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Add content filtering package
Co-authored-by: SamMorrowDrums <4811358+SamMorrowDrums@users.noreply.github.com>
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‎pkg/filtering/content_filter.go‎

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package filtering
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import (
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"regexp"
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"strings"
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)
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var (
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// Invisible Unicode characters
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// This includes zero-width spaces, zero-width joiners, zero-width non-joiners,
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// bidirectional marks, and other invisible unicode characters
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invisibleCharsRegex = regexp.MustCompile(`[\x{200B}-\x{200F}\x{2028}-\x{202E}\x{2060}-\x{2064}\x{FEFF}]`)
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// HTML comments
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htmlCommentsRegex = regexp.MustCompile(`<!--[\s\S]*?-->`)
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// HTML elements that could contain hidden content
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// This is a simple approach that targets specific dangerous tags
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// Go's regexp doesn't support backreferences, so we list each tag explicitly
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htmlScriptRegex = regexp.MustCompile(`<script[^>]*>[\s\S]*?</script>`)
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htmlStyleRegex = regexp.MustCompile(`<style[^>]*>[\s\S]*?</style>`)
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htmlIframeRegex = regexp.MustCompile(`<iframe[^>]*>[\s\S]*?</iframe>`)
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htmlObjectRegex = regexp.MustCompile(`<object[^>]*>[\s\S]*?</object>`)
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htmlEmbedRegex = regexp.MustCompile(`<embed[^>]*>[\s\S]*?</embed>`)
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htmlSvgRegex = regexp.MustCompile(`<svg[^>]*>[\s\S]*?</svg>`)
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htmlMathRegex = regexp.MustCompile(`<math[^>]*>[\s\S]*?</math>`)
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htmlLinkRegex = regexp.MustCompile(`<link[^>]*>[\s\S]*?</link>`)
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// HTML attributes that might be used for hiding content
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htmlAttributesRegex = regexp.MustCompile(`<[^>]*(?:style|data-[\w-]+|hidden|class)="[^"]*"[^>]*>`)
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// Detect collapsed sections (details/summary)
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collapsedSectionsRegex = regexp.MustCompile(`<details>[\s\S]*?</details>`)
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// Very small text (font-size or similar CSS tricks)
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smallTextRegex = regexp.MustCompile(`<[^>]*style="[^"]*font-size:\s*(?:0|0\.\d+|[0-3])(?:px|pt|em|%)[^"]*"[^>]*>[\s\S]*?</[^>]+>`)
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// Excessive whitespace (more than 3 consecutive newlines)
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excessiveWhitespaceRegex = regexp.MustCompile(`\n{4,}`)
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)
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// Config holds configuration for content filtering
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type Config struct {
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// DisableContentFiltering disables all content filtering when true
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DisableContentFiltering bool
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}
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// DefaultConfig returns the default content filtering configuration
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func DefaultConfig() *Config {
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return &Config{
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DisableContentFiltering: false,
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}
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}
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// FilterContent filters potentially hidden content from the input text
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// This includes invisible Unicode characters, HTML comments, and other methods of hiding content
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func FilterContent(input string, cfg *Config) string {
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if cfg != nil && cfg.DisableContentFiltering {
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return input
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}
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if input == "" {
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return input
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}
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// Process the input text through each filter
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result := input
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// Remove invisible characters
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result = invisibleCharsRegex.ReplaceAllString(result, "")
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// Replace HTML comments with a marker
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result = htmlCommentsRegex.ReplaceAllString(result, "[HTML_COMMENT]")
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// Replace potentially dangerous HTML elements
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result = htmlScriptRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlStyleRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlIframeRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlObjectRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlEmbedRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlSvgRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlMathRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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result = htmlLinkRegex.ReplaceAllString(result, "[HTML_ELEMENT]")
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// Replace HTML attributes that might be used for hiding
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result = htmlAttributesRegex.ReplaceAllStringFunc(result, cleanHTMLAttributes)
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// Replace collapsed sections with visible indicator
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result = collapsedSectionsRegex.ReplaceAllStringFunc(result, makeCollapsedSectionVisible)
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// Replace very small text with visible indicator
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result = smallTextRegex.ReplaceAllString(result, "[SMALL_TEXT]")
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// Normalize excessive whitespace
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result = excessiveWhitespaceRegex.ReplaceAllString(result, "\n\n\n")
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return result
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}
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// cleanHTMLAttributes removes potentially dangerous attributes from HTML tags
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func cleanHTMLAttributes(tag string) string {
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// This is a simple implementation that removes style, data-* and hidden attributes
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// A more sophisticated implementation would parse the HTML and selectively remove attributes
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tagWithoutStyle := regexp.MustCompile(`\s+(?:style|data-[\w-]+|hidden|class)="[^"]*"`).ReplaceAllString(tag, "")
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return tagWithoutStyle
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}
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// makeCollapsedSectionVisible transforms a <details> section to make it visible
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func makeCollapsedSectionVisible(detailsSection string) string {
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// Extract the summary if present
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summaryRegex := regexp.MustCompile(`<summary>(.*?)</summary>`)
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summaryMatches := summaryRegex.FindStringSubmatch(detailsSection)
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summary := "Collapsed section"
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if len(summaryMatches) > 1 {
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summary = summaryMatches[1]
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}
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// Extract the content (everything after </summary> and before </details>)
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parts := strings.SplitN(detailsSection, "</summary>", 2)
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content := detailsSection
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if len(parts) > 1 {
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content = parts[1]
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content = strings.TrimSuffix(content, "</details>")
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} else {
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// No summary tag found, remove the details tags
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content = strings.TrimPrefix(content, "<details>")
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content = strings.TrimSuffix(content, "</details>")
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}
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// Format as a visible section
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return "\n\n**" + summary + ":**\n" + content + "\n\n"
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}

