1 files changed, 200 insertions, 0 deletions
diff --git a/modules/charset/htmlstream.go b/modules/charset/htmlstream.go
new file mode 100644
index 0000000..61f2912
--- /dev/null
+++ b/modules/charset/htmlstream.go
@@ -0,0 +1,200 @@
+// Copyright 2022 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package charset
+
+import (
+	"fmt"
+	"io"
+
+	"golang.org/x/net/html"
+)
+
+// HTMLStreamer represents a SAX-like interface for HTML
+type HTMLStreamer interface {
+	Error(err error) error
+	Doctype(data string) error
+	Comment(data string) error
+	StartTag(data string, attrs ...html.Attribute) error
+	SelfClosingTag(data string, attrs ...html.Attribute) error
+	EndTag(data string) error
+	Text(data string) error
+}
+
+// PassthroughHTMLStreamer is a passthrough streamer
+type PassthroughHTMLStreamer struct {
+	next HTMLStreamer
+}
+
+func NewPassthroughStreamer(next HTMLStreamer) *PassthroughHTMLStreamer {
+	return &PassthroughHTMLStreamer{next: next}
+}
+
+var _ (HTMLStreamer) = &PassthroughHTMLStreamer{}
+
+// Error tells the next streamer in line that there is an error
+func (p *PassthroughHTMLStreamer) Error(err error) error {
+	return p.next.Error(err)
+}
+
+// Doctype tells the next streamer what the doctype is
+func (p *PassthroughHTMLStreamer) Doctype(data string) error {
+	return p.next.Doctype(data)
+}
+
+// Comment tells the next streamer there is a comment
+func (p *PassthroughHTMLStreamer) Comment(data string) error {
+	return p.next.Comment(data)
+}
+
+// StartTag tells the next streamer there is a starting tag
+func (p *PassthroughHTMLStreamer) StartTag(data string, attrs ...html.Attribute) error {
+	return p.next.StartTag(data, attrs...)
+}
+
+// SelfClosingTag tells the next streamer there is a self-closing tag
+func (p *PassthroughHTMLStreamer) SelfClosingTag(data string, attrs ...html.Attribute) error {
+	return p.next.SelfClosingTag(data, attrs...)
+}
+
+// EndTag tells the next streamer there is a end tag
+func (p *PassthroughHTMLStreamer) EndTag(data string) error {
+	return p.next.EndTag(data)
+}
+
+// Text tells the next streamer there is a text
+func (p *PassthroughHTMLStreamer) Text(data string) error {
+	return p.next.Text(data)
+}
+
+// HTMLStreamWriter acts as a writing sink
+type HTMLStreamerWriter struct {
+	io.Writer
+	err error
+}
+
+// Write implements io.Writer
+func (h *HTMLStreamerWriter) Write(data []byte) (int, error) {
+	if h.err != nil {
+		return 0, h.err
+	}
+	return h.Writer.Write(data)
+}
+
+// Write implements io.StringWriter
+func (h *HTMLStreamerWriter) WriteString(data string) (int, error) {
+	if h.err != nil {
+		return 0, h.err
+	}
+	return h.Writer.Write([]byte(data))
+}
+
+// Error tells the next streamer in line that there is an error
+func (h *HTMLStreamerWriter) Error(err error) error {
+	if h.err == nil {
+		h.err = err
+	}
+	return h.err
+}
+
+// Doctype tells the next streamer what the doctype is
+func (h *HTMLStreamerWriter) Doctype(data string) error {
+	_, h.err = h.WriteString("<!DOCTYPE " + data + ">")
+	return h.err
+}
+
+// Comment tells the next streamer there is a comment
+func (h *HTMLStreamerWriter) Comment(data string) error {
+	_, h.err = h.WriteString("<!--" + data + "-->")
+	return h.err
+}
+
+// StartTag tells the next streamer there is a starting tag
+func (h *HTMLStreamerWriter) StartTag(data string, attrs ...html.Attribute) error {
+	return h.startTag(data, attrs, false)
+}
+
+// SelfClosingTag tells the next streamer there is a self-closing tag
+func (h *HTMLStreamerWriter) SelfClosingTag(data string, attrs ...html.Attribute) error {
+	return h.startTag(data, attrs, true)
+}
+
+func (h *HTMLStreamerWriter) startTag(data string, attrs []html.Attribute, selfclosing bool) error {
+	if _, h.err = h.WriteString("<" + data); h.err != nil {
+		return h.err
+	}
+	for _, attr := range attrs {
+		if _, h.err = h.WriteString(" " + attr.Key + "=\"" + html.EscapeString(attr.Val) + "\""); h.err != nil {
+			return h.err
+		}
+	}
+	if selfclosing {
+		if _, h.err = h.WriteString("/>"); h.err != nil {
+			return h.err
+		}
+	} else {
+		if _, h.err = h.WriteString(">"); h.err != nil {
+			return h.err
+		}
+	}
+	return h.err
+}
+
+// EndTag tells the next streamer there is a end tag
+func (h *HTMLStreamerWriter) EndTag(data string) error {
+	_, h.err = h.WriteString("</" + data + ">")
+	return h.err
+}
+
+// Text tells the next streamer there is a text
+func (h *HTMLStreamerWriter) Text(data string) error {
+	_, h.err = h.WriteString(html.EscapeString(data))
+	return h.err
+}
+
+// StreamHTML streams an html to a provided streamer
+func StreamHTML(source io.Reader, streamer HTMLStreamer) error {
+	tokenizer := html.NewTokenizer(source)
+	for {
+		tt := tokenizer.Next()
+		switch tt {
+		case html.ErrorToken:
+			if tokenizer.Err() != io.EOF {
+				return tokenizer.Err()
+			}
+			return nil
+		case html.DoctypeToken:
+			token := tokenizer.Token()
+			if err := streamer.Doctype(token.Data); err != nil {
+				return err
+			}
+		case html.CommentToken:
+			token := tokenizer.Token()
+			if err := streamer.Comment(token.Data); err != nil {
+				return err
+			}
+		case html.StartTagToken:
+			token := tokenizer.Token()
+			if err := streamer.StartTag(token.Data, token.Attr...); err != nil {
+				return err
+			}
+		case html.SelfClosingTagToken:
+			token := tokenizer.Token()
+			if err := streamer.StartTag(token.Data, token.Attr...); err != nil {
+				return err
+			}
+		case html.EndTagToken:
+			token := tokenizer.Token()
+			if err := streamer.EndTag(token.Data); err != nil {
+				return err
+			}
+		case html.TextToken:
+			token := tokenizer.Token()
+			if err := streamer.Text(token.Data); err != nil {
+				return err
+			}
+		default:
+			return fmt.Errorf("unknown type of token: %d", tt)
+		}
+	}
+}