experiment: render headers directly to output buffer to avoid a copy; minor speed boost

block.go

@@ -186,10 +186,12 @@ func blockPrefixHeader(out *bytes.Buffer, rndr *render, data []byte) int {
 		end--
 	}
 	if end > i {
-		var work bytes.Buffer
-		parseInline(&work, rndr, data[i:end])
 		if rndr.mk.Header != nil {
-			rndr.mk.Header(out, work.Bytes(), level, rndr.mk.Opaque)
+			work := func() bool {
+				parseInline(out, rndr, data[i:end])
+				return true
+			}
+			rndr.mk.Header(out, work, level, rndr.mk.Opaque)
 		}
 	}
 	return skip
@@ -1071,9 +1073,14 @@ func blockParagraph(out *bytes.Buffer, rndr *render, data []byte) int {
 				renderParagraph(out, rndr, data[:prev])
 
 				// render the header
-				var work bytes.Buffer
-				parseInline(&work, rndr, data[prev:i-1])
-				rndr.mk.Header(out, work.Bytes(), level, rndr.mk.Opaque)
+				// this ugly, convoluted closure avoids forcing variables onto the heap
+				work := func(o *bytes.Buffer, r *render, d []byte) func() bool {
+					return func() bool {
+						parseInline(o, r, d)
+						return true
+					}
+				}(out, rndr, data[prev:i-1])
+				rndr.mk.Header(out, work, level, rndr.mk.Opaque)
 
 				// find the end of the underline
 				for ; i < len(data) && data[i] != '\n'; i++ {

html.go

@@ -163,10 +163,11 @@ func attrEscape(out *bytes.Buffer, src []byte) {
 	}
 }
 
-func htmlHeader(out *bytes.Buffer, text []byte, level int, opaque interface{}) {
+func htmlHeader(out *bytes.Buffer, text func() bool, level int, opaque interface{}) {
 	options := opaque.(*htmlOptions)
+	marker := out.Len()
 
-	if out.Len() > 0 {
+	if marker > 0 {
 		out.WriteByte('\n')
 	}
 
@@ -177,7 +178,10 @@ func htmlHeader(out *bytes.Buffer, text []byte, level int, opaque interface{}) {
 		out.WriteString(fmt.Sprintf("<h%d>", level))
 	}
 
-	out.Write(text)
+	if !text() {
+		out.Truncate(marker)
+		return
+	}
 	out.WriteString(fmt.Sprintf("</h%d>\n", level))
 }
 
@@ -572,8 +576,10 @@ func htmlNormalText(out *bytes.Buffer, text []byte, opaque interface{}) {
 	attrEscape(out, text)
 }
 
-func htmlTocHeader(out *bytes.Buffer, text []byte, level int, opaque interface{}) {
+func htmlTocHeader(out *bytes.Buffer, text func() bool, level int, opaque interface{}) {
 	options := opaque.(*htmlOptions)
+	marker := out.Len()
+
 	for level > options.tocData.currentLevel {
 		if options.tocData.currentLevel > 0 {
 			out.WriteString("<li>")
@@ -595,8 +601,9 @@ func htmlTocHeader(out *bytes.Buffer, text []byte, level int, opaque interface{}
 	out.WriteString("\">")
 	options.tocData.headerCount++
 
-	if len(text) > 0 {
-		out.Write(text)
+	if !text() {
+		out.Truncate(marker)
+		return
 	}
 	out.WriteString("</a></li>\n")
 }

latex.go

@@ -76,7 +76,9 @@ func latexBlockQuote(out *bytes.Buffer, text []byte, opaque interface{}) {
 
 //BlockHtml  func(out *bytes.Buffer, text []byte, opaque interface{})
 
-func latexHeader(out *bytes.Buffer, text []byte, level int, opaque interface{}) {
+func latexHeader(out *bytes.Buffer, text func() bool, level int, opaque interface{}) {
+	marker := out.Len()
+
 	switch level {
 	case 1:
 		out.WriteString("\n\\section{")
@@ -91,7 +93,10 @@ func latexHeader(out *bytes.Buffer, text []byte, level int, opaque interface{})
 	case 6:
 		out.WriteString("\n\\textbf{")
 	}
-	out.Write(text)
+	if !text() {
+		out.Truncate(marker)
+		return
+	}
 	out.WriteString("}\n")
 }
 

markdown.go

@@ -99,7 +99,7 @@ type Renderer struct {
 	BlockCode  func(out *bytes.Buffer, text []byte, lang string, opaque interface{})
 	BlockQuote func(out *bytes.Buffer, text []byte, opaque interface{})
 	BlockHtml  func(out *bytes.Buffer, text []byte, opaque interface{})
-	Header     func(out *bytes.Buffer, text []byte, level int, opaque interface{})
+	Header     func(out *bytes.Buffer, text func() bool, level int, opaque interface{})
 	HRule      func(out *bytes.Buffer, opaque interface{})
 	List       func(out *bytes.Buffer, text []byte, flags int, opaque interface{})
 	ListItem   func(out *bytes.Buffer, text []byte, flags int, opaque interface{})