Fix post previews rendering raw markdown by compscidr · Pull Request #474 · goblogplatform/goblog

compscidr · 2026-03-03T05:20:18Z

Summary

Post previews were displaying raw markdown syntax ([text](url), fenced code blocks, **bold**, etc.) because PreviewContent() simply truncated the raw content string
Add PlainTextPreview() that strips markdown to clean text (used for <meta description> tag)
Add HTMLPreview() that preserves links as clickable <a> tags and renders inline/fenced code as <code> elements, with visible-character-aware truncation so HTML tags don't consume preview length

Test plan

go test ./... passes
Footer "Most Recent Post" shows clean preview with clickable links and styled code
/posts page shows clean previews
/tag/:name pages show clean previews
Full post pages still render markdown normally via Showdown.js
Meta description in page source contains plain text (no HTML)

🤖 Generated with Claude Code

Post previews (footer, /posts, /tag pages) were displaying raw markdown syntax like [text](url), ```code blocks```, **bold**, etc. because PreviewContent() simply truncated the raw markdown string. Add PlainTextPreview() that strips markdown to clean text (used for meta description), and HTMLPreview() that preserves links as clickable <a> tags and renders code as inline <code> elements. HTMLPreview truncates by visible character count so HTML tags don't eat into preview length. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

codecov · 2026-03-03T05:22:57Z

Codecov Report

❌ Patch coverage is 67.27273% with 18 lines in your changes missing coverage. Please review.
✅ Project coverage is 43.23%. Comparing base (c5bb0b6) to head (a72df25).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
blog/post.go	67.27%	12 Missing and 6 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #474      +/-   ##
==========================================
+ Coverage   41.92%   43.23%   +1.30%     
==========================================
  Files           6        6              
  Lines        1016     1071      +55     
==========================================
+ Hits          426      463      +37     
- Misses        561      573      +12     
- Partials       29       35       +6

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Copilot

Pull request overview

This PR updates how post previews are generated so list pages and meta descriptions no longer show raw markdown syntax, introducing dedicated preview helpers on Post.

Changes:

Add Post.PlainTextPreview() to strip markdown into plain text (used for <meta name="description">).
Add Post.HTMLPreview() to render a limited subset of markdown (links/code) with visible-character-aware truncation.
Update post listing templates (posts/tag/footer) to use HTMLPreview instead of PreviewContent.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
`templates/tag.html`	Switch tag page previews to `HTMLPreview`.
`templates/posts.html`	Switch `/posts` previews to `HTMLPreview`.
`templates/header.html`	Use `PlainTextPreview` for meta description.
`templates/footer.html`	Switch “Most Recent Post” preview to `HTMLPreview` (and adjust length).
`blog/post.go`	Add markdown-stripping preview helpers and HTML-aware truncation logic.

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Copilot · 2026-03-03T05:24:15Z

blog/post.go

+func (p Post) HTMLPreview(length int) template.HTML {
+	s := p.Content
+	s = reFencedCode.ReplaceAllString(s, "<code>$1</code>")
+	s = reInlineCode.ReplaceAllString(s, "<code>$1</code>")
+	s = reImages.ReplaceAllString(s, "$1")
+	s = reLinksWithURL.ReplaceAllString(s, `<a href="$2">$1</a>`)
+	s = reHeadings.ReplaceAllString(s, "")


HTMLPreview returns template.HTML built from p.Content via regex replacements without HTML-escaping/sanitization. This disables Go template auto-escaping and allows raw HTML in post content (or crafted link text/URLs) to be rendered/executed in list pages; href is also inserted unescaped and could allow attribute injection or javascript: URLs. Prefer escaping all user content first and only allowing a very small, sanitized subset of tags/attributes (e.g., escape code/link text, validate/escape href, and/or run the output through an allowlist HTML sanitizer before casting to template.HTML).

Copilot · 2026-03-03T05:24:16Z

blog/post.go

+	s = reFencedCode.ReplaceAllString(s, "<code>$1</code>")
+	s = reInlineCode.ReplaceAllString(s, "<code>$1</code>")
+	s = reImages.ReplaceAllString(s, "$1")
+	s = reLinksWithURL.ReplaceAllString(s, `<a href="$2">$1</a>`)
+	s = reHeadings.ReplaceAllString(s, "")
+	s = reBold.ReplaceAllString(s, "$1")
+	s = reItalic.ReplaceAllString(s, "$1")
+	s = reUBold.ReplaceAllString(s, "$1")
+	s = reUItalic.ReplaceAllString(s, "$1")
+	s = reHR.ReplaceAllString(s, "")


The markdown-stripping pipeline wraps fenced/inline code in <code>...</code> and then runs bold/italic underscore regexes afterwards. That will also transform characters inside code blocks (e.g., *, _, **) and can corrupt the rendered code preview. Consider extracting code spans/blocks to placeholders before running emphasis/heading/whitespace cleanup, then reinserting them at the end (or otherwise ensuring later regexes do not run inside code).

Copilot · 2026-03-03T05:24:16Z

blog/post.go

+	runes := bytes.Runes([]byte(s))
+	if len(runes) > length {
+		return string(runes[:length]) + "..."
+	}
+	return s


PlainTextPreview appends "..." after truncating to length runes, so the returned string can exceed the requested length (e.g., length+3). For meta description usage, consider truncating to length-3 when adding an ellipsis (or make ellipsis optional) so callers can enforce a strict maximum length.

