refactor(rewriter): replace regex with URL parsing for referrer override

No need for brittle regex when matching plain strings or domain names.
This should save some negligible amount of heap memory as well as
tremendously speeding up the matching.

internal/reader/rewrite/rules.go

@@ -3,7 +3,10 @@
 
 package rewrite // import "miniflux.app/v2/internal/reader/rewrite"
 
-import "regexp"
+import (
+	"net/url"
+	"strings"
+)
 
 // List of predefined rewrite rules (alphabetically sorted)
 // Available rules: "add_image_title", "add_youtube_video"
@@ -39,49 +42,32 @@ var predefinedRules = map[string]string{
 	"youtube.com":            "add_youtube_video",
 }
 
-type RefererRule struct {
-	URLPattern *regexp.Regexp
-	Referer    string
-}
-
-// List of predefined referer rules
-var PredefinedRefererRules = []RefererRule{
-	{
-		URLPattern: regexp.MustCompile(`^https://\w+\.sinaimg\.cn`),
-		Referer:    "https://weibo.com",
-	},
-	{
-		URLPattern: regexp.MustCompile(`^https://i\.pximg\.net`),
-		Referer:    "https://www.pixiv.net",
-	},
-	{
-		URLPattern: regexp.MustCompile(`^https://cdnfile\.sspai\.com`),
-		Referer:    "https://sspai.com",
-	},
-	{
-		URLPattern: regexp.MustCompile(`^https://(?:\w|-)+\.cdninstagram\.com`),
-		Referer:    "https://www.instagram.com",
-	},
-	{
-		URLPattern: regexp.MustCompile(`^https://sp1\.piokok\.com`),
-		Referer:    "https://sp1.piokok.com",
-	},
-	{
-		URLPattern: regexp.MustCompile(`^https://f\.video\.weibocdn\.com`),
-		Referer:    "https://weibo.com",
-	},
-	{
-		URLPattern: regexp.MustCompile(`^https://img\.hellogithub\.com`),
-		Referer:    "https://hellogithub.com",
-	},
-}
-
 // GetRefererForURL returns the referer for the given URL if it exists, otherwise an empty string.
-func GetRefererForURL(url string) string {
-	for _, rule := range PredefinedRefererRules {
-		if rule.URLPattern.MatchString(url) {
-			return rule.Referer
-		}
+func GetRefererForURL(u string) string {
+	parsedUrl, err := url.Parse(u)
+	if err != nil {
+		return ""
 	}
+
+	switch parsedUrl.Hostname() {
+	case "i.pximg.net":
+		return "https://www.pixiv.net"
+	case "sp1.piokok.com":
+		return "https://sp1.piokok.com"
+	case "cdnfile.sspai.com":
+		return "https://sspai.com"
+	case "f.video.weibocdn.com":
+		return "https://weibo.com"
+	case "img.hellogithub.com":
+		return "https://hellogithub.com"
+	}
+
+	switch {
+	case strings.HasSuffix(parsedUrl.Hostname(), ".sinaimg.cn"):
+		return "https://weibo.com"
+	case strings.HasSuffix(parsedUrl.Hostname(), ".cdninstagram.com"):
+		return "https://www.instagram.com"
+	}
+
 	return ""
 }