Implement loading HTML from http.FileSystem

docs/doc.md

@@ -1341,13 +1341,17 @@ func main() {
 
 ### HTML rendering
 
-Using LoadHTMLGlob() or LoadHTMLFiles()
+Using LoadHTMLGlob() or LoadHTMLFiles() or LoadHTMLFS()
 
 ```go
+//go:embed templates/*
+var templates embed.FS
+
 func main() {
   router := gin.Default()
   router.LoadHTMLGlob("templates/*")
   //router.LoadHTMLFiles("templates/template1.html", "templates/template2.html")
+  //router.LoadHTMLFS(http.FS(templates), "templates/template1.html", "templates/template2.html")
   router.GET("/index", func(c *gin.Context) {
     c.HTML(http.StatusOK, "index.tmpl", gin.H{
       "title": "Main website",

fs.go

@@ -5,6 +5,7 @@
 package gin
 
 import (
+	"io/fs"
 	"net/http"
 	"os"
 )
@@ -25,6 +26,22 @@ func (o OnlyFilesFS) Open(name string) (http.File, error) {
 	return neutralizedReaddirFile{f}, nil
 }
 
+// OnlyHTMLFS implements an [fs.FS].
+type OnlyHTMLFS struct {
+	FileSystem http.FileSystem
+}
+
+// Open passes `Open` to the upstream implementation and return an [fs.File].
+func (o OnlyHTMLFS) Open(name string) (fs.File, error) {
+	f, err := o.FileSystem.Open(name)
+
+	if err != nil {
+		return nil, err
+	}
+
+	return fs.File(f), nil
+}
+
 // neutralizedReaddirFile wraps http.File with a specific implementation of `Readdir`.
 type neutralizedReaddirFile struct {
 	http.File

gin.go

@@ -285,6 +285,18 @@ func (engine *Engine) LoadHTMLFiles(files ...string) {
 	engine.SetHTMLTemplate(templ)
 }
 
+// LoadHTMLFS loads an http.FileSystem and a slice of patterns
+// and associates the result with HTML renderer.
+func (engine *Engine) LoadHTMLFS(fs http.FileSystem, patterns ...string) {
+	if IsDebugging() {
+		engine.HTMLRender = render.HTMLDebug{FS: OnlyHTMLFS{fs}, Patterns: patterns, FuncMap: engine.FuncMap, Delims: engine.delims}
+		return
+	}
+
+	templ := template.Must(template.New("").Delims(engine.delims.Left, engine.delims.Right).Funcs(engine.FuncMap).ParseFS(OnlyHTMLFS{fs}, patterns...))
+	engine.SetHTMLTemplate(templ)
+}
+
 // SetHTMLTemplate associate a template with HTML renderer.
 func (engine *Engine) SetHTMLTemplate(templ *template.Template) {
 	if len(engine.trees) > 0 {

ginS/gins.go

@@ -32,6 +32,11 @@ func LoadHTMLFiles(files ...string) {
 	engine().LoadHTMLFiles(files...)
 }
 
+// LoadHTMLFS is a wrapper for Engine.LoadHTMLFS.
+func LoadHTMLFS(fs http.FileSystem, patterns ...string) {
+	engine().LoadHTMLFS(fs, patterns...)
+}
+
 // SetHTMLTemplate is a wrapper for Engine.SetHTMLTemplate.
 func SetHTMLTemplate(templ *template.Template) {
 	engine().SetHTMLTemplate(templ)

gin_test.go

@@ -6,6 +6,7 @@ package gin
 
 import (
 	"crypto/tls"
+	"embed"
 	"fmt"
 	"html/template"
 	"io"
@@ -325,6 +326,116 @@ func TestLoadHTMLFilesFuncMap(t *testing.T) {
 	assert.Equal(t, "Date: 2017/07/01", string(resp))
 }
 
+//go:embed testdata/template/*
+var htmlFS embed.FS
+
+func TestLoadHTMLFSTestMode(t *testing.T) {
+	ts := setupHTMLFiles(
+		t,
+		TestMode,
+		false,
+		func(router *Engine) {