Suggested change

runes := bytes.Runes([]byte(s))

if len(runes) > length {

return string(runes[:length]) + "..."

}

return s

// Convert to runes so length is based on Unicode code points.

runes := bytes.Runes([]byte(s))

if length <= 0 {

return ""

}

if len(runes) > length {

// Ensure the returned string never exceeds the requested length.

// For very small lengths, just truncate without adding an ellipsis.

if length <= 3 {

return string(runes[:length])

}

return string(runes[:length-3]) + "..."

}

return string(runes)

Copilot · 2026-03-03T05:24:16Z

blog/post.go

+// PlainTextPreview strips markdown syntax and returns clean plain text for previews
+func (p Post) PlainTextPreview(length int) string {
+	s := p.Content
+	s = reFencedCode.ReplaceAllString(s, "$1")
+	s = reInlineCode.ReplaceAllString(s, "$1")
+	s = reImages.ReplaceAllString(s, "$1")
+	s = reLinks.ReplaceAllString(s, "$1")
+	s = reHeadings.ReplaceAllString(s, "")
+	s = reBold.ReplaceAllString(s, "$1")
+	s = reItalic.ReplaceAllString(s, "$1")
+	s = reUBold.ReplaceAllString(s, "$1")
+	s = reUItalic.ReplaceAllString(s, "$1")
+	s = reHR.ReplaceAllString(s, "")
+	s = reWhitespace.ReplaceAllString(s, " ")
+	s = strings.TrimSpace(s)
+
+	runes := bytes.Runes([]byte(s))
+	if len(runes) > length {
+		return string(runes[:length]) + "..."
+	}
+	return s
+}
+
+// HTMLPreview strips markdown syntax but preserves links as HTML hyperlinks
+func (p Post) HTMLPreview(length int) template.HTML {
+	s := p.Content
+	s = reFencedCode.ReplaceAllString(s, "<code>$1</code>")
+	s = reInlineCode.ReplaceAllString(s, "<code>$1</code>")
+	s = reImages.ReplaceAllString(s, "$1")
+	s = reLinksWithURL.ReplaceAllString(s, `<a href="$2">$1</a>`)
+	s = reHeadings.ReplaceAllString(s, "")
+	s = reBold.ReplaceAllString(s, "$1")
+	s = reItalic.ReplaceAllString(s, "$1")
+	s = reUBold.ReplaceAllString(s, "$1")
+	s = reUItalic.ReplaceAllString(s, "$1")
+	s = reHR.ReplaceAllString(s, "")
+	s = reWhitespace.ReplaceAllString(s, " ")
+	s = strings.TrimSpace(s)
+
+	// Truncate by visible character count, skipping HTML tags
+	runes := []rune(s)
+	visible := 0
+	cutoff := len(runes)
+	inTag := false
+	for i, r := range runes {
+		if r == '<' {
+			inTag = true
+		} else if r == '>' {
+			inTag = false
+		} else if !inTag {
+			visible++
+			if visible > length {
+				cutoff = i
+				break
+			}
+		}
+	}
+
+	if cutoff < len(runes) {
+		result := string(runes[:cutoff])
+		if strings.Count(result, "<a ") > strings.Count(result, "</a>") {
+			result += "</a>"
+		}
+		if strings.Count(result, "<code>") > strings.Count(result, "</code>") {
+			result += "</code>"
+		}
+		result += "..."
+		return template.HTML(result)
+	}
+	return template.HTML(s)
+}


New preview behavior is introduced via PlainTextPreview/HTMLPreview, but existing unit tests only cover PreviewContent. Since there is already test coverage for this file, please add tests for markdown stripping/link rendering/truncation (including edge cases like code spans containing */_ and potentially unsafe URLs/HTML) to prevent regressions.

Copilot AI review requested due to automatic review settings March 3, 2026 05:20

Copilot started reviewing on behalf of compscidr March 3, 2026 05:20 View session

compscidr merged commit f0720e6 into main Mar 3, 2026
8 of 9 checks passed

compscidr deleted the fix/markdown-preview-rendering branch March 3, 2026 05:24

Copilot AI reviewed Mar 3, 2026

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compscidr mentioned this pull request Mar 3, 2026

Parse out images in post summaries #53

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Fix post previews rendering raw markdown#474

Fix post previews rendering raw markdown#474
compscidr merged 1 commit intomainfrom
fix/markdown-preview-rendering

compscidr commented Mar 3, 2026

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-	runes := bytes.Runes([]byte(s))
-	if len(runes) > length {
-		return string(runes[:length]) + "..."
-	}
-	return s
+	// Convert to runes so length is based on Unicode code points.
+	runes := bytes.Runes([]byte(s))
+	if length <= 0 {
+		return ""
+	}
+	if len(runes) > length {
+		// Ensure the returned string never exceeds the requested length.
+		// For very small lengths, just truncate without adding an ellipsis.
+		if length <= 3 {
+			return string(runes[:length])
+		}
+		return string(runes[:length-3]) + "..."
+	}
+	return string(runes)

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compscidr commented Mar 3, 2026

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Pull request overview

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codecov bot commented Mar 3, 2026 •

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