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Reduce memory usage when rendering markdown #20326

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Reduce memory usage when rendering markdown #20326

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b9194bf
Reduce memory usage when rendering markdown
lunny Jul 12, 2022
e46f754
Reduce memory usage when rendering markdown
lunny Jul 12, 2022
ea3b13e
Merge branch 'main' into lunny/performance_renderer
lunny Jul 12, 2022
e2f2300
Fix bug
lunny Jul 12, 2022
4c2c466
Apply suggestions from code review
lunny Jul 12, 2022
d121484
Merge branch 'main' into lunny/performance_renderer
6543 Jul 12, 2022
424b7f8
Merge branch 'main' into lunny/performance_renderer
6543 Jul 13, 2022
d2bd8c2
Merge branch 'master' into lunny/performance_renderer
6543 Jul 16, 2022
d6ee57a
add BenchmarkPostProcess
6543 Jul 16, 2022
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31 changes: 20 additions & 11 deletions modules/markup/html.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,6 @@
package markup

import (
"bytes"
"io"
"net/url"
"path"
Expand Down Expand Up @@ -298,26 +297,36 @@ var (
nulCleaner = strings.NewReplacer("\000", "")
)

func postProcess(ctx *RenderContext, procs []processor, input io.Reader, output io.Writer) error {
defer ctx.Cancel()
// FIXME: don't read all content to memory
rawHTML, err := io.ReadAll(input)
type cleanReader struct {
io.Reader
}

func (c cleanReader) Read(bs []byte) (int, error) {
original := make([]byte, len(bs))
n, err := c.Reader.Read(original)
if err != nil {
return err
return n, err
}
n = copy(bs, tagCleaner.ReplaceAll([]byte(nulCleaner.Replace(string(original[:n]))), []byte("<$1")))
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I do not think it is correct.

The content is incomplete in the original buffer, the tagCleaner may not work correctly. And tagCleaner is quite a complex regexp, I am not sure whether it works for incomplete content.

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And one more thing, after the replacing, the returned string may be longer than before, it may overflow the bs buffer.

return n, nil
}

var _ io.Reader = cleanReader{}

func postProcess(ctx *RenderContext, procs []processor, input io.Reader, output io.Writer) error {
defer ctx.Cancel()

res := bytes.NewBuffer(make([]byte, 0, len(rawHTML)+50))
// prepend "<html><body>"
_, _ = res.WriteString("<html><body>")
htmlTagPrefix := strings.NewReader("<html><body>")

// Strip out nuls - they're always invalid
_, _ = res.Write(tagCleaner.ReplaceAll([]byte(nulCleaner.Replace(string(rawHTML))), []byte("&lt;$1")))
body := cleanReader{input}

// close the tags
_, _ = res.WriteString("</body></html>")
htmlTagSuffix := strings.NewReader("</body></html>")

// parse the HTML
node, err := html.Parse(res)
node, err := html.Parse(io.MultiReader(htmlTagPrefix, body, htmlTagSuffix))
if err != nil {
return &postProcessError{"invalid HTML", err}
}
Expand Down