+			router.LoadHTMLFS(http.FS(htmlFS), "testdata/template/hello.tmpl", "testdata/template/raw.tmpl")
+		},
+	)
+	defer ts.Close()
+
+	res, err := http.Get(fmt.Sprintf("%s/test", ts.URL))
+	if err != nil {
+		t.Error(err)
+	}
+
+	resp, _ := io.ReadAll(res.Body)
+	assert.Equal(t, "<h1>Hello world</h1>", string(resp))
+}
+
+func TestLoadHTMLFSDebugMode(t *testing.T) {
+	ts := setupHTMLFiles(
+		t,
+		DebugMode,
+		false,
+		func(router *Engine) {
+			router.LoadHTMLFS(http.FS(htmlFS), "testdata/template/hello.tmpl", "testdata/template/raw.tmpl")
+		},
+	)
+	defer ts.Close()
+
+	res, err := http.Get(fmt.Sprintf("%s/test", ts.URL))
+	if err != nil {
+		t.Error(err)
+	}
+
+	resp, _ := io.ReadAll(res.Body)
+	assert.Equal(t, "<h1>Hello world</h1>", string(resp))
+}
+
+func TestLoadHTMLFSReleaseMode(t *testing.T) {
+	ts := setupHTMLFiles(
+		t,
+		ReleaseMode,
+		false,
+		func(router *Engine) {
+			router.LoadHTMLFS(http.FS(htmlFS), "testdata/template/hello.tmpl", "testdata/template/raw.tmpl")
+		},
+	)
+	defer ts.Close()
+
+	res, err := http.Get(fmt.Sprintf("%s/test", ts.URL))
+	if err != nil {
+		t.Error(err)
+	}
+
+	resp, _ := io.ReadAll(res.Body)
+	assert.Equal(t, "<h1>Hello world</h1>", string(resp))
+}
+
+func TestLoadHTMLFSUsingTLS(t *testing.T) {
+	ts := setupHTMLFiles(
+		t,
+		TestMode,
+		true,
+		func(router *Engine) {
+			router.LoadHTMLFS(http.FS(htmlFS), "testdata/template/hello.tmpl", "testdata/template/raw.tmpl")
+		},
+	)
+	defer ts.Close()
+
+	// Use InsecureSkipVerify for avoiding `x509: certificate signed by unknown authority` error
+	tr := &http.Transport{
+		TLSClientConfig: &tls.Config{
+			InsecureSkipVerify: true,
+		},
+	}
+	client := &http.Client{Transport: tr}
+	res, err := client.Get(fmt.Sprintf("%s/test", ts.URL))
+	if err != nil {
+		t.Error(err)
+	}
+
+	resp, _ := io.ReadAll(res.Body)
+	assert.Equal(t, "<h1>Hello world</h1>", string(resp))
+}
+
+func TestLoadHTMLFSFuncMap(t *testing.T) {
+	ts := setupHTMLFiles(
+		t,
+		TestMode,
+		false,
+		func(router *Engine) {
+			router.LoadHTMLFS(http.FS(htmlFS), "testdata/template/hello.tmpl", "testdata/template/raw.tmpl")
+		},
+	)
+	defer ts.Close()
+
+	res, err := http.Get(fmt.Sprintf("%s/raw", ts.URL))
+	if err != nil {
+		t.Error(err)
+	}
+
+	resp, _ := io.ReadAll(res.Body)
+	assert.Equal(t, "Date: 2017/07/01", string(resp))
+}
+
 func TestAddRoute(t *testing.T) {
 	router := New()
 	router.addRoute("GET", "/", HandlersChain{func(_ *Context) {}})

render/html.go

@@ -6,6 +6,7 @@ package render
 
 import (
 	"html/template"
+	"io/fs"
 	"net/http"
 )
 
@@ -33,6 +34,8 @@ type HTMLProduction struct {
 type HTMLDebug struct {
 	Files    []string
 	Glob     string
+	FS       fs.FS
+	Patterns []string
 	Delims   Delims
 	FuncMap  template.FuncMap
 }
@@ -73,7 +76,10 @@ 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.FS != nil && len(r.Patterns) > 0 {
+		return template.Must(template.New("").Delims(r.Delims.Left, r.Delims.Right).Funcs(r.FuncMap).ParseFS(r.FS, 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.