Make HTML rendering more advanced

Also add Python-like HTML parser thing in lib/htmlparser

lib/htmlparser/htmlparser.go

@@ -0,0 +1,108 @@
+// gomuks - A terminal Matrix client written in Go.
+// Copyright (C) 2018 Tulir Asokan
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package htmlparser
+
+import (
+	"io"
+	"strings"
+
+	"golang.org/x/net/html"
+)
+
+type HTMLProcessor interface {
+	Preprocess()
+	HandleStartTag(tagName string, attrs map[string]string)
+	HandleSelfClosingTag(tagName string, attrs map[string]string)
+	HandleText(text string)
+	HandleEndTag(tagName string)
+	ReceiveError(err error)
+	Postprocess()
+}
+
+type HTMLParser struct {
+	*html.Tokenizer
+	processor HTMLProcessor
+}
+
+func NewHTMLParserFromTokenizer(z *html.Tokenizer, processor HTMLProcessor) HTMLParser {
+	return HTMLParser{
+		z,
+		processor,
+	}
+}
+
+func NewHTMLParserFromReader(reader io.Reader, processor HTMLProcessor) HTMLParser {
+	return NewHTMLParserFromTokenizer(html.NewTokenizer(reader), processor)
+}
+
+func NewHTMLParserFromString(html string, processor HTMLProcessor) HTMLParser {
+	return NewHTMLParserFromReader(strings.NewReader(html), processor)
+}
+
+var SelfClosingTags = []string{"img", "br", "hr", "area", "base", "basefont", "input", "link", "meta"}
+
+func (parser HTMLParser) mapAttrs() map[string]string {
+	attrs := make(map[string]string)
+	hasMore := true
+	for hasMore {
+		var key, val []byte
+		key, val, hasMore = parser.TagAttr()
+		attrs[string(key)] = string(val)
+	}
+	return attrs
+}
+
+func (parser HTMLParser) isSelfClosing(tag string) bool {
+	for _, selfClosingTag := range SelfClosingTags {
+		if tag == selfClosingTag {
+			return true
+		}
+	}
+	return false
+}
+
+func (parser HTMLParser) Process() {
+	parser.processor.Preprocess()
+Loop:
+	for {
+		tt := parser.Next()
+		switch tt {
+		case html.ErrorToken:
+			parser.processor.ReceiveError(parser.Err())
+			break Loop
+		case html.TextToken:
+			parser.processor.HandleText(string(parser.Text()))
+		case html.StartTagToken, html.SelfClosingTagToken:
+			tagb, _ := parser.TagName()
+			attrs := parser.mapAttrs()
+			tag := string(tagb)
+
+			selfClosing := tt == html.SelfClosingTagToken || parser.isSelfClosing(tag)
+
+			if selfClosing {
+				parser.processor.HandleSelfClosingTag(tag, attrs)
+			} else {
+				parser.processor.HandleStartTag(tag, attrs)
+			}
+		case html.EndTagToken:
+			tagb, _ := parser.TagName()
+			parser.processor.HandleEndTag(string(tagb))
+		}
+	}
+
+	parser.processor.Postprocess()
+}