feat(fs): Implement loading HTML from http.FileSystem (#4053)

* Implement loading HTML from http.FileSystem

* Add OnlyHTMLFS test

* Move OnlyHTMLFS to internal and add test

render/html.go

@@ -7,6 +7,8 @@ package render
 import (
 	"html/template"
 	"net/http"
+
+	"github.com/gin-gonic/gin/internal/fs"
 )
 
 // Delims represents a set of Left and Right delimiters for HTML template rendering.
@@ -31,10 +33,12 @@ type HTMLProduction struct {
 
 // HTMLDebug contains template delims and pattern and function with file list.
 type HTMLDebug struct {
-	Files   []string
-	Glob    string
-	Delims  Delims
-	FuncMap template.FuncMap
+	Files      []string
+	Glob       string
+	FileSystem http.FileSystem
+	Patterns   []string
+	Delims     Delims
+	FuncMap    template.FuncMap
 }
 
 // HTML contains template reference and its name with given interface object.
@@ -73,7 +77,11 @@ func (r HTMLDebug) loadTemplate() *template.Template {
 	if r.Glob != "" {
 		return template.Must(template.New("").Delims(r.Delims.Left, r.Delims.Right).Funcs(r.FuncMap).ParseGlob(r.Glob))
 	}
-	panic("the HTML debug render was created without files or glob pattern")
+	if r.FileSystem != nil && len(r.Patterns) > 0 {
+		return template.Must(template.New("").Delims(r.Delims.Left, r.Delims.Right).Funcs(r.FuncMap).ParseFS(
+			fs.FileSystem{FileSystem: r.FileSystem}, r.Patterns...))
+	}
+	panic("the HTML debug render was created without files or glob pattern or file system with patterns")
 }
 
 // Render (HTML) executes template and writes its result with custom ContentType for response.

render/render_test.go

@@ -489,10 +489,12 @@ func TestRenderHTMLTemplateEmptyName(t *testing.T) {
 func TestRenderHTMLDebugFiles(t *testing.T) {
 	w := httptest.NewRecorder()
 	htmlRender := HTMLDebug{
-		Files:   []string{"../testdata/template/hello.tmpl"},
-		Glob:    "",
-		Delims:  Delims{Left: "{[{", Right: "}]}"},
-		FuncMap: nil,
+		Files:      []string{"../testdata/template/hello.tmpl"},
+		Glob:       "",
+		FileSystem: nil,
+		Patterns:   nil,
+		Delims:     Delims{Left: "{[{", Right: "}]}"},
+		FuncMap:    nil,
 	}
 	instance := htmlRender.Instance("hello.tmpl", map[string]any{
 		"name": "thinkerou",
@@ -508,10 +510,33 @@ func TestRenderHTMLDebugFiles(t *testing.T) {
 func TestRenderHTMLDebugGlob(t *testing.T) {
 	w := httptest.NewRecorder()
 	htmlRender := HTMLDebug{
-		Files:   nil,
-		Glob:    "../testdata/template/hello*",
-		Delims:  Delims{Left: "{[{", Right: "}]}"},
-		FuncMap: nil,
+		Files:      nil,
+		Glob:       "../testdata/template/hello*",
+		FileSystem: nil,
+		Patterns:   nil,
+		Delims:     Delims{Left: "{[{", Right: "}]}"},
+		FuncMap:    nil,
+	}
+	instance := htmlRender.Instance("hello.tmpl", map[string]any{
+		"name": "thinkerou",
+	})
+
+	err := instance.Render(w)
+
+	require.NoError(t, err)
+	assert.Equal(t, "<h1>Hello thinkerou</h1>", w.Body.String())
+	assert.Equal(t, "text/html; charset=utf-8", w.Header().Get("Content-Type"))
+}
+
+func TestRenderHTMLDebugFS(t *testing.T) {
+	w := httptest.NewRecorder()
+	htmlRender := HTMLDebug{
+		Files:      nil,
+		Glob:       "",
+		FileSystem: http.Dir("../testdata/template"),
+		Patterns:   []string{"hello.tmpl"},
+		Delims:     Delims{Left: "{[{", Right: "}]}"},
+		FuncMap:    nil,
 	}
 	instance := htmlRender.Instance("hello.tmpl", map[string]any{
 		"name": "thinkerou",
@@ -526,10 +551,12 @@ func TestRenderHTMLDebugGlob(t *testing.T) {
 
 func TestRenderHTMLDebugPanics(t *testing.T) {
 	htmlRender := HTMLDebug{
-		Files:   nil,
-		Glob:    "",
-		Delims:  Delims{"{{", "}}"},
-		FuncMap: nil,
+		Files:      nil,
+		Glob:       "",
+		FileSystem: nil,
+		Patterns:   nil,
+		Delims:     Delims{"{{", "}}"},
+		FuncMap:    nil,
 	}
 	assert.Panics(t, func() { htmlRender.Instance("", nil) })
 }