Use List-Unsubscribe header URLs for unsubscribe link detection

Bug: https://github.com/happyDomain/happydeliver/issues/8

pkg/analyzer/content.go

@@ -27,6 +27,7 @@ import (
 	"net/http"
 	"net/url"
 	"regexp"
+	"slices"
 	"strings"
 	"time"
 	"unicode"
@@ -37,8 +38,9 @@ import (
 
 // ContentAnalyzer analyzes email content (HTML, links, images)
 type ContentAnalyzer struct {
-	Timeout    time.Duration
-	httpClient *http.Client
+	Timeout             time.Duration
+	httpClient          *http.Client
+	listUnsubscribeURLs []string // URLs from List-Unsubscribe header
 }
 
 // NewContentAnalyzer creates a new content analyzer with configurable timeout
@@ -110,6 +112,9 @@ func (c *ContentAnalyzer) AnalyzeContent(email *EmailMessage) *ContentResults {
 
 	results.IsMultipart = len(email.Parts) > 1
 
+	// Parse List-Unsubscribe header URLs for use in link detection
+	c.listUnsubscribeURLs = email.GetListUnsubscribeURLs()
+
 	// Get HTML and text parts
 	htmlParts := email.GetHTMLParts()
 	textParts := email.GetTextParts()
@@ -331,6 +336,11 @@ func (c *ContentAnalyzer) getAttr(n *html.Node, key string) string {
 
 // isUnsubscribeLink checks if a link is an unsubscribe link
 func (c *ContentAnalyzer) isUnsubscribeLink(href string, node *html.Node) bool {
+	// First check: does the href match a URL from the List-Unsubscribe header?
+	if slices.Contains(c.listUnsubscribeURLs, href) {
+		return true
+	}
+
 	// Check href for unsubscribe keywords
 	lowerHref := strings.ToLower(href)
 	unsubKeywords := []string{"unsubscribe", "opt-out", "optout", "remove", "list-unsubscribe"}
@@ -439,7 +449,8 @@ func (c *ContentAnalyzer) hasDomainMisalignment(href, linkText string) bool {
 	// Extract the actual destination domain/email based on scheme
 	var actualDomain string
 
-	if parsedURL.Scheme == "mailto" {
+	switch parsedURL.Scheme {
+	case "mailto":
 		// Extract email address from mailto: URL
 		// Format can be: mailto:user@domain.com or mailto:user@domain.com?subject=...
 		mailtoAddr := parsedURL.Opaque
@@ -457,7 +468,8 @@ func (c *ContentAnalyzer) hasDomainMisalignment(href, linkText string) bool {
 		} else {
 			return false // Invalid mailto
 		}
-	} else if parsedURL.Scheme == "http" || parsedURL.Scheme == "https" {
+	case "http":
+	case "https":
 		// Check if URL has a host
 		if parsedURL.Host == "" {
 			return false
@@ -469,7 +481,7 @@ func (c *ContentAnalyzer) hasDomainMisalignment(href, linkText string) bool {
 			actualDomain = actualDomain[:idx]
 		}
 		actualDomain = strings.ToLower(actualDomain)
-	} else {
+	default:
 		// Skip checks for other URL schemes (tel, etc.)
 		return false
 	}
@@ -492,10 +504,8 @@ func (c *ContentAnalyzer) hasDomainMisalignment(href, linkText string) bool {
 		"email us", "contact us", "send email", "get in touch", "reach out",
 		"contact", "email", "write to us",
 	}
-	for _, generic := range genericTexts {
-		if linkText == generic {
-			return false
-		}
+	if slices.Contains(genericTexts, linkText) {
+		return false
 	}
 
 	// Extract domain-like patterns from link text using regex
@@ -562,10 +572,8 @@ func (c *ContentAnalyzer) isSuspiciousURL(urlStr string, parsedURL *url.URL) boo
 		"bit.ly", "tinyurl.com", "goo.gl", "ow.ly", "t.co",
 		"buff.ly", "is.gd", "bl.ink", "short.io",
 	}
-	for _, shortener := range shorteners {
-		if strings.ToLower(parsedURL.Host) == shortener {
-			return true
-		}
+	if slices.Contains(shorteners, strings.ToLower(parsedURL.Host)) {
+		return true
 	}
 
 	// Check for excessive subdomains (possible obfuscation)

pkg/analyzer/parser.go

@@ -301,3 +301,20 @@ func (e *EmailMessage) GetHeaderValue(key string) string {
 func (e *EmailMessage) HasHeader(key string) bool {
 	return e.Header.Get(key) != ""
 }
+
+// GetListUnsubscribeURLs parses the List-Unsubscribe header and returns all URLs.
+// The header format is: <url1>, <url2>, ...
+func (e *EmailMessage) GetListUnsubscribeURLs() []string {
+	value := e.Header.Get("List-Unsubscribe")
+	if value == "" {
+		return nil
+	}
+	var urls []string
+	for _, part := range strings.Split(value, ",") {
+		part = strings.TrimSpace(part)
+		if strings.HasPrefix(part, "<") && strings.HasSuffix(part, ">") {
+			urls = append(urls, part[1:len(part)-1])
+		}
+	}
+	return urls
+}