‎pkg/filtering/content_filter_test.go‎

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package filtering
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import (
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"testing"
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)
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func TestFilterContent(t *testing.T) {
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tests := []struct {
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name string
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input string
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expected string
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cfg *Config
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}{
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{
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name: "Empty string",
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input: "",
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expected: "",
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cfg: DefaultConfig(),
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},
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{
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name: "Normal text without hidden content",
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input: "This is normal text without any hidden content.",
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expected: "This is normal text without any hidden content.",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with invisible characters",
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input: "Hidden\u200Bcharacters\u200Bin\u200Bthis\u200Btext",
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expected: "Hiddencharactersinthistext",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with HTML comments",
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input: "This has a <!-- hidden comment --> in it.",
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expected: "This has a [HTML_COMMENT] in it.",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with HTML elements",
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input: "This has <script>alert('hidden')</script> scripts.",
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expected: "This has [HTML_ELEMENT] scripts.",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with details/summary",
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input: "Collapsed content: <details><summary>Click me</summary>Hidden content</details>",
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expected: "Collapsed content: \n\n**Click me:**\nHidden content\n\n",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with small font",
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input: "This has <span style=\"font-size:1px\">hidden tiny text</span> in it.",
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expected: "This has <span>hidden tiny text</span> in it.",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with excessive whitespace",
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input: "Line 1\n\n\n\n\n\nLine 2",
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expected: "Line 1\n\n\nLine 2",
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cfg: DefaultConfig(),
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},
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{
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name: "Text with HTML attributes",
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input: "<p data-hidden=\"true\" style=\"display:none\">Hidden paragraph</p>",
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expected: "<p>Hidden paragraph</p>",
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cfg: DefaultConfig(),
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},
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{
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name: "Filtering disabled",
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input: "Hidden\u200Bcharacters and <!-- comments -->",
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expected: "Hidden\u200Bcharacters and <!-- comments -->",
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cfg: &Config{DisableContentFiltering: true},
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},
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{
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name: "Nil config uses default (filtering enabled)",
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input: "Hidden\u200Bcharacters",
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expected: "Hiddencharacters",
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cfg: nil,
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},
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{
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name: "Normal markdown with code blocks",
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input: "# Title\n\n```go\nfunc main() {\n fmt.Println(\"Hello, world!\")\n}\n```",
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expected: "# Title\n\n```go\nfunc main() {\n fmt.Println(\"Hello, world!\")\n}\n```",
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cfg: DefaultConfig(),
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},
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{
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name: "GitHub flavored markdown with tables",
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input: "| Header 1 | Header 2 |\n| -------- | -------- |\n| Cell 1 | Cell 2 |",
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expected: "| Header 1 | Header 2 |\n| -------- | -------- |\n| Cell 1 | Cell 2 |",
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cfg: DefaultConfig(),
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},
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}
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for _, tc := range tests {
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t.Run(tc.name, func(t *testing.T) {
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result := FilterContent(tc.input, tc.cfg)
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if result != tc.expected {
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t.Errorf("FilterContent() = %q, want %q", result, tc.expected)
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}
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})
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}
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}
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func TestMakeCollapsedSectionVisible(t *testing.T) {
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tests := []struct {
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name string
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input string
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expected string
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}{
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{
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name: "Simple details/summary",
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input: "<details><summary>Click me</summary>Hidden content</details>",
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expected: "\n\n**Click me:**\nHidden content\n\n",
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},
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{
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name: "Details without summary",
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input: "<details>Hidden content</details>",
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expected: "\n\n**Collapsed section:**\nHidden content\n\n",
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},
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{
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name: "Nested content",
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input: "<details><summary>Outer</summary>Content<details><summary>Inner</summary>Nested</details></details>",
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expected: "\n\n**Outer:**\nContent<details><summary>Inner</summary>Nested</details>\n\n",
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},
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}
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for _, tc := range tests {
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t.Run(tc.name, func(t *testing.T) {
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result := makeCollapsedSectionVisible(tc.input)
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if result != tc.expected {
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t.Errorf("makeCollapsedSectionVisible() = %q, want %q", result, tc.expected)
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}
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})
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}
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}
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func TestCleanHTMLAttributes(t *testing.T) {
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tests := []struct {
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name string
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input string
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expected string
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}{
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{
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name: "Tag with style attribute",
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input: "<p style=\"display:none\">Hidden</p>",
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expected: "<p>Hidden</p>",
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},
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{
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name: "Tag with data attribute",
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input: "<p data-hidden=\"true\">Hidden</p>",
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expected: "<p>Hidden</p>",
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},
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{
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name: "Tag with multiple attributes",
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input: "<p id=\"para\" style=\"display:none\" data-test=\"value\">Hidden</p>",
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expected: "<p id=\"para\">Hidden</p>",
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},
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{
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name: "Tag with allowed attributes",
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input: "<a href=\"https://example.com\" target=\"_blank\">Link</a>",
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expected: "<a href=\"https://example.com\" target=\"_blank\">Link</a>",
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},
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}
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for _, tc := range tests {
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t.Run(tc.name, func(t *testing.T) {
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result := cleanHTMLAttributes(tc.input)
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if result != tc.expected {
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t.Errorf("cleanHTMLAttributes() = %q, want %q", result, tc.expected)
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}
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})
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}
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}

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