Adds domain exclusion configuration for first-party proxy for creatives. (#103)

Author: ChristianPavilonis

crates/common/src/creative.rs

@@ -43,11 +43,18 @@ use crate::tsjs;
 use lol_html::{element, html_content::ContentType, text, HtmlRewriter, Settings as HtmlSettings};
 
 // Helper: normalize to absolute URL if http/https or protocol-relative. Otherwise None.
-pub(super) fn to_abs(u: &str) -> Option<String> {
+// Checks against the rewrite blacklist to exclude configured domains/patterns from proxying.
+pub(super) fn to_abs(u: &str, settings: &Settings) -> Option<String> {
     let t = u.trim();
     if t.is_empty() {
         return None;
     }
+
+    // Skip if excluded from rewrites in settings
+    if settings.rewrite.is_excluded(t) {
+        return None;
+    }
+
     // Skip non-network schemes commonly found in creatives
     let lower = t.to_ascii_lowercase();
     if lower.starts_with("data:")
@@ -59,6 +66,7 @@ pub(super) fn to_abs(u: &str) -> Option<String> {
     {
         return None;
     }
+
     if t.starts_with("//") {
         Some(format!("https:{}", t))
     } else if lower.starts_with("http://") || lower.starts_with("https://") {
@@ -106,7 +114,7 @@ pub(super) fn rewrite_style_urls(style: &str, settings: &Settings) -> String {
             (s, e)
         };
         let url_val = &style[qs..qe];
-        let new_val = if let Some(abs) = to_abs(url_val) {
+        let new_val = if let Some(abs) = to_abs(url_val, settings) {
             build_proxy_url(settings, &abs)
         } else {
             url_val.to_string()
@@ -196,7 +204,7 @@ pub(super) fn build_click_url(settings: &Settings, clear_url: &str) -> String {
 
 #[inline]
 pub(super) fn proxy_if_abs(settings: &Settings, val: &str) -> Option<String> {
-    to_abs(val).map(|abs| build_proxy_url(settings, &abs))
+    to_abs(val, settings).map(|abs| build_proxy_url(settings, &abs))
 }
 
 /// Split a srcset/imagesrcset attribute into candidate strings.
@@ -259,7 +267,7 @@ pub(super) fn rewrite_srcset(srcset: &str, settings: &Settings) -> String {
         let mut parts = it.split_whitespace();
         let url = parts.next().unwrap_or("");
         let descriptor = parts.collect::<Vec<_>>().join(" ");
-        let rewritten = if let Some(abs) = to_abs(url) {
+        let rewritten = if let Some(abs) = to_abs(url, settings) {
             build_proxy_url(settings, &abs)
         } else {
             url.to_string()
@@ -404,7 +412,7 @@ pub fn rewrite_creative_html(markup: &str, settings: &Settings) -> String {
                 // Click-through links
                 element!("a[href], area[href]", |el| {
                     if let Some(href) = el.get_attribute("href") {
-                        if let Some(abs) = to_abs(&href) {
+                        if let Some(abs) = to_abs(&href, settings) {
                             let click = build_click_url(settings, &abs);
                             let _ = el.set_attribute("href", &click);
                             let _ = el.set_attribute("data-tsclick", &click);
@@ -508,26 +516,27 @@ mod tests {
 
     #[test]
     fn to_abs_conversions() {
+        let settings = crate::test_support::tests::create_test_settings();
         assert_eq!(
-            to_abs("//cdn.example/x"),
+            to_abs("//cdn.example/x", &settings),
             Some("https://cdn.example/x".to_string())
         );
         assert_eq!(
-            to_abs("HTTPS://cdn.example/x"),
+            to_abs("HTTPS://cdn.example/x", &settings),
             Some("HTTPS://cdn.example/x".to_string())
         );
         assert_eq!(
-            to_abs("http://cdn.example/x"),
+            to_abs("http://cdn.example/x", &settings),
             Some("http://cdn.example/x".to_string())
         );
-        assert_eq!(to_abs("/local/x"), None);
+        assert_eq!(to_abs("/local/x", &settings), None);
         assert_eq!(
-            to_abs("   //cdn.example/y  "),
+            to_abs("   //cdn.example/y  ", &settings),
             Some("https://cdn.example/y".to_string())
         );
-        assert_eq!(to_abs("data:image/png;base64,abcd"), None);
-        assert_eq!(to_abs("javascript:alert(1)"), None);
-        assert_eq!(to_abs("mailto:[email protected]"), None);
+        assert_eq!(to_abs("data:image/png;base64,abcd", &settings), None);
+        assert_eq!(to_abs("javascript:alert(1)", &settings), None);
+        assert_eq!(to_abs("mailto:[email protected]", &settings), None);
     }
 
