Refactor renders (#15175)

* Refactor renders

* Some performance optimization

* Fix comment

* Transform reader

* Fix csv test

* Fix test

* Fix tests

* Improve optimaziation

* Fix test

* Fix test

* Detect file encoding with reader

* Improve optimaziation

* reduce memory usage

* improve code

* fix build

* Fix test

* Fix for go1.15

* Fix render

* Fix comment

* Fix lint

* Fix test

* Don't use NormalEOF when unnecessary

* revert change on util.go

* Apply suggestions from code review

Co-authored-by: zeripath <art27@cantab.net>

* rename function

* Take NormalEOF back

Co-authored-by: zeripath <art27@cantab.net>

modules/markup/renderer.go

@@ -0,0 +1,201 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package markup
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"path/filepath"
+	"strings"
+	"sync"
+
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// Init initialize regexps for markdown parsing
+func Init() {
+	getIssueFullPattern()
+	NewSanitizer()
+	if len(setting.Markdown.CustomURLSchemes) > 0 {
+		CustomLinkURLSchemes(setting.Markdown.CustomURLSchemes)
+	}
+
+	// since setting maybe changed extensions, this will reload all renderer extensions mapping
+	extRenderers = make(map[string]Renderer)
+	for _, renderer := range renderers {
+		for _, ext := range renderer.Extensions() {
+			extRenderers[strings.ToLower(ext)] = renderer
+		}
+	}
+}
+
+// RenderContext represents a render context
+type RenderContext struct {
+	Ctx         context.Context
+	Filename    string
+	Type        string
+	IsWiki      bool
+	URLPrefix   string
+	Metas       map[string]string
+	DefaultLink string
+}
+
+// Renderer defines an interface for rendering markup file to HTML
+type Renderer interface {
+	Name() string // markup format name
+	Extensions() []string
+	Render(ctx *RenderContext, input io.Reader, output io.Writer) error
+}
+
+var (
+	extRenderers = make(map[string]Renderer)
+	renderers    = make(map[string]Renderer)
+)
+
+// RegisterRenderer registers a new markup file renderer
+func RegisterRenderer(renderer Renderer) {
+	renderers[renderer.Name()] = renderer
+	for _, ext := range renderer.Extensions() {
+		extRenderers[strings.ToLower(ext)] = renderer
+	}
+}
+
+// GetRendererByFileName get renderer by filename
+func GetRendererByFileName(filename string) Renderer {
+	extension := strings.ToLower(filepath.Ext(filename))
+	return extRenderers[extension]
+}
+
+// GetRendererByType returns a renderer according type
+func GetRendererByType(tp string) Renderer {
+	return renderers[tp]
+}
+
+// Render renders markup file to HTML with all specific handling stuff.
+func Render(ctx *RenderContext, input io.Reader, output io.Writer) error {
+	if ctx.Type != "" {
+		return renderByType(ctx, input, output)
+	} else if ctx.Filename != "" {
+		return renderFile(ctx, input, output)
+	}
+	return errors.New("Render options both filename and type missing")
+}
+
+// RenderString renders Markup string to HTML with all specific handling stuff and return string
+func RenderString(ctx *RenderContext, content string) (string, error) {
+	var buf strings.Builder
+	if err := Render(ctx, strings.NewReader(content), &buf); err != nil {
+		return "", err
+	}
+	return buf.String(), nil
+}
+
+func render(ctx *RenderContext, parser Renderer, input io.Reader, output io.Writer) error {
+	var wg sync.WaitGroup
+	var err error
+	pr, pw := io.Pipe()
+	defer func() {
+		_ = pr.Close()
+		_ = pw.Close()
+	}()
+
+	pr2, pw2 := io.Pipe()
+	defer func() {
+		_ = pr2.Close()
+		_ = pw2.Close()
+	}()
+
+	wg.Add(1)
+	go func() {
+		buf := SanitizeReader(pr2)
+		_, err = io.Copy(output, buf)
+		_ = pr2.Close()
+		wg.Done()
+	}()
+
+	wg.Add(1)
+	go func() {
+		err = PostProcess(ctx, pr, pw2)
+		_ = pr.Close()
+		_ = pw2.Close()
+		wg.Done()
+	}()
+
+	if err1 := parser.Render(ctx, input, pw); err1 != nil {
+		return err1
+	}
+	_ = pw.Close()
+
+	wg.Wait()
+	return err
+}
+
+// ErrUnsupportedRenderType represents
+type ErrUnsupportedRenderType struct {
+	Type string
+}
+
+func (err ErrUnsupportedRenderType) Error() string {
+	return fmt.Sprintf("Unsupported render type: %s", err.Type)
+}
+
+func renderByType(ctx *RenderContext, input io.Reader, output io.Writer) error {
+	if renderer, ok := renderers[ctx.Type]; ok {
+		return render(ctx, renderer, input, output)
+	}
+	return ErrUnsupportedRenderType{ctx.Type}
+}
+
+// ErrUnsupportedRenderExtension represents the error when extension doesn't supported to render
+type ErrUnsupportedRenderExtension struct {
+	Extension string
+}
+
+func (err ErrUnsupportedRenderExtension) Error() string {
+	return fmt.Sprintf("Unsupported render extension: %s", err.Extension)
+}
+
+func renderFile(ctx *RenderContext, input io.Reader, output io.Writer) error {
+	extension := strings.ToLower(filepath.Ext(ctx.Filename))
+	if renderer, ok := extRenderers[extension]; ok {
+		return render(ctx, renderer, input, output)
+	}
+	return ErrUnsupportedRenderExtension{extension}
+}
+
+// Type returns if markup format via the filename
+func Type(filename string) string {
+	if parser := GetRendererByFileName(filename); parser != nil {
+		return parser.Name()
+	}
+	return ""
+}
+
+// IsMarkupFile reports whether file is a markup type file
+func IsMarkupFile(name, markup string) bool {
+	if parser := GetRendererByFileName(name); parser != nil {
+		return parser.Name() == markup
+	}
+	return false
+}
+
+// IsReadmeFile reports whether name looks like a README file
+// based on its name. If an extension is provided, it will strictly
+// match that extension.
+// Note that the '.' should be provided in ext, e.g ".md"
+func IsReadmeFile(name string, ext ...string) bool {
+	name = strings.ToLower(name)
+	if len(ext) > 0 {
+		return name == "readme"+ext[0]
+	}
+	if len(name) < 6 {
+		return false
+	} else if len(name) == 6 {
+		return name == "readme"
+	}
+	return name[:7] == "readme."
+}