}
+			req.Header.Set("Accept", "text/plain")
+
+			resp, err := client.Do(req)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -563,3 +580,4 @@ func newTLSTestHelper() (*tlsTestHelper, error) {
 	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: privateKeyBytes})
 	return &tlsTestHelper{cert: certPEM, key: keyPEM}, nil
 }
+