     #[test]
@@ -981,13 +990,14 @@ mod tests {
 
     #[test]
     fn to_abs_additional_cases() {
+        let settings = crate::test_support::tests::create_test_settings();
         assert_eq!(
-            to_abs("   https://cdn.example/a   "),
+            to_abs("   https://cdn.example/a   ", &settings),
             Some("https://cdn.example/a".to_string())
         );
-        assert_eq!(to_abs("blob:xyz"), None);
-        assert_eq!(to_abs("tel:+123"), None);
-        assert_eq!(to_abs("about:blank"), None);
+        assert_eq!(to_abs("blob:xyz", &settings), None);
+        assert_eq!(to_abs("tel:+123", &settings), None);
+        assert_eq!(to_abs("about:blank", &settings), None);
     }
 
     #[test]
@@ -1003,4 +1013,134 @@ mod tests {
         // relative candidate remains
         assert!(out.contains("/local/img.png 1x"));
     }
+
+    #[test]
+    fn to_abs_respects_exclude_domains() {
+        let mut settings = crate::test_support::tests::create_test_settings();
+        settings.rewrite.exclude_domains = vec!["trusted-cdn.example.com".to_string()];
+
+        // Excluded domain should return None (not proxied)
+        assert_eq!(
+            to_abs("https://trusted-cdn.example.com/lib.js", &settings),
+            None
+        );
+
+        // Non-excluded domain should return Some
+        assert_eq!(
+            to_abs("https://other-cdn.example.com/lib.js", &settings),
+            Some("https://other-cdn.example.com/lib.js".to_string())
+        );
+    }
+
+    #[test]
+    fn to_abs_respects_wildcard_domains() {
+        let mut settings = crate::test_support::tests::create_test_settings();
+        settings.rewrite.exclude_domains = vec!["*.cloudflare.com".to_string()];
+
+        // Should exclude base domain
+        assert_eq!(to_abs("https://cloudflare.com/cdn.js", &settings), None);
+
+        // Should exclude subdomain
+        assert_eq!(
+            to_abs("https://cdnjs.cloudflare.com/lib.js", &settings),
+            None
+        );
+
+        // Should not exclude different domain
+        assert_eq!(
+            to_abs("https://notcloudflare.com/lib.js", &settings),
+            Some("https://notcloudflare.com/lib.js".to_string())
+        );
+    }
+
+    #[test]
+    fn rewrite_html_excludes_blacklisted_domains() {
+        let mut settings = crate::test_support::tests::create_test_settings();
+        settings.rewrite.exclude_domains = vec!["trusted-cdn.example.com".to_string()];
+
+        let html = r#"
+            <img src="https://trusted-cdn.example.com/logo.png">
+            <img src="https://other-cdn.example.com/banner.jpg">
+        "#;
+
+        let out = rewrite_creative_html(html, &settings);
+
+        // Excluded domain should NOT be rewritten
+        assert!(out.contains(r#"src="https://trusted-cdn.example.com/logo.png"#));
+
+        // Non-excluded domain SHOULD be rewritten
+        assert!(out.contains("/first-party/proxy?tsurl="));
+        assert!(out.contains("other-cdn.example.com"));
+    }
+
+    #[test]
+    fn rewrite_srcset_excludes_blacklisted_domains() {
+        let mut settings = crate::test_support::tests::create_test_settings();
+        settings.rewrite.exclude_domains = vec!["trusted.example.com".to_string()];
+
+        let html = r#"
+            <img srcset="https://trusted.example.com/img-1x.png 1x, https://cdn.example.com/img-2x.png 2x">
+        "#;
+
+        let out = rewrite_creative_html(html, &settings);
+
+        // Excluded domain should remain as-is
+        assert!(out.contains("https://trusted.example.com/img-1x.png 1x"));
+
+        // Non-excluded should be proxied
+        assert!(out.contains("/first-party/proxy?tsurl="));
+        assert!(out.contains("cdn.example.com"));
+    }
+
+    #[test]
+    fn rewrite_style_urls_excludes_blacklisted_domains() {
+        let mut settings = crate::test_support::tests::create_test_settings();
+        settings.rewrite.exclude_domains = vec!["fonts.googleapis.com".to_string()];
+
+        let html = r#"
+            <style>
+                @font-face {
+                    font-family: 'Test';
+                    src: url(https://fonts.googleapis.com/font.woff2);
+                }
+                body {
+                    background: url(https://cdn.example.com/bg.png);
+                }
+            </style>
+        "#;
+
+        let out = rewrite_creative_html(html, &settings);
+
+        // Excluded domain should remain unchanged
+        assert!(out.contains("url(https://fonts.googleapis.com/font.woff2)"));
+
+        // Non-excluded should be proxied
+        assert!(out.contains("/first-party/proxy?tsurl="));
+        assert!(out.contains("cdn.example.com"));
+    }
+
+    #[test]
+    fn rewrite_click_urls_excludes_blacklisted_domains() {
+        let mut settings = crate::test_support::tests::create_test_settings();
+        settings.rewrite.exclude_domains = vec!["trusted-landing.example.com".to_string()];
+
+        let html = r#"
+            <a href="https://trusted-landing.example.com/page">Trusted Link</a>
+            <a href="https://advertiser.example.com/landing">Ad Link</a>
+        "#;
+
+        let out = rewrite_creative_html(html, &settings);
+
+        // Excluded domain should NOT be rewritten to first-party click
+        assert!(out.contains(r#"href="https://trusted-landing.example.com/page"#));
+        // The excluded link should NOT have data-tsclick since it wasn't rewritten
+        assert!(
+            !out.contains(r#"<a href="https://trusted-landing.example.com/page" data-tsclick="#)
+        );
+
+        // Non-excluded should be rewritten and SHOULD have data-tsclick
+        assert!(out.contains("/first-party/click?tsurl="));
+        assert!(out.contains("advertiser.example.com"));
+        assert!(out.contains("data-tsclick=\"/first-party/click"));
+    }
 }

crates/common/src/proxy.rs

@@ -473,7 +473,7 @@ pub async fn handle_first_party_proxy_sign(
             .unwrap_or_else(|| "https".to_string());
         format!("{}:{}", default_scheme, trimmed)
     } else {
-        crate::creative::to_abs(trimmed).ok_or_else(|| {
+        crate::creative::to_abs(trimmed, settings).ok_or_else(|| {
             Report::new(TrustedServerError::Proxy {
                 message: "unsupported url".to_string(),
             })

crates/common/src/settings.rs

@@ -244,6 +244,41 @@ impl Synthetic {
     }
 }
 
+#[derive(Debug, Default, Deserialize, Serialize, Validate)]
+pub struct Rewrite {
+    /// List of domains to exclude from rewriting. Supports wildcards (e.g., "*.example.com").
+    /// URLs from these domains will not be proxied through first-party endpoints.
+    #[serde(default)]
+    pub exclude_domains: Vec<String>,
+}
+
+impl Rewrite {
+    /// Checks if a URL should be excluded from rewriting based on domain matching
+    #[allow(dead_code)]
+    pub fn is_excluded(&self, url: &str) -> bool {
+        // Parse URL to extract host
+        let Ok(parsed) = url::Url::parse(url) else {
+            return false;
+        };
+
+        let host = parsed.host_str().unwrap_or("");
+
+        // Check exact domain matches (with wildcard support)
+        for domain in &self.exclude_domains {
+            if let Some(suffix) = domain.strip_prefix("*.") {
+                // Wildcard: *.example.com matches both example.com and sub.example.com
+                if host == suffix || host.ends_with(&format!(".{}", suffix)) {
+                    return true;
+                }
+            } else if host == domain {
+                return true;
+            }
+        }
+
+        false
+    }
+}
+
 #[derive(Debug, Default, Deserialize, Serialize, Validate)]
 pub struct Handler {
     #[validate(length(min = 1), custom(function = validate_path))]
@@ -298,6 +333,9 @@ pub struct Settings {
     #[serde(default)]
     pub response_headers: HashMap<String, String>,
     pub request_signing: Option<RequestSigning>,
+    #[serde(default)]
+    #[validate(nested)]
+    pub rewrite: Rewrite,
 }
 
 #[allow(unused)]
@@ -893,4 +931,30 @@ mod tests {
 
         assert!(config.is_none(), "Disabled integrations should be skipped");
     }
+
+    #[test]
+    fn test_rewrite_is_excluded() {
+        let rewrite = Rewrite {
+            exclude_domains: vec!["cdn.example.com".to_string(), "*.example2.com".to_string()],
+        };
+
+        // Exact domain match
+        assert!(rewrite.is_excluded("http://cdn.example.com/image.png"));
+
+        // Wildcard match - base domain
+        assert!(rewrite.is_excluded("https://example2.com/cdn.js"));
+        // Wildcard match - subdomains
+        assert!(rewrite.is_excluded("https://cdnjs.example2.com/lib.js"));
+        assert!(rewrite.is_excluded("https://sub.domain.example2.com/asset.js"));
+
+        // Should NOT match
+        assert!(!rewrite.is_excluded("https://other.example.com/asset.js"));
+        assert!(!rewrite.is_excluded("https://sub.cdn.example.com/asset.js"));
+        assert!(!rewrite.is_excluded("https://example2.com.fake.com/asset.js"));
+        assert!(!rewrite.is_excluded("https://notexample.com/asset.js"));
+
+        // Invalid URLs should not crash and should return false
+        assert!(!rewrite.is_excluded("not a url"));
+        assert!(!rewrite.is_excluded(""));
+    }
 }

trusted-server.toml

@@ -48,3 +48,11 @@ secret_store_id = "<fastly-secret-store-id>"
 endpoint = "https://testlight.example/openrtb2/auction"
 timeout_ms = 1200
 rewrite_scripts = true
+
+# Rewrite configuration for creative HTML/CSS processing
+# [rewrite]
+# Domains to exclude from first-party rewriting (supports wildcards like "*.example.com")
+# URLs from these domains will be left as-is and not proxied
+# exclude_domains = [
+#     "*.edgecompute.app",
+# ]